David Mateos, Carlos Toledano, Abel Calle, Roberto Román, Marcos Herreras-Giralda, Ramiro González, Sara Herrero-Anta, Daniel González-Fernández, Celia Herrero-del Barrio, Argyro Nisantzi, Rodanthi E. Mamouri, Silke Groß, Victoria E. Cachorro, Ángel M. de Frutos, Bernadett Weinzierl,
Saharan and Arabian dust optical properties registered by sun photometry during A-LIFE field experiment in Cyprus,
https://doi.org/10.5194/acp-26-1993-2026
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The A-LIFE (Absorbing aerosol layers in a changing climate: aging, lifetime, and dynamics) field experiment, conducted in Cyprus in April 2017, employed a wide range of ground-based and airborne instruments, including passive/active remote sensing and in-situ techniques. This study presents the columnar records obtained by sun photometry. Two sun/sky/lunar photometers, belonging to AERONET network, were strategically placed at two sites: Pafos and Limassol, 40 km apart. Aerosol optical and microphysical properties derived from direct sun and sky radiance measurements are analysed to determine an inventory of aerosol event days during the experiment, with mineral dust being present in nearly 75 % of days. Ångström exponent values obtained from 1020 and 1640 nm channels (0.5 for Saharan dust and 0.34 for Arabian dust) can be served as a classification criterion. Dust sources are key point for a well understanding of the size distribution and absorption power. According to columnar records, Saharan dust exhibited less absorbing particles. The columnar volume efficiency factor (linear fit between aerosol optical depth and total volume concentration) was proved as a reliable proxy for the identification of dust origin since Arabian and Saharan dusts exhibit different slopes: 1.28 and 1.68 µm2 µm−3, respectively. Analysing all the inversion products mixtures of mineral dust were mainly dominated by Arabian dust, while mixtures of fine and coarse aerosols showed no clear prevalence of dust origin. No significant presence of black carbon-rich aerosols was detected in the atmospheric column, as absorption Ångström exponent values ranged from 1.6 to 3 across aerosol types identified.
Nikolaos Papadimitriou, Ilias Fountoulakis, Antonis Gkikas, Kyriakoula Papachristopoulou, Andreas Kazantzidis, Stelios Kazadzis, Stefan Pfenninger, John Kapsomenakis, Kostas Eleftheratos, Athanassios A. Argiriou, Lionel Doppler, Christos S. Zerefos, PV power modelling using solar radiation from ground-based measurements and CAMS: Assessing the diffuse component related uncertainties leveraging the Global Solar Energy Estimator (GSEE), https://doi.org/10.5194/amt-19-1227-2026
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Accurate PV power production modelling requires precise knowledge of the distribution of solar irradiance among its direct and diffuse components. Since this information is rarely available, this requirement can be addressed through the use of diffuse fraction models. In this study, we try to quantify the errors in PV modelling when measurements of the diffuse solar irradiance are not available. For this purpose, we use total and diffuse solar
irradiance data obtained from ground-based measurements of BSRN to simulate the PV electric output using GSEE. We have chosen five sites in Europe and North Africa, with different prevailing conditions, where BSRN measurements are available. GSEE incorporates an
implementation of the Boland-Ridley-Lauret (BRL) diffuse fraction model, along with a Climate Data Interface that enables simulations across different time scales. We evaluate the capability of BRL in providing accurate estimations of the diffuse fraction under diverse atmospheric conditions, with particular attention on the presence of clouds and aerosols and assess the extent to which its associated errors propagate to energy production modelling. Furthermore, we compare GSEE outputs when using CAMS radiation time-series as input instead of ground-based measurements, to quantify the impact of the CAMS radiation product uncertainties in PV modelling.
Sophie Vandenbussche, Christodoulos Biskas, Maria-Elissavet Koukouli, Stelios Kazadzis, Martine De Mazière, The mineral aerosol profiling from infrared radiances version 5.1 algorithm and its evaluation, https://doi.org/10.5194/amt-19-4889-2026
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Mineral (desert) dust aerosols are small sand/dust particles entrained by winds from bare areas and possibly transported over long distances. These aerosols are climate forcers and affect human health and many socio-economic sectors. They are therefore important to monitor both in near-real time and on the long term. In this work, the Infrared Atmospheric Sounding Interferometer (IASI) instrument is used to retrieve vertical profiles of mineral dust aerosols concentration, from which a 10 µm aerosol optical depth (AOD) and a mean aerosol altitude are obtained. In addition, the dust AOD is converted to 550 nm using the same aerosol optical properties as in the retrieval. The theoretically calculated conversion factor is 1.78 (the 550 nm AOD being larger than the 10 µm AOD). This conversion step adds significant uncertainties due to different sensitivity at the different wavelengths. Specifically, we present here the new version 5.1 of the Mineral Aerosol Profiling from Infrared Radiances (MAPIR) algorithm and its changes with respect to previous versions. MAPIR v5.1 was used to produce a consistent time series of dust profiles since the start of the IASI observations in 2007 and until now, using data from IASI onboard Metop-A and Metop-C. The capabilities of the instrument and retrieval are illustrated, showing good event detection, expected AOD seasonal cycles, good profiling capabilities and reasonable mean aerosol altitude, good time and cross-platform consistency. A true validation exercise is not possible as there exist no reference aerosols data from thermal infrared measurements (around 10 µm). Therefore, the absolute value of the obtained AOD can not be validated, although the best possible evaluation is provided using data obtained in the visible spectral range. The evaluation shows a strong correlation of respectively about 0.8 and 0.7 between MAPIR dust AOD and AERONET 550 nm coarse mode AOD solar and lunar observations. The MAPIR converted 550 nm AOD shows a small median bias with respect to AERONET, but this bias varies with the AOD, suggesting an underestimation of the AOD conversion factor.
Akriti Masoom, Stelios Kazadzis, Robin Lewis Modini, Martin Gysel-Beer, Julian Gröbner, Martine Collaud Coen, Francisco Navas-Guzman, Natalia Kouremeti, Benjamin Tobias Brem, Nora Kristina Nowak, Giovanni Martucci, Maxime Hervo,
Long range transport of Canadian wildfire smoke to Europe in 2023: aerosol properties and spectral features of smoke particles, https://doi.org/10.5194/acp-26-10801-2026
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The Canadian wildfires of 2023 had an unprecedented biomass burning season spanning from mid-April to late October. Towards the end of this long biomass burning season, there was a rare observation of smoke properties that occurred in about a week interval, that were different from the whole biomass burning season and that makes it quite notable. The observed aerosol properties were studied using remote sensing and in situ measurements for both short-range and long-range transported plumes across North America and Europe. One of the highlights was the observation of concave spectral curvature in aerosol optical depth (AOD) having maxima at higher wavelengths than th
e minimum measured wavelength (i.e., 340 nm) which led to negative values of Ångström exponent in spectral ranges below 500 nm. Along with this, large accumulation mode size distributions with volume median diameters reaching about 800 nm were observed. Another rare observation was the non-monotonic spectral curvature in single scattering albedo (SSA) associated with submicron size particles. For most of the stations, SSA increased in the UV-Visible region and/or further remaining either constant or decreasing at longer wavelengths as obse
rved from column integrated (AOD) retrievals from remote sensing and coefficients from in situ measurements. Additionally, two stations in Canada and one in Europe were found to have a well-defined peak in AOD at 500 nm. These Canadian stations also displayed a non-monotonic spectral SSA with maxima at 675 nm, while the high altitude stations of Europe showed monotonically increasing SSA. Finally, a much higher (approximately 5 times) UV absorption than visible absorption indicated the presence of brown carbon and/or tar balls, which have a strong spectral dependence in imaginary refractive index. The SSA concave spectral curvature denotes the mix of black carbon and non-absorbing particulate matter and influence of particle size, while the AOD concave spectral curvature is attributed to particle size. The comparison of the ground based AOD measurements with satellite observation and model reanalysis showed an AOD underestimation ranging from 0.1 to 1.5.
William Wandji Nyamsi, Ville Leinonen, Antti Lipponen, Else van den Besselaar, Santtu Mikkonen, Arturo Sanchez-Lorenzo, Martin Wild, Doris Folini, Tero Mielonen, Harri Kokkola, Antti Kukkurainen, Neus Sabater, Rei Kudo, Ben Liley, Raghav Srinivasan, Bruce W. Forgan, Alexandru Dumitrescu, Grzegorz Urban, Michał K. Kowalewski, Márcia Akemi Yamasoe, Nilton Évora do Rosário, Dimitra Founda, Stelios Kazadzis, Veronica Manara, Derbetini A. Vondou, Christian Gueymard, Anders V. Lindfors, Atsumu Ohmura, Antti Arola, Long-term trends in reconstructed atmospheric aerosol load based on large-scale sunshine duration records since 1900, https://doi.org/10.5194/acp-26-10767-2026
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Aerosol emissions from anthropogenic sources have increased considerably since pre-industrial times. However, global climate models exhibit substantial discrepancies in the radiative forcing attributed to anthropogenic aerosols, a primary factor contributing to uncertainties in total anthropogenic forcing estimates. Therefore, achieving a sufficiently accurate quantification of historical aerosol optical depth (AOD) would be crucial to enhance our ability to project future climate changes and formulate effective mitigation and adaptation strategies. This study uses multiple observational networks, utilizing sunshine duration as a proxy for broadband AOD (BAOD), together with cloud cover observations from 2700 sites across the world, to reconstruct BAOD trends since the late 19th century. In particular, this analysis provides, for the first time, historical BAOD estimates for Europe dating back to the early 1900s. The findings include a general trend toward cleaner atmospheres at most European observation sites during both the 1900–1925 and 1926–1959 periods, amounting to regional trends of −0.014 and −0.004 per decade, respectively. The mean-annual BAOD is found to increase at only a few stations during those periods, likely because of local industrialization. Conversely, based on sunshine data from around 400 sites during the 1960–1985 period, the analysis, underscores the role of anthropogenic aerosols in the dimming observed across Europe (0.004 per decade), as well as the modulating relevance of volcanic aerosols. A continuous increase in BAOD is also observed over Southeast Brazil during 1960–1985, with a noticeable higher rate of 0.015 per decade, which is approximately four times as large as that found in Europe. At the same time, Japan experienced a notable decrease in BAOD with a rate of −0.015 per decade, owing to stringent environmental regulations implemented between 1960 and 1985. Meanwhile, Oceania exhibited a modest negative trend of −0.004 per decade during that period. During the 1986–2015 period, commonly referred to as a “brightening phase”, a general decline of annual BAOD is observed in each studied region: higher rate of decreasing aerosol load in Southeast Brazil, Japan, and Europe by −0.010, −0.015, and −0.013 per decade, respectively, compared to much lower rate of −0.003 per decade over Oceania. This comprehensive assessment sheds new light on the historical BAOD variability and highlights region-specific differences, contributing valuable insights that can help refine climate models and advance our understanding of the complex interplay between aerosols and climate.
Rosa D. García, África Barreto, Victoria E. Cachorro, Pablo González-Sicilia, Sergio Léon-Luis, Ayoze Álvarez-Hernández, Juan José Bustos, Ramón Ramos, Fernando Almansa, Óscar Álvarez-Losada, Yenny González, Pedro Pablo Rivas, Carlos Javier Torres,
Impact of spectral aerosol radiative forcing at the Izaña observatory during the August 2023 extreme wildfires, https://doi.org/10.5194/amt-19-3151-2026
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Extreme wildfires represent a highly variable source of atmospheric aerosols with potentially strong impacts on surface solar radiation. In August 2023, an exceptional wildfire on Tenerife (Canary Islands, Spa
in) reached the neighbourhoods of the Izaña Observatory (IZO, 2400 m a.s.l.). This near-source configuration enabled a rare observational characterisation of the spectral radiative effects of biomass-burning aerosols. During the most intense phases of the event (17–18 August), aerosol optical depth (AOD) at 500 nm reached extreme values of 3.63 and 2.25, respect
ively, with Ångström Exponent (AE) above 2, indicating a strong dominance of fine-mode smoke particles. Spectral measurements of global-horizontal, direct-normal and diffuse-horizontal solar irradiance (300–1100 nm) show a pronounced attenuation of direct and global irradiances, particularly in the visible range, together with a strong enhancement of diffuse radiation. Relative to clean-sky conditions, daily global irradiance decreased by 21 %–27 %, while direct-normal irradiance was reduced by 72 %–99 %. Spectral aerosol radiative forcing and radiative forcing efficiency at the surface were quantified using radiative transfer simulations under pristine atmospheric conditions as a reference. The integrated spectral radiative forcing (300–1100
nm) for global irradiance reached −395 and −299 W m−2 on 17 and 18 August, respectively, indicating strong surface cooling dominated by scattering processes. Maximum forcing and efficiency occurred in the visible spectral range, consistent with the optical properties of freshly emitted smoke aerosols. At the same time, increases in the amount of present particles, equivalent black carbon (eBC) and greenhouse gases (CO2, CH4 and CO) confirm the direct influence of the wildfire plume on atmospheric composition at IZO. These observations provide one of the few detailed spectral assessments of surface radiative forcing by extreme biomass-burning aerosols at a high-altitude site and highlight the need to accurately represent fine-mode smoke aerosols in radiative transfer and climate models.
Marilena Gidarakou, Alexandros Papayannis, Maria Mylonaki, Eleni Kralli, Kostas Eleftheratos, Ilias Fountoulakis, Olga Zografou, Evangelia Diapouli, Maria I. Gini, Stergios Vratolis, Konstantinos Granakis, Konstantinos Eleftheriadis, Nikolaos Evangeliou, Christine Groot Zwaaftink, Eugenia Giagka, Marios-Andreas Zagklis, Igor Veselovskii, Exceptional wildfire smoke over Greece in summer 2023: a synergistic study of aerosol optical-microphysical and UVB radiative impacts, https://doi.org/10.5194/acp-26-4313-2026
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During summer 2023, Greece experienced one of its most severe wildfire seasons in recent decades, with widespread fires across Evros, Rodopi, Attica, the Peloponnese, and several islands. This study investigates the aerosol optical and microphysical properties, as well as the impact on ground-level ultraviolet-B (UVB) radiation over Athens, focusing on two major wildfire episodes (18–21 July and 22–25 August). A synergistic approach was deployed, combining satellite imagery (MODIS), FLEXPART simulations, ground-based remoter sensing, in situ aerosol and radiation measurements. Elevated aerosol optical depths (AOD) up to 1.2, high fine-mode fractions (FMF) (> 0.85), and Ångström exponents (AE) above 1.5 indicated a strong dominance of fine biomass burning aerosols. The Single scattering albedo (SSA) ranged from 0.85 to 0.98, showing enhanced absorption during biomass burning periods and weaker absorption when smoke was mixed with dust. At 320 nm, dust presence resulted in stronger absorption, with SSA below 0.8 for pure dust cases compared to smoke mixtures. Particle linear depolarization ratios (PLDR), varied between 0.03 and 0.20, with higher values (∼ 0.10–0.20) reflecting the presence of non-spherical dust particles, and lower values (∼ 0.03–0.08) indicating spherical smoke particles. Ground-level UVB irradiance decreased by up to 50 % during peak smoke episodes, highlighting strong aerosol radiative impacts. Concurrently, PM10 and PM2.5 concentrations increased to 94 and 49 µg m−3, respectively, while organic aerosols peaked at 22.77 µg m−3, consistent with intense fire activity. FLEXPART simulations confirmed long-range transport of smoke from active fire regions, with additional contributions from regional pollution and Saharan dust.
Javier Gatón, Roberto Román, Cesar Guzman, Daniel González-Fernández, Bruno Longarela, Carlos Toledano, Ramiro González,
Multi-frame cloud prediction in all-sky images from RGB images and segmented masks,
https://doi.org/10.1016/j.solener.2026.114515
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This paper presents a comparative study on the impact of input representation on deterministic artificial intelligence models for short-term multi-frame prediction in all-sky images. This work compares a model operating on 8-bit RGB all-sky images with a m
odel that shares the same backbone, but operates directly on semantically segmented masks that encode cloud-related classes. Using an available sky segmentation model, predictions are evaluated in the segmentation label space using segmenter-derived masks as a proxy reference. Within this evaluation framework, the use of semantic masks as input for short-term prediction leads to improved temporal stability and higher agreement across standard segmentation metrics such as intersection over union, Dice coefficient, and categorical cross-entropy. While these results suggest potential relevance for weather and solar energy nowcasting applications, further validation against physical irradiance measurements is required.
África Barreto, Francisco Quirós, Omaira E. García, Jorge Pereda-de-Pablo, Daniel González-Fernández, Andrés Bedoya-Velásquez, Michael Sicard, Carmen Córdoba-Jabonero, Marco Iarlori, Vincenzo Rizi, Nickolay Krotkov, Simon Carn, Reijo Roininen, Antonio J. Molina-Arias, A. Fernando Almansa, Óscar Álvarez-Losada, Carla Aramo, Juan José Bustos, Romain Ceolato, Adolfo Comerón, Alicia Felpeto, Rosa D. García, Pablo González-Sicilia, Yenny González, Pascal Hedelt, Miguel Hernández, María-Ángeles López-Cayuela, Diego Loyola, Stavros Meletlidis, Constantino Muñoz-Porcar, Ermanno Pietropaolo, Ramón Ramos, Alejandro Rodríguez-Gómez, Roberto Román, Pedro M. Romero-Campos, Martin Stuefer, Carlos Toledano, Ellsworth J. Welton,
Volcanic plume height during the 2021 Tajogaite eruption (La Palma) from two complementary monitoring methods – implications for satellite-based products,
https://doi.org/10.5194/amt-19-1385-2026
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Volcanic emissions from the Tajogaite volcano, located on the Cumbre Vieja edifice on the island of La Palma (Canary Islands, Spain), caused significant public health and aviation disruptions throughout the eruption (19 September–13 December 2021, officially declared over on 25 December). Nonetheless, it is considered the most significant volcanic event in Europe over the past 75 years due to the substantial amount of SO2 released into the atmosphere. The Instituto Geográfico Nacional (IGN), the authority responsible for volcano surveillance in Spain, implemented extensive operational monitoring to track volcanic activity and to provide a robust estimation of the volcanic plume height using a video-surveillance network. In parallel, the State Meteorological Agency of Spain (AEMET), in partnership with other Spanish ACTRIS (Aerosol, Clouds, and Trace Gases Research Infrastructure) members and collaborating institutions, conducted an unprecedented instrumental deployment to evaluate the impacts of this volcanic event on atmospheric composition. This effort included a network of aerosol profilers surrounding the volcano. A total of four profiling instruments were installed on La Palma: one MPL-4B lidar and three ceilometers. Additionally, a pre-existing Raman lidar on the island contributed valuable data to this study. These efforts are undertaken due to the importance of monitoring volcanic plume height in terms of air quality (necessary for the implementation of effective civil protection policies), volcanic activity surveillance (for tracking and forecasting eruptive behaviour), and, from a scientific perspective, for improving our understanding of the climatic and radiative impacts of this type of aerosol.
In this study, the eruptive process was characterised in terms of the altitude of the dispersive volcanic plume (hd), measured by both IGN and AEMET-ACTRIS, and the altitude of the eruptive column (hec), measured by IGN. Modulating factors such as seismicity and meteorological conditions were also analysed. The consistency between the two independent and complementary datasets (hd,IGN and hd,AEMET) was assessed throughout the eruption (mean difference of 258.6 m).
Our results confirmed the existence of three distinct eruptive phases, encompassing a range of styles from Strombolian explosive to effusive activity. While these phases have been characterised in previous studies, the results of the present work provide complementary information and novel insights from an alternative observational approach, which may be of use in future volcanic crises and will be applied to operational surveillance during such events.
A subsequent comparison of hd,AEMET with the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol layer height product (ALHCALIOP) revealed a systematic underestimation by the satellite product, with a mean difference of 392.2 m.
Finally, the impact of using hec in estimating SO2 emissions from the NASA MSVOLSO2L4 satellite-based product was evaluated. When a fixed (standard) plume altitude of 8 km was used instead of the observed hec, the total SO2 emission was significantly underestimated by an average of 56.2 %, and by up to 84.7 %. These findings underscore the importance of accurately determining the volcanic plume height when deriving SO2 emissions from satellite data.
Anna Moustaka, Nikolaos Siomos, Stelios Kazadzis, Emmanouil Proestakis, Kalliopi Artemis Voudouri, Anton Lopatin, Oleg Dubovik, Kleareti Tourpali, Christos Zerefos, Vassilis Amiridis, Antonis Gkikas,
Enhancing dust aerosols monitoring capabilities across North Africa and the Middle East using the A-Train satellite constellation,
https://doi.org/10.5194/amt-19-1201-2026
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North Africa and the Middle East encompass the most active dust sources on the planet. Due to the limited availability of ground-based aerosol observations across the deserts, spaceborne retrievals represent the most reliable source of information for monitoring dust particles over these vast areas. In the current study, we present a synergistic approach incorporating aerosol retrievals acquired by active (CALIOP) and passive (POLDER-3, MODIS) instruments mounted on satellites of the A-Train constellation. Our main objective is to dynamically (in terms of space and time) estimate the dust lidar ratio (LR) at 532 nm throughout a 12-year period (2006–2017) by collocating columnar aerosol optical depth observations (POLDER-3/GRASP, MIDAS) and vertically resolved dust aerosol profiles obtained by CALIPSO. According to our findings, the derived dust LRs reveal a clear spatial variability. The highest LRs are found over major Saharan source regions such as the Bodélé Depression and the Libyan Desert, while moderate to low values dominate the Arabian Peninsula. Enhanced values also appear across Central Asia, particularly over the Karakum and Kyzylkum deserts. The corresponding uncertainty fields demonstrate that LR estimates are most robust over regions with a larger number of dust cases, whereas higher uncertainties occur along transition zones – such as the Sahel and parts of Central Asia – where dust mixing or aerosol-type misclassification increases retrieval variability. A key objective of this work is to establish a robust methodology for deriving aerosol-speciated LRs using synergies between active and passive observations. Although focused here on dust over North Africa and the Middle East, the same framework can be readily applied to other CALIPSO aerosol subtypes – such as marine, polluted dust, or smoke – when implemented over regions where these aerosol types predominate. The advent of the EarthCARE satellite mission, along with the incorporation of new aerosol models into the forthcoming CALIPSO Version 5 aerosol retrieval algorithm, will serve as a reference for our calculations. In this context, our findings also highlight that a synergy of multisensor aerosol products with modelling tools can enhance the spatiotemporal representation of aerosol properties, such as the LR, further improving retrieval utility.
Alkistis Papetta, Maria Kezoudi, Holger Baars, Athina Floutsi, Eleni Drakaki, Konrad Kandler, Sudharaj Aryasree, Elena Louca, Theodoros Christoudias, Eleni Marinou, Chris Stopford, Troy Thornberry, Vassilis Amiridis, Jean Sciare, Franco Marenco, Volume-to-extinction ratio: an important property of dust, https://doi.org/10.5194/acp-26-2055-2026
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The volume-to-extinction ratio (ζ) is an important aerosol property, allowing to relate gravimetric and optical quantifications, widely used in remote sensing and in climate models. The ζ ratio is affected by the microphysical properties of aerosol particles, including their size, shape and composition. This study presents a synergistic approach combining airborne in-situ observations and ground-based remote sensing to study this ratio during dust events originating in the Middle East and Saharan regions, and to examine its vertical variability and general estimation uncertainty. The data were collected during the 2021 Cyprus Fall Campaign and the 2022 ASKOS campaign in Cabo Verde. The combination of observations offered vertically-resolved information on the particle size-distribution and volume-to-extinction ratio. The findings of this study reveal pronounced differences in the ζ ratio and effective radius across events and regions, reflecting variations in the degree of mixing with fine particles, as well as some variability with altitude due to varying particle size and shape. During Middle East dust events in Cyprus in fall 2021 the observed average ζ was the lowest with µm, whilst for a Saharan dust case in Cabo Verde in summer 2022 observations showed the highest values with µm, both values obtained at the dust layer altitude in some of the reported cases. The analysis highlights large discrepancies compared to AERONET-derived values and previous literature, especially in the presence of super-coarse and giant particles. Scattering computations allowed to evaluate the experimental results and provide insights into the role of particle asphericity. Atmospheric model simulations also showed discrepancies, mainly due to assumptions that neglect larger particles. These findings suggest that improved dust representation in models is essential for accurate climate assessment.
Simone Pulimeno, Angelo Lupi, Vito Vitale, Claudia Frangipani, Carlos Toledano, Stelios Kazadzis, Natalia Kouremeti, Christoph Ritter, Sandra Graßl, Kerstin Stebel, Vitali Fioletov, Ihab Abboud, Sandra Blindheim, Lynn Ma, Norm O’Neill, Piotr Sobolewski, Pawan Gupta, Elena Lind, Thomas F. Eck, Antti Hyvärinen, Veijo Aaltonen, Rigel Kivi, Janae Csavina, Dmitry Kabanov, Sergey M. Sakerin, Olga R. Sidorova, Robert S. Stone, Hagen Telg, Laura Riihimaki, Raul R. Cordero, Martin Radenz, Ronny Engelmann, Michel Van Roozendal, Anatoli Chaikovsky, Philippe Goloub, Junji Hisamitsu, Mauro Mazzola,
Recent advances in aerosol optical depth measurements in polar regions: insights from the Polar-AOD Program,
https://doi.org/10.5194/acp-26-1809-2026
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A multi-year analysis of aerosol optical depth (AOD, τ) and Ångström exponent (α) was conducted using ground-based photometer data from 15 Arctic and 11 Antarctic sites. Extending the dataset of (Tomasi et al., 2015) through December 2024, the study incorporates stellar and lunar photometric observations to fill data gaps during the polar night. Daily mean values of τ at 0.500 µm and α (0.440–0.870 µm) were used to derive monthly means and seasonal histograms.
In the Arctic, persistent haze events in winter and early spring lead to peak τ values. A decreasing trend in Arctic τ suggests the impact of European emission regulations, while biomass-burning aerosols are becoming more significant. In Antarctica, τ increases from the plateau to the coast. Fine-mode aerosols dominate in summer-autumn, while coarse-mode particles are more prevalent in winter-spring. Shipborne photometer data align well with ground-based measurements, confirming the reliability of mobile observations.
Trend analyses using the Mann-Kendall test and Theil-Sen regression indicate a significant negative trend in τ at Andenes (−2.43 % per year), likely driven by reduced anthropogenic emissions. Antarctic stations such as Syowa and South Pole show positive trends (+3.84 % and +3.54 % per year), though these are subject to uncertainties from data limitations and instrument changes.
This work contributes to the Polar-AOD network (
https://polaraod.net/, last access: 15 May 2025), enhancing the understanding of aerosol variability and long-term trends in polar regions while promoting open data access for the scientific community.
Sara Herrero-Anta, Sabine Eckhardt, Nikolaos Evangeliou, Stefania Gilardoni, Sandra Graßl, Dominic Heslin-Rees, Stelios Kazadzis, Natalia Kouremeti, Radovan Krejci, David Mateos, Mauro Mazzola, Christoph Ritter, Roberto Román, Kerstin Stebel, Tymon Zielinski,
Exceptional high AOD over Svalbard in summer 2019: a multi-instrumental approach,
https://doi.org/10.5194/acp-26-1435-2026
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In the summer of 2019, the Arctic region registered exceptionally high aerosol optical depth (AOD) values over Svalbard, linked to intense biomass burning (BB) and volcanic activity across the Northern Hemisphere. This study presents a comprehensive, multi-instrumental analysis of the aerosol conditions in and around Ny-Ålesund (Spitsbergen, Norway), combining data from ground-based sun-photometry, in-situ observations, active remote sensing (ground-based and on satellite), and atmospheric dispersion modelling (FLEXPART). Despite high AOD was observed during all the period, three different aerosol events are identified in the atmospheric column (6–10 July, 25–28 July, and 6–17 August). In contrast, in-situ surface stations only recorded significant aerosol load during 5–9 July, 30 August, and 12 September, suggesting that most of the aerosol particles remained above the boundary layer. Lidar and photometric observations revealed the presence of spherical, weakly absorbing Accumulation-mode particles (with effective radii between 0.1 and 0.2 µm) in both the troposphere and stratosphere, with persistent layers extending above 10 km. Simulations carried out with FLEXPART correlate well with the measurements, attributing the observed aerosol events to multiple sources, including Siberian and North American wildfires, the Raikoke (Russia) volcanic eruption, and anthropogenic pollution. While the simulations show a contribution from volcanic aerosols, the contribution from biomass-burning aerosols in the upper troposphere and lower stratosphere were likely more significant under the atmospheric conditions of summer 2019. Overall, the aerosol radiative impact during this long-lasting event was substantial, with a mean reduction in direct solar radiation of approximately −74 W m−2 during July and August. This work shows how the use of dispersion modelling together with multiple observation sources allows to achieve a more complete description of the atmospheric aerosol events and contributes to a better understanding of the overall picture.
Emmanouil Proestakis, Kyriakoula Papachristopoulou, Thanasis Georgiou, Sofia Eirini Chatoutsidou, Mihalis Lazaridis, Antonis Gkikas, Ilias Fountoulakis, Ioanna Tsikoudi, Manolis P. Petrakis, Vassilis Amiridis,
Atmospheric dust and air quality over large-cities and megacities of the world, https://doi.org/10.5194/acp-25-14777-2025
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According to the United Nations (UN) more than 55 % of the global population resided in urban areas in 2018, a number projected to increase to an estimated 60 % of the world’s population by 2030. As urbanization accelerates, degradation of air quality becomes an increasing environmental pressure to human welfare and health. To date, epidemiological studies reveal a strong connection between airborne dust and adverse health effects. This study investigates the fine-mode and coarse-mode dust particulate matter levels within the planetary boundary layer (PBL) over major cities and megacities of the world (population > 5 million), leveraging on the European Space Agency (ESA) – “LIdar climatology of Vertical Aerosol Structure” (LIVAS) multiyear satellite-based dust climate data record. Results show that current dust levels exceed World Health Organization (WHO) annual-mean air quality guidelines (A
QGs) for PM2.5 and PM10 in 87.7 % and 49.4 % of the cities considered, respectively, exposing ∼ 700 million people to hazardous dust concentrations. Moreover, according to the outcomes of the study, this number is expected to increase to ∼ 850 million individuals (∼ 22 % increase) by 2030s, though due to the general declining dust tendencies the health hazard is projected to be diminished in severity. Particularly affected are cities in the regions of Middle East, Indian subcontinent, East Asia, North Africa, and the Sahel. Epidemiological models are employed to estimate associated health risks. The study provides an informative mitigation and adaptation tool to support observational-based policymaking, air quality management, and public health planning to protect human health in the context of accelerating urbanization.
Ilias Fountoulakis, Kyriaki Papachristopoulou, Stelios Kazadzis, Gregor Hülsen, Julian Gröbner, Ioannis-Panagiotis Raptis, Dimitra Kouklaki, Akriti Masoom, Natalia Kouremeti, Charalampos Kontoes, Christos S. Zerefos,
Assessment of the accuracy in UV index modelling using the UVIOS2 system during the UVC-III campaign,
https://doi.org/10.5194/gmd-18-7451-2025
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The third campaign for the calibration and intercomparison of solar UV radiometers (UVC III) took place at Davos, Switzerland in June–August 2022. More than 70 radiometers participated in the campaign and measured side-by-side with the portable reference spectroradiometer QASUME. The UVIOS2 system is a flexible UVI modelling tool that can be exploited for different applications depending on the inputs. Thus, different combinations of satellite, reanalysis, and/or ground-based inputs were used to test the UVIOS2 performance when it is used as a tool for UVI nowcasting or for climatological studies. While UVIOS2 provided quite accurate estimates of the average (for the period of the campaign) UVI levels, larger deviations were found for individual estimates. The average agreement between the UVI from the UVIOS2 and QASUME was better than 1 % for all the different sets of inputs
that were used for the study. The range of the variability was of the order of 40 % for instantaneous measurements (15 min), mainly due to the model’s inability to capture the instantaneous effects of cloudiness, especially under broken cloud conditions. Under clear-sky conditions the model was found to perform much better, with the differences between the model estimates and the QASUME measurements being smaller than 12 % for 95 % of the studied cases. Even at the pristine environment of Davos, single scattering albedo (SSA) was found to contribute significantly to the modelling uncertainties under cloudless conditions. For Aerosol Optical Depth (AOD) of the order of 0.2–0.4 at 550 nm, the role of the SSA was found to be comparable to the role of AOD in the modelling of the UVI.
Tsvetina Evgenieva, Stefan Dosev, Ljuan Gurdev, Liliya Vulkova, Zahari Peshev, Eleonora Toncheva, Lyubomir Popov, Orlin Vankov, Tanja Dreischuh, Canadian Wildfire Smoke Episode over Europe in October 2023: Lidar, Sun-Photometer, and Model Characterization of Smoke Layers Observed Above Sofia, Bulgaria, https://doi.org/10.3390/rs17162899
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Massive wildfires release enormous amounts of biomass-burning (BB) aerosols into the atmosphere, which might have a major impact on its thermal and radiative budget, as well as the environment and human health. This work presents the results of a study and characterization of a long-range transport episode of smoke aerosols from Canadian forest fires towards the entirety of Europe, as observed over Sofia, Bulgaria, in early October 2023. This study makes use of data from combined lidar, ceilometer, and sun-photometer measurements, supported by model and forecast data, meteorological radiosonde profiling, and (re)analyses, together with tracking and mapping of the aerosol air transport. A distinctive feature of the considered episode over Europe is the downward movement of the air masses, entraining smoke aerosols from the continental mid-troposphere down to the near-surface layers. The driving mechanism of the long-range transport of BB aerosols and their spread over Europe is revealed. Optical parameters of the registered aerosols are determined and vertically profiled with a high range resolution by lidar data analysis. A wide set of columnar optical and microphysical aerosol characteristics is also provided by sun-photometer measurements. The results show a dominance of relatively fine modes of dry smoke particles in the submicron size range, with a predominantly low degree of non-sphericity, indicating minimal up-size aging during the BB aerosol transport from Canada to the Sofia region. The average daily aerosol radiative forcing is determined by sun-photometer measurements and briefly discussed.
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Given certain cloud fractions in the sky, derived from satellite observations or sky images, surface solar radiation (SSR) attenuated by clouds can differ when the sun is visible (based on sunshine duration threshold defined by World Meteorological Organization) or shaded by clouds. Sun visibility is among the most uncertain factors in solar forecasting. With sky images taken by sky cameras and solar radiation measurements at the World Radiation Center (Davos, Switzerland), this work examines the relationship between cloud cover and sun visibility. By integrating sun visibility into a forecasting system, an improvement in accuracy and reliability of the SSR forecast is aimed. A multivariate deep learning model based on a Long- and Short-term Time-series network is used. The model is trained with extensive cloud information including cloud fraction and cloud types extracted from sky images taken at a ground station, and predicts intrahour (15 min- to 1 hr-ahead) sun visibility and cloud modification factor (CMF). With the distinct patterns of visible and occulted sun, initial CMF forecasts are post-processed based on the prediction bias. Next, we derive all-sky global horizontal irradiance (GHI) from both CMF and clear-sky GHI obtained from radiative transfer modeling. The experimental results show a high accuracy of 96% for the 15-min ahead prediction of sun visibility. The SSR forecasts are validated using ground-based measurements. Compared with the persistence reference, our forecast method achieved a significant skill score of 47% for the 15-min ahead prediction. Higher skill scores are found for certain cloud types, e.g., 55% for stratus-altostratus.
Stelios Kazadzis, Illias Fountoulakis, Athanasios Damialis, Akriti Masoom, Kyriakoula Papachristopoulou, Stefanie Gilles, Martine Collaud Coen, Fiona Tummon,
Aerosol Measurements and Decadal Changes: The Role of Climatic Changes and How It Reflects in Respiratory Allergies and Asthma,
https://doi.org/10.1111/all.16602
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The causative agents of respiratory allergies are bioaerosols, such as house dust mite feces, pollen grains, and fungal spores. Climate change and urbanization are considered to lead to an increase in the load of allergenic bioaerosols due to impacts on plant phenophases and allergenicity. Continuous and efficient monitoring of the atmospheric composition worldwide is essential, given the major changes involved and their impact on climate change. The complexity of the exposome, evolving from single to multiple complex exposures, is explored in this work. Acquiring information from interdisciplinary scientific disciplines, such as aerobiology (for airborne particles of biological origin), aerosol science (for airborne particles of chemical or inorganic material), and integrating this with the actual reactome of patients with respiratory diseases, we aim to provide evidence of the multifactorial nature of this interaction in real life. The objective of this review is to present how we can monitor aerosols and mostly monitor the exposome, especially the biological one, i.e., pollen and fungal spores, and what their impact is, or could be, on respiratory allergies. A huge technological advancement has been required, as traditional methods of particle collection and identification have been based on tedious laboratory procedures, with delays of more than a week. This has limited their practical use to allergic patients and their treating physicians. Automation, real-time high temporal resolution, and the use of artificial intelligence are being increasingly used in medicine. Likewise, this overview summarizes the current aerosol measurement and modeling capabilities and discusses the classification of various aerosol particles and their impact on respiratory allergies. Satellite remote sensing is highlighted as a solution to the gaps in global aerosol representation by examining aerosol load in the atmospheric column in major cities worldwide. We also discuss potential novel threats, such as pioneer bioaerosols and the respiratory epithelial barrier, as well as future insights into the impact of climate change on allergy and asthma. We conclude with a discussion of emerging co-exposures and co-diseases resulting from the ongoing climate change.
Peter Hrabčák, Meritxell Garcia-Suñer, Violeta Matos, Víctor Estellés, Anna Pribullová, Jozef Depta, Martin Staněk, Martin Stráník,
30 years of total column ozone and aerosol optical depth measurements using the Brewer spectrophotometer in Poprad-Gánovce, Slovakia,
https://doi.org/10.5194/acp-25-16263-2025
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Long-term observations (1993–2024) of total column ozone (TCO) and aerosol optical depth at 320 nm (AOD320) from the Brewer spectrophotometer at Poprad-Gánovce, Slovakia, were analysed. The data used in this study are closely tied to three environmental issues driven by human activities: ozone depletion, climate change, and air pollution caused by aerosols. Both parameters exhibit distinct seasonal variability, with AOD320 peaks in April and August and TCO maxima from February to April. AOD320 shows a statistically significant long-term decrease (−0.057 ± 0.005 per decade), reflecting reduced anthropogenic emissions. The lowest annual mean occurred in 2020, corresponding to the first year of the COVID-19 pandemic. In contrast, TCO shows no clear trend (0.0 ± 0.4 DU per decade), whereas the tropopause height increases markedly (105 ± 7 m per decade) and exerts an inverse influence on TCO. After removing this effect, a positive TCO trend (1.3 ± 0.3 DU per decade) appears, while the tropopause-related component decreases (−1.3 ± 0.1 DU per decade). The most significant positive linear trend in tropopause height was identified in August (200 ±70 m per decade), while the strongest negative TCO trend also occurred in August (−3.6 ± 1.8 DU per decade). Only about one third of this August TCO decrease is explained by the tropopause rise. LOTUS regression confirmed the inverse TCO-tropopause relationship and revealed significant ENSO (positive) and QBOB (negative) influences. A weak positive trend in TCO since 1997 (2.0 ± 1.2 DU) indicates ongoing recovery from ODS reductions.
Christos Spyrou, Ilias Fountoulakis, Stavros Solomos, Nikolaos Papadimitriou, Alkiviadis Bais, Julian Gröbner, Daniela Meloni, Christos Zerefos,
Implications of dust minerals on radiative transfer at regional scale, using the METAL-WRF model,
https://doi.org/10.5194/amt-18-7717-2025
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Dust particles originating from desert areas of the planet have significant radiative impacts on the ground and atmospheric column, changing the energy distribution of the entire earth system, which cannot be underestimated, as dust is considered a climatic regulator. The magnitude of the dust radiative effect is dependent on the optical properties of desert dust aerosols, which in turn is regulated by the composition and mineralogical content of desert dust plumes. The mineralogical composition in atmospheric models is commonly related to the soil type at dust sources and the optical properties needed are provided by observational campaigns and dedicated measurements. In this work we upgrade the METAL-WRF model to incorporate the direct radiative impact of the minerals in dust and test the impact of the direct radiative feedback on a 2-month simulation period, namely March and April 2022, when consecutive intense dust outbursts affected the Mediterranean Basin. The simulation results were compared against Global Horizontal Irradiance data and AERONET optical properties that were measured at five sites. An improvement was observed in all sites, especially close to the sources, when the minerals and dust are treated as interacting in the radiative transfer calculations, thus improving the capabilities of METAL-WRF to simulate the chemical composition of dust particles in the atmosphere along with their contribution to radiative transfer processes.
Angelos Karanikolas, Benjamin Torres, Masahiro Momoi, Marcos Herreras Giralda, Natalia Kouremeti, Julian Gröbner, Lionel Doppler, Stelios Kazadzis,
Retrieval of aerosol properties from aerosol optical depth measurements with high temporal resolution and spectral range,
https://doi.org/10.5194/amt-18-7651-2025
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Several sun photometer networks worldwide include instruments for aerosol optical depth (AOD) observations, such as Global Atmospheric Atmosphere Watch-Precision Filter Radiometer (GAW-PFR) and Aerosol Robotic Network (AERONET). AERONET provides additional aerosol properties such as the detailed volume size distribution and the single scattering albedo through inversion modelling of sky radiance measurements. However, the data availability for such properties is limited due to the limited number of daily almucantar sky radiance scans and cloudiness. AOD is measured significantly more frequently as there can be one measurement even every minute. Also, the AOD measurements are affected only by clouds being too close or covering the solar disk. The Generalized Retrieval of Atmosphere and Surface Properties (GRASP) is a flexible inversion model to retrieve aerosol properties from various observations. One of its capabilities is the retrieval of the volume concentration, the volume median radius and geometric standard deviation for each aerosol size distribution mode and the separation of AOD to each mode using only spectral AOD as an input parameter (known as the GRASP-AOD application). Such properties are important for various applications, as the size of aerosols affects their interaction with solar radiation, clouds and radiative forcing modelling. Particle size also shows significant differences depending on the aerosol type such as dust or biomass burning. In this study, we selected four common stations of GAW-PFR and AERONET, used GRASP to retrieve the bimodal size distribution parameters from AOD measured by GAW-PFR instruments (PFRs) and validated the results for different conditions using AERONET data as reference. One of those sites includes a multi-year parallel timeseries from two different BTS spectroradiometers that combined can provide direct spectral irradiance (and as a result AOD) in the 300–2150≯nm range. Using this dataset, we were able to investigate the effect and potential benefits of the increased spectral range on GRASP-AOD retrievals. This is mostly focused on the retrieval of the coarse mode volume median radius, which is particularly challenging with the filter radiometers measuring up to 862 or 1020≯nm. We also assessed the performance for certain dust and biomass burning cases. Our results showed good agreement between PFR AOD-based and AERONET sky radiance inversions for AOD modal separation and volume concentrations. Significant improvement of the PFR-AERONET intercomparison was also possible for the fine mode volume and effective radius when restricting the datasets to AOD at 500≯nm≯>≯0.1 and Ångström Exponent (AE)≯>≯1. Also, the results showed consistency with previous study regarding the validation of such retrievals using AERONET AOD. Focusing on conditions with high proportion of dust particles, we found consistent results with the general cases
Using AOD with a larger spectral range (from BTS spectroradiometer), we found that the wavelength selection may affect the results and that using longer wavelengths can increase the sensitivity of coarse mode volume median radius to AOD and improve the correlation of the GRASP BTS AOD-based and AERONET datasets. However, the available data were limited, so it is not clear under what conditions the inclusion of such wavelengths will result in more accurate retrievals or to what extent.
Finally, we were able to reproduce with GRASP the aerosol size characteristics of unusual biomass burning cases from the Canadian wildfires during 2023, but the results showed systematically increased fine mode radius and concentration compared to the AERONET output.
Xinyuan Hou, Kyriakoula Papachristopoulou, Stelios Kazadzis, Assessment of aerosol optical depth forecast for day-ahead clear-sky direct irradiance, https://doi.org/10.5194/amt-18-4543-2025
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We used aerosol data from surface-based AErosol RObotic NETwork (AERONET) and day-ahead aerosol optical depth (AOD) forecasts from the Copernicus Atmosphere Monitoring Service (CAMS) to examine the spatiotemporal variations in AOD at selected sites worldwide. We evaluated three methods for day-ahead AOD forecasting: AERONET 1 d (and 2 d) persistence or monthly mean, along with CAMS forecast. High values of daily mean AOD indicates larger day-to-day variability in AOD and lower predictability. Using radiative transfer modeling, we qua
ntify deviations in forecasts of cloud-free direct normal irradiance (DNI) induced by errors in AOD forecasts. The performance of each AOD forecast method in DNI forecast is assessed and compared. Taking into account the characteristic aerosol types at selected locations, we also draw quantitative implications about the reliability and usability of CAMS AOD forecasts for DNI forecasts as alternatives to AOD forecasts based on approaches using ground-based measurements. For example, CAMS forecasts perform better at more si
tes than AERONET persistence approaches do, among them many urban-industrial aerosol sites. AERONET persistence forecasts AOD with lower errors at dust aerosol sites. To date, none of the forecast methods for AOD discussed here reliably achieve an accuracy of < 5 % deviation in day-ahead forecasts of direct normal irradiation (daily sum), but most of the sites can expect better DNI forecasts with a threshold of 20 % DNI deviation.
Roberto Román, Daniel González-Fernández, Juan Carlos Antuña-Sánchez, Celia Herrero del Barrio, Sara Herrero-Anta, África Barreto, Victoria E. Cachorro, Lionel Doppler, Ramiro González, Christoph Ritter, David Mateos, Natalia Kouremeti, Gustavo Copes, Abel Calle, María José Granados-Muñoz, Carlos Toledano, Ángel M. de Frutos,
Star photometry with all-sky cameras to retrieve aerosol optical depth at nighttime,
https://doi.org/10.5194/amt-18-2847-2025
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The lack of aerosol optical depth (AOD) data at night can be partially addressed through Moon photometer measurements or fully covered with star photometer observations. However, the limited availabil
ity and complexity of star photometers have motivated this study to use all-sky cameras to extract starlight signals and derive AOD at night using star photometry. For this purpose, eight all-sky cameras were configured and deployed in nine different locations to capture raw images with varying exposure times every 2 min during the night. This work proposes a novel methodology to extract
the starlight signal from the raw data from all-sky cameras and convert it into AOD values. This process consists of the following steps: removing the background image, selecting the pixels, and extracting the signal for each star from a predefined list of 56 stars; performing in situ Langley calibration of the instruments and retrieving the total optical depth (TOD); calculating the effective wavelength for each camera channel; deriving the AOD by subtracting the gas contribution to TOD; and averaging, cloud-screening, and quality-assuring the AOD time series. The AOD time series obtained through this methodology are compared with independent AOD measurements from collocated Moon photometers in the nine locations. The obtained results show that the AOD values derived with the proposed method generally correlate with reference values, often achieving correlation coefficients (r) above 0.90. The AOD values retrieved using the cameras tend to overestimate the reference values by approximately 0.02 and exhibit a precision of arou
nd 0.03–0.04. The agreement between the two datasets varies with wavelength and decreases at high-latitude locations, likely due to the poorer performance of Langley calibration in these regions. AOD values align well with day-to-night transitions obtained by solar photometers, demonstrating their reliability. Despite the slight overestimation, the AOD values derived by this new method approximate the real values and provide coverage throughout the entire night, without requiring the presence of the Moon. Therefore, they serve to study and monitor the nocturnal evolution of AOD.
Yenny González, María F. Sánchez-Barrero, Ioana Popovici, África Barreto, Stephane Victori, Ellsworth J. Welton, Rosa D. García, Pablo G. Sicilia, Fernando A. Almansa, Carlos Torres, Philippe Goloub, Compact dual-wavelength depolarization lidar for aerosol characterization over the subtropical North Atlantic, https://doi.org/10.5194/amt-18-1885-2025
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We present a comprehensive characterization o
f the optical properties of various aerosol types based on data collected using a compact dual-wavelength depolarization elastic lidar (532 and 808 nm, CIMEL CE376). This study evaluates the vertical distribution and temporal evolution of aerosols observed in the subtropical North Atlantic region, covering Saharan dust, volcanic aerosols, and fresh and aged wildfire plumes. Measurements were conducted between August 2021 and August 2023, using a modified two-wavelength Klett inversion method to derive the aerosol backscatter and extinction coefficients from CE376 lidar measurements. To assess the performance of the CE376 system, an intercomparison campaign with an MPL-4B lidar (MPLNET) was conducted, with both systems were collocated at the Izaña Atmospheric Research Centre (Canary Islands, Spain). Both instruments depicted the vertical aerosol structure similarly. Discrepancies were primarily attributed to errors in determining the overlap function and depolarization calibration in each instrument, as well as the greater influence of solar background radiation on the CE376 system during daylight. The absolute difference in the volume depolarization ratio (δv) was 0.003, which decreased to 0.002 when only nighttime data were analyzed. The combination of the two channels of the CE376 provided valuable insights into particle linear depolarization (δP), extinction Ångström exponent (EAE ()) and attenuated color ratio (ACR ()). Fresh Saharan dust particles, characterized by large, non-spherical morphology and a well-mixed vertical layer, exhibited the lowest EAE
(), the highest ACR () and δP (532) >0.15. In contrast, smaller particles with quasi-homogeneous morphology were attributed to sulfate aerosols from the early stages of the Cumbre Vieja volcano eruption and aged Canadian wildfire plumes traveling across the Atlantic. These aerosols showed the lowest δP (0.03 for volcanic sulfate and 0.08 for aged
wildfire aerosols) and the highest EAE () (1.5 and 1.2, respectively). Intermediate values of these retrieved parameters were associated with a heterogenous mixture of ash, soot and charred vegetation from fresh local forest wildfires. The retrieved properties underscore the suitability of the CE376 micro-lidar for continuous monitoring and characterization of the temporal and vertical distribution of atmospheric aerosols.
Sara Herrero-Anta, Roberto Román, Daniel González-Fernández, Claudia Emde, David Mateos, Celia Herrero del Barrio, Ramiro González, Oleg Dubovik, Carlos Toledano, Abel Calle, Victoria E. Cachorro, Bernhard Mayer, Ángel M. de Frutos, Impact of cloud presence on sky radiances and the retrieval of aerosol properties, https://doi.org/10.1016/j.atmosres.2025.107938
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This paper explores the influence of the presence of clouds on sky radiances. It also analyses their impact on the retrieval of aerosol properties when using an inversion algorithm whose radiative transfer model (RTM) is designed for cloud-free atmospheres. For that, synthetic observations are simulated for 9 partially cloudy skies and for their equivalent cloud-free skies, considering 16 different aerosol scenarios. A parameter named cloud enhancement factor (CEF) has been used to determine the modifications induced in the sky radiances by each partially cloudy scenario with respect to the cloud-free sky. This parameter indicates that the sky radiances remaining after applying a cloud-screening are affected by the presence of clouds. In general, they show enhancements between 0 and 20 % with respect to the cloud-free radiances, depending on the cloudy conditions and the scattering angle. The synthetic observations used as input for the retrieval of aerosol properties are the ones required by the inversion strategy used, GRASPpac: the aerosol optical depth (AOD) and sky radiances at 4 different wavelengths together with the ceilometer range corrected signal (RCS). In partially cloudy scenarios with low CEFs, the aerosol properties do not present significant changes with respect to the cloud-free conditions. However, for partially cloudy scenarios with higher CEFs, a clear differentiation between the aerosol optical properties retrieved with and without clouds is observed. In these scenarios, the precision of the retrieval is similar for both conditions, but the accuracy is lower for the cloudy conditions. In particular, under partially cloudy conditions, it is observed an overestimation of the real refractive index (RRI) and the single scattering albedo (SSA) between 0.05 and 0.06 and between 0.03 and 0.06 respectively, and an underestimation of the asymmetry factor (g) and the imaginary refractive index (IRI) of about −0.02 and − 0.005, respectively. These values slightly vary with the aerosol load and wavelength for the RRI and SSA. The effects on the size distribution parameters are very small, concluding that the impact of clouds is noticeable in the optical properties but not so much in the microphysical part.
Rosa D. García, África Barreto, Celia Rey, Eugenio Fraile-Nuez, Alba González-Vega, Sergio F. León-Luis, Antonio Alcantara, A. Fernando Almansa, Carmen Guirado-Fuentes, Pablo González-Sicilia, Victoria E. Cachorro, Frederic Bouchar,Aerosol retrievals derived from a low-cost Calitoo sun-photometer taken on board a research vessel, https://doi.org/10.1016/j.atmosenv.2024.120888
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This study presents a comprehensive 5-year period assessment of aerosol optical depth (AOD) and Å ngströn Exponent (AE) data from a hand-held Calitoo sun photometer on board the
Ángeles Alvariño research vessel. Observations spanned March 2018 to September 2023, focusing on key maritime regions such as the
Canary Islands, coasts of
North Africa, the Mediterranean, Portugal, the Cantabrian, and the Bay of Biscay. The Calitoo device measures solar irradiance at three wavelengths (465, 540, and 619 nm). Uncertainty analysis for Calitoo AOD retrievals was performed using the Monte Carlo method, yielding an expanded uncertainty (U
𝐴𝑂𝐷) ranging between 0.008 and 0.050 with a mean and standard deviation of 0.032 ± 0.008 for the three wavelengths. Our results also highlight the remarkable calibration stability of the Calitoo (
< 2.6%) over this 5-year period. Calitoo AOD values were assessed using reference AOD data from Santa Cruz de Tenerife (the Canary Islands), El Arenosillo (Huelva), and Palma de Mallorca (the Balearic Islands) AERONET (Aerosol Robotic Network) stations. The comparison revealed a good agreement with
correlation coefficients ranging from 0.727 to 0.917 and mean bias ranging from -0.030 to -0.001. Additionally, the Calitoo AOD data were compared with MODIS (Moderate Resolution Imaging Spectroradiometer) and CAMS-ECMWF (Copernicus Atmosphere Monitoring Service-European Centre for Medium-Range Weather Forecasts) aerosol products obtaining that Calitoo AOD values were generally lower, showing negative mean bias of -0.063 and -0.024, respectively.
The aerosol characterizations using AE vs. AOD plots in the three maritime study regions using 5-years of non-routine Calitoo data are similar to the corresponding aerosol characterizations performed with simultaneous AERONET-Cimel data.
These findings underscore Calitoo’s reliability for aerosol studies in regions where AERONET instruments or other aerosol networks are unavailable. Likewise, given the low cost of Calitoo photometers, they could be deployed onboard a large number of merchant and passenger ships or in other remote or under-monitored areas, providing near real-time AOD/AE data to enhance our understanding of aerosols processes or for model or satellite assimilation/validation.
Daskalopoulou, V., Raptis, P. I., Tsekeri, A., Amiridis, V., Kazadzis, S., Ulanowski, Z., Charmandaris, V., Tassis, K., and Martin, W.: Linear polarization signatures of atmospheric dust with the SolPol direct-sun polarimeter, Atmos. Meas. Tech., 16, 4529–4550, https://doi.org/10.5194/amt-16-4529-2023, 2023.
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Dust particles in lofted atmospheric layers may present a preferential orientation, which could be detected from the resulting dichroic extinction of the transmitted sunlight. The first indications were provided relatively recently on atmospheric dust layers using passive polarimetry, when astronomical starlight observations of known polarization were found to exhibit an excess in linear polarization, during desert dust events that reached the observational site. We revisit the previous observational methodology by targeting dichroic extinction of transmitted sunlight through extensive atmospheric dust layers utilizing a direct-sun polarimeter, which is capable to continuously monitor the polarization of elevated aerosol layers. In this study, we present the unique observations from the Solar Polarimeter (SolPol) for different periods within 2 years, when the instrument was installed in the remote monitoring station of PANGEA – the PANhellenic GEophysical observatory of Antikythera – in Greece. SolPol records polarization, providing all four Stokes parameters, at a default wavelength band centred at 550 nm with a detection limit of 10−7. We, overall, report on detected increasing trends of linear polarization, reaching up to 700 parts per million, when the instrument is targeting away from its zenith and direct sunlight propagates through dust concentrations over the observatory. This distinct behaviour is absent on measurements we acquire on days with lack of dust particle concentrations and in general of low aerosol content. Moreover, we investigate the dependence of the degree of linear polarization on the layers’ optical depth under various dust loads and solar zenith angles and attempt to interpret these observations as an indication of dust particles being preferentially aligned in the Earth’s atmosphere.
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Spectroradiometric measurements of direct solar irradiance traceable to the SI were performed by three spectroradiometer systems during a 3-week campaign in September 2022 at the Izaña Atmospheric Observatory (IZO) located on the island of Tenerife, Canary Islands, Spain. The spectroradiometers provided direct spectral irradiance measurements in the spectral ranges 300 to 550 nm (QASUME), 550 to 1700 nm (QASUME-IR), 300 to 2150 nm (BiTec Sensor, BTS), and 316 to 1030 nm (Precision Solar Spectroradiometer, PSR), with relative standard uncertainties of 0.7 %, 0.9 %, and 1 % for QASUME/QASUME-IR, the PSR, and the BTS respectively. The calibration of QASUME and QASUME-IR was validated prior to this campaign at Physikalisch-Technische Bundesanstalt (PTB) by measuring the spectral irradiance from two spectral irradiance sources, the high-temperature blackbody BB3200pg as a national primary standard and the tuneable laser facility TULIP. The top-of-atmosphere (ToA) solar irradiance spectra from the spectroradiometers were retrieved from direct solar irradiance measurements using zero-air-mass extrapolation during cloud-free conditions, which were then compared to the TSIS-1 Hybrid Solar Reference Spectrum (HSRS). These ToA solar spectra agreed to within 1 % for spectral ranges longer than 400 nm (for QASUME also at shorter wavelengths) in the spectral regions free of significant trace gas absorption and were well within the combined uncertainties over the full investigated spectral range. Using the results from the comparison with QASUME, the relative standard uncertainty of the TSIS-1 HSRS ToA solar spectrum in the spectral range 308 to 400 nm could be reduced from its nominal 1.3 % to 0.8 %, representing the relative standard uncertainty of the QASUME ToA solar spectrum in this spectral range. The spectral aerosol optical depth (AOD) retrieved from the solar irradiance measurements of these spectroradiometers using the TSIS-1 HSRS as the reference ToA solar spectrum agreed to within 0.01 in optical depth in nearly all common spectral channels of two narrowband filter radiometers belonging to the Global Atmosphere Watch Precision Filter Radiometer (GAW-PFR) network and Aerosol Robotic Network (AERONET). This study shows that it is now possible to retrieve spectral AOD over the extended spectral range from 300 to 1700 nm using solar irradiance measurements traceable to the SI using laboratory-calibrated spectroradiometers with similar quality to that from traditional Langley-based calibrated instruments. The main improvement to previous investigations is the recent availability of the high-spectral-resolution TSIS-1 HSRS with very low uncertainties, which provides the top-of-atmosphere reference for the spectral atmospheric transmission measurements obtained from ground-based solar irradiance measurements.
Tsekeri A., Gialitaki A., Di Paolantonio M., Dionisi D., Liberti G.L., Fernandes A., Szkop A., Pietruczuk A., Pérez-Ramírez D., Granados Muñoz
M.J., Guerrero-Rascado J.L., Alados-Arboledas L., Bermejo-Pantaleón D., Bravo-Aranda J.A., Kampouri A., Marinou E., Amiridis V., Sicard M., Comerón A., Muñoz-Porcar C., Rodríguez-Gómez A., Romano S., Perrone M.R., Shang X., Komppula M., Mamouri R.-E., Nisantzi A., Hadjimitsis D., Navas-Guzmán F., Haefele A., Szczepanik D., Tomczak A., Stachlewska I., Bele, 2023, Combined sun-photometer/lidar inversion: lessons learned during the EARLINET/ACTRIS COVID-19 Campaign, Atmospheric Measurement Techniques, vol. 16(24), 6025-6050, 10.5194/amt-16-6025-2023
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The European Aerosol Research Lidar Network (EARLINET), part of the Aerosols, Clouds and Trace gases Research Infrastructure (ACTRIS), organized an intensive observational campaign in May 2020, with the objective of monitoring the atmospheric state over Europe during the COVID-19 lockdown and relaxation period. Besides the standard operational processing of the lidar data in EARLINET, for seven EARLINET sites having collocated sun-photometric observations in the Aerosol Robotic Network (AERONET), a network exercise was held in order to derive profiles of the concentration and effective column size distributions of the aerosols in the atmosphere, by applying the GRASP/GARRLiC (from Generalized Aerosol Retrieval from Radiometer and Lidar Combined data – GARRLiC – part of the Generalized Retrieval of Atmosphere and Surface Properties – GRASP) inversion algorithm. The objective of this network exercise was to explore the possibility of identifying the anthropogenic component and of monitoring its spatial and temporal characteristics in the COVID-19 lockdown and relaxation period. While the number of cases is far from being statistically significant so as to provide a conclusive description of the atmospheric aerosols over Europe during this period, this network exercise was fundamental to deriving a common methodology for applying GRASP/GARRLiC to a network of instruments with different characteristics. The limits of the approach are discussed, in particular the missing information close to the ground in the lidar measurements due to the instrument geometry and the sensitivity of the GRASP/GARRLiC retrieval to the settings used, especially for cases with low aerosol optical depth (AOD) like the ones we show here. We found that this sensitivity is well-characterized in the GRASP/GARRLiC products, since it is included in their retrieval uncertainties.
Campanelli, M., Estellés, V., Kumar, G., Nakajima, T., Momoi, M., Gröbner, J., Kazadzis, S., Kouremeti, N., Karanikolas, A., Barreto, A., Nevas, S., Schwind, K., Schneider, P., Harju, I., Kärhä, P., Diémoz, H., Kudo, R., Uchiyama, A., Yamazaki, A., Iannarelli, A. M., Mevi, G., Di Bernardino, A., and Casadio, S.: Evaluation of on-site calibration procedures for SKYNET Prede POM sun–sky photometers, Atmos. Meas. Tech., 17, 5029–5050, https://doi.org/10.5194/amt-17-5029-2024, 2024.
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To retrieve columnar intensive aerosol properties from sun–sky photometers, both irradiance and radiance calibration factors are needed. For the irradiance the solar calibration constant, V0, which denotes the instrument counts for a direct normal solar flux extrapolated to the top of the atmosphere, must be determined. The solid view angle, SVA, is a measure of the field of view of the instrument, and it is important for obtaining the radiance from sky diffuse irradiance measurements. Each of the three sun-photometer networks considered in the present study (SKYNET, AERONET, WMO GAW) adopts different protocols of calibration, and we evaluate the performance of the on-site calibration procedures, applicable to every kind of sun–sky photometer but tested in this analysis only on SKYNET Prede POM01 instruments, during intercomparison campaigns and laboratory calibrations held in the framework of the Metrology for Aerosol Optical Properties (MAPP) European Metrology Programme for Innovation and Research (EMPIR) project. The on-site calibration, performed as frequently as possible (ideally monthly) to monitor changes in the device conditions, allows operators to track and evaluate the calibration status on a continuous basis, considerably reducing the data gaps incurred by the periodic shipments for performing centralized calibrations. The performance of the on-site calibration procedures for V0 was very good at sites with low turbidity, showing agreement with a reference calibration between 0.5 % and 1.5 % depending on wavelengths. In the urban area, the agreement decreases between 1.7 % and 2.5 %. For the SVA the difference varied from a minimum of 0.03 % to a maximum of 3.46 %.
Masoom, A., Kazadzis, S., Valeri, M., Raptis, I.-P., Brizzi, G., Papachristopoulou, K., Barnaba, F., Casadio, S., Kreuter, A., and Niro, F.: Assessment of the impact of NO2 contribution on aerosol-optical-depth measurements at several sites worldwide, Atmos. Meas. Tech., 17, 5525–5549, https://doi.org/10.5194/amt-17-5525-2024, 2024
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This work aims at investigating the effect of NO2 absorption on aerosol-optical-depth (AOD) measurements and Ångström exponent (AE) retrievals of sun photometers by the synergistic use of accurate NO2 characterization for optical-depth estimation from co-located ground-based measurements. The analysis was performed for ∼ 7 years (2017–2023) at several sites worldwide for the AOD measurements and AE retrievals by Aerosol Robotic Network (AERONET) sun photometers which use OMI (Ozone Monitoring Instrument) climatology for NO2 representation. The differences in AOD and AE retrievals by NO2 absorption are accounted for using high-frequency columnar NO2 measurements by a co-located Pandora spectroradiometer belonging to the Pandonia Global Network (PGN). NO2 absorption affects the AOD measurements in UV-Vis (visible) range, and we found that the AOD bias is the most affected at 380 nm by NO2 differences, followed by 440, 340, and 500 nm, respectively. AERONET AOD was found to be overestimated in half of the cases, while also underestimated in other cases as an impact of the NO2 difference from “real” (PGN NO2) values. Overestimations or underestimations are relatively low. About one-third of these stations showed a mean difference in NO2 and AOD (at 380 and 440 nm) above 0.5 × 10−4 mol m−2 and 0.002, respectively, which can be considered a systematic contribution to the uncertainties in the AOD measurements that are reported to be of the order of 0.01. However, under extreme NO2 loading scenarios (i.e. 10 % highest differences) at highly urbanized/industrialized locations, even higher AOD differences were observed that were at the limit of or higher than the reported 0.01 uncertainty in the AOD measurement. PGN NO2-based sensitivity analysis of AOD difference suggested that for PGN NO2 varying between 2 × 10−4 and 8 × 10−4 mol m−2, the median AOD differences were found to rise above 0.01 (even above 0.02) with the increase in NO2 threshold (i.e. the lower limit from 2 × 10−4 to 8 × 10−4 mol m−2). The AOD-derivative product, AE, was also affected by the NO2 correction (discrepancies between the AERONET OMI climatological representation of NO2 values and the real PGN NO2 measurements) on the spectral AOD. Normalized frequency distribution of AE (at 440–870 and 340–440 nm wavelength pair) was found to be narrower for a broader AOD distribution for some stations, and vice versa for other stations, and a higher relative error at the shorter wavelength (among the wavelength pairs used for AE estimation) led to a shift in the peak of the AE difference distribution towards a higher positive value, while a higher relative error at a lower wavelength shifted the AE difference distribution to a negative value for the AOD overestimation case, and vice versa for the AOD underestimation case. For rural locations, the mean NO2 differences were found to be mostly below 0.50 × 10−4 mol m−2, with the corresponding AOD differences being below 0.002, and in extreme NO2 loading scenarios, it went above this value and reached above 1.00 × 10−4 mol m−2 for some stations, leading to higher AOD differences but below 0.005. Finally, AOD and AE trends were calculated based on the original AERONET AOD (based on AERONET OMI climatological NO2), and its comparison with the mean differences in the AERONET and PGN NO2-corrected AOD was indicative of how NO2 correction could potentially affect realistic AOD trends.
Karanikolas, A., Kouremeti, N., Campanelli, M., Estellés, V., Momoi, M., Kumar, G., Nyeki, S., and Kazadzis, S.: Intercomparison of aerosol optical depth retrievals from GAW-PFR and SKYNET sun photometer networks and the effect of calibration, Atmos. Meas. Tech., 17, 6085–6105, https://doi.org/10.5194/amt-17-6085-2024, 2024.
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In this study, we assess the homogeneity of aerosol optical depth (AOD) between two sun photometer networks, the Global Atmosphere Watch-Precision Filter Radiometer (GAW-PFR) and the European SKYNET radiometers network (ESR), at the common wavelengths of their main instruments (500 and 870 nm). The main focus of this work is to evaluate the effect of the improved Langley plot calibration method (ILP) used by SKYNET and to investigate the factors affecting its performance. We used data from three intercomparison campaigns that took place during 2017–2021. Each campaign was organized at two locations (mountainous rural – Davos, Switzerland; urban – Rome, Italy). Our analysis shows that differences in AOD due to post-processing and instrument differences are minor. The main factor leading to AOD differences is the calibration method. We found a systematic underestimation of AOD in ESR compared to in GAW-PFR due to underestimation of the calibration constant calculated with the ILP method compared to the calibration transfers using the PFR as a reference. The calibration and AOD differences are smaller in Davos, where the traceability criteria are satisfied at 870 nm and where the median differences are below 0.01 at 500 nm. In Rome, the AOD median differences at 500 nm were in the 0.015–0.034 range. We conducted a sensitivity study, which shows that part of the difference can potentially be explained by errors in the assumed surface albedo and instrument solid-view angle provided as inputs to the ILP code (based on Skyrad pack 4.2). Our findings suggest that the ILP method is mainly sensitive to the measured sky radiance. The underestimation in calibration is probably caused by an error in the retrieved scattering AOD (sc-AOD) through the sky radiance inversion. Using an alternative retrieval method (Skyrad MRI pack version 2) to derive sc-AOD and to recalibrate the instruments with the ILP method, we found no significant differences between the retrieved sc-AOD and no systematic increase in the ILP-derived calibration constant when using the MRI pack for sc-AOD inversion instead of the Skyrad 4.2. The potential error may be a result of the model assumptions used for the sky radiance simulations. In conclusion, the on-site calibration of sun photometers has several advantages, including the fact that instrument shipments and data gaps can be avoided. However, it has also the disadvantages of a larger uncertainty and significant systematic differences compared to the traditional Langley calibration performed under low- and constant-AOD conditions at high-altitude sites. The larger uncertainty of the ILP method can be attributed to the required modelling and input parameters.
Moustaka, A.Korras-Carraca, M.-B. Papachristopoulou, K.; Stamatis, M. Fountoulakis, I.; Kazadzis, S. Proestakis, E.; Amiridis, V.Tourpali, K.; Georgiou, T. Assessing Lidar Ratio Impact on CALIPSO Retrievals Utilized for the Estimation of Aerosol SW Radiative Effects across North Africa, Middle East and Europe. Remote Sens. 2024, 16, 1689. https://doi.org/10.3390/rs16101689
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North Africa, the Middle East, and Europe (NAMEE domain) host a variety of suspended particles characterized by different optical and microphysical properties. In the current study, we investigate the importance of the lidar ratio (LR) on Cloud-Aerosol Lidar with Orthogonal Polarization–Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIOP-CALIPSO) aerosol retrievals towards assessing aerosols’ impact on the Earth-atmosphere radiation budget. A holistic approach has been adopted involving collocated Aerosol Robotic Network (AERONET) observations, Radiative Transfer Model (RTM) simulations, as well as reference radiation measurements acquired using spaceborne (Clouds and the Earth’s Radiant Energy System-CERES) and ground-based (Baseline Surface Radiation Network-BSRN) instruments. We are assessing the clear-sky shortwave (SW) direct radiative effects (DREs) on 550 atmospheric scenes, identified within the 2007–2020 period, in which the primary tropospheric aerosol species (dust, marine, polluted continental/smoke, elevated smoke, and clean continental) are probed using CALIPSO. RTM runs have been performed relying on CALIOP retrievals in which the default and the DeLiAn (Depolarization ratio, Lidar ratio, and Ångström exponent)-based aerosol-speciated LRs are considered. The simulated fields from both configurations are compared against those produced when AERONET AODs are applied. Overall, the DeLiAn LRs leads to better results mainly when mineral particles are either solely recorded or coexist with other aerosol species (e.g., sea-salt). In quantitative terms, the errors in DREs are reduced by ~26–27% at the surface (from 5.3 to 3.9 W/m2) and within the atmosphere (from −3.3 to −2.4 W/m2). The improvements become more significant (reaching up to ~35%) for moderate-to-high aerosol loads (AOD ≥ 0.2).
Amiridis, V.; Kazadzis, S.; Gkikas, A.; Voudouri, K.A.; Kouklaki, D.; Koukouli, M.-E.; Garane, K.; Georgoulias, A.K.; Solomos, S.; Varlas, G.; et al. Natural Aerosols, Gaseous Precursors and Their Impacts in Greece: A Review from the Remote Sensing Perspective. Atmosphere 2024, 15, 753. https://doi.org/10.3390/atmos15070753, 2024
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The Mediterranean, and particularly its Eastern basin, is a crossroad of air masses advected from Europe, Asia and Africa. Anthropogenic emissions from its megacities meet over the Eastern Mediterranean, with natural emissions from the Saharan and Middle East deserts, smoke from frequent forest fires, background marine and pollen particles emitted from ocean and vegetation, respectively. This mixture of natural aerosols and gaseous precursors (Short-Lived Climate Forcers—SLCFs in IPCC has short atmospheric residence times but strongly affects radiation and cloud formation, contributing the largest uncertainty to estimates and interpretations of the changing cloud and precipitation patterns across the basin. The SLCFs’ global forcing is comparable in magnitude to that of the long-lived greenhouse gases; however, the local forcing by SLCFs can far exceed those of the long-lived gases, according to the Intergovernmental Panel on Climate Change (IPCC). Monitoring the spatiotemporal distribution of SLCFs using remote sensing techniques is important for understanding their properties along with aging processes and impacts on radiation, clouds, weather and climate. This article reviews the current state of scientific know-how on the properties and trends of SLCFs in the Eastern Mediterranean along with their regional interactions and impacts, depicted by ground- and space-based remote sensing techniques
Masoom, A., Fountoulakis, I., Kazadzis, S., Raptis, I.-P., Kampouri, A., Psiloglou, B. E., Kouklaki, D., Papachristopoulou, K., Marinou, E., Solomos, S., Gialitaki, A., Founda, D., Salamalikis, V., Kaskaoutis, D., Kouremeti, N., Mihalopoulos, N., Amiridis, V., Kazantzidis, A., Papayannis, A., Zerefos, C. S., and Eleftheratos, K.: Investigation of the effects of the Greek extreme wildfires of August 2021 on air quality and spectral solar irradiance, Atmos. Chem. Phys., 23, 8487–8514, https://doi.org/10.5194/acp-23-8487-2023, 2023.
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In August 2021, a historic heatwave was recorded in Greece which resulted in extreme wildfire events that strongly affected the air quality over the city of Athens. Saharan dust was also transferred over Greece on certain days of the same period due to the prevailing southern winds. The impact of these events on air quality and surface solar radiation is investigated in this study. Event characterization based on active and passive remote sensing instrumentation has been performed. The study shows that significantly increased levels of air pollution were recorded from the end of July to the first week of August. The smoke led to unusually high aerosol optical depth (AOD) values (up to 3.6 at 500 nm), high Ångström exponent (AE) (up to 2.4 at 440–870 nm), and a strong and negative dependence of single-scattering albedo (SSA) on wavelength that was observed to decrease from 0.93 at 440 nm to 0.86 at 1020 nm, while the dust event led to high AOD (up to 0.7 at 500 nm), low AE (up to 0.9 at 440–870 nm), and a positive dependence of SSA on wavelength that was observed to increase from 0.89 at 440 nm to 0.95 at 1020. Furthermore, the smoke plume was also detected over the PANhellenic GEophysical observatory of Antikythera on 7 August, which is about 240 km away from Athens. Increased AOD values (up to ∼ 0.90 at 500 nm) associated with a high fine-mode AOD (up to ∼ 0.85 at 500 nm) and decrease in SSA with wavelength suggested the dominance of fine biomass burning aerosols. The impact of dust and smoke on solar irradiance revealed significant differences in the spectral dependence of the attenuation caused by the two different aerosol types. The attenuation of solar irradiance in the ultraviolet (UV-B) spectrum was found to be much lower in the case of dust compared to smoke for similar AOD500 values. Differences were less pronounced in the near-infrared and visible spectral regions. The large AODs during the wildfires resulted in a decrease in the noon UV index by up to 53 %, as well as in the daily effective doses for the production of vitamin D (up to 50 %), in the daily photosynthetically active radiation (up to 21 %) and in the daily global horizontal irradiance (up to 17 %), with serious implications for health, agriculture, and energy. This study highlights the wider impacts of wildfires that are part of the wider problem for Mediterranean countries, whose frequency is predicted to increase in view of the projected increasing occurrence of summer heatwaves.
Solomos, S.; Spyrou, C.; Barreto, A.; Rodríguez, S.; González, Y.; Neophytou, M.K.A.; Mouzourides, P.; Bartsotas, N.S.; Kalogeri, C.; Nickovic, S.; et al. The Development of METAL-WRF Regional Model for the Description of Dust Mineralogy in the Atmosphere. Atmosphere 2023, 14, 1615. https://doi.org/10.3390/atmos14111615
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The mineralogical composition of airborne dust particles is an important but often neglected parameter for several physiochemical processes, such as atmospheric radiative transfer and ocean biochemistry. We present the development of the METAL-WRF module for the simulation of the composition of desert dust minerals in atmospheric aerosols. The new development is based on the GOCART-AFWA dust module of WRF-Chem. A new wet deposition scheme has been implemented in the dust module alongside the existing dry deposition scheme. The new model includes separate prognostic fields for nine (9) minerals: illite, kaolinite, smectite, calcite, quartz, feldspar, hematite, gypsum, and phosphorus, derived from the GMINER30 database and also iron derived from the FERRUM30 database. Two regional model sensitivity studies are presented for dust events that occurred in August and December 2017, which include a comparison of the model versus elemental dust composition measurements performed in the North Atlantic (at Izaña Observatory, Tenerife Island) and in the eastern Mediterranean (at Agia Marina Xyliatos station, Cyprus Island). The results indicate the important role of dust minerals, as dominant aerosols, for the greater region of North Africa, South Europe, the North Atlantic, and the Middle East, including the dry and wet depositions away from desert sources. Overall, METAL-WRF was found to be capable of reproducing the relative abundances of the different dust minerals in the atmosphere. In particular, the concentration of iron (Fe), which is an important element for ocean biochemistry and solar absorption, was modeled in good agreement with the corresponding measurements at Izaña Observatory (22% overestimation) and at Agia Marina Xyliatos site (4% overestimation). Further model developments, including the implementation of newer surface mineralogical datasets, e.g., from the NASA-EMIT satellite mission, can be implemented in the model to improve its accuracy.
Herrero del Barrio, C.; Mateos, D.; Román, R.; González, R.; Herrero-Anta, S.; González-Fernández, D.; Calle, A.; Toledano, C.; Cachorro, V.E.; De Frutos Baraja, Á.M. Analysis of Daytime and Night-Time Aerosol Optical Depth from Solar and Lunar Photometry in Valladolid (Spain). Remote Sens. 2023, 15, 5362. https://doi.org/10.3390/rs15225362
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Aerosol optical depth (AOD) at night-time has become a hot topic in recent years due to the development of new instruments recording accurate ground-based lunar irradiance measurements, and the development of calibration methods and extraterrestrial irradiance models adapted to lunar photometry. This study uses all daytime and night-time AOD data available at Valladolid (Spain) from October 2016 to March 2022 in order to analyze its behavior and the added contribution of night data. The annual, monthly and daily AOD evolution is studied comparing daytime and night-time values and checking the correlation between them. For this purpose, the daily averages are computed, showing an annual pattern, with low AOD values throughout the year (mean value of AOD at 440 nm: 0.122), where winter months have the lower and summer the higher values, as observed in previous studies. All these AOD values are modulated by frequent desert dust events over the Iberian Peninsula, with a strong influence on daily and monthly mean values in February and March, where the strongest desert outbreaks occurred. The added new data confirm these results and the good correlation between daytime and night-time data. Also, a complete daily evolution is shown, observing that AOD and Ångström exponent (AE) mean values vary by only ±0.02 in 24 h, with a maximum value at 06:00 UTC and minimum at 18:00 UTC for both parameters.
González-Fernández, D.; Román, R.; Mateos, D.; Herrero del Barrio, C.; Cachorro, V.E.; Copes, G.; Sánchez, R.; García, R.D.; Doppler, L.; Herrero-Anta, S.; AntuñaSánchez, J.C.; Barreto, A.; González, R.; Gatón, J.; Calle, A.; Toledano, C; de Frutos A. Retrieval of Solar Shortwave Irradiance from All-Sky Camera Images. Remote Sens. 2024, 16, 3821. https://doi.org/10.3390/rs16203821
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The present work proposes a new model based on a convolutional neural network (CNN) to retrieve solar shortwave (SW) irradiance via the estimation of the cloud modification factor (CMF) from daytime sky images captured by all-sky cameras; this model is named CNN-CMF. To this end, a total of 237,669 sky images paired with SW irradiance measurements obtained by using pyranometers were selected at the following three sites: Valladolid and Izaña, Spain, and Lindenberg, Germany. This dataset was randomly split into training and testing sets, with the latter excluded from the training model in order to validate it using the same locations. Subsequently, the test dataset was compared with the corresponding SW irradiance measurements obtained by the pyranometers in scatter density plots. The linear fit shows a high determination coefficient (𝑅2) of 0.99. Statistical analyses based on the mean bias error (MBE) values and the standard deviation (SD) of the SW irradiance differences yield results close to −2% and 9%, respectively. The MBE indicates a slight underestimation of the CNN-CMF model compared to the measurement values. After its validation, model performance was evaluated at the Antarctic station of Marambio (Argentina), a location not used in the training process. A similar comparison between the model-predicted SW irradiance and pyranometer measurements yielded 𝑅2=0.95, with an MBE of around 2% and an SD of approximately 26%. Although the precision provided by the SD at the Marambio station is lower, the MBE shows that the model’s accuracy is similar to previous results but with a slight overestimation of the SW irradiance. Finally, the determination coefficient improved to 0.99, and the MBE and SD are about 3% and 11%, respectively, when the CNN-CMF model is used to estimate daily SW irradiation values.
Herrero-Anta, S., Román, R., Mateos, D., González, R., Antuña-Sánchez, J. C., Herreras-Giralda, M., Almansa, A. F., González-Fernández, D., Herrero del Barrio, C., Toledano, C., Cachorro, V. E., and de Frutos, Á. M.: Retrieval of aerosol properties from zenith sky radiance measurements, Atmos. Meas. Tech., 16, 4423–4443, https://doi.org/10.5194/amt-16-4423-2023, 2023.
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This study explores the potential to retrieve aerosol properties with the GRASP algorithm (Generalized Retrieval of Atmosphere and Surface Properties) using as input measurements of zenith sky radiance (ZSR), which are sky radiance values measured in the zenith direction, recorded at four wavelengths by a ZEN-R52 radiometer. To this end, the ZSR measured at 440, 500, 675 and 870 nm by a ZEN-R52 (ZSRZEN), installed in Valladolid (Spain), is employed. This instrument is calibrated by intercomparing the signal of each channel with coincident ZSR values simulated (ZSRSIM) at the same wavelengths with a radiative transfer model (RTM). These simulations are carried out using the GRASP forward module as RTM and the aerosol information from a co-located CE318 photometer belonging to AERONET (AErosol RObotic NETwork) as input. The dark signal and the signal dependence on temperature are characterized and included in the calibration process. The uncertainties for each channel are quantified by an intercomparison with a co-located CE318 photometer, obtaining lower values for shorter wavelengths; they are between 3 % for 440 nm and 21 % for 870 nm. The proposed inversion strategy for the aerosol retrieval using the ZSRZEN measurements as input, i.e. so-called GRASP-ZEN, assumes the aerosol as an external mixture of five pre-calculated aerosol types. A sensitivity analysis is conducted using synthetic ZSRZEN measurements, pointing out that these measurements are sensitive to aerosol load and type. It also assesses that the retrieved aerosol optical depth (AOD) values in general overestimate the reference ones by 0.03, 0.02, 0.02 and 0.01 for 440, 500, 675 and 870 nm, respectively. The calibrated ZSRZEN measurements, recorded during 2.5 years at Valladolid, are inverted by the GRASP-ZEN strategy to retrieve some aerosol properties like AOD. The retrieved AOD shows a high correlation with respect to independent values obtained from a co-located AERONET CE318 photometer, with determination coefficients (r2) of 0.86, 0.85, 0.79 and 0.72 for 440, 500, 675 and 870 nm, respectively, and finding uncertainties between 0.02 and 0.03 with respect to the AERONET values. Finally, the retrieval of other aerosol properties, like aerosol volume concentration for total, fine and coarse modes (VCT, VCF and VCC, respectively), is also explored. The comparison against independent values from AERONET presents r2 values of 0.57, 0.56 and 0.66 and uncertainties of 0.009, 0.016 and 0.02 µm3 µm−2 for VCT, VCF and VCC, respectively.
Scarlatti, J.L. Gómez-Amo, P.C. Valdelomar, V. Estellés, M.P. Utrillas. An improved approach to determine aerosol properties from all-sky camera imagery: Sensitivity to the partially cloud scenes. Atmospheric Environment 327 (2024) 120495. https://doi.org/10.1016/j.atmosenv.2024.120495
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We present a new approach to determine
aerosol properties from radiometrically calibrated images provided by an all-sky camera. It is designed to be used regardless of the sky conditions. However, we especially focus on partially cloudy scenes, which is the main novelty of this work. Our methodology is based on using a small sector of the image that contains the principal plane of the Sun. The RGB principal plane radiances are associated to the aerosol optical depth (AOD) and Angstrom exponent (AE)
AERONET observations through a
Gaussian Process Regression (GPR) machine learning (ML) model. We identify the cloudy points within our working sector and the principal plane signal for the RGB radiances is averaged and smoothed. Then, we use the Pérez model to synthesize the principal plane signal in the cloudy spots. Finally, 2-year dataset has been used to test the method considering different atmospheric conditions related to the presence of clouds and aerosols, according to their amount and type. In addition, we have developed a method to evaluate the quality of predictions based on the standard deviation of the GPR. This quality assurance method may be fine-tuned according to the desired accuracy based on the application for which it is intended. Our AOD and AE predictions show an excellent overall agreement with AERONET measurements that substantially improves when our quality assurance method is applied. In that case, we obtain a high degree of correlation (
¿ 0.97) and an overall MAE lower than the nominal uncertainty of AERONET measurements (0.006 and 0.05 for AOD and AE, respectively). Moreover, more than 83% and 77% of the predictions fall within the nominal uncertainty associated with AERONET measurements for AOD and AE, respectively. A comprehensive sensitivity analysis of the factors affecting the performance of the proposed methodology confirms that our method is stable and not very sensitive to external and methodological factors, especially when we apply quality assurance criteria. All this supports that our methodology is a reliable alternative to retrieve the
optical properties of aerosols independently of the cloud conditions. Our results may contribute to the operational use of all-sky cameras, which may be an interesting complement regarding the study of aerosol-cloud interactions in partially cloud scenarios.
Graßl, S., Ritter, C., Wilsch, J., Herrmann, R., Doppler, L. and Román, R.. From Polar Day to Polar Night: A Comprehensive Sun and Star Photometer Study of Trends in Arctic Aerosol Properties in Ny-Ålesund, Svalbard. Remote Sensing, 16(19), p.3725., 2024, https://www.mdpi.com/2072-4292/16/19/3725
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The climate impact of Arctic aerosols, like the Arctic Haze, and their origin are not fully understood. Therefore, long-term aerosol observations in the Arctic are performed. In this study, we present a homogenised data set from a sun and star photometer operated in the European Arctic, in Ny-Ålesund, Svalbard, of the 20 years from 2004–2023. Due to polar day and polar night, it is crucial to use observations of both instruments. Their data is evaluated in the same way and follows the cloud-screening procedure of AERONET. Additionally, an improved method for the calibration of the star photometer is presented. We found out, that autumn and winter are generally more polluted and have larger particles than summer. While the monthly median Aerosol Optical Depth (AOD) decreases in spring, the AOD increases significantly in autumn. A clear signal of large particles during the Arctic Haze can not be distinguished from large aerosols in winter. With autocorrelation analysis, we found that AOD events usually occur with a duration of several hours. We also compared AOD events with large-scale processes, like large-scale oscillation patterns, sea ice, weather conditions, or wildfires in the Northern Hemisphere but did not find one single cause that clearly determines the Arctic AOD. Therefore the observed optical depth is a superposition of different aerosol sources.
Kouklaki, D.; Kazadzis, S.; Raptis, I.-P.; Papachristopoulou, K.; Fountoulakis, I.; Eleftheratos, K. Photovoltaic Spectral Responsivity and Efficiency under Different Aerosol Conditions. Energies 2023, 16, 6644. https://doi.org/10.3390/en16186644
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While solar power applications are growing rapidly worldwide, information about solar energy availability, its characteristics and the factors that affect it are essential. Among other parameters, a reference spectrum (ASTMG-173-03) is adopted, relying on Standard Test Conditions (STC), under which Photovoltaic (PV) devices are evaluated. However, these rigorously defined conditions can vary considerably from realistic environmental conditions. The objective of the present work is to assess the impact of the variability of atmospheric composition on the spectral distribution of the incident solar spectral irradiance (SSI) and, therefore, its implication on various PV materials performance. Ground-based measurements of global horizontal SSI have been conducted using a Precision Spectroradiometer (PSR) in the framework of the ASPIRE (Atmospheric parameters affecting SPectral solar IRradiance and solar Energy) project in Athens, Greece. The gathered data in combination with spectrally resolved radiative transfer under clear-sky conditions contributed to the investigation of the atmospheric variables that attenuate irradiance (e.g., aerosols). In addition, since PV modules’ spectral absorptivity differs according to the semiconductor material used, the impact of the above-mentioned spectral features on PV performance has been investigated in order to estimate the spectral impact between the theoretical and outdoor conditions on the yield of different PV technologies. Overall, the results denote that smoke has a more significant effect than dust, while the effect on various technologies varies. The highest deviation compared to the STC was observed in the case of a-Si, reaching an absolute difference of 45% in the case of smoke particles in the atmosphere, while the maximum deviation between the different technologies reached approximately 7%.
Papachristopoulou, K., Fountoulakis, I., Bais, A. F., Psiloglou, B. E., Papadimitriou, N., Raptis, I.-P., Kazantzidis, A., Kontoes, C., Hatzaki, M., and Kazadzis, S.: Effects of clouds and aerosols on downwelling surface solar irradiance nowcasting and short-term forecasting, Atmos. Meas. Tech., 17, 1851–1877, https://doi.org/10.5194/amt-17-1851-2024, 2024.
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Solar irradiance nowcasting and short-term forecasting are important tools for the integration of solar plants into the electricity grid. Understanding the role of clouds and aerosols in those techniques is essential for improving their accuracy. In this study, we introduce improvements in the existing nowcasting and short-term forecasting operational systems SENSE (Solar Energy Nowcasting System) and NextSENSE achieved by using a new configuration and by upgrading cloud and aerosol inputs, and we also investigate the limitations of evaluating such models using surface-based sensors due to cloud effects. We assess the real-time estimates of surface global horizontal irradiance (GHI) produced by the improved SENSE2 operational system at high spatial and temporal resolution (∼ 5 km, 15 min) for a domain including Europe and the Middle East–North Africa (MENA) region and the short-term forecasts of GHI (up to 3 h ahead) produced by the NextSENSE2 system against ground-based measurements from 10 stations across the models’ domain for a whole year (2017).
Results for instantaneous (every 15 min) comparisons show that the GHI estimates are within ±50 W m−2 (or ±10 %) of the measured GHI for 61 % of the cases after the implementation of the new model configuration and a proposed bias correction. The bias ranges from −12 to 23 W m−2 (or from −2 % to 6.1 %) with a mean value of 11.3 W m−2 (2.3 %). The correlation coefficient is between 0.83 and 0.96 and has a mean value of 0.93. Statistics are significantly improved when integrating on daily and monthly scales (the mean bias is 3.3 and 2.7 W m−2, respectively). We demonstrate that the main overestimation of the SENSE2 GHI is linked with the uncertainties of the cloud-related information within the satellite pixel, while relatively low underestimation, linked with aerosol optical depth (AOD) forecasts (derived from the Copernicus Atmospheric Monitoring Service – CAMS), is reported for cloudless-sky GHI. The highest deviations for instantaneous comparisons are associated with cloudy atmospheric conditions, when clouds obscure the sun over the ground-based station. Thus, they are much more closely linked with satellite vs. ground-based comparison limitations than the actual model performance. The NextSENSE2 GHI forecasts based on the cloud motion vector (CMV) model outperform the persistence forecasting method, which assumes the same cloud conditions for future time steps. The forecasting skill (FS) of the CMV-based model compared to the persistence approach increases with cloudiness (FS is up to ∼ 20 %), which is linked mostly to periods with changes in cloudiness (which persistence, by definition, fails to predict). Our results could be useful for further studies on satellite-based solar model evaluations and, in general, for the operational implementation of solar energy nowcasting and short-term forecasting, supporting solar energy production and management.
Fountoulakis, I., Tsekeri, A., Kazadzis, S., Amiridis, V., Nersesian, A., Tsichla, M., Proestakis, E., Gkikas, A., Papachristopoulou, K., Barlakas, V., Emde, C., and Mayer, B.: A sensitivity study on radiative effects due to the parameterization of dust optical properties in models, Atmos. Chem. Phys., 24, 4915–4948, https://doi.org/10.5194/acp-24-4915-2024, 2024.
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Most of the dust models underestimate the load of the large dust particles, consider spherical shapes instead of irregular ones, and have to deal with a wide range of the dust refractive index (RI) to be used. This leads to an incomplete assessment of the dust radiative effects and dust-related impacts on climate and weather. The current work aims to provide an assessment, through a sensitivity study, of the limitations of models to calculate the dust direct radiative effect (DRE) due to the underrepresentation of its size, RI, and shape. We show that the main limitations stem from the size and RI, while using a more realistic shape plays only a minor role, with our results agreeing with recent findings in the literature. At the top of the atmosphere (TOA) close to dust sources, the underestimation of size issues an underestimation of the direct warming effect of dust of ∼ 18–25 W m−2, for DOD = 1 (dust optical depth) at 0.5 µm, depending on the solar zenith angle (SZA) and RI. The underestimation of the dust size in models is less above the ocean than above dust sources, resulting in an underestimation of the direct cooling effect of dust above the ocean by up to 3 W m−2, for aerosol optical depth (AOD) of 1 at 0.5 µm. We also show that the RI of dust may change its DRE by 80 W m−2 above the dust sources and by 50 W m−2 at downwind oceanic areas for DOD = 1 at 0.5 µm at TOA. These results indicate the necessity of including more realistic sizes and RIs for dust particles in dust models, in order to derive better estimations of the dust DRE, especially near the dust sources and mostly for studies dealing with local radiation effects of dust aerosols.
V. Salgueiro, J.L. Guerrero-Rascado, M.J. Costa, R. Román, A. Cazorla, A. Serrano, F. Molero, M. Sicard, C. Córdoba-Jabonero, D. Bortoli, A. Comerón, F.T. Couto, M.Á. López-Cayuela, D. Pérez-Ramírez, M. Potes, J.A. Muñiz-Rosado, M.A. Obregón, R. Barragán, D.C.F.S. Oliveira, J. Abril-Gago, R. González, C. Gíl-Díaz, I. Foyo-Moreno, C. Muñoz-Porcar, M.J. Granados-Muñoz, A. Rodríguez-Gómez, M. Herreras-Giralda, J.A. Bravo-Aranda, C.V. Carvajal-Pérez, A. Barreto, L. Alados-Arboledas,Characterization of Tajogaite volcanic plumes detected over the Iberian Peninsula from a set of satellite and ground-based remote sensing instrumentation,https://doi.org/10.1016/j.rse.2023.113684
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Three volcanic plumes were detected during the Tajogaite volcano eruptive activity (Canary Islands, Spain, September–December 2021) over the Iberian Peninsula. The spatiotemporal evolution of these events is characterised by combining passive satellite
remote sensing and ground-based
lidar and sun-photometer systems. The inversion algorithm
GRASP is used with a suite of ground-based remote sensing instruments such as lidar/ceilometer and sun-photometer from eight sites at different locations throughout the Iberian Peninsula. Satellite observations showed that the volcanic ash plumes remained nearby the
Canary Islands covering a mean area of 120 ± 202 km
2 during the whole period of eruptive activity and that
sulphur dioxide plumes reached the Iberian Peninsula. Remote sensing observations showed that the three events were mainly composed of sulphates, which were transported from the volcano into the free
troposphere. The high backscatter-related Ångström exponents for wavelengths 532–1064 nm (1.17 ± 0.20 to 1.40 ± 0.24) and low particle depolarization ratios (0.08 ± 0.02 to 0.09 ± 0.02), measured by the multi-wavelength Raman lidar, hinted at the presence of spherical small particles. The layer aerosol optical depth at 532 nm (AOD
L532) obtained from lidar measurements contributed between 49% and 82% to the
AERONET total column AOD at 532 nm in event II (11–13 October). According to the GRASP retrievals, the layer aerosol optical depth at 440 nm (AOD
L440) was higher in all sites during event II with values between 0.097 (Badajoz) and 0.233 (Guadiana-UGR) and lower in event III (19–21 October) varying between 0.003 (Granada) and 0.026 (Évora). Compared with the GRASP retrievals of total column AOD at 440 nm, the AOD
L440 had contributions between 21% and 52% during event II. In the event I (25–28 September), the mean volume concentrations (VC) varied between 5 ± 4 μm
3cm
−3 (El-Arenosillo/Huelva) and 17 ± 10 μm
3cm
−3 (Guadiana-UGR), while in event II this variation was from 11 ± 7 μm
3cm
−3 (Badajoz) to 27 ± 10 μm
3cm
−3 (Guadiana-UGR). Due to the impact of volcanic events on atmospheric and economic fields, such as
radiative forcing and
airspace security, a proper characterization is required. This work undertakes it using advanced instrumentation and methods.
