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In this study, the performance of two types of source apportionment models was evaluated by assessing the results provided by 40 different groups in the framework of an intercomparison organised by FAIRMODE WG3 (Forum for air quality modelling in Europe, Working Group 3). The evaluation was based on two performance indicators: z-scores and the root mean square error weighted by the reference uncertainty (RMSEu), with pre-established acceptability criteria. By involving models based on completely different and independent input data, such as receptor models (RMs) and chemical transport models (CTMs), the intercomparison provided a unique opportunity for their cross-validation. In addition, comparing the CTM chemical profiles with those measured directly at the source contributed to corroborate the consistency of the tested model results. The most commonly used RM was the US EPA- PMF version 5. RMs showed very good performance for the overall dataset (91% of z-scores accepted) while more difficulties were observed with the source contribution time series (72% of RMSEu accepted). Industrial activities proved to be the most difficult sources to be quantified by RMs, with high variability in the estimated contributions. In the CTMs, the sum of computed source contributions was lower than the measured gravimetric PM10 mass concentrations. The performance tests pointed out the differences between the two CTM approaches used for source apportionment in this study: brute force (or emission reduction impact) and tagged species methods. The sources meeting the z-score and RMSEu acceptability criteria tests were 50% and 86%, respectively. The CTM source contributions to PM10 were in the majority of cases lower than the RM averages for the corresponding source. The CTMs and RMs source contributions for the overall dataset were more comparable (83% of the z-scores accepted) than their time series (successful RMSEu in the range 25% - 34%). The comparability between CTMs and RMs varied depending on the source: traffic/exhaust and industry were the source categories with the best results in the RMSEu tests while the most critical ones were soil dust and road dust. The differences between RMs and CTMs source reconstructions confirmed the importance of cross validating the results of these two families of models. © 2019 The Authors, The authors warmly thank J. Vercauteren (VMM) for providing the CHEMKAR dataset. The CARA program was funded by the French Ministry of environment . IMT Lille Douai participates in the CaPPA project funded by the ANR through the PIA under contract ANR-11-LABX-0005-01 , the “Hauts de France” Regional Council and the European Regional Development Fund (ERDF). The C2TN/IST author gratefully acknowledges the FCT support through the UID/Multi/04349/2013 project. J.L. Jaffrezo would like to thank F. Donnaz, F. Masson, and S. Ngo for the chemical analyses of the Lens samples performed at IGE (ECOC, ions, sugars). These were possible on the Air-O-Sol analytical platform supported by Labex OSUG@2020 (ANR10 LABX56). A. Angyal was supported by National Research, Development and Innovation Office – NKFIH , contract number PD 125086 . H. Jorquera acknowledges support from Grant CONICYT/FONDAP/15110020. P . Thunis commented on an early version of the manuscript.

The atmosphere represents an underexplored temporary habitat for airborne microbial communities such as eukaryotes, whose taxonomic structure changes across different locations and/or regions as a function of both survival conditions and sources. A preliminary dataset on the seasonal dependence of the airborne eukaryotic community biodiversity, detected in PM10 samples collected from July 2018 to June 2019 at a coastal site representative of the Central Mediterranean, is provided in this study. Viridiplantae and Fungi were the most abundant eukaryotic kingdoms. Streptophyta was the prevailing Viridiplantae phylum, whilst Ascomycota and Basidiomycota were the prevailing Fungi phyla. Brassica and Panicum were the most abundant Streptophyta genera in winter and summer, respectively, whereas Olea was the most abundant genus in spring and autumn. With regards to Fungi, Botrytis and Colletotrichum were the most abundant Ascomycota genera, reaching the highest abundance in spring and summer, respectively, while Cryptococcus and Ustilago were the most abundant Basidiomycota genera, and reached the highest abundance in winter and spring, respectively. The genus community structure in the PM10 samples varied day-by-day, and mainly along with the seasons. The impact of long-range transported air masses on the same structure was also proven. Nevertheless, rather few genera were significantly correlated with meteorological parameters and PM10 mass concentrations. The PCoA plots and non-parametric Spearman’s rank-order correlation coefficients showed that the strongest correlations generally occurred between parameters reaching high abundances/values in the same season or PM10 sample. Moreover, the screening of potential pathogenic fungi allowed us to detect seven potential pathogenic genera in our PM10 samples. We also found that, with the exception of Panicum and Physcomitrella, all of the most abundant and pervasive identified Streptophyta genera could serve as potential sources of aeroallergens in the studied area.

The performance of aerosol classification schemes based on intensive optical parameters and applied to mixed particle populations monitored at the surface has been investigated to test the ability of optical parameters to identify different types of particles/particle mixtures and explore their complex features. The results show that the combination of two intensive optical parameters does not allow for the unique identification of different particle types. The classification scheme based on the Absorption Angstrom Exponent (AAE) as a function of the Scattering Angstrom Exponent (SAE) and color-coded by the Single Scattering Albedo difference (dSSA) is a good graphical framework to discriminate between different types of particle/particle mixtures. This aerosol classification scheme has been applied to study the optical properties of heterogeneous PM2.5 particles that were monitored at a coastal site of the Central Mediterranean and were significantly affected by both natural and anthropogenic sources also because of long-range transport from surrounding countries. The calculated AAE, SAE, and dSSA hourly means smoothly and continuously vary within their respective range (0.6-3.4, -0.7-3.0, and -0.33-0.52, respectively) because of the different mixing degree of different types of particles. Consequently, the main features of the particle populations depend on the range of the AAE, SAE, and dSSA values. Eight different clusters have been selected within the used graphical framework to identify four key particle populations (dust, marine, OC-dominated, and BC-dominated particles) and four particle mixtures dominated by key aerosol populations. In addition, their main features have been characterized. Particle mixtures consisting of large and low-absorbing particles (LLAP), small and high-absorbing particles (SHAP), dominated by dust, and large organic particles have been characterized. Marine, LLAP, and mixed dust clusters with a SAE value below 1 are responsible for aerosol scattering coefficients (sigma(s); at 470 nm) below 100 Mm(-1). Conversely, SHAP, BC-dominated, and OC-based mixtures are responsible for the highest sigma(s) values and represent dominant particles species.

Lidar measurements at 355, 532, and 1064 nm have been performed at Lecce (40.3°N, 18.1°E), in south-eastern Italy, to investigate for the first time the impact of the 20 March 2015 solar eclipse on both the planetary boundary layer (PBL) height and the aerosol optical and microphysical properties along the whole aerosol column. The partial solar eclipse lasted from 08:30 up to 10:47 UTC and reached the full phase at 09:37 UTC. The maximum percentage obscuration of the solar disk was 43.6%. The eclipse cooling effect was responsible at the full phase time (tF) for the downward solar irradiance decrease at the top of the atmosphere, at the surface, and within the atmosphere of 429.2 ± 0.6, 373 ± 25, and 56 ± 26 W m−2, respectively. The turbulent kinetic energy, the potential temperature flux, the sensible heat flux, the variance of air temperature, and the vertical wind speed at the surface revealed that the turbulence activity reached the maximum weakening at the time tF. The standard deviation (SD) technique has been applied to both the lidar range corrected signals (RCS) at 1064 nm and the linear volume depolarization ratio (δV) profiles at 355 nm to determine the time evolution of the shallow PBL height and the aloft aerosol layers. The SD technique applied to RCS and δV profiles revealed similar results within experimental uncertainties. The PBL height, which was equal to 380 ± 40 m above ground level (AGL) at the eclipse full phase (09:37 UTC), decreased up to 220 ± 20 m at 09:45 UTC because of the eclipse cooling effect and, then, increased up to 320 ± 30 m at 10:17 UTC. The determined PBL height time evolution was in good agreement with the ones of the main turbulence parameters at the surface after tF. The vertical profiles of the aerosol backscatter coefficient (ββ), the δV at 355 nm, and the extinction-related Angstrom exponent (A), calculated at the 355–1064 nm wavelength pair revealed a marked decrease of β, δV, and A at the eclipse full phase within the aloft aerosol layers. The abrupt β, δV, and A decrease due to the aerosol concentration and type changes has mainly been associated with the decrease of the fine-mode particle contribution.

A preliminary local database of potential (opportunistic) airborne human and plant pathogenic and non-pathogenic species detected in PM10 samples collected in winter and spring is provided, in addition to their seasonal dependence and relationships with meteorological parameters and PM10 chemical species. The PM10 samples, collected at a Central Mediterranean coastal site, were analyzed by the 16S rRNA gene metabarcoding approach, and Spearman correlation coefficients and redundancy discriminant analysis tri-plots were used to investigate the main relationships. The screening of 1187 detected species allowed for the detection of 76 and 27 potential (opportunistic) human and plant pathogens, respectively. The bacterial structure of both pathogenic and non-pathogenic species varied from winter to spring and, consequently, the inter-species relationships among potential human pathogens, plant pathogens, and non-pathogenic species varied from winter to spring. Few non-pathogenic species and even fewer potential human pathogens were significantly correlated with meteorological parameters, according to the Spearman correlation coefficients. Conversely, several potential plant pathogens were strongly and positively correlated with temperature and wind speed and direction both in winter and in spring. The number of strong relationships between presumptive (human and plant) pathogens and non-pathogens, and meteorological parameters slightly increased from winter to spring. The sample chemical composition also varied from winter to spring. Some potential human and plant pathogens were correlated with chemicals mainly associated with marine aerosol and/or with soil dust, likely because terrestrial and aquatic environments were the main habitats of the detected bacterial species. The carrier role on the species seasonal variability was also investigated.

Aerosol particles are essential constituents of the Earth’s atmosphere, impacting the earth radiation balance directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei. In contrast to most greenhouse gases, aerosol particles have short atmospheric residence times, resulting in a highly heterogeneous distribution in space and time. There is a clear need to document this variability at regional scale through observations involving, in particular, the in situ near-surface segment of the atmospheric observation system. This paper will provide the widest effort so far to document variability of climate-relevant in situ aerosol properties (namely wavelength dependent particle light scattering and absorption coefficients, particle number concentration and particle number size distribution) from all sites connected to the Global Atmosphere Watch network. High-quality data from almost 90 stations worldwide have been collected and controlled for quality and are reported for a reference year in 2017, providing a very extended and robust view of the variability of these variables worldwide. The range of variability observed worldwide for light scattering and absorption coefficients, single-scattering albedo, and particle number concentration are presented together with preliminary information on their long-term trends and comparison with model simulation for the different stations. The scope of the present paper is also to provide the necessary suite of information, including data provision procedures, quality control and analysis, data policy, and usage of the ground-based aerosol measurement network. It delivers to users of the World Data Centre on Aerosol, the required confidence in data products in the form of a fully characterized value chain, including uncertainty estimation and requirements for contributing to the global climate monitoring system., European Commission Joint Research Centre 654109, European ERDF funds through different Spanish R&D projects of the Spanish Ministerio de Economia, Industria y Competitividad, NorthWest University, University of Helsinki, Academy of Finland 272041, Academy of Finland project Greenhouse gas 269095 296302, Korea Meteorological Administration Research and Development Program "Development of Monitoring and Analysis Techniques for Atmospheric Composition in Korea KMA2018-00522, National Research Foundation of Korea 2017R1D1A1B06032548, Korea Meteorological Administration Research and Development Program KMI2018-01111, Taiwan Environmental Protection Administration, Ministry of Research, France, French Ministry of the Environment, United States Environmental Protection Agency, MeteoSwiss (GAW-CH aerosol monitoring programme), Swiss State Secretariat for Education, Research and Innovation (SERI), Ministry of Education, Youth and Sports of CR within National Sustainability Program I (NPU I) LO1415, ERDF "ACTRISCZ RI" CZ.02.1.01/0.0/0.0/16_013/0001315 CGL2017-85344-R MINECO/AEI/FEDER, TIGAS-CM (Madrid Regional Government) Y2018/EMT-5177, AIRTECCM (Madrid Regional Government) P2018/EMT4329 REDMAAS2020 RED2018-102594-T CIENCIA, Spanish Ministry of Economy, Industry and Competitiveness, European Union (EU) CGL2016-78594-R, Generalitat de Catalunya AGAUR 2017 SGR41, National Institute for Aerospace Technology, Ministerio Espanol de Economia, Industria y Competitividad (MINECO) MIS 5021516, Competitiveness, Entrepreneurship and Innovation, NSRF, Ministry of Education, Universities and Research (MIUR), Norwegian Environment Agency, Swedish FORMAS; Swedish Research Council (VR), Magnus Bergvall foundation, Marta och Erik Holmberg foundation, Swedish EPA

The development of analytical methods capable of discriminating between bio-derived and fossil-derived carbon in Particulate Matter (PM) is a crucial aspect in the general efforts of identifying effective strategies for health-risks mitigations. The large difference in the isotopic signature between bio-derived and fossil derived materials in term of the concentration of 14C the radioactive carbon isotope can be effectively used for this purpose. Indeed, though the detection and measurement of 14C by AMS (Accelerator Mass Spectrometry) is a well established methodology, the reduced amount of carbon in PM samples (typically in the μg range) requires the use of proper ion sources with a high efficiency. We present here the set-up developed at CEDAD-University of Salento as based on a gas-accepting hybrid ion source and an in-house designed gas handling interface. The performances of the system are also shown by presenting the firsts tests carried out on PM sampled on quartz filters in Lecce, Italy.

The COVID-19 pandemic caused the shutdown of entire nations all over the world. In addition to mobility restrictions of people, the World Health Organization and the Governments have prescribed maintaining an inter-personal distance of 1.5 or 2 m (about 6 feet) from each other in order to minimize the risk of contagion through the droplets that we usually disseminate around us from nose and mouth. However, recently published studies support the hypothesis of virus transmission over a distance of 2 m from an infected person. Researchers have proved the higher aerosol and surface stability of SARS-COV-2 as compared with SARS-COV-1 (with the virus remaining viable and infectious in aerosol for hours) and that airborne transmission of SARS-CoV can occur besides close-distance contacts. Indeed, there is reasonable evidence about the possibility of SARS-COV-2 airborne transmission due to its persistence into aerosol droplets in a viable and infectious form. Based on the available knowledge and epidemiological observations, it is plausible that small particles containing the virus may diffuse in indoor environments covering distances up to 10 m from the emission sources, thus representing a kind of aerosol transmission. On-field studies carried out inside Wuhan Hospitals showed the presence of SARS-COV-2 RNA in air samples collected in the hospitals and also in the surroundings, leading to the conclusion that the airborne route has to be considered an important pathway for viral diffusion. Similar findings are reported in analyses concerning air samples collected at the Nebraska University Hospital. On March 16th, we have released a Position Paper emphasizing the airborne route as a possible additional factor for interpreting the anomalous COVID-19 outbreaks in northern Italy, ranked as one of the most polluted areas in Europe and characterized by high particulate matter (PM) concentrations. The available information on the SARS-COV-2 spreading supports the hypothesis of airborne diffusion of infected droplets from person to person at a distance greater than two meters (6 feet). The inter-personal distance of 2 m can be reasonably considered as an effective protection only if everybody wears face masks in daily life activities.

The relationship between the Planetary Boundary Layer (PBL) height and the particle scattering coefficient (σp) at the surface has been investigated with the main goal of estimating the PBL height from the ground-level particle optical properties that are simpler to measure and are provided by instruments as nephelometers, which can run continuously. A lidar system and an integrating nephelometer operating within the European infrastructure ACTRIS (Aerosols, Clouds, and Trace gases Research InfraStructure) have been used to simultaneously monitor the daily evolution of both the PBL height and σp. Measurements have been performed at a coastal site of south-eastern Italy, characterized by a shallow PBL (

Irradiance and LiDAR measurements at the surface combined with satellite products from SEVIRI (Spinning Enhanced Visible and InfraRed Imager) and MODIS (MODerate resolution Imaging Spectroradiometer) were used to detect and characterize the Etna volcano (Italy) plume that crossed southeastern Italy on 3 December 2015, from about 10:00 up to 11:30 UTC, and estimate its radiative impact. The volcanic plume was delivered by a violent and short paroxysmal eruption that occurred from 02:30 to 03:10 UTC of 3 December 2015, about 400 km away from the monitoring site. Measurements from the LiDAR combined with model results showed that the aerosol optical depth of the volcanic plume, located from about 11 to 13 km above sea level (asl), was equal to 0.80 ± 0.07 at 532 nm. A low tropospheric aerosol load, located up to about 7 km asl, with optical depth equal to 0.19 ± 0.01 at 532 nm was also revealed by the LiDAR measurements. Short-Wave (SW) downward and upward irradiance measurements revealed that the instantaneous SW direct radiative forcing at the surface (DRFsurf) decreased to −146 ± 16 W m−2 at 10:50 UTC because of the volcanic plume passage. A Two-Stream radiative transfer model integrated with experimental measurements, which took into account the volcanic plume and the low tropospheric aerosol properties, was used to reproduce the SW radiative flux measurements at the surface and estimate the aerosol DRF both at the top of the atmosphere (TOA) and at the surface, in addition to the aerosol heating rate vertical profile. We found that the clear-sky, instantaneous, SW DRF at the TOA and the atmospheric forcing were equal to −112 and 33 W m-2, respectively, at 10:50 UTC that represented the time at which the volcanic plume radiative impact was the highest. The SW aerosol heating rate reached the peak value of 1.24 K day−1 at 12 km asl and decreased to −0.06 K day−1 at 11 km asl, at 10:50 UTC. The role of the aerosol load located up to about 7 km asl and the corresponding radiative impact has also been evaluated.

In this study, PM2.5 airborne particulate matter was collected over a full year at a costal site of the Central Mediterranean Sea and analysed for its chemical composition and oxidative potential (OP), determined by the dithiothreitol (DTT) and the ascorbic acid (AA) assays. In autumn-winter, the volume normalized oxidative OP (OPV) were 0.29 ± 0.03 nmol min−1 m−3 and 0.21 ± 0.03 nmol min−1 m−3 for the DTT (OPDTTV) and AA (OPAAV) assay, respectively. In spring-summer the OPDTTV values were higher than OPAAV responses, i.e., 0.19 ± 0.02 nmol min−1 m−3 vs. 0.09 ± 0.01 nmol min−1 m−3. Overall, marked seasonality was observed with higher values in Autumn-Winter (AW) than in Spring-Summer (SS), i.e., 1.5 and 2.3 times increase for OPDTTV and OPAAV, respectively. In the cold season, the OPV activity was broadly correlated with metals and carbon species, such as K+, NO3−, Ba, Cd, Cu, Fe, Mn, P, V, OC, EC, Acetate, Oxalate and Glycolate (p For each sampling day, PM2.5 and PM10 samples were simultaneously collected and analysed to investigate the variation of the OP activity in relation with the particle size and chemical composition. OPDTTV values exhibited a poor particle-size dependence, with similar values close to 0.20 ± 0.04 nmol min−1 m−3 in both fractions. This could be explained by the association of OPDTTV with species mainly accumulated in the fine fraction, i.e., OC, POC and EC and K+. Otherwise, the OPAAV responses exhibited a clear particle-size dependence, with significantly higher values for PM10 than for PM2.5, i.e., 0.35 ± 0.06 vs. 0.21 ± 0.03 nmol min−1 m−3 in AW and 0.23 ± 0.04 vs. 0.09 ± 0.01 in SS. This may be supported by the strong correlation of OPAAV with Cu and Fe, which were most abundant metals in the PM10 fraction. The data of specific monitoring days were investigated in detail to better highlight the impact of some individual redox active species on the OPDTTV and OPAAV responses.

A methodology to detect the weekly cycle impact of the particulate matter (PM), and PM sources on the near surface temperature and wind speed is discussed in the paper. Chemically-speciated PM10 and PM2.5 samples are analyzed to detect the weekly cycle of both the PM mass concentrations and the PM sources identified by the Positive Matrix Factorization technique. The average percent departure (APD) of the PM mass concentration from the mean value calculated for each day of the week shows that a positive (higher values during midweek) and a negative (higher values during weekend) weekly cycle characterizes the PM10 and PM2.5 mass concentrations in Autumn-Winter (AW, September–February) and Spring-Summer (SS, March–August), respectively. The westerly transport of pollution seems to have a role on the negative PM weekly cycle found in SS. The analysis of the six identified aerosol sources indicates that in SS the mixed anthropogenic and the reacted dust sources likely impact the PM10 negative weekly cycle and that the mixed anthropogenic source likely impacts the PM2.5 negative weekly cycle. The mixed anthropogenic and soil dust sources likely affect in AW the positive weekly cycle of the PM10 mass concentration. Both sources in addition to the reacted dust source seem to affect the PM2.5 mass concentration in AW. The APD analysis of the temperature (T) and wind speed (WS) at the surface from measurements co-located in space and time with the PM ones reveals that the WS and T values are characterized by a negative weekly cycle in AW. Conversely, in SS, the WS-APD value decreases on Sunday and the T-APD values increase in the second half of the week. These last results likely give evidence of the PM impact on the near-surface temperature and wind speed at the study site.

A new methodology based on optical parameters from integrating nephelometer measurements and chemically speciated PM10 mass concentrations, to associate intensive optical parameters with pollution sources identified by the Positive Matrix Factorization (PMF) technique, is presented. PM10 samplings and integrating nephelometer measurements at 450, 525, and 635 nm, co-located in space and time, were performed from November 2011 to November 2012. The PM10 samples were chemically characterized for 16 species, including ions (Na+, NH4+, K+, Mg2+, Ca2+, Cl−, NO3−, and SO42−), metals (Al, Cd, Cu, Fe, Mn, and Ti), OC, and EC. The scattering σs and backscattering βs coefficients at 450, 525, and 635 nm, and the PM10 chemically speciated data were used as input of the PMF model. Traffic (TRA, 28.3%), Biomass Burning and Nitrates (BBN, 27.4%), Soil Dust (SDU, 14.7%), ammonium Sulphate (SUL, 17.0%), and Aged Sea-salt (ASS, 12.6%) were the identified pollution sources, according to the PM10 mass apportionment, which did not show any significant difference in terms of source assignment and contribution, with respect to the solution without optical variables. The possibility of retrieving intensive optical parameters associated with the pollution sources from the related spectrally resolved σs and βs values is the main feature of the proposed approach. The mass scattering efficiency (ΣPM10), the scattering Angstrom exponent (A), the spectral curvature of the scattering Angstrom exponent (ΔA), and the asymmetry parameter (g) were the main intensive parameters calculated at different wavelengths or wavelength pairs to characterize the identified pollution sources. ΣPM10 and g at 450 nm, A(450, 635 nm) and ΔA were equal to 3.4 m2 g−1, 0.57, 0.96, and 0.54 for the TRA-source, to 5.0 m2 g−1, 0.58, 1.57, and − 0.06 for the BBN-source, to 5.0 m2 g−1, 0.67, 1.54, and 0.24 for the SUL-source, and to 0.6 m2 g−1, 0.33, −0.65, and 0.12 for the ASS-source, respectively. The analysis of monitoring days with a prevailing pollution source and the comparison of the paper's results with literature values have demonstrated the reliability of the used methodology.

Background The burden of COVID-19 was extremely severe in Northern Italy, an area characterized by high concentrations of particulate matter (PM), which is known to negatively affect human health. Consistently with evidence already available for other viruses, we initially hypothesized the possibility of SARS-CoV-2 presence on PM, and we performed a first experiment specifically aimed at confirming or excluding this research hyphotesys. Methods We have colelcted 34 PM10 samples in Bergamo area (the epicenter of the Italian COVID-19 epidemic) by using two air samplers over a continuous 3-weeks period. Filters were properly stored and underwent RNA extraction and amplification according to WHO protocols in two parallel blind analyses performed by two different authorized laboratories. Up to three highly specific molecular marker genes (E, N, and RdRP) were used to test the presence of SARS-CoV-2 RNA on particulate matter. Results The first test showed positive results for gene E in 15 out of 16 samples, simultaneously displaying positivity also for RdRP gene in 4 samples. The second blind test got 5 additional positive results for at least one ofthe three marker genes. Overall, we tested 34 RNA extractions for the E, N and RdRP genes, reporting 20 positive results for at least one of the three marker genes, with positivity separately confirmed for all the three markers. Control tests to exclude false positivities were successfully accomplished. Conclusion This is the first evidence that SARS-CoV-2 RNA can be present on PM, thus suggesting a possible use as indicator of epidemic recurrence., Highlights • COVID-19 burden seems more severe in areas with high concentrations of PM. • Particulate matter is already known to have negative effects on human health. • This is the first evidence that SARS-CoV-2RNA can be found on particulate matter.

The aim of the present work was to investigate the likely toxicological impact of atmospheric PM10 particles by comparing different effect-based methodologies, namely the Vibrio fischeri bioluminescence inhibition bioassay to evaluate ecotoxicity, the SOS Chromotest assay to estimate genotoxicity, and the Dithiothreitol (DTT) and Ascorbic Acid (AA) acellular assays to assess oxidative potential. The chemical composition was characterized for about 30 species, to assess the potential health impact of specific chemical components. Atmospheric particles were collected from spring to summer at a coastal site of the Central Mediterranean, away from large sources of local pollution. The Toxicity Unit (TU) index, used to assess the ecotoxicity, showed that 33% of the samples were toxic. The Induction Factor (IF), generally used to assess particle's genotoxicity, varied from 0.3 to 1.5 that represents the threshold value for genotoxicity. The oxidative potential (OP) determined by the DTT and AA assay varied within the 4.9–34.5 and 4.8–140.6 nmol min−1 range, respectively. DTT-OP and TU values were significantly correlated with OC, EC, and nss-K+, likely because the DTT and Vibrio fischeri responses were mainly associated with species from combustion sources. The IF factor was significantly correlated with some metals (Al, Ba, La, P, Sr, and Ti) likely from traffic sources and did not show any significant correlation with TU and OP values. Overall, paper's results proved the episodic occurrence of ecotoxicity and genotoxicity levels in PM10 particles sampled directly from their natural environment and away from strong pollution sources, highlighting the role mainly of carbonaceous compounds and heavy metals. The impact of spurious correlations between DTT- and AA-OPV and chemical species concentration has also been addressed.

Integrating nephelometer measurements have been combined with co-located in space and time PM10 and PM1 mass concentration measurements to highlight the benefits of integrating aerosol optical properties with the chemical speciation of PM1 and PM10 samples. Inorganic ions (SO42−, NO3−, NH4+, Cl−, Na+, K+, Mg2+, and Ca2+), metals (Fe, Al, Zn, Ti, Cu, V, Mn, and Cr), and the elemental and organic carbon (EC and OC, respectively) have been monitored to characterize the chemical composition of PM1 and PM10 samples, respectively. The scattering coefficient (σp) at 450 nm, the scattering Angstrom coefficient (A) calculated at the 450–635 nm wavelength pair, and the scattering Angstrom coefficient difference (∆A) retrieved from nephelometer measurements have been used to characterize the optical properties of the particles at the surface. The frequency distribution of the A daily means during the one-year monitoring campaign, performed at a southeastern Italian site, has allowed identifying three main A variability ranges: A ≤ 0.8, 0.8 1.2. We found that σp and ∆A mean values and the mean chemical composition of the PM1 and PM10 samples varied with the A variability range. σp and ∆A reached the highest (149 Mm−1) and the smallest (0.16) mean value, respectively, on the days characterized by A > 1.2. EC, SO42−, and NH4+ mean mass percentages also reached the highest mean value on the A > 1.2 days, representing on average 8.4, 9.8, and 4.2%, respectively, of the sampled PM10 mass and 12.4, 10.6, and 7.7%, respectively, of the PM1 mass. Conversely, σp and ∆A mean values were equal to 85 Mm−1 and 0.55, respectively, on the days characterized by A ≤ 0.8 and the EC, SO42−, and NH4+ mean mass percentages reached smaller values on the A ≤ 0.8 days, representing 4.5, 6.0, and 1.9% of the PM10 mass and 9.4, 7.3, and 5.8% of the PM1 mass, respectively. Primary and secondary OC (POC and SOC, respectively) contributions also varied with the A variability range. POC and SOC mean mass percentages reached the highest and the smallest value, respectively, on the days characterized by A > 1.2. Conversely, POC and SOC mean mass percentages reached the smallest and the highest value, respectively, on the days characterized by A ≤ 0.8. It has also been shown that the PM, OC, OC + EC, POC, and SOC mass scattering cross sections varied significantly with the A variability range, because of the A dependence on aerosol sources and/or emission, transport, and transformation mechanisms. Therefore, it has been shown that A daily mean values can represent a good tool to better differentiate the chemical speciation of size-fractioned PM samples.

An extended study on the oxidative potential (OP) of PM10 particles collected from December 2014 to October 2015 at a peninsular site of the Central Mediterranean basin has been performed. PM10 particles have been selected to better account for all different aged/fresh particle types. Two acellular assays, i.e., the dithiothreitol (DTT) and ascorbic acid (AA) methods, were used to measure the OP of PM10 particles chemically speciated by more than 40 species. DTT and AA assays provide close mean values of volume normalized OPV responses, with similar variability range, i.e., mean OPDTTV = 0.24 ± 0.12 nmolDTT min−1 m−3 and mean OPAAV = 0.29 ± 0.18 nmolAA min−1 m−3. Also mass normalized OPm responses are similar for both assays, with mean value close to 0.008 nmol min−1 μg−1. The measured OPDTTV and OPAAV are correlated with several inorganic species, namely ions and metals, and with organic/elemental carbon. The discrimination of the data according seasonality, i.e., Autumn-Winter (AW, October–March) and Spring-Summer (SS, April–September) days, shows a clear seasonal trend of correlation coefficients. In AW, OPDTTV is strongly correlated with nss-K+ and nss-Ca2+, in addition to Ba, Cd, Ce, Cr, Cu, Fe, and Mn (traffic-related metals) and with EC, OC, and POC associated with the traffic exhaust source and/or with the combustion including biomass-burning source. Otherwise, OPDTTV of SS samples is correlated only with NH4+, Cu, EC, OC, and POC. The OPAAV of AW samples is well correlated with Ba, Ce, Cr, Cu, Fe, Mn, nss-K+, EC, OC, and POC, which are related with traffic and/or combustion emissions. Conversely, in SS, OPAAV is mainly correlated with NH4+, nss-K+, nss-Mg2+, nss-Ca2+, nss-SO42−, Cu, Mn, P, Pb, and oxalate, that are species related to secondary aerosols and resuspended soil from vehicular traffic and/or transported Saharan dust. These findings point the importance of both organic components and transition metals to PM oxidative properties, and also suggest that synergistic/antagonistic interactions and cross-correlations between the PM redox-active components are likely responsible for the seasonal variation of the AA and DTT assay response. The inter-correlation among all analysed species has been investigated to explain contrasting results and the negative correlations between OP values and some chemical species.

The collection of atmospheric particles on not-filtering substrates via dry deposition, and the subsequent study of the particle-induced material decay, is trivial due to the high number of variables simultaneously acting on the investigated surface. This work reports seasonally resolved data of chemical composition and size distribution of particulate matter deposed on stone and surrogate surfaces obtained using a new method, especially developed at this purpose. A “Deposition Box” was designed allowing the particulate matter dry deposition to occur selectively removing, at the same time, variables that can mask the effect of airborne particles on material decay. A pitched roof avoided rainfall and wind variability; a standardised gentle air exchange rate ensured a continuous “sampling” of ambient air leaving unchanged the sampled particle size distribution and, at the same time, leaving quite calm condition inside the box, allowing the deposition to occur. Thus, the “Deposition Box” represents an affordable tool that can be used complementary to traditional exposure systems. With this system, several exposure campaigns, involving investigated stone materials (ISMs) (Carrara Marble, Botticino limestone, Noto calcarenite and Granite) and surrogate (Quartz, PTFE, and Aluminium) substrates, have been performed in two different sites placed in Milan (Italy) inside and outside the low emission zone. Deposition rates (30–90 μg cm−2 month−1) showed significant differences between sites and seasons, becoming less evident considering long-period exposures due to a positive feedback on the deposition induced by the deposited particles. Similarly, different stone substrates influenced the deposition rates too. The collected deposits have been observed with optical and scanning electron microscopes and analysed by ion chromatography. Ion deposition rates were similar in the two sites during winter, whereas it was greater outside the low emission zone during summer and considering the long-period exposure. The dimensional distribution of the collected deposits showed a significant presence of fine particles in agreement with deposition rate of the ionic fraction. The obtained results allowed to point out the role of the fine particles fraction and the importance of making seasonal studies.

[oThe effects of the partial solar eclipse of 20 March 2015 on short-wave (SW) and long-wave (LW) irradiance measurements, meteorological variables, and near surface particle properties have been investigated. Measurements were performed at three southern Italy observatories of the Global Atmospheric Watch - World Meteorological Organization (GAW-WMO): Lecce (LE, 40.3°N, 18.1°E, 30 m a.s.l.), Lamezia Terme (LT, 38.9°N, 16.2°E, 50 m a.s.l.), and Capo Granitola (CG, 37.6°N, 12.7°E, 50 m a.s.l.), to investigate the dependence of the eclipse effects on monitoring site location and meteorology. LE, LT, and CG were affected by a similar maximum obscuration of the solar disk, but meteorological parameters and aerosol optical and microphysical properties varied from site to site on the eclipse's day. The maximum obscuration of the solar disk, which was equal to 43.6, 42.8, and 45.1% at LE, LT, and CG, respectively, was responsible for the decrease of the downward SW irradiance up to 45, 44, and 45% at LE, LT, and CG, respectively. The upward SW irradiance decreased up to 45, 48, and 44% at LE, LT, and CG, respectively. Consequently, the eclipse SW direct radiative forcing (DRF) was equal to - 307, - 278, and - 238 W m- 2 at LE, LT, and CG, respectively, at the maximum obscuration of the solar disk. The downward and upward LW irradiance decrease was quite small (up to 4%) at the three sites. The time evolution of the meteorological parameters and aerosol optical and microphysical properties and their response strength to the solar eclipse impact varied from site to site, mainly because of the local meteorology and geographical location. Nevertheless, the solar eclipse was responsible at the study sites for a temperature decrease within 0.5-0.8 K, a relative humidity increase within 3.5-4.5%, and a wind speed decrease within 0.5-1.0 m s- 1, because of its cooling effect. The solar eclipse was also responsible at all the sites for the increase of near surface particle scattering coefficient (?sp) and scattering color ratio (CR?), mainly for the increase of both ultrafine and fine mode particle concentrations. In more detail, ?sp, CR?, and number concentration increased up to 2 Mm- 1, 0.2, and 9 · 103 cm- 3, respectively. The atmospheric turbulence weakening, driven by the eclipse cooling effect and revealed by the decrease of turbulent kinetic energy and potential temperature flux, mainly contributed to the changes of near surface particle concentrations and size distributions.bject Object]

During the summers of 2011 and 2012, two scientific cruises were carried out over the Arctic Ocean aiming at the determination of the aerosol chemical composition in this pristine environment. First, mass spectrometry was applied to study the concentration and gas/particle partitioning of polycyclic aromatic hydrocarbons (PAHs) and n-alkanes. Experimental and modelled data of phase partitioning were compared: results demonstrated an equilibrium between gas and particle phase for PAHs, while n-alkanes showed a particle-oriented partitioning, due to the local marine origin of them, confirmed by the extremely low value of their carbon preference index. Moreover, the inorganic and organic ions (carboxylic acids and amines) concentrations, together with those of elemental carbon (EC) and organic matter (OM), were analyzed: 63% of aerosol was composed of ionic compounds (&gt, 90% from sea-salt) and the OM content was very high (30.5%, close to 29.0% of Cl&minus, ) in agreement with n-alkanes&rsquo, marine signature. Furthermore, the amines&rsquo, (dimethylamine, trimethylamine, diethylamine) concentrations were 3.98 &plusmn, 1.21, 1.70 &plusmn, 0.82, and 1.06 &plusmn, 0.56 p.p.t.v., respectively, fully in keeping with concentration values used in the CLOUD (Cosmics Leaving OUtdoor Droplet)-chamber experiments to simulate the ambient nucleation rate in a H2SO4-DMA-H2O system, showing the amines&rsquo, importance in polar regions to promote new particle formation. Finally, high resolution mass spectrometry was applied to determine trace elements, including Rare Earth Elements (REEs), highlighting the dominant natural versus anthropic inputs for trace metals (e.g., Fe, Mn, Ti vs. As, Cd, Ni) and possible signatures of such anthropic activity.

Human exposure to polycyclic aromatic hydrocarbons (PAHs) in indoor environments can be particularly relevant because people spend most of their time inside buildings, especially in homes. This study aimed to investigate the most important particle-bound PAH sources and exposure determinants in PM2.5 samples collected in 19 homes located in northern Italy. Complementary information about ion content in PM10 was also collected in 12 of these homes. Three methods were used for the identification of PAH sources and determinants: diagnostic ratios with principal component and hierarchical cluster analyses (PCA and HCA), chemical mass balance (CMB) and linear mixed models (LMMs). This combined and tiered approach allowed the infiltration of outdoor PAHs into indoor environments to be identified as the most important source in winter, with a relevant role played by biomass burning and traffic exhausts to be identified as a general source of PAHs in both seasons. Tobacco smoke exhibited an important impact on PAH levels in smokers' homes, whereas in the whole sample, cooking food and natural gas sources played a minor or negligible role. Nitrate, sulfate and ammonium were the main inorganic constituents of indoor PM10 owing to the secondary formation of ammonium sulfates and nitrates.

International audience; In the framework of the Chemistry-Aerosol Mediterranean Experiment (ChArMEx; http://charmex.lsce.ipsl.fr/) initiative, a field campaign took place in the western Mediterranean Basin between 10 June and 5 July 2013 within the ADRIMED (Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region) project. The scientific objectives of ADRIMED are the characterization of the most common ‘Mediterranean aerosols’ and their direct radiative forcing (column closure and regional scale). During 15–24 June a multi-intrusion dust event took place over the western and central Mediterranean Basin. Extra measurements were carried out by some EARLINET/ACTRIS (European Aerosol Research Lidar Network /Aerosols, Clouds, and Trace gases Research InfraStructure Network, http://www.actris.net/) lidar stations in Spain and Italy, in particular on 22 June in support to the flight over southern Italy of the Falcon 20 aircraft involved in the campaign. This article describes the physical and optical properties of dust observed at the different lidar stations in terms of dust plume centre of mass, optical depth, lidar ratio, and particle depolarization ratio. To link the differences found in the origin of dust plumes, the results are discussed on the basis of back-trajectories and air- and space-borne lidars. This work puts forward the collaboration between a European research infrastructure (ACTRIS) and an international project (ChArMEx) on topics of interest for both parties, and more generally for the atmospheric community.

We present results from a systematic study of vertical profiles of aerosol number size distribution and black carbon (BC) concentrations conducted in the Arctic, over Ny-Ålesund (Svalbard). The campaign lasted 2 years (2011–2012) and resulted in 200 vertical profiles measured by means of a tethered balloon (up to 1200 m a.g.l.) during the spring and summer seasons. In addition, chemical analysis of filter samples, aerosol size distribution and a full set of meteorological parameters were determined at ground. The collected experimental data allowed a classification of the vertical profiles into different typologies, which allowed us to describe the seasonal phenomenology of vertical aerosol properties in the Arctic. During spring, four main types of profiles were found and their behavior was related to the main aerosol and atmospheric dynamics occurring at the measuring site. Background conditions generated homogenous profiles. Transport events caused an increase of aerosol concentration with altitude. High Arctic haze pollution trapped below thermal inversions promoted a decrease of aerosol concentration with altitude. Finally, ground-based plumes of locally formed secondary aerosol determined profiles with decreasing aerosol concentration located at different altitude as a function of size. During the summer season, the impact from shipping caused aerosol and BC pollution plumes to be constrained close to the ground, indicating that increasing shipping emissions in the Arctic could bring anthropogenic aerosol and BC in the Arctic summer, affecting the climate.

Clear-sky downward and upward radiative flux measurements both in the short- and in the long-wave spectral range have been used to estimate and analyze the radiation changes at the surface due to the mineral dust advection at a Central Mediterranean site. Then, short- and long-wave radiative fluxes retrieved from the CERES (Clouds and the Earth’s Radiant Energy System) radiometer sensors operating on board the EOS (Earth Observing System) AQUA and TERRA platforms have been used to evaluate the mineral dust radiative impact at the top of the atmosphere. Satellite-derived radiative fluxes at the surface have been compared with corresponding ground-based flux measurements, collocated in space and time, to better support and understand the desert dust radiative impact. Results referring to the year 2012 are reported.

Recent epidemiological evidence support the hypothesis that health effects from inhalation of air particles are governed by more than just particle mass, since specific chemical components have been identified as important contributors to mortality and hospitality admissions.We studied the chemical composition and the oxidative potential (OP) of total suspended particle (TSP) samples from Milan at two sites with different traffic loads: a site in the low emission zone (LEZ) and a traffic site (TR) outside. Two a-cellular assays; dithiothreitol (OPDTT) and 2',7' dichlorofluorescin (OPDCFH) were used to characterize the OP of the soluble fraction of particles.TSP samples from LEZ showed significantly lower concentrations of traffic-related chemical components compared to TR. The decrease in the concentrations from TR to LEZ was maximum for EC, with a LEZ/TR ratio of 0.64 (±0.18), and a significant reduction (p < 0.01) was also observed for PAHs (LEZ/TR = 0.73 ± 0.16), elements (Mn, Cu, Zn, Cd, Pb: LEZ/TR ranged between 0.64 and 0.82), OC (LEZ/TR = 0.85 ± 0.12) and NH4+ (LEZ/TR = 0.92 ± 0.07).OP measures, expressed as OP/m3 or OP/mg, were comparable between sites both for OPDTT and OPDCFH, thus not showing any significant impact of local traffic on OP values at sites. OPDTT and OPDCFH showed contrasting seasonal and daily trends, indicating that the two a-cellular assays gave complementary information on the OP of particles in Milan. The two OP assays resulted to be sensitive to different chemical properties of PM samples. OPDTT correlated positively only with Global Radiation (Spearman's rs = 0.38, p < 0.05), which could be considered as a proxy for high concentrations of secondary oxidizing organics, while OPDCFH was related to various PM chemical species, mainly correlated with total mass (rs = 0.65; p < 0.01), elements (e.g. Zn, rs = 0.67; As, rs = 0.65; p < 0.01) and the sum of sulfate and nitrate (rs = 0.63; p < 0.01), a proxy for secondary aerosol.

Pollen aeroallergens are present in atmospheric particulate matter (PM) where they can be found in coarse biological particles such as pollen grains (aerodynamic diameter dae > 10 μm), as well as fragments in the finest respirable particles (PM2.5; dae < 2.5 μm). Nitration of tyrosine residues in pollen allergenic proteins can occur in polluted air, and inhalation and deposition of these nitrated proteins in the human respiratory tract may lead to adverse health effects by enhancing the allergic response in population. Previous studies investigated protein nitration by atmospheric gaseous pollutants such as nitrogen dioxide and ozone. In this work we report, for the first time, a study on protein nitration by nitrate ion in aqueous solution, at nitrate concentrations and pH conditions simulating those occurring in the atmospheric aerosol liquid water phase. Experiments have been carried out on the Bovine serum albumin (BSA) protein and the recombinant Phleum pratense allergen (Phl p 2) both in the dark and under UV-A irradiation (range 4–90 W m− 2) to take into account thermal and/or photochemical nitration processes. For the latter protein, modifications in the allergic response after treatment with nitrate solutions have been evaluated by immunoblot analyses using sera from grass-allergic patients. Experimental results in bulk solutions showed that protein nitration in the dark occurs only in dilute nitrate solutions and under very acidic conditions (pH < 3 for BSA; pH < 2.2 for Phl p 2), while nitration is always observed (at pH 0.5–5) under UV-A irradiation, both in dilute and concentrated nitrate solutions, being significantly enhanced at the lowest pH values. In some cases, protein nitration resulted in an increase of the allergic response.

Atmospheric aerosols deliquescence and crystallization relative humidity (DRH and CRH) are rarely measured compared to the worldwide number of hygroscopicity measurements; this feature comes from the lack of an efficient method able to capture the whole complexity of chemical composition of aerosols. Despite this, the knowledge of both DRH and CRH are crucial for a correct parameterization of the aerosol hygroscopic growth used in different applications, among which the remote sensing is very important. In this paper, a newly developed technique (direct current conductance method) was applied in an aerosol chamber to Milan PM2.5 samples, to identify aerosol DRH and CRH both during winter and summer. These results were compared with those independently obtained by gravimetric measurements conducted in the chamber using a microbalance. Microbalance data allowed also the determination of the mass hygroscopic growth factor on the collected PM2.5 samples. Results evidenced first a good agreement between the two methods (RMSE = 2.7% and 2.3% for DRH and CRH, respectively). Collected data evidenced the hysteresis behavior of ambient particles and variability in both DRH and CRH between the two seasons. Summer samples showed higher DRH and CRH (on average 71.4 ± 1.0% RH and 62.6 ± 1.2% RH, respectively) than the winter ones (on average 55.2 ± 0.7% RH and 46.9 ± 0.6% RH). This behavior was related to the higher content of sulfates during the summer season. Conversely, the mass hygroscopic growth factor at 90% RH was higher for winter samples (2.76 ± 0.06) with respect to the summer ones (1.91 ± 0.11). Since hysteresis behavior affects optical properties of aerosols, when RH conditions are within the loop, the hygroscopic growth factor could be assigned in a wrong way. Thus, the growth factor was calculated within the hysteresis loop for both upper and lower branches: results showed that difference in hygroscopic growth factor could reach up the 24%.

The performance and the uncertainty of receptor models (RMs) were assessed in intercomparison exercises employing real-world and synthetic input datasets. To that end, the results obtained by different practitioners using ten different RMs were compared with a reference. In order to explain the differences in the performances and uncertainties of the different approaches, the apportioned mass, the number of sources, the chemical profiles, the contribution-to-species and the time trends of the sources were all evaluated using the methodology described in Bells et al. (2015). In this study, 87% of the 344 source contribution estimates (SCEs) reported by participants in 47 different source apportionment model results met the 50% standard uncertainty quality objective established for the performance test. In addition, 68% of the SCE uncertainties reported in the results were coherent with the analytical uncertainties in the input data. The most used models, EPA-PMF v.3, PMF2 and EPA-CMB 8.2, presented quite satisfactory performances in the estimation of SCEs while unconstrained models, that do not account for the uncertainty in the input data (e.g. APCS and FA-MLRA), showed below average performance. Sources with well-defined chemical profiles and seasonal time trends, that make appreciable contributions (>10%), were those better quantified by the models while those with contributions to the PM mass close to 1% represented a challenge. The results of the assessment indicate that RMs are capable of estimating the contribution of the major pollution source categories over a given time window with a level of accuracy that is in line with the needs of air quality management. (C) 2015 The Authors. Published by Elsevier Ltd.

Size-segregated particle samples were collected in the Arctic (Ny-Ålesund, Svalbard) in April 2011 both at ground level and in the free atmosphere exploiting a tethered balloon equipped also with an optical particle counter (OPC) and meteorological sensors. Individual particle properties were investigated by scanning electron microscopy coupled with energy dispersive microanalysis (SEM-EDS). Results of the SEM-EDS were integrated with particle size and optical measurements of the aerosols properties at ground level and along the vertical profiles. Detailed analysis of two case studies reveals significant differences in composition despite the similar structure (layering) and the comparable texture (grain size distribution) of particles in the air column. Differences in the mineral chemistry of samples point at both local (plutonic/metamorphic complexes in Svalbard) and remote (basic/ultrabasic magmatic complexes in Greenland and/or Iceland) geological source regions for dust. Differences in the particle size and shape are put into relationship with the mechanism of particle formation, that is, primary (well sorted, small) or secondary (idiomorphic, fine to coarse grained) origin for chloride and sulfate crystals and transport/settling for soil (silicate, carbonate and metal oxide) particles. The influence of size, shape, and mixing state of particles on ice nucleation and radiative properties is also discussed.

During the ADRIMED (Aerosol Direct Radiative Impact on the regional climate in the Mediterranean region) special observation period (SOP-1a), conducted in June 2013 in the framework of the ChArMEx (Chemistry-Aerosol Mediterranean Experiment) project, a moderate Saharan dust event swept the Western and Central Mediterranean Basin (WCMB) from west to east during a 9-day period between 16 and 24 June. This event was monitored from the ground by six EARLINET/ACTRIS (European Aerosol Research Lidar Network/Aerosols, Clouds, and Trace gases Research Infrastructure Network) lidar stations (Granada, Barcelona, Naples, Potenza, Lecce and Serra la Nave) and two ADRIMED/ChArMEx lidar stations specially deployed for the field campaign in Cap d’en Font and Ersa, in Minorca and Corsica Islands, respectively. The first part of the study shows the spatio-temporal monitoring of the dust event during its transport over the WCMB with ground-based lidar and co-located AERONET (Aerosol Robotic Network) Sun-photometer measurements. Dust layer optical depths, Ångström exponents, coarse mode fractions, linear particle depolarization ratios (LPDRs), dust layer heights and the dust radiative forcing estimated in the shortwave (SW) and longwave (LW) spectral ranges at the bottom of the atmosphere (BOA) and at the top of the atmosphere (TOA) with the Global Atmospheric Model (GAME), have been used to characterize the dust event. Peak values of the AERONET aerosol optical depth (AOD) at 440 nm ranged between 0.16 in Potenza and 0.37 in Cap d’en Font. The associated Ångström exponent and coarse mode fraction mean values ranged from 0.43 to 1.26 and from 0.25 to 0.51, respectively. The mineral dust produced a negative SW direct radiative forcing at the BOA ranging from −56.9 to −3.5 W m−2. The LW radiative forcing at the BOA was positive, ranging between +0.3 and +17.7 W m-2. The BOA radiative forcing estimates agree with the ones reported in the literature. At the TOA, the SW forcing varied between −34.5 and +7.5 W m−2. In seven cases, the forcing at the TOA resulted positive because of the aerosol strong absorbing properties (0.83 < single-scattering albedo (SSA) < 0.96). The multi-intrusion aspect of the event is examined by means of air- and space-borne lidar measurements, satellite images and back trajectories. The analysis reported in this paper underline the arrival of a second different intrusion of mineral dust observed over southern Italy at the end of the considered period which probably results in the observed heterogeneity in the dust properties., Spanish Ministry of Economy and Competitiveness (project TEC2012-34575 and TEC2015-63832-P), Science and Innovation (project UNPC10-4E-442), Andalusia Regional Government through projects P12-RNM-2409 and P10-RNM-6299