Biomass burning is a major source of Brown Carbon (BrC), strongly contributing to radiative forcing. In urban areas of the climate-sensitive Southeastern European region, where strong emissions from residential wood burning (RWB) are reported, radiative impacts of carbonaceous aerosols remain largely unknown. This study examines the absorption properties of water-and methanol-soluble organic carbon (WSOC, MeS_OC) in a city (Ioannina, Greece) heavily im-pacted by RWB. Measurements were performed during winter (December 2019 - February 2020) and summer (July - August 2019) periods, characterized by RWB and photochemical processing of organic aerosol (OA), respectively. PM2.5 filter extracts were analyzed spectrophotometrically for water-and methanol-soluble BrC (WS_BrC, MeS_BrC) absorption. WSOC concentrations were quantified using TOC analysis, while those of MeS_OC were determined using a newly developed direct quantification protocol, applied for the first time to an extended series of ambient sam-ples. The direct method led to a mean MeS_OC/OC of 0.68 and a more accurate subsequent estimation of absorption efficiencies. The mean winter WS_BrC and MeS_BrC absorptions at 365 nm were 13.9 Mm-1 and 21.9 Mm-1, respec-tively, suggesting an important fraction of water-insoluble OA. Mean winter WS_BrC and MeS_BrC absorptions were over 10 times those observed in summer. MeS_OC was more absorptive than WSOC in winter (mean mass absorption efficiencies - MAE365: 1.81 vs 1.15 m2 gC-1) and especially in summer (MAE: 1.12 vs 0.27 m2 gC-1) due to photo -dissociation and volatilization of BrC chromophores. The winter radiative forcing (RF) of WS_BrC and MeS_BrC rela-tive to elemental carbon (EC) was estimated at 8.7 % and 16.7 %, respectively, in the 300-2500 nm band. However, those values increased to 48.5 % and 60.2 % at 300-400 nm, indicating that, under intense RWB, BrC forcing becomes comparable to that of soot. The results highlight the consideration of urban BrC emissions in radiative transfer models, as a considerable climate forcing factor.

An 8-year dataset from 7 AERONET (Aerosol Robotic Network) sites is used to analyzed the variation characteristics of aerosol optical and microphysical properties over the Middle East (ME) and Eastern Mediterranean Sea (EMS) regions. The aerosol optical properties, including aerosol optical depth (AOD), Angstrom exponent (AE), volume size distribution (VSD), aerosol absorption optical depth (AAOD), single scattering albedo (SSA), dominant types, aerosol radiative forcing (ARF) and its efficiency (ARFE), are presented and analyzed over the two regions. The regional mean AODs (AEs) are 0.31 (0.69) and 0.19 (1.10) over ME and EMS, respectively. Although the linear trend of annual averages is not significant at these sites, the variations of seasonal and annual AODs and AEs are remarkable. The mean AODs are generally higher over ME than over EMS, while the AEs show the opposite pattern. AOD appears the maximum in summer and the minimum in winter both at ME and EMS sites. AE shows the maximum in autumn and winter over ME, while in summer over EMS. The lowest AE appears in spring over both regions due to the frequent dust events. The AAOD ranges from 0.03 to 0.04 and the SSA from 0.89 to 0.93 at these sites. The seasonal AAOD presents very different features over the two regions. The AAOD appears its minimum in winter at most ME sites, while the maximum appears in the same season at EMS sites. The differences of seasonal SSAs at ME sites are relatively small, while at EMS sites the SSAs are much higher in summer and autumn than those in spring and winter. The aerosol types are discussed based on four selected classification methods. It shows that the desert dust (DD) and the mixtures (Mix) are the two dominant aerosol types at most sites except ERD which is dominated by urban industry aerosol (UI). To the radiative forcing, the ARF at bottom of atmosphere (BOA) is generally larger at ME sites than at EMS sites, while the ARFs at top of atmosphere (TOA) are numerically similar at most sites. The ARFE shows higher value at sites in Arabian Peninsula both at BOA and TOA.

Surface concentration of black carbon (BC) is a key factor for the understanding of the impact of anthropogenic pollutants on human health. The majority of Italian cities lack long-term measurements of BC concentrations since such a metric is not regulated by EU legislation. This work attempts a long-term (2001-2017) inference of equivalent black carbon (eBC) concentrations in the city of Rome (Italy) based on sun-photometry data. To this end, aerosol light absorption coefficients at the surface are inferred from the columnar aerosol aerosol light absorption coefficient records from the Rome Tor Vergata AERONET sun-photometer. The main focus of this work is to rescale aerosol light absorption columnar data (AERONET) to ground-level BC data. This is done by using values of mixing layer height (MLH) derived from ceilometer measurements and then by converting the absorption into eBC mass concentration through a mass-to-absorption conversion factor, the Mass Absorption Efficiency (MAE). The final aim is to obtain relevant data representative of the BC aerosol at the surface (i.e., in-situ)-so within the MLH- and then to infer a long-term record of surface equivalent black carbon mass concentration in Rome. To evaluate the accuracy of this procedure, we compared the AERONET-based results to in-situ measurements of aerosol light absorption coefficients (alpha(abs)) collected during some intensive field campaigns performed in Rome between 2010 and 2017. This analysis shows that different measurement methods, local emissions, and atmospheric conditions (MLH, residual layers) are some of the most important factors influencing differences between inferred and measured alpha(abs). As a general result, inferred and measured alpha(abs) resulted to reach quite a good correlation (up to r = 0.73) after a screening procedure that excludes one of the major cause of discrepancy between AERONET inferred and in-situ measured alpha(abs): the presence of highly absorbing aerosol layers at high altitude (e.g., dust), which frequently affects the Mediterranean site of Rome. Long-term trends of inferred alpha(abs), eBC, and of the major optical variables that control aerosol's direct radiative forcing (extinction aerosol optical depth, AOD(EXT), absorption aerosol optical depth, AOD(ABS), and single scattering albedo, SSA) have been estimated. The Mann-Kendall statistical test associated with Sen's slope was used to test the data for long-term trends. These show a negative trend for both AOD(EXT) (-0.047/decade) and AOD(ABS), (-0.007/decade). The latter converts into a negative trend for the alpha(abs) of -5.9 Mm(-1)/decade and for eBC mass concentration of -0.76 mu g/m(3)/decade. A positive trend is found for SSA (+0.014/decade), indicating that contribution of absorption to extinction is decreasing faster than that of scattering. These long-term trends are consistent with those of other air pollutant concentrations (i.e., PM2.5 and CO) in the Rome area. Despite some limitations, findings of this study fill a current lack in BC observations and may bear useful implications with regard to the improvement of our understanding of the impact of BC on air quality and climate in this Mediterranean urban region.

The main purpose of this study is to provide new estimations of optical properties for different aerosol species (Elemental (EC) and Organic Carbon (OC), sulfate (S), ammonium (AM) and nitrate (N)) over the Western Mediterranean Sea. This study is based on chemical measurements obtained over the French Mediterranean coastal region which were used to calculate the main optical properties (i.e., Mass Extinction Efficiency (MEE), Single Scattering Albedo (SSA) and asymmetry parameter (g)), which are relevant for Regional Climate Models (RCMs). Our results indicate that EC particles display averaged MEE (with associated uncertainty range) of 5.7 (4.6-6.9) m(2) g(-1) (at 550 nm), that is significantly lower than the value generally used (similar to 10 m(2) g(-1)) in RCM simulations conducted over this region. Such differences are mainly due to the inclusion of additional coarse modes in our optical calculations, which are not taken into account in RCMs that generally treat only fine EC particles. Concerning organics aerosols, we obtained a mean dry MEE (with associated uncertainty) of 2.7 (1.8-3.6) m(2) g(-1) (at 550 nm) lower than usually (similar to 5-7 m(2) g(-1)) referenced in RCMs. We also investigated the possible impact of absorbing brown carbon C-brown in our calculations showing large changes on dry MEE (from 2.7 to 4.5 m(2) g(-1), at 550 nm) and SSA (from 0.99 to 0.45, at 550 nm) for pure scattering and absorbing C-brown organics, respectively. Nitrate and ammonium particles, which are not well documented over this region, are characterized respectively by dry mean (and associated errors) MEE of 1 (0.8-1.2) m(2) g(-1) and 4 (2.4-5.6) m(2) g(-1) (at 550 nm), together with SSA of 0.89 (0.88-0.90) and 0.97 (0.96-0.98) at 550 nm. Such proposed values could be used to optimize RCMs over the Mediterranean basin for studying aerosol-climate interaction through feedbacks of particles on sea-surface fluxes, and hydrological cycle. (C) 2011 Elsevier B.V. All rights reserved.

High levels of ozone as well as particles, including Black Carbon (BC), have been observed at sites around the Mediterranean Sea, and several studies have shown very high aerosol radiative forcing in the area, but systematical, long term observations are scarce. A collaboration between the JRC and the Italian company 'Costa Crociere' has allowed to install a monitoring station on board the cruise liner 'Costa Fortuna' that performs cruises on the Mediterranean, with regular weekly tracks in the Western Mediterranean during spring, summer and autumn, and in the Eastern Mediterranean during winter. Measurements of ozone, Black Carbon (aethalometer) and particle size distributions (optical particle sizer) have been performed, starting from the autumn of 2005; this activity will continue for several years. The measured ozone concentrations are compared to those obtained by simulations in a recent model intercomparison (ACCENT-PHOTOCOM); the initial measurements are in the higher end of the range of modeled values in the winter and in the lower end during the summer. Measured concentrations of ozone and BC in 2006 are compared to model simulations for previous years and the results are discussed.