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An upgraded three-dimensional (3D) version of the back-trajectory based Concentration Weighted Trajectory (CWT) model, segregating distinct vertical layers of atmospheric transport, was combined with two years of PM 10 chemical composition measurements from the Finokalia superstation on the island of Crete, Greece, in the Eastern Mediterranean basin. Three altitudinal transport layers were studied: a) 0 m ≤ Layer 1 < 1000 m b) 1000 m ≤ Layer 2 < 2000 m c) 2000 m ≤ Layer 3, and the analysis was conducted separately for the cold (16 October – 15 April) and the warm (16 April – 15 October) periods. Mediterranean airflows in all layers enriched the concentrations of sea salt water soluble ions (Na+, Cl−, Mg2+ and K+) whilst during the warm period long-range northeastern airflows in layer 2 and layer 3 increased the levels of carbonaceous aerosols (OC and EC) and K+ due to intensive biomass burning in areas around the Black Sea. Peak concentrations of PM 10 -bound SO 4 2− and NH 4 + were associated with continental Northern airflows in layer 2 and layer 3, and were attributed to emissions in Northern Greece, Turkey, Balkan Peninsula and Eastern Europe. In addition, episodes of crustal constituents such as Ca2+, Mn , Al and Fe , were triggered by Saharan dust intrusions occurring mainly during cold period through all altitudinal layers. Moreover, the impact of heavy fuel oil combustion from shipping during warm period was reflected by maritime flows enhancing V concentrations, whilst a Saharan dust source for V was observed in all layers during cold period. [Display omitted] • 3D-CWT model revealed spatial and altitudinal PM 10 transport pathways in Finokalia. • Crustal PM 10 species are strongly affected by Saharan dust intrusions. • Sea salt PM 10 constituents were enhanced mainly by Mediterranean airflows. • Biomass burning around the Black Sea affected K+, OC and EC levels in warm period. • North-Northeastern continental flows enriched the SO 4 2− and NH 4 + PM 10 constituents. [ABSTRACT FROM AUTHOR]

While the effects of aging on the mass, chemical composition, and hygroscopicity of organic aerosols are becoming better understood, the corresponding impacts on their direct radiative forcing and adverse health effects remain unclear. Through a combination of laboratory experiments and field observations, the objective of this work is to investigate the effects of atmospheric processing on the light absorptivity and oxidative potential (ability to generate Reactive Oxygen Species, ROS) of biomass burning organic aerosols (BBOA). In the laboratory, changes in the light absorptivity of molecular weight separated BBOA due to photochemical aging were systemically examined. Results suggest that the extent to which photo-bleaching and photo-enhancement occurs is dependent on the molecular weight fraction of BBOA. The effects of atmospheric aging on ambient BBOA, using filter samples collected in Crete, Greece, were also investigated. Focusing on samples that transition from freshly emitted to highly aged BBOA, results suggest that light absorbing large molecular weight compounds can be long-lived components in BBOA, thus more likely to have a larger impact on the aerosol direct radiative forcing. To better understand the health impacts of BBOA, results elucidating the role of atmospheric aging on their oxidative potential will also be presented. [ABSTRACT FROM AUTHOR]

Measurements of the composition of the gas and particulate phases were conducted from May 9 to June 4 of 2016 at the Finokalia (Greece) remote coastal site in the eastern Mediterranean, continuing the effort to track long term changes of the atmospheric chemical composition in the area. Finokalia is influenced by air masses arriving in the site from regional sources in Europe, Africa, and other locations. In this study, a series of instruments and analysis techniques were used for the first time at the Finokalia site to characterize the composition of the organic aerosol (OA). The PM 1 was composed of ammonium sulfate/bisulfate (60%), followed by organics (35%) and black carbon (BC) (4%). The OA was highly oxidized with an average oxygen-to-carbon (O:C) ratio of 0.81. Source apportionment of high-resolution organic aerosol mass spectra via positive matrix factorization (PMF) identified four factors: less oxidized oxygenated organic aerosol (LO-OOA), more oxidized oxygenated organic aerosol (MO-OOA), marine-related oxygenated organic aerosol (marine-OOA) and hydrocarbon-like organic aerosol (HOA). The LO-OOA (O:C = 0.92) was the dominant factor for most of the campaign (51% of the PM 1 OA), while the MO-OOA (O:C = 1.1) was responsible for 11% of the OA. The marine-OOA factor was also highly oxidized (O:C = 1.03), contributing on average 24% to the total OA and was found to be well correlated with sulfate (R2 = 0.83). The anthropogenic HOA factor (O:C = 0.36) was related to activities in the island of Crete. Its mass spectrum was quite similar (R2 = 0.86–0.95) to those of other HOA factors in the literature and its average concentration was 0.2 μg m−3 (14% of OA). High molecular weight compounds were found, suggesting the presence of oligomers in agreement with the presence of a highly oxidized quenching agent. Aromatic VOCs, like benzene, toluene, and xylenes were on average 0.17, 0.66 and 0.36 ppb, respectively with toluene concentrations indicating the presence of a local source despite the remote nature of the site. New particle formation (NPF) was observed during 26% of the days. The air masses during NPF events passed over the island of Crete and the Balkans and were characterized by a low condensation sink (5.9 ± 2.2 10−3 s−1). Nucleation mode particle concentrations during NPF days had an additional evening peak between 17:00 and 22:00, which was accompanied by an HOA peak implying the influence of a source of sub-25 nm particles in the extended area. These findings show that even a relatively remote site like Finokalia is occasionally affected by sources located tens of kilometers away, something that should be taken into account in the interpretation of past and future measurements in this location. • Highly oxygenated organic aerosol in the Eastern Mediterranean area. • Effects of sources from Crete during stagnation periods. • Evidence for significant contributions of organosulfates. • Effects of vertical mixing even in a remote area. • NPF during clean days with air masses passing over land. [ABSTRACT FROM AUTHOR]