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Measurements of cloud condensation nuclei (CCN) concentrations between 0.2-1.0% supersaturation and aerosol size distribution were performed at an urban background site of Athens during HygrA-CD. The site is affected by local and long-range transported emissions as portrayed by the external mixing of the particles, as the larger ones appear to be more hygroscopic and more CCN-active than smaller ones. Activation fractions at all supersaturations exhibit a diurnal variability with minimum values around noon, which are considerably lower than unity. This reinforces the conclusion that the aerosol is mostly externally mixed between “fresher”, less hygroscopic components with more aged, CCN active constituents.

Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants in fine particulate matter (PM) long known to have mutagenic and carcinogenic effects, but much is unknown about the importance of local and remote sources to PAH levels observed in population-dense urban environments. A year-long sampling campaign in Athens, Greece, where more than 150 samples were analyzed for 31 PAHs and a wide range of chemical markers were used in combination with Positive Matrix Factorization (PMF) to constrain the temporal variability, sources and carcinogenic risk associated with PAHs. We find that biomass burning (BB), a source mostly effective during wintertime intense pollution events (observed for 18 % of measurement days in 2017), lead to wintertime PAH levels 7 times higher than in other seasons and was responsible for annual mean PAH concentrations (31 %) comparable to those from diesel/oil (33 %) and gasoline (29 %) sources. The contribution of non-local sources, although limited on an annual basis (7 %), was increased during summer, becoming comparable to that of local sources combined. The fraction of PAHs associated with BB is linked to increased health risk compared to the other sources, accounting for almost half the annual carcinogenic potential of PAHs (43 %). This can result in a larger number of excess cancer cases due to BB-related high PM levels and urges immediate action to reduce residential BB emissions in urban areas facing similar issues. [ABSTRACT FROM AUTHOR]

In an attempt to take effective action towards mitigating pollution episodes in the Greater Athens Area (GAA), precise knowledge of PM2.5 composition and their sources is a prerequisite. Thus, a two year chemical composition data set from aerosol samples collected in an urban-background site of central Athens, from December 2013 till March 2016, has been obtained and Positive Matrix Factorization (PMF) was applied in order to identify and apportion fine aerosols to their sources. A total of 850 aerosol samples, were collected on a 12 to 24 h basis and analyzed for major ions, trace elements, organic and elemental carbon, allowing us to further assess the impact of residential heating as a source of air pollution over the GAA. The ionic and carbonaceous components were found to constitute the major fraction of the PM2.5 aerosol mass. The annual contribution of the Ion Mass (IM), Particulate Organic Mass (POM), dust, Elemental Carbon (EC) and Sea Salt (SS) were calculated at 31 %, 34 %, 18 %, 8 % and 3 %, respectively. However, carbonaceous aerosols (POM + EC) and IM exhibited considerable seasonal variation. In winter, IM was estimated down to 23 %, with POM + EC being the dominant component accounting for 48 % of the PM2.5 mass, while in summer IM was the dominant component (42 %), followed by carbonaceous aerosols 37 %. Results from samples collected on a 12 h basis (day and night) during the 3 intensive winter campaigns indicated the impact of heating on the levels of a series of compounds. Indeed PM2.5, EC, POM, NO3−, C2O42−, nssK+ and selected trace metals including Cd and Pb were increased by almost a factor of 4 during night compared to day, highlighting the importance of heating on air quality of the GAA. Furthermore, in order to better characterize winter-time aerosol sources in the city centre of Athens and quantify the input of biomass burning as a source to winter night-time PM2.5 concentrations, source apportionment was performed. Τhe data can be interpreted on the basis of six sources namely biomass burning (32 %), vehicular emissions (19 %), heavy oil combustion (7 %), regional secondary (20 %), marine aerosol (9 %) and dust particles (8 %). With specific emphasis on night to day contrasts their contributions shifted from 19, 19, 8, 30, 11 and 9 % of the PM2.5 mass during day to 39, 19, 6, 14, 7 and 6 % during night, underlining the significance of biomass burning as the main contributor to fine particle levels during night-time. [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]