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Many studies have drawn attention to the associations of oxygenated polycyclic aromatic hydrocarbons (OPAHs) with harmful health effects, advocating for their systematic monitoring alongside simple PAHs to better understand the aerosol carcinogenic potential in urban areas. To address this need, this study conducted an extensive PM 2.5 sampling campaign in Athens, Greece, at the Thissio Supersite of the National Observatory of Athens, from December 2018 to July 2021, aiming to characterize the levels and variability of polycyclic aromatic compounds (PACs), perform source apportionment, and assess health risk. Cumulative OPAH concentrations (Σ-OPAHs) were in the same range as Σ-PAHs (annual average 4.2 and 5.6 ng m -3 , respectively). They exhibited a common seasonal profile with enhanced levels during the heating seasons, primarily attributed to residential wood burning (RWB). The episodic impact of biomass burning was also observed during a peri-urban wildfire event in May 2021, when PAH and OPAH concentrations increased by a factor of three compared to the monthly average. The study period also included the winter 2020-2021 COVID-19 lockdown, during which PAH and OPAH levels decreased by >50 % compared to past winters. Positive matrix factorization (PMF) source apportionment, based on a carbonaceous aerosol speciation dataset, identified PAC sources related to RWB, local traffic (gasoline vehicles) and urban traffic (including diesel emissions), as well as an impact of regional organic aerosol. Despite its seasonal character, RWB accounted for nearly half of Σ-PAH and over two-thirds of Σ-OPAH concentrations. Using the estimated source profiles and contributions, the source-specific carcinogenic potency of the studied PACs was calculated, revealing that almost 50 % was related to RWB. These findings underscore the urgent need to regulate domestic biomass burning at a European level, which can provide concrete benefits for improving urban air quality, towards the new stricter EU standards, and reducing long-term health effects., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Abstract The oxidative potential (OP) of fine and coarse fractions of ambient aerosols was studied in the urban environment of Athens, Greece. OP was quantified using a dithiothreitol (DTT) assay, applied to the water soluble fraction of aerosol that was extracted from 361 fine and 84 coarse mode of 24-h and 12-h filter samples over a one-year period. During the cold period, samples were collected on a 12-h basis, to assess the impact of night-time biomass burning emissions from domestic heating on OP. The chemical characteristics of aerosols were measured in parallel using an Aerosol Chemical Speciation Monitoring (ACSM) and a 7-wavelength Aethalometer. A source apportionment analysis on the ACSM data resulted in the identification of organic aerosol (OA) factors on a seasonal basis. A good correlation of OP with NO 3 −, NH 4 +, BC (Black Carbon), Organics and LV-OOA (low volatility oxygenated OA) was found during winter, revealing the importance of combustion and aging processes for OP. During the summertime, a good correlation between OP and SO 4 −2 and NH 4 +indicates its association with regional aerosol – thus the importance of oxidative aging that reduces its association with any characteristic source. Multiple regression analysis during winter revealed that highly oxygenated secondary aerosol (LV-OOA) and, to a lesser extent, fresh biomass burning (BBOA) and fossil fuel (HOA) organic aerosol, are the prime contributors to the OP of fine aerosol, with extrinsic toxicities of 54 ± 22 pmol min−1 μg−1, 28 ± 7 and 17 ± 4 pmol min−1μg−1, respectively. In summer, OP cannot be attributed to any of the identified components and corresponds to a background aerosol value. In winter however, the regression model can reproduce satisfactorily the water soluble DTT activity of fine aerosol, providing a unique equation for the estimation of aerosol OP in an urban Mediterranean environment. Graphical abstract Image 1 Highlights • Yearlong oxidative potential measurements on 367 fine aerosol samples. • Fine urban aerosol oxidative potential is 3 times higher compared to coarse mode. • Winter elevated oxidative potential attributed to fresh aerosol emissions. • Summer background aerosol oxidative potential due to long-range transport. • Satisfactory reconstruction of fine aerosol water-soluble dithiothreitol activity. [ABSTRACT FROM AUTHOR]

To identify the sources of aerosols in Greater Athens Area (GAA), a total of 1510 daily samples of fine (PM 2.5 ) and coarse (PM 10–2,5 ) aerosols were collected at a suburban site (Penteli), during a five year period (May 2008–April 2013) corresponding to the period before and during the financial crisis. In addition, aerosol sampling was also conducted in parallel at an urban site (Thissio), during specific, short-term campaigns during all seasons. In all these samples mass and chemical composition measurements were performed, the latest only at the fine fraction. Particulate organic matter (POM) and ionic masses (IM) are the main contributors of aerosol mass, equally contributing by accounting for about 24% of the fine aerosol mass. In the IM, nss-SO 4 − 2 is the prevailing specie followed by NO 3 − and NH 4 + and shows a decreasing trend during the 2008–2013 period similar to that observed for PM masses. The contribution of water in fine aerosol is equally significant (21 ± 2%), while during dust transport, the contribution of dust increases from 7 ± 2% to 31 ± 9%. Source apportionment (PCA and PMF) and mass closure exercises identified the presence of six sources of fine aerosols: secondary photochemistry, primary combustion, soil, biomass burning, sea salt and traffic. Finally, from winter 2012 to winter 2013 the contribution of POM to the urban aerosol mass is increased by almost 30%, reflecting the impact of wood combustion (dominant fuel for domestic heating) to air quality in Athens, which massively started in winter 2013. [ABSTRACT FROM AUTHOR]

Organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC) and main ions were measured in a total of 1510 PM2.5 daily aerosol samples collected from May 2008 to April 2013 in Athens, Greece. OC and EC concentrations were 2.1 ± 1.3 μgm-3 and 0.54 ± 0.39 μgm-3 , accounting for 11 ± 3 % and 3 ± 1 % of PM2.5 mass, respectively, with an average OC / EC ratio of 4.7 ± 3.1. Significant correlation was found between OC and EC during the whole period, indicating emissions by common primary sources on a regional scale. WSOC concentration ranged from 0.03 to 10.6pgm-3 , with an average of 1.5 ± 0.9 μgm-3 . By considering the Finokalia (Crete) station as a reference, it was estimated that, during the warm season in Athens, 67 ± 7% of emitted OC and 53 ± 12% of emitted EC is regional, while, during cold months, the regional contribution of OC is only 33 ± 7 % and of EC 29 ± 8 %. Furthermore, secondary organic carbon (SOC) was calculated for the warm period of the year (April to October). The estimated SOC constituted about 75 ± 6 % of PM2.5 organic carbon in Athens, highlighting significant aging processes on a regional scale. In the period 2011-2013 and during wintertime, an increase in OC and EC levels was observed, attributed to an increase in wood burning for domestic heating due to the economic crisis. [ABSTRACT FROM AUTHOR]

During the summer of 2012 a coordinated field campaign was conducted in multiple locations in Greece in order to characterize the ambient particulate matter (PM) levels, its chemical composition and the contribution of the regional and local sources. PM 1 , PM 2.5 and PM 10 samples were collected simultaneously at seven different sites in Greece: an urban and a suburban station in Patras, a suburban station in Thessaloniki, a suburban and an urban background station in Athens, a rural background station at the Navarino Environmental Observatory (NEO) in southwestern Peloponnese and a remote background site at Finokalia in the northeastern part of Crete. The sites were selected to facilitate the estimation of the contribution of the local emission sources and long range transport. Sulfate and organics were the major PM 1 components in all sites suggesting that high sulfate levels still remain in parts of Europe. The photochemistry of the Eastern Mediterranean can convert rapidly the emitted sulphur dioxide to sulfate. Our analysis indicated significant sulfate production over the area, with high sulfate levels, especially in the remote site of Finokalia, associated with air masses that had passed over Turkey. There was high regional secondary organic aerosol production dominating organic aerosol levels even in a major city like Athens. High organic aerosol levels were associated with air masses that had crossed the Balkans with a significant biogenic component. The average PM 2.5 concentration ranged from 13 to 18 μg m−3 in the different sites. There were unexpected significant gradients in the concentrations of secondary aerosol components in length scales of a few hundred kilometers. The low concentrations of measured PM 2.5 nitrate are mostly organic nitrates and supermicrometer nitrate associated with sea-salt and dust. Dust was a significant PM 10 constituent in all areas and was quite variable in space showing the importance of the local sources. • High sulfate levels still remain in parts of Europe. • High regional secondary organic aerosol production during summer. • Significant spatial gradients in secondary organic aerosol levels. • Most of the fine PM nitrates are organonitrates. [ABSTRACT FROM AUTHOR]