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This work evaluates the aerosol oxidative potential (OP) and its changes from modified air pollution emissions during the COVID-19 lockdown period in 2020, with the intent of elucidating the contribution of aerosol sources and related components to aerosol OP. For this, daily particulate matter (PM) samples at an urban background site were collected and analyzed with a chemical (acellular) assay based on Dithiothreitol (DTT) during the COVID-19 restriction period in Athens (Greece). The obtained time-series of OP, PM2.5, organic matter (OM) and SO42− of the pre-, post- and lockdown periods were also compared to the data of the same time periods during the years 2017–2019. Even though all traffic-related emissions have been significantly reduced during the lockdown period (by 30%), there is no reduction in water-soluble OP, organics and sulfate concentrations of aerosol during 2020. The results reveal that the decrease in traffic was not sufficient to drive any measurable change on OP, suggesting that other sources—such as biomass burning and secondary aerosol from long-range transport, which remained unchanged during the COVID lockdown—are the main contributors to OP in Athens, Greece. [ABSTRACT FROM AUTHOR]

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 for 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, was combined with positive matrix factorization (PMF) to constrain the temporal variability, sources, and carcinogenic risk associated with PAHs. It was found that biomass burning (BB), a source mostly present during wintertime intense pollution events (observed for 18 % of measurement days in 2017), led to wintertime PAH levels that were 7 times higher than in other seasons and was as important for annual mean PAH concentrations (31 %) as diesel and oil (33 %) and gasoline (29 %) sources. The contribution of non-local sources, although limited on an annual basis (7 %), increased during summer, becoming comparable to that of local sources combined. The fraction of PAHs (12 members that were included in the PMF analysis) that was associated with BB was also linked to increased health risk compared to the other sources, accounting for almost half the annual PAH carcinogenic potential (43 %). This can result in a large 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]

Biomass burning is a major source of atmospheric brown carbon (BrC), and through its absorption of UV/VIS radiation, it can play an important role in the planetary radiative balance and atmospheric photochemistry. The considerable uncertainty of BrC impacts is associated with its poorly constrained sources, transformations, and atmospheric lifetime. Here we report laboratory experiments that examined changes in the optical properties of the water-soluble (WS) BrC fraction of laboratory-generated biomass burning particles from hardwood pyrolysis. Effects of direct UVB photolysis and OH oxidation in the aqueous phase on molecular-weight-separated BrC were studied. Results indicated that the majority of low-molecular-weight (MW) BrC (<400 Da) was rapidly photobleached by both direct photolysis and OH oxidation on an atmospheric timescale of approximately 1 h. High MW BrC (≥400 Da) underwent initial photoenhancement up to ∼15 h, followed by slow photobleaching over ∼10 h. The laboratory experiments were supported by observations from ambient BrC samples that were collected during the fire seasons in Greece. These samples, containing freshly emitted to aged biomass burning aerosol, were analyzed for both water- and methanol-soluble BrC. Consistent with the laboratory experiments, high-MW BrC dominated the total light absorption at 365 nm for both methanol and water-soluble fractions of ambient samples with atmospheric transport times of 1 to 68 h. These ambient observations indicate that overall, biomass burning BrC across all molecular weights has an atmospheric lifetime of 15 to 28 h, consistent with estimates from previous field studies – although the BrC associated with the high-MW fraction remains relatively stable and is responsible for light absorption properties of BrC throughout most of its atmospheric lifetime. For ambient samples of aged (>10 h) biomass burning emissions, poor linear correlations were found between light absorptivity and levoglucosan, consistent with other studies suggesting a short atmospheric lifetime for levoglucosan. However, a much stronger correlation between light absorptivity and total hydrous sugars was observed, suggesting that they may serve as more robust tracers for aged biomass burning emissions. Overall, the results from this study suggest that robust model estimates of BrC radiative impacts require consideration of the atmospheric aging of BrC and the stability of high-MW BrC. [ABSTRACT FROM AUTHOR]

In an attempt to take effective action towards mitigating pollution episodes in Athens, precise knowledge of PM2.5 composition and its sources is a prerequisite. Thus, a 2-year chemical composition dataset from aerosol samples collected in an urban background site in central Athens from December 2013 to March 2016 has been obtained and a 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, and organic and elemental carbon, allowing us to further assess the impact of residential heating as a source of air pollution over Athens. 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) was calculated at 31 %, 38 %, 18 %, 8 %, and 3 %, respectively, and exhibited considerable seasonal variation. In winter, the share of IM was estimated down to 23 %, with POMC EC being the dominant component accounting for 52% of the PM2.5 mass, while in summer, IM (42 %) and carbonaceous aerosols (41 %) contributed almost equally. Results from samples collected on a 12 h basis (day and night) during the three intensive winter campaigns indicated the impact of heating on the levels of a series of compounds. Indeed, PM2.5, EC, POM, NO-3, C2O2-4, non sea salt (nss) K+ and selected trace metals including Cd and Pb were increased by up to a factor of 4 in the night compared to the day, highlighting the importance of heating on air quality in Athens. Furthermore, in order to better characterize wintertime aerosol sources and quantify the impact of biomass burning on PM2:5 levels, source apportionment was performed. The data can be interpreted on the basis of six sources, namely biomass burning (31 %), vehicular emissions (19 %), heavy oil combustion (7 %), regional secondary (21 %), marine aerosols (9 %), and dust particles (8 %). Regarding night-to-day patterns their contributions shifted from 19 %, 19 %, 8 %, 31 %, 12 %, and 10% of the PM2.5 mass during day to 39 %, 19 %, 6 %, 14 %, 7 %, and 7% during the night, underlining the significance of biomass burning as the main contributor to fine particle levels during nighttime in winter. [ABSTRACT FROM AUTHOR]

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]

Port cities are affected by a wide array of emissions, including those from the shipping, road transport, and residential sectors; therefore, the characterization and apportionment of such sources in a high temporal resolution is crucial. This study presents measurements of fine aerosol chemical composition in Piraeus, one of the largest European ports, during two monthly periods (winter vs. summer) in 2018–2019, using online instrumentation (Aerosol Chemical Speciation Monitor—ACSM, 7-λ aethalometer). PMF source apportionment was performed on the ACSM mass spectra to quantify organic aerosol (OA) components, while equivalent black carbon (BC) was decomposed to its fossil fuel combustion and biomass burning (BB) fractions. The combined traffic, shipping and, especially, residential emissions led to considerably elevated submicron aerosol levels (22.8 μg m−3) in winter, which frequently became episodic late at night under stagnant conditions. Carbonaceous compounds comprised the major portion of this submicron aerosol in winter, with mean OA and BC contributions of 61% (13.9 μg m−3) and 16% (3.7 μg m−3), respectively. The contribution of BB to BC concentrations was considerable and spatially uniform. OA related to BB emissions (fresh and processed) and hydrocarbon-like OA (from vehicular traffic and port-related fossil fuel emissions including shipping) accounted for 37% and 30% of OA, respectively. In summer, the average PM1 concentration was significantly lower (14.8 μg m−3) and less variable, especially for the components associated with secondary aerosols (such as OA and sulfate). The effect of the port sector was evident in summer and maintained BC concentrations at high levels (2.8 μg m−3), despite the absence of BB and improved atmospheric dispersion. Oxygenated components yielded over 70% of OA in summer, with the more oxidized secondary component of regional origin being dominant (41%) despite the intensity of local sources, in the Piraeus environment. In general, with respect to local sources that can be the target of mitigation policies, this work highlights the importance of port-related activities but also reveals the extensive wintertime impact of residential wood burning. While a separation of the BB source is feasible, more research is needed on how to disentangle the short-term effects of different fossil-fuel combustion sources. [ABSTRACT FROM AUTHOR]

This study aims to characterize the variability and sources of water-soluble organic nitrogen (WSON) in aerosol over Cyprus in the Eastern Mediterranean. Measurements of PM 10 particles were conducted during the calendar year of 2011 at two sites, located at a roadside location in Nicosia (urban traffic) and in the rural area of Agia Marina Xyliatou (regional background). Filter samples were analyzed for water-soluble total nitrogen (WSTN), nitrate and ammonium, to determine WSON. Additional analyses were performed, for water-soluble organic carbon (WSOC), organic and elemental carbon (OC and EC), major ions and trace metals. Annual mean WSON concentrations of 0.20 and 0.16 μgN m−3 were determined at the urban traffic and regional background sites, respectively. The organic fraction of WSTN was about 20%, with limited inter-site and seasonal variability. Distinct seasonal patterns were observed at the two sites, with warm-period concentrations being significantly higher at the regional background site, while the enhanced local emissions during winter at the traffic site smoothed out the observed variability. Mean WSON/WSOC ratios of 0.09–0.12 were calculated at the two sites, with the two parameters being weakly correlated. A roadside WSON enhancement was verified, although moderate on an annual basis (9%). However, concentrations in Nicosia were more than one time higher than the background during winter. The observed temporal and inter-site variability highlighted the necessity of source apportionment, which was performed using Positive Matrix Factorization (PMF) modeling, utilizing the analytical datasets at the two sites. In this way, the estimated contribution of regional transport of processed aerosols was found to be more pronounced at the regional background site (59% vs. 38%), while a sizeable input (35%) was linked to vehicular emissions at the traffic site. An additional anthropogenic impact, probably related to biomass burning, was estimated at both sites (16%), while contributions of natural sources like mineral dust (4–8%) and marine aerosol (2–3%) were smaller. • First WSON measurements and PMF source apportionment at urban/rural sites in Cyprus. • Water-soluble ON/TN ratios circa 20% with small seasonal and inter-site variability. • Higher WSON during summer at the background site, larger urban increments in winter. • Regional secondary WSON sources dominant at the background EMEP site (≈60%). • Notable WSON contribution (35%) of vehicular emissions at the traffic site. [ABSTRACT FROM AUTHOR]

This study examines the carbonaceous-aerosol characteristics at three contrasting urban environments in Greece (Ioannina, Athens, and Heraklion), on the basis of 12 h sampling during winter (January to February 2013), aiming to explore the inter-site differences in atmospheric composition and carbonaceous-aerosol characteristics and sources. The winter-average organic carbon (OC) and elemental carbon (EC) concentrations in Ioannina were found to be 28.50 and 4.33 µg m−3, respectively, much higher than those in Heraklion (3.86 µg m−3 for OC and 2.29 µg m−3 for EC) and Athens (7.63 µg m−3 for OC and 2.44 µg m−3 for EC). The winter OC/EC ratio in Ioannina (6.53) was found to be almost three times that in Heraklion (2.03), indicating a larger impact of wood combustion, especially during the night, whereas in Heraklion, emissions from biomass burning were found to be less intense. Estimations of primary and secondary organic carbon (POC and SOC) using the EC-tracer method, and specifically its minimum R-squared (MRS) variant, revealed large differences between the sites, with a prevalence of POC (67–80%) in Ioannina and Athens and with a larger SOC fraction (53%) in Heraklion. SOC estimates were also obtained using the 5% and 25% percentiles of the OC/EC data to determine the (OC/EC)pri, leading to results contrasting to the MRS approach in Ioannina (70–74% for SOC). Although the MRS method provides generally more robust results, it may significantly underestimate SOC levels in environments highly burdened by biomass burning, as the fast-oxidized semi-volatile OC associated with combustion sources is classified in POC. Further analysis in Athens revealed that the difference in SOC estimates between the 5% percentile and MRS methods coincided with the semi-volatile oxygenated organic aerosol as quantified by aerosol mass spectrometry. Finally, the OC/Kbb+ ratio was used as tracer for decomposition of the POC into fossil-fuel and biomass-burning components, indicating the prevalence of biomass-burning POC, especially in Ioannina (77%). [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]

The Mediterranean Sea is an oligotrophic semi-closed environment where atmospheric deposition is expected to be an important driver for biological activity. The present study uses a three-dimensional atmospheric chemistry transport model to evaluate the nitrogen (N), phosphorus (P) and iron (Fe) atmospheric deposition fluxes to the Mediterranean Sea. The model takes into account both the inorganic and organic fractions of these fluxes and compares them to other sources of these nutrients that are external to the ocean. The estimated atmospheric deposition fluxes of soluble nutrients amount to 1281 Gg-N y−1, 4.31 Gg-P y−1 and 6.32 Gg-Fe y−1 for the present day, and are within the range of the few estimates available in literature. An almost 6-fold increase in the atmospheric deposition of soluble N is also calculated to be the result of the increase in anthropogenic and biomass burning emissions since 1850, while soluble P and Fe deposition fluxes have increased by 59% and 114%, respectively. For future (2100) emissions, however, N deposition is projected to increase only slightly (4%) while soluble P and Fe fluxes will decrease by 34% and 32% compared to current estimates. The soluble organic N and P annual deposition fluxes are calculated to be 12% and 28–83% of total soluble N and P present-day annual deposition fluxes into the Mediterranean Sea, respectively. However, to reconcile with the observed fluxes in the west and the east Mediterranean, ∼14 times higher flux of soluble P, in particular organic P, and at least 2.5 times higher flux of soluble Fe need to be considered in the model. Such high fluxes can be due to higher combustion emissions of soluble Fe and P, to higher dust emissions or solubilisation of Fe and P contained in dust aerosols, and also higher organic P flux associated with bioaerosols than currently used in the global models. Overall, the calculated deposition fluxes provide an integrated spatially complete picture of the atmospheric inputs to the Mediterranean marine ecosystem, which are potentially important for net primary production and the ocean carbon cycle. [ABSTRACT FROM AUTHOR]