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11.
Assessment of the COVID-19 lockdown effects on spectral aerosol scattering and absorption properties in Athens, Greece
Dimitris G. Kaskaoutis, Georgios Grivas, Eleni Liakakou, Nikos Kalivitis, Giorgos Kouvarakis, Iasonas Stavroulas, Panayiotis Kalkavouras, Pavlos Zarmpas, Umesh Chandra Dumka, Evangelos Gerasopoulos, Nikolaos Mihalopoulos, 2021, original scientific article

Abstract: COVID-19 is evolving into one of the worst pandemics in recent history, claiming a death toll of over 1.5 million as of December 2020. In an attempt to limit the expansion of the pandemic in its initial phase, nearly all countries imposed restriction measures, which resulted in an unprecedented reduction of air pollution. This study aims to assess the impact of the lockdown effects due to COVID-19 on in situ measured aerosol properties, namely spectral-scattering (bsca) and absorption (babs) coefficients, black carbon (BC) concentrations, single-scattering albedo (SSA), scattering and absorption Ångström exponents (SAE, AAE) in Athens, Greece. Moreover, a comparison is performed with the regional background site of Finokalia, Crete, for a better assessment of the urban impact on observed differences. The study examines pre-lockdown (1–22 March 2020), lockdown (23 March–3 May 2020) and post-lockdown (4–31 May 2020) periods, while the aerosol properties are also compared with a 3–4 year preceding period (2016/2017–2019). Comparison of meteorological parameters in Athens, between the lockdown period and respective days in previous years, showed only marginal variation, which is not deemed sufficient in order to justify the notable changes in aerosol concentrations and optical properties. The largest reduction during the lockdown period was observed for babs compared to the pre-lockdown (−39%) and to the same period in previous years (−36%). This was intensified during the morning traffic hours (−60%), reflecting the large decrease in vehicular emissions. Furthermore, AAE increased during the lockdown period due to reduced emissions from fossil-fuel combustion, while a smaller (−21%) decrease was observed for bsca along with slight increases (6%) in SAE and SSA values, indicating that scattering aerosol properties were less affected by the decrease in vehicular emissions, as they are more dependent on regional sources and atmospheric processing. Nighttime BC emissions related to residential wood-burning were slightly increased during the lockdown period, with respect to previous-year means. On the contrary, aerosol and pollution changes during the lockdown period at Finokalia were low and highly sensitive to natural sources and processes.
Keywords: COVID-19, traffic, aerosol scattering, absorption, SSA, Greece
Published in RUNG: 10.05.2024; Views: 219; Downloads: 3
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12.
Apportionment of black and brown carbon spectral absorption sources in the urban environment of Athens, Greece, during winter
Dimitris G. Kaskaoutis, Georgios Grivas, Iasonas Stavroulas, Aikaterini Bougiatioti, Eleni Liakakou, Umesh Chandra Dumka, Evangelos Gerasopoulos, Nikolaos Mihalopoulos, 2021, original scientific article

Abstract: This study examines the spectral properties and source characteristics of absorbing aerosols (BC: Black Carbon; BrC: Brown Carbon, based on aethalometer measurements) in the urban background of Athens during December 2016–February 2017. Using common assumptions regarding the spectral dependence of absorption due to BC (AAEBC = 1) and biomass burning (AAEbb = 2), and calculating an optimal AAEff value for the dataset (1.18), the total spectral absorption was decomposed into five components, corresponding to absorption of BC and BrC from fossil-fuel (ff) combustion and biomass burning (bb), and to secondary BrC estimated using the BC-tracer minimum R-squared (MRS) method. Substantial differences in the contribution of various components to the total absorption were found between day and night, due to differences in emissions and meteorological dynamics, while BrC and biomass burning aerosols presented higher contributions at shorter wavelengths. At 370 nm, the absorption due to BCff contributed 36.3% on average, exhibiting a higher fraction (58.1%) during daytime, while the mean BCbb absorption was estimated at 18.4%. The mean absorption contributions due to BrCff, BrCbb and BrCsec were 6.7%, 32.3% and 4.9%, respectively. The AbsBCff,370 component maximized during the morning traffic hours and was strongly correlated with NOx (R2 = 0.76) and CO (R2 = 0.77), while a similar behavior was seen for the AbsBrCff,370 component. AbsBCbb and AbsBrCbb levels escalated during nighttime and were highly associated with nss-K+ and with the organic aerosol (OA) components related to fresh and fast-oxidized biomass burning (BBOA and SV-OOA) as obtained from ACSM measurements. Multiple linear regression was used to attribute BrC absorption to five OA components and to determine their absorption contributions and efficiencies, revealing maximum contributions of BBOA (33%) and SV-OOA (21%). Sensitivity analysis was performed in view of the methodological uncertainties and supported the reliability of the results, which can have important implications for radiative transfer models.
Keywords: spectral absorption, black carbon, brown carbon, fossil fuel, biomass burning, source apportionment
Published in RUNG: 10.05.2024; Views: 250; Downloads: 0
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13.
Impacts of severe residential wood burning on atmospheric processing, water-soluble organic aerosol and light absorption, in an inland city of Southeastern Europe
Dimitris G. Kaskaoutis, Georgios Grivas, K. Oikonomou, P. Tavernaraki, Kyriaki Papoutsidaki, M. Tsagkaraki, Iasonas Stavroulas, Pavlos Zarmpas, D. Paraskevopoulou, Aikaterini Bougiatioti, 2022, original scientific article

Abstract: This study examines the concentrations and characteristics of carbonaceous aerosols (including saccharides) and inorganic species measured by PM2.5 filter sampling and a multi-wavelength Aethalometer during two campaigns in a mountainous, medium-sized, Greek city (Ioannina). The first campaign was conducted in summer and used as a baseline of low concentrations, while the second took place in winter under intensive residential wood burning (RWB) emissions. Very high winter-mean OC concentrations (26.0 μg m−3) were observed, associated with an OC/EC ratio of 9.9, and mean BCwb and PM2.5 levels of 4.5 μg m−3 and 57.5 μg m−3, respectively. Simultaneously, record-high levoglucosan (Lev) concentrations (mean: 6.0 μg m−3; max: 15.9 μg m−3) were measured, revealing a severely biomass burning (BB)-laden environment. The water-soluble OC component (WSOC) accounted for 56 ± 9% of OC in winter, exhibiting high correlations (R2 = 0.93–0.97) with BB tracers (nss-K+, BCwb, Lev), nitrate and light absorption, potentially indicating the formation of water-soluble brown carbon (BrC) from fast oxidation processes. The examination of diagnostic ratios involving BB tracers indicated the prevalence of hardwood burning, while the mean Lev/OC ratio (22%) was remarkably higher than literature values. Applying a mono-tracer method based on levoglucosan, we estimated very high BB contributions to OC (∼92%), EC (∼64%) and WSOC (∼87%) during winter. On the contrary, low levels were registered during summer for all carbonaceous components, with winter/summer ratios of 4–5 for PM2.5 and BC, 10 for OC, 30 for BCwb and ∼1100 for levoglucosan. The absence of local BB sources in summer, combined with the photochemical processing and aging of regional organic aerosols, resulted in higher WSOC/OC fractions (64 ± 13%). The results indicate highly soluble fine carbonaceous aerosol fraction year-round, which when considered alongside the extreme concentration levels in winter can have important implications for short- and long-term health effects.
Keywords: carbonaceous aerosols, biomass burning, levoglucosan, WSOC, heterogeneous chemistry, Greece
Published in RUNG: 10.05.2024; Views: 251; Downloads: 2
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Intra- and inter-city variability of ▫$PM_2.5$▫ concentrations in Greece as determined with a low-cost sensor network
Konstantinos Dimitriou, Iasonas Stavroulas, Georgios Grivas, Charalampos Chatzidiakos, Georgios Kosmopoulos, Andreas Kazantzidis, Konstantinos Kourtidis, Athanasios Karagioras, Nikolaos Hatzianastassiou, Spyros N. Pandis, 2023, original scientific article

Abstract: Measurements of PM2.5 concentrations in five major Greek cities over a two-year period using calibrated low-cost sensor-based particulate matter (PM) monitors (Purple Air PA-II) were combined with local meteorological parameters, synoptic patterns and air mass residence time models to investigate the factors controlling PM2.5 spatiotemporal variability over continental Greece. Fourteen sensors nodes in Athens, Patras, Ioannina, Xanthi, and Thermi (in the Metropolitan Area of Thessaloniki) were selected out of more than 100 of a countrywide network for detailed analysis. The cities have populations ranging from 65k to 3M inhabitants and cover different latitudes along the South-North axis. High correlations between the daily average PM2.5 levels were observed among all sites, indicating strong intra- and inter-city covariance of concentrations, both in cold and warm periods. Higher PM2.5 concentrations in all cities during the cold period were primarily associated with low temperatures and stagnant anticyclonic conditions, favoring the entrapment of residential heating emissions from biomass burning. Anticyclonic conditions were also connected to an increased frequency of PM2.5 episodes, exceeding the updated daily guideline value (15 μg m−3) of the World Health Organization (WHO). During the warm period, nearly uniform PM2.5 levels were encountered across continental Greece, independently of their population size. This uniformity strongly suggests the importance of long-range transport and regional secondary aerosol formation for PM2.5 during this period. Peak concentrations were associated mainly with regional northern air flows over Greece and the Balkan Peninsula. The use of the measurements from dense air quality sensor networks, provided that a robust calibration protocol and continuous data quality assurance practices are followed, appears to be an efficient tool to gain insights on the levels and variability of PM2.5 concentrations, underpinning the characterization of spatial and seasonal particularities and supporting real-time public information and warning.
Keywords: particulate matter, PM2.5, biomass burning, low-cost sensors, purple air PA-II, concentration weighted trajectory, potential source contribution function
Published in RUNG: 10.05.2024; Views: 246; Downloads: 2
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