Abstract
High-resolution measurements of sulfur dioxide (SO2), nitric acid (HNO3), and hydrochloric acid (HCl) were conducted in Athens, Greece, from 2014 to 2016 via a wet rotating annular denuder system paired with an ion chromatograph. Decreased mean annual levels of SO2 and HNO3 (equal to 3.3 ± 4.8 μg m−3 and 0.7 ± 0.6 μg m−3, respectively) were observed relative to the past, whereas for HCl (mean of 0.4 μg m−3 ) no such comparison was possible as the past measurements are very scarce. Regional and local emission sources regulated the SO2 levels and contributed to both the December and the July maxima of 6.6 μg m−3 and 5.5 μg m−3, respectively. Similarly, the significant enhancement at noon and during the winter nighttime was due to transported SO2 and residential heating, respectively. The oxidation of NO2 by OH radicals and the heterogeneous reactions of HNO3 on sea salt seemed to drive the HNO3 and HCl formation, respectively, whereas nighttime biomass burning affected only the former by almost 50%. During summer, the sulfate anions dominated over the SO2, in contrast to the chloride and nitrate ions that prevailed during the winter and were linked to the aerosol acidity that influences their lifetime as well as their impact on ecosystems.
Highlights
Accepted: 23 January 2022Nitric acid, hydrochloric acid, and sulfur dioxide (HNO3, HCl, and SO2, respectively) are the main atmospheric acidic gases that impact on the air quality and oxidative capacity of the atmosphere
Hydrochloric acid, and sulfur dioxide (HNO3, HCl, and SO2, respectively) are the main atmospheric acidic gases that impact on the air quality and oxidative capacity of the atmosphere
After corrections for multiple-scattering and shadowing effects, as described in [39,49,50,51], the 7-λ aethalometer measurements were decomposed to the Black Carbon (BC) fractions associated with fossil fuel combustion (BCff ) and wood burning (BCwb ) [52]
Summary
Hydrochloric acid, and sulfur dioxide (HNO3 , HCl, and SO2 , respectively) are the main atmospheric acidic gases that impact on the air quality and oxidative capacity of the atmosphere. As the changes in the type and strength of the emission sources are expected to have a bearing on the levels of inorganic gaseous acidic compounds, relative to the past, the current work aims to: (i) provide information on the levels and variability of SO2 , HNO3 , and HCl under the current atmospheric conditions in the Greater Athens Area (GAA), using high-resolution measurement techniques that facilitate the investigation of their diurnal and seasonal patterns; (ii) assess the factors controlling their formation and removal, emphasizing the role of residential wood burning; and (iii) investigate the gas/particle partitioning of the various acidic compounds which can drive their fate and impacts on the atmosphere. Our measurements, apart from being valuable for atmospheric modelers, can fill a gap in the literature of more than 20 years on the levels of inorganic aerosol precursors in Greece
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