High-Resolution Measurements of SO 2 , HNO 3 and HCl at the Urban Environment of Athens, Greece: Levels, Variability and Gas to Particle Partitioning.

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. [ABSTRACT FROM AUTHOR]