Influence of atmospheric oxidation capacity on atmospheric particulate matters concentration in Lanzhou

The atmospheric oxidation capacity (AOC) reflects the removal rate of atmospheric pollutants, and this index is typically characterized by the oxidant concentration or total reaction rate. The AOC plays a crucial role in the formation of atmospheric particulate matters and serves as an important indicator for studying changes in the concentration. In this study, we analyse the characteristics of atmospheric oxidants in Lanzhou based on data in the year of 2020 and 2021 retrieved from the Atmospheric Comprehensive Observation Station in Lanzhou. Empirical equations are applied to estimate the impact of atmospheric oxidative properties secondary generation concentrations of atmospheric particulate matters with different particle sizes. The results indicate that the annual average values of O_x were 146 μg/m³ in 2020 and 139 μg/m³ in 2021. The AOC was the highest in summer and lowest in winter. The correlation coefficient between O₃ and O_x was significantly higher than that between NO₂ and O_x, suggesting that O₃ exerted a greater impact on the AOC in Lanzhou. A low AOC (MDA8 O₃ ≤ 100 μg/m³) promoted the oxidation process of VOCs and other precursors, leading to the generation of secondary aerosols and subsequent formation of secondary particles. There were negative correlations between O_x and atmospheric particulate matters, secondary inorganic components, sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR), indicating that excessively high levels of O_x could inhibit the conversion rate of SO₂ and NO₂ into their respective forms to a certain extent.