Spatiotemporal Characteristics and Driving Mechanisms of Atmospheric Oxidation Capacity in Guangdong, Southern China

Atmospheric oxidation capacity is a key parameter for measuring the atmosphere’s self-cleaning ability. Its strength directly affects the degradation rate of pollutants such as methane, carbon monoxide, and nitrogen oxides, and has a profound impact on regional air quality, ecosystem health, and even global climate chemistry processes. Against the backdrop of increasing global anthropogenic emissions and rapid climate system changes, quantitatively assessing the spatiotemporal evolution of atmospheric oxidation capacity is particularly important. This study systematically simulated and assessed the atmospheric oxidation capacity of Guangdong Province in October 2017 based on the Weather Research and Forecasting with Chemistry model (WRF-Chem). To more scientifically quantify atmospheric oxidation capacity, this study examined a new observational index, AOC_TOX (the rate atmospheric oxidants being reduced), and compared it to the traditionally used index AOC_ODT (the rate atmospheric reductants being oxi32dized). The results show that the AOC_TOX and AOC_ODT indices exhibit a high degree of consistency in both temporal variation trends and spatial distribution patterns. Temporally, the diurnal variation characteristics of the AOC_TOX and AOC_ODT indices are highly consistent, with 24 h averages of 1.8 × 107 cm−3 s−1 and 2.0 × 107 cm−3 s−1, respectively, showing minimal difference. Spatially, the high-value and low-value regions of both indices significantly overlap. This result demonstrates the internal consistency of the new AOC_TOX index in characterizing atmospheric oxidation capacity. Furthermore, by analyzing the contributions of different oxidants, this study clarifies that hydroxyl radicals (OH) are the main driving force of atmospheric oxidation capacity during the day, while nitrate radicals (NO3) play a dominant role at night. Finally, simulation analysis further reveals that human activity emissions are a key factor regulating the spatial pattern of regional atmospheric oxidation capacity.