Winter-spring droughts exacerbated PM_2.5-O₃ compound pollution? Evidence from China

With the impact of global climate change, drought events are becoming more frequent, making it critically important to quantitatively evaluate the effects of these events on air pollution. This study uses the augmented synthetic control method and the mediation effect model to quantitatively evaluate the impact effect of the winter-spring drought of 2023 on PM_2.5-O₃ compound pollution and its driving factors with Chinese prefecture-level city data. This study indicates that: firstly, compared to non-drought periods, both the monthly averaged and diurnal variations pattern of PM_2.5 and O₃ significantly increased during drought periods. Secondly, the winter-spring drought of 2023 led to an average increase of 101.05 μg/m³(28.14 %) for PM_2.5 and 153.74 μg/m³(13.32 %) for O₃ in Yunnan Province, while the average increases in Guizhou Province were 25.71 μg/m³(11.59 %) and 23.95 μg/m³(4.09 %), respectively. Thirdly, the increase in temperature and the decrease in precipitation and relative humidity during the winter-spring drought were among the main driving factors for the increased risk of "double-high" PM_2.5-O₃ compound pollution. The article expands the research on the impact of abnormal weather events on atmospheric compound pollution, providing new insights for preventing compound pollution events in the context of abnormal weather.