Abstract: The hourly average concentrations of PM_2.5 and O₃ in the three cities of the Chang-Zhu-Tan urban agglomeration (Changsha,Zhuzhou,and Xiangtan) were analyzed for both drought (July 1 to December 31,2022) and non-drought periods (corresponding periods in 2020 and 2021).The objective was to explore the impact of drought events on the intrinsic dynamic mechanisms of PM_2.5-O₃ compound pollution and its influencing factors.Initially,the diurnal patterns of PM_2.5 and O₃ concentrations during the study period were examined.It was observed that PM_2.5 concentrations followed an M-shaped diurnal variation pattern,with a decrease during the drought period and significant shifts in the timing of peaks and troughs.Conversely,O₃ concentrations showed a unimodal pattern of being higher during the day and lower at night,with an increase during the drought period.Subsequently,Multifractal Detrended Cross-Correlation Analysis (MF-DCCA) was employed to investigate the multi-timescale characteristics of the cross-correlation between PM_2.5 and O₃.The results revealed significant long-term persistence and multifractal characteristics in the cross-correlation of PM_2.5 and O₃ across all cities and years,with a decrease in persistence indices and an increase in multifractal intensity during the drought periods.Furthermore,the sliding window method,MF-DCCA,and Granger causality tests were utilized to analyze the evolution and influencing factors of the long-term persistence characteristics of PM_2.5-O₃ cross-correlation.This study found that atmospheric pressure was the primary factor influencing the evolution of long-term persistence in PM_2.5-O₃ cross-correlation during the drought periods,while temperature and wind speed were the main factors during the non-drought periods.Finally,the Self-Organized Criticality theory (SOC) was applied to discuss the internal dynamic mechanisms of PM_2.5-O₃ cross-correlation during both drought and non-drought periods.The findings of this study provided a useful reference for coping with atmospheric composite pollution under the global warming condition.