干旱事件下PM_(2.5)和臭氧复合污染动力机制及其影响因素

Internal Dynamic Mechanism of Atmospheric Composite Pollution and Its Driving Factors During Drought Events

以长株潭城市群3个城市(长沙、株洲和湘潭)干旱期间(2022年7月1日至12月31日)和非干旱期间(2020和2021年同期)PM_(2.5)和O_(3)小时平均浓度序列为研究对象,探究干旱事件对PM_(2.5)-O_(3)复合污染演化的内在动力机制的影响及其影响因素。首先,对研究期间3个城市PM_(2.5)和O_(3)浓度的日变化模式进行分析,结果发现PM_(2.5)浓度均呈现出M型的日变化规律,但干旱期间PM_(2.5)浓度下降,且波峰和波谷时段发生显著变化。O_(3)浓度日变化均呈现出“昼高夜低”单峰型模式,干旱期间O_(3)浓度上升。接下来,应用多重分形去趋势互相关分析法(MF-DCCA)研究PM_(2.5)-O_(3)互相关性的多时间尺度特征。研究结果发现,各年各城市PM_(2.5)-O_(3)互相关关系均呈现出显著地长期持续性特征和多重分形结构,且干旱期间各城市长期持续性指数均降低,多重分形强度增强。进而,应用滑移窗口方法、MF-DCCA以及格兰杰因果检验方法分析PM_(2.5)-O_(3)互相关长期持续性特征演化规律及其影响因素。结果发现,干旱期间各城市PM_(2.5)-O_(3)互相关的长期持续性演化的影响因素主要是气压,而非干旱期间的影响因素主要是气温和风速。最后,基于自组织临界理论(SOC)探讨非干旱期间和干旱期间PM_(2.5)-O_(3)互相关关系的内在动力机制。结果发现,长期持续性特征主要受SOC机制所主导,即SOC机制是驱动PM_(2.5)-O_(3)复合污染演化的主要非线性动力机制,但干旱事件使得主要影响因素由气温和风速变成气压。文章拓展了复合污染的内在动力机制的相关研究,为我国深入推进全球变暖背景下复合污染防控提供了新的启示。

The hourly average concentrations of PM_(2.5) and O_(3) 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)-O_(3) compound pollution and its influencing factors.Initially,the diurnal patterns of PM_(2.5) and O_(3) 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,O_(3) 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 O_(3).The results revealed significant long-term persistence and multifractal characteristics in the cross-correlation of PM_(2.5) and O_(3) 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)-O_(3) cross-correlation.This study found that atmospheric pressure was the primary factor influencing the evolution of long-term persistence in PM_(2.5)-O_(3) 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)-O_(3) 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.