A study of cross-correlations between PM2.5 and O3 based on Copula and Multifractal methods

As typical nonlinear dynamic system, the interactions between PM2.5 and O-3 have complexity characteristics at different spatiotemporal scales. The deep understanding of the multi-scale cross-correlation between PM2.5 and O-3 is helpful to the achievement of the target on two pollutants coordinated control in environmental management. Based on copula model and Multifractal Detrended Fluctuation Analysis (MFDFA) method, this paper studies the multi-scale cross-correlation between PM2.5 and O-3 in three metropolises in China (Beijing, Shanghai and Guangzhou). Furthermore, a new multifractal index is established to evaluate the difficulty degree of PM2.5-O-3 coordinated control based on enlarged window method. The hourly PM2.5 and O(3 )concentrations in these three metropolises from 1 January 2015 to 31 December 2018 are chosen as the research objects in order to analyze the effect of Air Pollution Prevention and Control Action Plan on air quality. The results show that PM2.5 and O-3 have negative correlation in January and positive correlation in July. However, compared with Beijing and Shanghai, PM2.5 and O-3 have upper tail dependence in Guangzhou in July. Furthermore, the strength of multifractality for PM2.5 is the weakest and that for O-3 is the strongest in Guangzhou, which may be due to the special climatic conditions in Guangzhou. Then, the difficulty degree of PM2.5-O-3 coordinated control in three metropolises is quantified based on new multifractal index. Moreover, it discusses the influence of meteorological factors on PM2.5-O-3 coordinated control in different metropolises. The comparative analysis confirms the availability of the multifractal index. This index can evaluate the difficulty degree of PM2.5-O-3 coordinated control of metropolis according to field observation, which reduces the influence of personal subjective factors. The new method maybe contribute to the new evaluate index of atmospheric environmental management. (C)& nbsp;2021 Published by Elsevier B.V.