Detecting causal relationships between fine particles and ozone based on observations in four typical cities of China

Abstract

As concentration of fine particles (PM2.5) is declining, ozone (O3) concentration is increasing in China in recent years. To collaboratively control PM2.5 and O3, it is critical to understand the relationship between the two and identify major controlling factors. We use convergent cross mapping method to detect the causal relationship between daily PM2.5 and maximum daily 8h average O3 concentrations in Beijing, Taizhou, Shenzhen and Chengdu in China in the four seasons in 2015–2022. In addition, we also examined causal effects of atmospheric oxidation capacity, precursors, and meteorological elements on PM2.5 and O3 in the four cities. In summer, PM2.5 and O3 are strongly positively correlated and show bidirectional causal relationships. The causal effects of atmospheric oxidation capacity on PM2.5 was larger than those of nitrogen dioxide (NO2) in Beijing and Shenzhen, while in Chengdu the latter was larger than the former. In winter, PM2.5 and O3 show bidirectional causal relationship, but the two are significantly negatively correlated in Beijing and positively correlated in Shenzhen. In Beijing NO2 was positively related to PM2.5 and negatively related to O3 and the causal effects of NO2 on PM2.5 and O3 exceed those from other factors, indicating that NO2 is possibly the driving force of relationship of PM2.5 and O3 in Beijing. In contrast, atmospheric oxidation capacityshows the largest causal effects on PM2.5 and O3 in Shenzhen. Thus, we suggest different control measures in different regions and seasons.