Spatiotemporal variations in the association between PM2.5 and ozone in the yangtze river economic belt: Impacts of meteorological and emissions factors

Abstract

PM2.5 and O3 are the primary air pollutants affecting air quality in the Yangtze River Economic Belt (YREB). We analyzed the spatiotemporal distribution characteristics of the association between PM2.5 and O3 using the Pearson correlation coefficient and geographically weighted regression methods, as well as the effects of meteorological and emissions factors. In the YREB, pollution days attributed to PM2.5 have consistently decreased, while pollution days attributed to O3 began decreasing in 2020 after a continuous increase. When PM2.5 levels were below approximately 37 μg/m3, O3 levels increased as PM2.5 levels rose. However, as PM2.5 levels continued to increase, O3 levels began to decline, except in the Yunnan-Kweichow Plateau (YKP). The inflection point gradually decreased from 64 μg/m3 in 2015 to 31 μg/m3 in 2021. The positive PM2.5–O3 association strengthened from 2015 to 2018, and it reached a relatively stable state after 2018. Further investigation revealed that the O3 levels were significantly affected by the boundary layer height (BLH) in the Sichuan Basin (SCB). In the YKP, PM2.5 levels were more strongly affected by wind speed and BLH in spring. Emissions were predominantly positively associated with PM2.5, exhibiting a positive association with O3 in summer but a negative one in winter. Temperature and solar radiation were the key factors affecting the PM2.5–O3 association. In addition, the emission reductions of primary PM2.5, NH3, and NOx enhanced the PM2.5–O3 association.