The correlation between PM2.5 and O3 pollution in urban areas of China: spatiotemporal variation from 2017 to 2022 and implication for synergistic prevention and control

Based on air quality monitoring data in all cities nationwide from 2017 to 2022, the Pearson correlation coefficient (Rp) between PM2.5 daily average concentration (DA PM2.5) and the maximum daily 8-hour moving average of O3 (MDA8_O3) was calculated, and the spatiotemporal variation characteristics of Rp was investigated. The results show that: There was no statistically significant correlation between DA PM2.5 and MDA8_O3 in the first and fourth quarters nationwide (Rp=-0.11~0.03), and positive correlation was only found in Southwest and South China (Rp=0.11~0.32). A nationwide positive correlation existed between DA PM2.5 and MDA8_O3 in the second (Rp=0.26~0.36) and the third quarters (Rp=0.46~0.55), but no correlation in Fen-Wei Plain and Northwest China for some years. Pollutant emission is the main factor affecting the correlation between PM2.5 and O3 pollution. Temporally, the emission characteristic values of primary PM2.5 and sulfur dioxide (ECVPM2.5 and ECVSO2) decreased while those of nitrogen oxides and volatile organic compounds (ECVNOx and ECVVOCs) increased, which is consistent with the increasing trend of the average Rp values in most provinces (autonomous regions and municipalities directly under the Central Government). Spatially, for regions with relatively lower ECVPM2.5 and ECVSO2 but higher ECVVOCs and ECVNOx, the positive correlation between PM2.5 and O3 pollution is stronger. Based on the findings above, it is proposed that Beijing-Tianjin-Hebei and its surrounding area (BTH), Yangtze River Delta (YRD), Northeast and Southwest China (in the second and third quarters), and Southern China (year-round) shall pay attention to NOx and VOCs emission control, while BTH, YRD, Northeast and Southwest China (in the first and fourth quarters), and Fen-Wei Plain and the Northwest China (year-round), need to mitigate primary PM2.5 emission. © 2024 Chinese Society for Environmental Sciences. All rights reserved.