The Characteristics of PM2.5 Pollution Episodes during 2016–2019 in Sichuan Basin, China

ABSTRACT Many studies have been conducted to explore the characteristics of PM2.5 pollution events in Sichuan Basin, China. However, they focused on either specific regional pollution events from different aspects or the megacities, such as Chengdu and Chongqing. To provide a panorama gram of PM2.5 pollution episodes in the whole basin area, we identified all the PM2.5 pollution events in 17 cities during 2016-2019 and analyzed the characteristics of these events. In total, 1342 episodes were identified and the characteristics of episode numbers, durations and PM2.5 concentrations were analyzed in each city. We found that the characteristics of the temporal and spatial distribution of the episode numbers and durations were similar to the annual average of PM2.5 concentrations, which were higher in the Southern Sichuan and Western Sichuan Plain spatially and occurred most frequently in winter, followed by spring, autumn and summer. Non-monotonical relationships were obtained between the PM2.5 concentrations and pollution durations and there was a duration threshold in each city. For episodes with durations shorter than the threshold, their PM2.5 concentrations increased with duration. The duration thresholds were 6-8 days and 5-7 days in Southern Sichuan and Western Sichuan Plain, respectively. We also found that the air quality deteriorated in 2019 in most cities. Synthetically considering the numbers, durations and concentrations of pollution episodes, more concerns should be taken for the prevention of PM2.5 pollution in Yibin in the Southern Sichuan, Chengdu and Leshan in the Western Sichuan Plain, Neijiang in the Central Hills, and Bazhong, Dazhou, Nanchong in the Northeastern Sichuan. These results could help understanding the characteristics of PM2.5 episodes in Sichuan Basin and providing implications for pollution control strategies in future.