Contribution of Secondary Particles to Wintertime PM_2.5 During 2015–2018 in a Major Urban Area of the Sichuan Basin, Southwest China

Abstract

Abstract A novel method, noted as approximate envelope method (AEM), was developed to estimate the secondary PM 2.5 concentrations based on the air quality monitoring data. This approach made it possible to obtain the long‐term characteristics of the secondary PM 2.5 using only conventional observations. The secondary PM 2.5 concentrations and their variation characteristics under different PM 2.5 pollution levels during wintertime of 2015 to 2018 in Chengdu, a major urban area of Sichuan Basin over Southwest China, were analyzed. The results showed that the secondary PM 2.5 concentrations ranged from 52.3 to 122.8 μg·m −3 and accounted for 56.3%, 63.6%, and 67.4% of the total PM 2.5 in slight, moderate, and heavy pollution status, respectively. Additionally, the concentrations of secondary PM 2.5 increased year by year, while the concentrations of primary PM 2.5 performed significant decreasing trends from 2015 to 2018. The diurnal variations of primary and secondary PM 2.5 presented a significantly unimodal patterns but with maximum at morning and noon, respectively. Specific meteorological conditions such as high (low) relative humidity and temperature (wind speed and air pressure) aggravated the secondary particulate pollution in wintertime of Chengdu, reflecting an influence of regional climate change over the Sichuan Basin of Southwest China on the urban air pollution.