Online Observation of Pm2.5 Chemical Composition in Coastal Cities of the Yangtze River Delta: Temporal Variation and Comparative Analysis of Pollution Types

Abstract

Aerosol chemical composition significantly impacts air quality, radiation balance, and human health. This study analyzed the temporal variation characteristics of PM2.5 chemical composition and its variation characteristics during different pollution episodes (haze, ozone (O3), and dust pollution) using online observational data of atmospheric pollutants (pollutant gases and PM2.5 components) and meteorological elements in Jiaxing during 2023. The top five annual average concentrations of chemical components were as follows: NO3− (30.02%) > POC (14.26%) > NH4+ (13.92%) > SO42− (13.58%) > SOC (12.52%). The contribution of NO3− to PM2.5 significantly decreased in summer and increased in winter, while SO42− exhibited the opposite trend, with its summer percentage nearly double that in winter. The percentage of SOC was significantly higher in summer and autumn compared to that in spring and winter. The percentage of POC notably increased in autumn. The percentage of NH4+ remained stable throughout the year, ranging from 12.84% to 14.49%. Water-soluble ions (WSI) and carbonaceous aerosols reached their highest mass concentrations in December (35.73 μg/m3 and 15.97 μg/m3, respectively) and their lowest in July (8.34 μg/m3) and April (6.93 μg/m3), respectively. Seasonal differences in diurnal variation were minimal. The evolution of aerosol chemical composition varied under different pollution types. During haze episodes, as PM2.5 concentration increased, the percentage of NO3− increased, while O3 concentration decreased. Under severe haze pollution conditions, NO3− percentage increased by 50.51%, and O3 concentration decreased by 39.09%. During O3 pollution episodes, as O3 concentration increased, SOC and SO42− percentages increased but NO3− percentage decreased. Under O3 pollution conditions, SOC and SO42− percentages increased by 61.80% and 58.74%, respectively, while NO3− percentage decreased by 41.03%. During dust pollution episodes, as PM2.5–10 concentration increased, the percentage of metal sharp increase. Under dust pollution conditions, metal percentage increased by 457.94%, with Al increasing by 974.30%.

Keywords: PM2.5 Chemical components, Haze pollution, O3 pollution, dust pollution