Long-term Trends of Size-Resolved Secondary Inorganic Aerosols in Beijing During the Summer and Winter Seasons from 2013 to 2023

Liang Luo, SHILI TIAN, Yanju Liu, Beijing Center for Physical and Chemical Analysis

     Abstract Number: 300
     Working Group: Aerosol Chemistry

Abstract
In recent years, Beijing has experienced severe air pollution, with sulfate (SO₄²⁻), nitrate (NO₃⁻), and ammonium (NH₄⁺) (collectively, SNA) playing critical roles in particulate pollution. SNA not only impact air quality but also pose significant risks to climate and public health. However, the interannual variation in SNA concentrations across particle sizes and formation mechanisms remain understudied. This study employed an Andersen cascade impactor to collect size-segregated particulate samples in Beijing’s urban area during the summers and winters of 2013, 2015, 2017, and 2023. Key findings include: (1) A significant decrease in PM2.1 SNA concentrations from 2013 to 2023, especially for SO₄²⁻, NO₃⁻, and NH₄⁺ in winter (declining by 77.6%, 33.1%, and 73.0%, respectively); (2) Lowered SOR under RH but increased NOR under photochemical influence in fine particles during summer, reflecting the heightened role of photochemical reactions in nitrate formation; (3) Size distribution shifts toward larger particles under high humidity, indicating notable hygroscopic growth in polluted conditions; and (4) Enhanced alkalinity in coarse particles and acidity in finer ones due to sulfate and nitrate enrichment. This research offers critical insights into SNA variation and size distribution dynamics under diverse meteorological conditions, supporting targeted pollution control strategies.