Summer urban synergistic effects of anthropogenic pollutants and low-molecular-weight biogenic volatile organic compounds on secondary organic aerosol presented by PM1.

Abstract

Biogenic volatile organic compounds (BVOCs) are emitted by urban vegetation and can interact with anthropogenic pollutants to generate secondary organic aerosols (SOA) that are atmospheric pollutants in urban environments. In urban forests, SOA comprise up to 90 % of all fine aerosols (particulate matter smaller than 1 μm [PM₁]) in the summer. PM₁ can greatly affect urban air quality and public health. The formation of SOA is affected by both environmental conditions and the presence of light BVOCs-predominantly isoprene, pentene, butene, and 1,3-butadiene. These factors exhibit complex interactions and nonlinear relationships. In this study, high-frequency field observations were conducted in two urban forest sites in Shanghai during the summers of 2022 and 2023. Data were collected regarding the concentrations of light BVOCs; SOA; and the anthropogenic pollutants NO_x, O₃, and SO₂, as well as solar radiation, temperature, and humidity. A model was developed to identify the synergistic effects of anthropogenic pollutants, meteorological factors, and BVOCs on SOA concentrations. Increases in short-term SOA concentrations were most strongly correlated with O₃, which had a synergistic effect alongside NO_x. The empirical analysis indicated that 0.144-0.585 μg/m³ SOA is produced per μg/m³ of urban BVOCs but can be augmented by 0.072-0.491 μg/m³ in the presence of O₃, NOx, and SO₂. However, long-term feedback mechanisms in urban forests contribute to the maintenance of stable SOA concentrations. The field data and models in this study provide a scientific basis for regulating atmospheric pollutants in urban forests under real-world conditions and offer intuitive and straightforward solutions for managing complex urban air pollution. Synopsis: Anthropogenic pollutants NO_x, O₃, and SO₂ boost BVOCs' SOA production in summer urban forests. Short-term, pollutants are restrictive factors in SOA generation, but long-term forest SOA production exhibits negative feedback.