Insights Into the Influence of Anthropogenic Emissions on the Formation of Secondary Organic Aerosols Based on Online Measurements

To investigate the combined impacts of anthropogenic and biogenic emissions on the formation of secondary organic aerosols (SOA), SOA molecular tracers, their corresponding volatile organic compound precursors, and other air pollutants were measured online during the winter and summer seasons of 2022 in an industrial city, Zibo, China. The results indicate that the average concentrations of SOA tracers were 16.1 ± 9.8 ng m⁻³ in winter and 99.4 ± 57.2 ng m⁻³ in summer. During winter, anthropogenic SOA (ASOA, the sum of SOA derived from naphthalene and mono-aromatic volatile organic compounds) dominated, whereas isoprene SOA (SOA_I) prevailed in summer. Correlation analysis between SO₄²⁻ and both SOA_I and high-order monoterpene SOA tracers (SOA_M-H) (R = 0.46–0.72, p < 0.001) revealed that higher aerosol acidity facilitated the formation of SOA_I and SOA_M-H, with SO₂ emissions playing a significant role in leading to higher acidity. Most biogenic SOA (BSOA) tracers exhibited a significant positive correlation with NO₃⁻, particularly in winter, implying the remarkable influence of NO_x emissions on BSOA formation. The levels of BSOA tracers increased with NH₃, indicating that NH₃ can enhance the formation of BSOA. In summer, SOA formation correlated with O_x (O_x = O₃ + NO₂), indicating the substantial impact of atmospheric oxidizing capacity on SOA formation. During winter, aerosol liquid water content (ALWC) correlated well with SOA_I tracers (i.e., 3-hydroxyglutaric acid (3-HGA) and 3-hydroxy-4,4-dimethylglutaric acid (3-HDMGA)), and 2,3-dihydroxy-4-oxopentanoic acid (DHOPA) (R > 0.5, p < 0.001), indicating the important contribution of aqueous-phase formation of SOA. These findings underscore the significant role of anthropogenic pollutant emissions in the formation of ASOA and BSOA in urban environments.