Gu, Y., Huang, R.-J., Duan, J., Xu, W., Lin, C., Zhong, H., Wang, Y., Ni, H., Liu, Q., Xu, R., Wang, L., and Li, Y. J.: Multiple pathways for the formation of secondary organic aerosol in the North China Plain in summer, Atmos. Chem. Phys., 23, 5419–5433, https://doi.org/10.5194/acp-23-5419-2023, 2023.
Secondary organic aerosol (SOA) has been identified as a major contributor to fine particulate matter (PM2.5) in the North China Plain (NCP). However, the chemical mechanisms involved are still unclear due to incomplete understanding of its multiple formation processes. In this study, we report field observations in summer in Handan of the NCP, based on high-resolution online measurements. Our results reveal four types of formation pathway via aqSOA、Ox-initiated SOA、fresh SOA and primary-related SOA. The photochemical pathway formed efficiently with growth rate of 0.8 μg m−3 h−1 during daytime (65 % to OA). During the high-relative-humidity period, strong nocturnal aqueous-phase SOA formation (45%) and daytime aqueous-phase photochemistry (39%) played significant role in SOA production Moreover, the conversion and rapid oxidation of primary-related SOA to aqSOA were possible in the aqueous phase under high-RH conditions. This work improves our understanding of ambient SOA formation and aging in summer with high oxidation capacity.
Fig. 1 Time series of (a) relative humidity (RH) and wind speed (WS), (b) Ox and Ox-initiated SOA, (c) fresh SOA, aqSOA and ALWC, (d) primary-related SOA, (e) the O:C ratio and H:C ratio. The time series were categorized to be three typical periods based on total SOA mass concentrations and meteorology conditions: reference period (P1), high Ox period (P2) and high RH period (P3).