Characteristics, sources of volatile organic compounds, and their contributions to secondary air pollution during different periods in Beijing, China.

Continuous measurements of volatile organic compounds (VOCs), ozone (O), fine particulate matter (PM), and related parameters were conducted between April 2020 and March 2021 in Beijing, China, to characterize potential sources of VOCs and their impacts on secondary organic aerosols (SOAs) and O levels. The annual average mixing ratio of VOCs was 17.4 ± 10.1 ppbv, with monthly averages ranging from 11.6 to 25.2 ppbv. According to the empirical kinetic modeling approach (EKMA), O formation during O season was "VOCs-limited", while it was in a "transition" regime during O pollution episodes. In the O season, higher ozone formation potential (OFP) of m/p-xylene, o-xylene, toluene, isopentane, and n-butane were evident during O pollution episodes, in line with the increasing contributions of solvent usage and coating, as well as gasoline evaporation to OFP obtained through a matrix factorization model (PMF). Aromatics contributed the most to the secondary organic aerosol formation potential (SOAFP). In the non-O season, the contribution of vehicle exhaust to SOAFP elevated on hazy days, thereby revealing the importance of traffic-derived VOCs for PM pollution. Our results indicate that the prior control of different VOC sources should vary by season, thereby facilitating the synergistic control of O and PM in Beijing.