Ozone and SOA formation potential based on photochemical loss of VOCs during the Beijing summer

Volatile organic compounds (VOCs) are easily degraded by oxidants during atmospheric transport. Therefore, the contribution of VOCs to ozone (O₃) and secondary organic aerosol (SOA) formation at a receptor site is different from that in a source area. In this study, hourly concentrations of VOCs and other pollutants, such as O₃, NOx, HONO, CO, and PM₂.₅, were measured in the suburbs (Daxing district) of Beijing in August 2019. The photochemical initial concentrations (PICs), in which the photochemical losses of VOCs were accounted for, were calculated to evaluate the contribution of the VOCs to O₃ and SOA formation. The mean (±standard deviation) measured VOC concentrations and the PICs were 11.2 ± 5.7 and 14.6 ± 8.4 ppbv, respectively, which correspond to O₃ formation potentials (OFP) of 57.8 ± 26.3 and 103.9 ± 109.4 ppbv and SOA formation potentials (SOAP) of 8.4 ± 4.1 and 10.3 ± 7.4 μg m⁻³, respectively. Alkenes contributed 80.5% of the consumed VOCs, followed by aromatics (13.3%) and alkanes (6.2%). The contributions of the alkenes and aromatics to the OFPPICₛ were 56.8% and 30.3%, respectively; while their corresponding contributions to the SOAPPICₛ were 1.9% and 97.3%, respectively. The OFPPICₛ was linearly correlated with the observed O₃ concentrations (OFPPICₛ = 41.5 + 1.40 × cO₃, R² = 0.87). The O₃ formation was associated with a VOC-limited regime at the receptor site based on the measured VOCs and changed to a transition regime and a NOx sensitive regime based on the PIC. Our results suggest that more attention should be paid to biogenic VOCs when studying O₃ formation in summer in Beijing, while the control of anthropogenic aromatic compounds should be given priority in terms of SOA formation.