Significant decreases in the volatile organic compound concentration, atmospheric oxidation capacity and photochemical reactivity during the National Day holiday over a suburban site in the North China Plain.

To what extent anthropogenic emissions could influence volatile organic compound (VOCs) concentrations and related atmospheric reactivity is still poorly understood. China's 70th National Day holidays, during which anthropogenic emissions were significantly reduced to ensure good air quality on Anniversary Day, provides a unique opportunity to investigate these processes. Atmospheric oxidation capacity (AOC), OH reactivity, secondary transformation, O3 formation and VOCs-PM2.5 sensitivity are evaluated based on parameterization methods and simultaneous measurements of VOCs, O3, NOx, CO, SO2, PM2.5, JO1D, JNO2, JNO3 carried out at a suburban site between Beijing and Tianjin before, during, and after the National Day holiday 2019. During the National Day holidays, the AOC, OH reactivity, O3 formation potential (OFP) and secondary organic aerosol formation potential (SOAP) were 1.6 × 107 molecules cm-3 s-1, 41.8 s-1, 299.2 μg cm-3 and 1471.8 μg cm-3, respectively, which were 42%, 29%, 47% and 42% lower than pre-National Day values and -12%, 42%, 36% and 42% lower than post-National Day values, respectively. Reactions involving OH radicals dominated the AOC during the day, but OH radicals and O3 reactions at night. Alkanes (the degree of unsaturation = 0, (D, Equation (1)) accounted for the largest contributions to the total VOCs concentration, oxygenated VOCs (OVOCs; D ≤ 1) to OH reactivity and OFP, and aromatics (D = 4) to the SOAP. O3 production was identified as VOCs-limited by VOCs (ppbC)/NOx (ppbv) ratios during the sampling campaign, with greater VOCs limitation during post- National Day and more-aged air masses during the National Day. The VOCs-sensitivity coefficient (VOCs-S) suggested that VOCs were more sensitive to PM2.5 in low-pollution domains and during the National Day holiday. This study emphasizes the importance of not only the abundance, reactivity, and secondary transformation of VOCs but also the effects of VOCs on PM2.5 for the development of effective control strategies to minimize O3 and PM2.5 pollution.