Bridging the Gap Between Total Peroxyl Radical Observations and Models by Measuring OH Reactivity to Improve Estimates of Ozone Production: A Case Study From the 24th Winter Olympics Games

Ozone (O 3 ) concentration is a function of the catalytic cycles of RO x radical (hydroxyl (OH), hydroperoxyl (HO 2 ) and organic peroxy (RO 2 ) radical) and NO x (NO and NO 2 ). Total OH reactivity ( k ′ OH ) and total peroxyl radicals (RO 2 * = RO 2 + HO 2 ) play an important role in this cycle and have a major impact on O 3 mitigation. The currently used atmospheric models generally underestimate the measured values of k ′ OH and RO 2 * concentrations, therefore the ozone production processes remains unclear. This paper presents observation of k ′ OH , RO 2 *, and ancillary trace species from February and March 2022 in Beijing, covering the 24th Olympic Winter Games period. We aim to accurately predict the ozone production processes by exploring the impact of k ′ OH on the RO 2 * chemistry. During the Games period, observed k ′ OH were significantly higher than calculations, and average RO 2 * concentrations at noontime of 6.9 pptv were observed, which is about 1.3–10 times higher than previous winter observations. A zero‐dimensional model underestimated the observed RO 2 *. Constraining k ′ OH to the measured value by introducing the oxidation chemistry of unknown or unmeasured volatile organic compounds (VOCs) species ( X ) can effectively close the gap between modeled and measured RO 2 *. By considering measured k ′ OH and RO 2 *, the ozone production potential increased by a factor of 1.3–2.1, the O 3 production regime sensitivity showed a significant trend shift from VOCs to NO x limited, and enhanced the absolute ozone production sensitivity on VOCs by an order of magnitude. This means that simultaneously measurement of k ′ OH and RO 2 * provides a more accurate approach to O 3 control.