Reduced Responsiveness of Peroxyacetyl Nitrate (PAN) to Temporary Control Measures: A Case Study in Chengdu, China

Abstract To explore the impact of temporary control measures on photochemical pollution, a comprehensive observation of peroxyacetyl nitrate (PAN) and other pollutants as well as meteorological conditions was conducted during the Chengdu 2023 Summer World University Games. Based on the measurement results and box model simulations, the temporary control measures achieved a good effect in reducing air pollution. Most pollutants included SO 2 , NO 2 , TVOCs, O 3 and HONO have been significantly reduced by 22%–38% compared to the pre‐control period. Nevertheless, the PAN reduction was only about 2% during the control measures period. Methylglyoxal and acetaldehyde were the two largest precursors for PA radicals, which accounted for more than 50% of PA radical formation. As a reservoir molecule, temporary control measures result in lower reductions in PAN concentration than in the case of other pollutants. Therefore, it is inappropriate to evaluate the effectiveness of temporary emission reduction measures on photochemical pollution solely through PAN concentration assessments. PAN concentrations are significantly influenced by the volatile organic compound (VOC)/NO 2 ratio, and reducing NO x emissions alone could have an adverse effect on controlling PAN pollution. Therefore, reducing VOC emissions is the preferred measure for controlling PAN pollution.