The Importance of NO<sub>x</sub> Control for Peak Ozone Mitigation Based on a Sensitivity Study Using CMAQ‐HDDM‐3D Model During a Typical Episode Over the Yangtze River Delta Region, China
Yangjun Wang, Elly Yaluk, Hui Chen, Sen Jiang, Ling Huang, Ansheng Zhu, Shilin Xiao, Jin Xue, Guibin Lu, Jinting Bian, Kasemsan Manomaiphiboon, Kun Zhang, Hanqing Liu, Huanhuan Tong, Maggie Chel Gee Ooi, Andy Chan, Li Li
Abstract
Abstract In recent years, ground‐level ozone (O 3 ) has been one of the main pollutants hindering air quality compliance in China's large city‐clusters including the Yangtze River Delta (YRD) region. In this work, we utilized the process analysis (PA) and the higher‐order decoupled direct method (HDDM‐3D) tools embedded in the Community Multiscale Air Quality model (CMAQ) to characterize O 3 formation and sensitivities to precursors during a typical O 3 pollution episode over the YRD region in July 2018. Results indicate that gas‐phase chemistry contributed dominantly to the ground‐level O 3 although a significant proportion was chemically produced at the middle and upper boundary layer before reaching the surface via diffusion process. Further analysis of the chemical pathways of O 3 and O x formation provided deep insights into the sensitivities of O 3 to its precursors that were consistent with the HDDM results. The first‐order sensitivities of O 3 to anthropogenic volatile organic compounds (AVOC) were mainly positive but small, and temporal variations were negligible compared with those to NO x . During the peak O 3 time in the afternoon, the first‐ and second‐order sensitivities of O 3 to NO x were significantly positive and negative, respectively, suggesting a convex response of O 3 to NO x over most areas including Shanghai, Hangzhou, Nanjing and Hefei. These findings further highlighted an accelerated decrease in ground‐level O 3 in the afternoon corresponding to continuous decrease of NO x emissions in the afternoon. Therefore, over the YRD region including its metropolises, NO x emission reductions will be more important in reducing the afternoon peak O 3 concentration compared with the effect of VOC emission control alone.