[Summer Ozone Mechanism and Control Strategy in Beijing-Tianjin-Hebei Region Using Brute-Force Method]

In recent years, the ozone (O₃) volume fraction in the Beijing-Tianjin-Hebei Region in summer have remained high, light to moderate pollution occurs frequently, and research on related response mechanisms is urgently needed. This study applied the WRF-Chem model to simulate the change in ozone volume fraction in this region by setting 13 precursor emission scenarios in a representative month in the summer of 2018. The results revealed that VOC-sensitivity and no-sensitivity regimes commonly occurred in the Beijing-Tianjin-Hebei Region in July, and the VOC-sensitivity regimes were mainly accumulated in the central Beijing-Tianjin-Hebei Region, with a north-to-south zonal distribution and an area share of 15.60%-26.59%. The relative response intensity (RRI) of O₃ volume fraction to precursor emissions in urban areas had large spatial variability, with RRI_VOC and RRI_NO in the ranges of 0.03-0.16 and -0.40-0.03, respectively. The higher the latitude of urban areas, the more dramatic were the RRI values, indicating a more significant regional transport influence. The lower RRI_NO values in urban areas with high intensity of precursor emissions implied a negative dependence of RRI_NO on local NO₂ concentrations; however, RRI_VOC was not significantly correlated with NO₂levels and was more dependent on the relative abundance of precursors (VOCs:NO). The ratio of RRI_VOC to RRI_NO showed negative values in majority of the cities; therefore, collaborative VOCs emission reduction is necessary to suppress the deterioration of O₃ volume fraction. The absolute value of this ratio was much lower in cities with high industrialization and urbanization than in ordinary small and medium-sized cities, implying that the demand for collaborative VOCs emission reduction in these cities will be higher. However, even under 50% reduction of precursors, the improvement in O₃ volume fraction was limited in regional cities, and the combined prevention in neighboring cities remains important.