[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_NOx 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_NOx values in urban areas with high intensity of precursor emissions implied a negative dependence of RRI_NOx on local NO2 concentrations; however, RRI_VOC was not significantly correlated with NO2levels and was more dependent on the relative abundance of precursors (VOCs:NOx). The ratio of RRI_VOC to RRI_NOx 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.