Spatiotemporal dynamics of near-surface ozone concentration and potential source areas in northern China during...

Near-surface ozone (O₃) pollution has become one of the main factors hampering urban air quality in northern China. However, on a spatiotemporal scale, dynamic transport paths and potential source areas of O₃ in northern China are ambiguous. In addition, we suspect that the contribution of transportation activities to urban O₃ concentrations developed in northern China may be underestimated. In this study, the HYSPLIT, PSCF, CWT and GTWR model were used to study the transmission paths, potential source areas and driving factors of urban O₃ concentration on a spatiotemporal scale. The average annual concentration of surface O₃ (the 90th percentile of MDA8) was 172 ± 29 μg/m³ in northern China from 2015 to 2020. In terms of inter-annual variation, the urban O₃ concentration increased from 2015 to 2018, and decreased after 2018. On the spatial scale, the areas with high O₃ concentration were mainly clustered in industrial cities (Tangshan, Baoding, Shijiazhuang, Xingtai and Handan). During the study period, the area with high O₃ concentration in northern China shifted from northwest to southeast. From 2015 to 2020, the influence of long-distance air mass trajectories from Xinjiang and Siberi on airflow transport in Beijing city dominates (78.60%) The average percentage of short-distance transport trajectories from Shandong Peninsula region is about 21.40%. The core potential source areas of O₃ pollution shifted from northwest to southeast, but the contribution to O₃ pollution in Beijing gradually weakened during the same period. Temperature and relative humidity were the main meteorological driving factors affecting O₃ concentration in the study area, while population density, the proportion of secondary industry in GDP, industrial smoke (dust) emissions, and passenger traffic were the main non-meteorological factors. During the period study, the influence of industrial and traffic emissions had a more significant impact on O₃ concentration in northern China, which will require that more attention be paid to emission mitigation in the regional industrial and passenger transportation sector, as well as the joint prevention and control of O₃ pollution in northern China in the future.