Spatio-temporal evolution of ozone pollution and its influencing factors in the Beijing-Tianjin-Hebei Urban Agglomeration.

Ozone has become a major atmospheric pollutant in China as the pattern of urban energy usage has changed and the number of motor vehicles has grown rapidly. The Beijing-Tianjin-Hebei Urban Agglomeration, also known as the Jing-Jin-Ji Urban Agglomeration (hereafter, JJJUA), with a precarious balance between protecting the ecological environment and sustaining economic development, is challenged by high levels of ozone pollution. Based on ozone observation data from 13 cities in the JJJUA from 2014 to 2017, the spatio-temporal trends in the evolution of ozone pollution and its associated influencing factors were analyzed using Moran's I Index, hot-spot analysis, and Geodetector using ArcGIS and SPSS software. Five key results were obtained. 1) There was an increase in the annual average ozone concentration, for the period 2014-2017. Comparing the 13 prefecture-level cities, ozone pollution in Chengde and Hengshui decreased, while it worsened in the remaining 11 cities. 2) Ozone pollution was worse in spring and summer than in autumn and winter; the peak ozone pollution season was from May to September; the average ozone concentration on workdays was higher than that on non-workdays, showing a counter-weekend effect. 3) Annual average concentrations were high in the central and southern parts of the study region but low in the north. 4) Prominent positive spatial correlations were observed in ozone concentration, with the best correlations shown in summer and autumn; concentrations were high in Baoding and Xingtai but low in Beijing and Chengde. 5) Concentrations of PM10, NO2, CO, SO2, and PM2.5, as well as average wind speed, sunshine duration, evaporation, precipitation, and temperature, all had significant effects on ozone pollution, and interactions between these influencing factors increased it.

[Control Models and Effect Evaluation of Air Pollution in Jing-Jin-Ji Urban Agglomeration].

Controlling air pollution in the Jing-jin-ji urban agglomeration (JJJUA), the most seriously polluted area in China, is related to the integrated development strategy for the region. Based on the national and regional implementation of air pollution control measures in recent years, the hierarchical cross-regional multi-directional linkage (HCML) air pollution prevention and control model was applied in this study. The effect of air pollution control was evaluated by monitoring the pollutants, SO2, NO2, PM10, PM2.5, O3, and CO, at 112 monitoring sites in 13 cities in 2014-2015. The results can be summarized as follows:① The HCML model is an interrelated framework at the horizontal and vertical level. Under the efforts provided by the central, urban agglomeration, and city governments, this multi-level governance model serves as an effective tool to resolve the issues related to air pollution beyond the borders of municipalities. Environmental regulations on certain industries, energy consumption structure, car ownership and usage, and air quality supervision and warning systems are well established under this governance model. ② The air quality of the JJJUA has improved significantly in the past two years. The concentrations of air pollutants significantly decreased, with the exception of O3, and high pollution ranges significantly reduced from north to south. The annual average concentrations of PM2.5, PM10, SO2, NO2, and CO decreased by 17.84%, 14.61%, 37.55%, 4.82%, and 16.18%, respectively. The number of days meeting the air quality standards increased for all pollutants except NO2. Based on the current situation and unsolved problems of air pollution, the JJJUA area needs certain measures including diversifying the governance subjects, joint legislation (beyond municipalities) on air pollution to regulate pollution discharge, enhancing public awareness on air pollution and its health impacts, carefully examining sources of air pollution in winter to reduce pollution, and to better understand the sources of ozone and adopt effective control measures.