Sources and Control Area Division of Ozone Pollution in Cities at Prefecture Level and Above in China

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Based on the ground-level ozone concentration monitoring data in 2018, the ozone concentrations in 338 cities at the prefecture level and above were analyzed, and the TCEQ method was utilized to calculate the amount of locally generated ozone and regionally transported ozone in each city to divide the national ozone pollution control area and develop appropriate ozone pollution control measures. Correlation analysis was conducted between the amount of locally generated ozone and the daily maximum 8 h average ozone in each city to determine the main source of ozone pollution by determination coefficient (R2). The results show that 121 cities (35.8%) in China exceeded the standard in O3 concentration in 2018. The local generation of O3 in 104 cities has a great impact on the local O3 pollution, and is its main cause. In the other 234 cities, the main source of O3 pollution is regionally transported O3. Cities are classified into four categories based on their ozone concentration levels and pollution sources:cities with a nonattainment ozone situation and mainly locally generated ozone (N-L), cities with a nonattainment ozone situation and mainly regionally transported ozone (N-T), cities with a standard ozone situation and mainly locally generated ozone (S-L), and cities with a standard ozone situation and mainly regionally transported ozone (S-T). Finally, according to the proportion of four city types in each province, the whole country is divided into three types of control areas:severe, moderate, and general. N-L cities in the severe control area account for the largest proportion (20.3%) of the three types of control areas and the pollution is the highest; the proportion of the four categories of cities in the moderate control area are all medium; the general control area mainly includes S-T cities (65.4%), and the pollution is the lowest.