Accurate identification and quantitative source apportionment of fine particulate matter ( PM 2.5 ) provide an important prerequisite for design and implementation of emission control strategies to reduce PM pollution. Therefore, a source-oriented version of the WRF-Chem model is developed in the study to conduct source apportionment of PM 2.5 in the North China Plain (NCP). A persistent and heavy haze event that occurred in the NCP from 5?December 2015 to 4?January 2016 is simulated using the model as a case study to quantify PM 2.5 contributions of local emissions and regional transport. Results show that local and nonlocal emissions contribute 36.3?% and 63.7?% of the PM 2.5 mass in Beijing during the haze event on average. When Beijing's air quality is excellent or good in terms of hourly PM 2.5 concentrations, local emissions dominate the PM 2.5 mass, with contributions exceeding 50?%. However, when the air quality is severely polluted, the PM 2.5 contribution of nonlocal emissions is around 75?%. Nonlocal emissions also dominate Tianjin's air quality, with average PM 2.5 contributions exceeding 65?%. The PM 2.5 level in Hebei and Shandong is generally controlled by local emissions, but in Henan, local and nonlocal emissions play an almost equivalent role in the PM 2.5 level, except when the air quality is severely polluted, with nonlocal PM 2.5 contributions of over 60?%. Additionally, the primary aerosol species are generally dominated by local emissions, with the average contribution exceeding 50?%. However, the source apportionment of secondary aerosols shows more evident regional characteristics. Therefore, except for cooperation with neighboring provinces to carry out strict emission mitigation measures, reducing primary aerosols is a priority to alleviate PM pollution in the NCP, especially in Beijing and Tianjin.
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