Insights into particulate matter pollution in the North China Plain during wintertime: local contribution or regional transport?

Abstract

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 PM2.5 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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