Abstract
Abstract. Accurate identification and quantitative source apportionment of fine particulate matter (PM2.5) 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 PM2.5 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 PM2.5 contributions of local emissions and regional transport. Results show that local and nonlocal emissions contribute 36.3 % and 63.7 % of the PM2.5 mass in Beijing during the haze event on average. When Beijing's air quality is excellent or good in terms of hourly PM2.5 concentrations, local emissions dominate the PM2.5 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 PM2.5 contributions exceeding 65 %. The PM2.5 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 PM2.5 level, except when the air quality is severely polluted, with nonlocal PM2.5 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.
Highlights
As the most polluted area in China, the North China Plain (NCP) has been suffering from severe particulate pollution in recent decades, during wintertime, caused by a synergy of local emissions, trans-boundary transport, specific topography, and unfavorable meteorological situations (Long et al, 2016; Wu et al, 2017, 2020; An et al, 2019)
The model generally performs well in reproducing the temporal variation of PM2.5 concentrations in the NCP, with an index of agreement (IOA) of 0.96, but slightly overestimates PM2.5 concentrations compared to measurements, with a mean bias (MB) of 2.2 μg m−3
The diurnal O3 variation is successfully replicated by the model, such as peak afternoon O3 concentrations caused by active photochemistry and low nighttime O3 concentrations due to the NOx titration, with an IOA of 0.88
Summary
As the most polluted area in China, the North China Plain (NCP) has been suffering from severe particulate pollution in recent decades, during wintertime, caused by a synergy of local emissions, trans-boundary transport, specific topography, and unfavorable meteorological situations (Long et al, 2016; Wu et al, 2017, 2020; An et al, 2019). Liu et al (2017) have emphasized that the contribution of regional transport to the PM pollution in Henan is significant during the wintertime, with an average PM2.5 contribution of 11.95 %, 11.69 %, 7.95 %, and 7.4 % from BTH, Anhui, Jiangsu, and Shandong, respectively These studies suggest that there is uncertainty regarding whether local contribution or regional transport is dominant during PM pollution events in the NCP. A source-oriented WRF-Chem model is developed to comprehensively quantify the contribution of local emissions and trans-boundary transport to the PM pollution in the NCP, including Beijing, Tianjin, Hebei, Henan, and Shandong, as well as the adjacent province in the west, Shanxi, under different pollution levels during wintertime in 2015.
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