Modeling Study Of PM_2.5 Pollutant Transport For A Severe Haze Episode In Beijing And Surrounding Regions

To study the influence of particulate matter (PM) transported from surrounding regions on the high PM2.5 pollution levels in Beijing, the air quality model GRAPES-CUACE was used to simulate a serious haze episode occurring during 6-7 December 2013. The modeling results demonstrate the model’s suitability for describing haze episodes throughout China, especially in the Beijing—Tianjin-Hebei (Jing-Jin-Ji) region. A very close positive correlation was found between the southerly wind speed over the plain to the south of Beijing and changes in PM2.5 in Beijing, both reaching maximum values at ca.900hPa, suggesting the lower atmosphere was a principal layer for pollutant PM2.5 transport from its southern neighboring region to Beijing. During the haze episode, Beijing was either a pollutant source or sink for its surrounding area depending on the temporal change of haze period,. The PM import from Beijing’s surroundings was much higher than the export from the urban, resulting in the peak of PM2.5 values occurring from 0000 to 1000 UTC on 7 December 2013. The transported PM pollutants from the surrounding regions contributed over 50% of PM2.5 for the peak pollutants values in Beijing, while the Beijing area was also a pollutant source with a net contributor to the surrounding regions after the peak pollution period.