Abstract.To study the influence of particulate matter (PM) transported from surrounding regions on the high PM 2.5 pollution levels in Beijing, the GRAPES-CUACE model was used to simulate a serious haze episode that occurred on 6-7 December 2013. The 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 PM 2.5 in Beijing, both reaching maximum values at about 900 hPa, suggesting that the lower atmosphere

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