| At present, most cities of our country are suffering from the high concentrations of fine particulates(PM2.5), especially in Jing-Jin-Ji region which isfacing with themost serious pollution and shows a strong regional pollution characteristic. It is important that quantitatively analyzing regional transport and identifying the regional sources of PM 2.5using scientific methods to fundamentallysolve the PM2.5 pollution of Jing-Jin-Ji region.Aset of research methods is developed for studying regional transport, and it is applied for systematicallyanalyzing the regional transport contribution of PM 2.5 over Jing-Jin-Ji region.The main contents include three parts as follows: First of all, influencing regionsfor studying regional transport of PM 2.5is semiquantitatively defined based on the backward trajectory model（HYSPLIT） and high-resolution emission inventories. Second, influencing regions can be provided as the modeling domain of CMAQ, and then regional transport will be quantitatively analyzed based on CMAQ model.Third, contributions of transport types can be quantitatively analyzed using CMAQ.The results show that:（1） A set of research method for studing regional transport of PM2.5 using numerical simulation is developed based on HYSPLIT, CMAQ and high-resolution emission inventories.（2） Influencing region of PM2.5 over Jing-Jin-Ji is identified, and it includes Jing-Jin-Ji, Shandong, Shanxi, Inner Mongolia,Henan, Liaoning, Anhui, Jiangsu, Hubei and Shannxi.（3）Influencing region isprovided as the modeling domain, and January, April, July and October in 2013 is simulated which can represent winter, spring, summer and autumn. And the matrix of regional transport among 13 cities in Jing-Jin-Ji region is obtained in four seasons and the regional transport contributions from provinces outside Jing-Jin-Jin are analyzed.（4） The results of regional transport indicate that more than 50% of the PM2.5 in Xingtai, Handan, Hengshui,Cangzhou, Qinhuangdao and Langfang is from regional transport in four season, and the transport contributions of PM2.5 in the Beijing and Tianjin are bigger than 50% in spring and summer. To improve PM2.5 pollution of above cities,theynot only reduce emissions of pollutants in the city, but also depend on the process and strength of the regional joint prevention and control.（5） On the basis of the regional transport results from the provinces outside Jing-Jin-Ji region, Shandong and Henan contribute the biggest transoport contributions for PM2.5to Handan, Hengshui, Cangzhou and Qinhuangdao of Hebei Province with up to 28.8%and 18.7%, respectively. It is obvious that the southern cities in Hebei are contributed by Shanxi, while Inner Mongolia contributes more to northern cities in Jing-Jin-Ji. Therefore, Shandong and Henan cannot be ignored forjointing prevention and control of the Jing-Jin-Ji region, followed by Shanxi and Inner Mongolia.（6） Regional transport contributions to Beijing, Tianjin and Shijiazhuang increas e with the increase of PM2.5 concentration. In other words, it shows the positive correlation between regional transport contribution and PM 2.5 concentrations.（7） The transport types(The precursor in receptor region is participated with the precursor in source region to form PM 2.5, which is called indirect transport. The precursors of forming PM2.5 are all from the soure region, which is named direct transport) are analyzed in the three typical cities in January, April, July and October in 2013. Direct and indirect transport are qualitatively identified in four above seasons in Beijing, Tianjin and Shijiazhuang. The research shows that the direct transport is dominated in three cities. And the contributions from direct transport contributes more than 87% to above three cities.（8） The direct transport is dominated in three cities in clean days or heavy pollution days in four seasons. Strengthening the joint prevention and control is the importantway to improvethe PM2.5 concentrationover Jing-Jin-Ji region. |
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