Characteristics of Regional Transport of PM2.5 in Pearl River Delta City Cluster Under Typical Meteorological Conditions in Southern China Monsoon Region

With the development of economy, atmospheric environment problems in the Pearl River Delta (PRD) have progressively worsened, PM_2.5 not only reduce visibility, but also hazardous for human health. This study used the 2006-2013 Regional Air Quality Index (RAQI) data to analyze the characteristics of spatial distribution for pollution in the PRD. The results showed that under typical Southern China Monsoon’s meteorological conditions, pollution events in the PRD can be classified into "Western type", "Central type" and "Eastern type", with the relative frequency of 67%, 24% and 9%, respectively. Numerical simulation was performed by WRF-Chem model for three pollution cases, and PM_2.5 transport contribution rates between 9 cities in the PRD has been quantitative. In the "Western type" pollution case, PRD region was under the control of a high pressure system with easterly prevailing winds. PM_2.5 concentrations in western PRD were higher than those in the east, with Huizhou, Guangzhou, Shenzhen and Dongguan having relatively higher impact on the total PM_2.5 in the PRD. Within the PRD’s urban cluster, PM_2.5 in Huizhou, Guangzhou, Shenzhen, Zhuhai and Dongguan were mainly due to local emissions, while PM_2.5 in other cities were mainly due to external transport. In the "Eastern type" case, the PRD was influenced by Typhoon Soulik with westerly prevailing winds. PM_2.5 concentrations in eastern PRD were higher. Cities in western PRD, such as Jiangmen and Foshan, had the highest proportion of impacts on overall PM_2.5 concentration in PRD, at 19% and 18%, respectively. PM_2.5 in Jiangmen, Zhaoqing, Zhuhai, Foshan and Shenzhen were mainly due to local emissions. In the "Central type" case, PRD region was under the control of a uniform pressure field, whereas wind speeds were low. The impact from Guangzhou and Foshan were both exceeded 16% and the PM_2.5 transport capacity between PRD’s urban cluster was relatively weak.