Source Apportionment of PM2.5 during a Heavy Pollution Episode in Qinhuangdao in Winter 2019 Using a Chemical Transport Model

Qinhuangdao is an important port city located in the northeast of Hebei province, China. In recent years, emission reductions were effective in improving the air quality over the North China Plain. However, a heavy PM2.5 pollution event appeared in Qinhuangdao area in January. (In contrast, continuous pollution that contained PM2.5 particles was evident during January 2019 at Qinhuangdao.) In this paper, the regional air quality model RAMS-CMAQ coupled with the integrated source apportionment method (ISAM) was employed to simulate the PM2.5 pollution process and analyze the impact of local sources on PM2.5 mass concentration. Two periods were defined: (1) Clean period in which the PM2.5 mass concentration over Qinhuangdao was below 75 μg m⁻³ and (2) pollution period in which the PM2.5 mass concentration over Qinhuangdao was above 75 μg m⁻³. Contributions of local emission sources to PM2.5 mass concentration between the two periods were then compared, and the regional transport pattern of PM2.5 particles from different areas to four air quality monitoring sites was evaluated. The results showed that a high PM2.5 mass burden was distributed in the south part of Qinhuangdao. During the clean period, PM2.5 concentration was greatly contributed by local areas, with the contribution of 40%–50% in most areas of Qinglong and Lulong, and more than 60% in most areas of Haigang, Funing, Beidaihe, Tiiguan, and Changli.(Local emission sources of Qinglong greatly contributed to the PM2.5 mass burden. Lulong contributed 40%–50% and Haigang, Funing, Beidaihe, Diyiguan, and Changli together contributed more than 60% of the PM2.5 mass burden.) Regional transport during the clean period accounted for 34.7%–41.6% of the concentration of PM2.5 at the four monitoring sites. Compared with the clean period, the PM2.5 mass concentration from local areas decreased by approximately 10% and the effect of regional transport increased during the pollution period. Among the four monitoring sites, the PM2.5 concentration contributed by regional transport at Beidaihe and Diyiguan sites decreased by 1.0% and 2.3%, respectively while the contribution from surrounding regions increased by 2.9% and 2.0% at Shijiance and Jianshedasha sites, respectively.