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To understand the impact of transported PM2.5 pollution on urban Zhoushan, we first analyzed the seasonal variation of daily average PM2.5 mass concentration in urban Zhoushan from March 2016 to February 2019, and then we applied the backward trajectory cluster analysis, potential source contribution function, and concentration weighted trajectory method to analyze the seasonal characteristics of pathways and potential sources of transported PM2.5 pollution in urban Zhoushan. The results showed that: In spring and autumn, the transported PM2.5 pollution was mainly from the north-northeast pathways and partially from the southerly pathways, while in summer and winter the southerly and northwest pathways were dominant. In spring, the northwest pathways and the southerly pathways contributed the most to the PM2.5 average and maximum mass concentration, respectively. In summer, the average and the maximum value of PM2.5 mass concentration were significantly affected by the north-northwest pathways and southerly pathways, respectively. The partially southerly pathways and the northwest pathways contributed the most in autumn and in winter, respectively. Northern, central, and southeastern Anhui, eastern Henan, and the northern coast of Fujian were the main potential sources of PM2.5 in urban Zhoushan in spring. Southeastern Anhui, southern Jiangsu, and southwestern Zhejiang were the main potential sources in summer and autumn. Southwestern Shandong, northwestern Jiangsu, northern Zhejiang, northeastern Anhui, and eastern Henan were the main potential sources in winter. Compared with the results of the years from 2013 to 2016, the prevailing directions of transport pathways in different seasons were consistent. In summer and winter, it was still mainly affected by those from southerly pathways and northwest pathways, respectively. The differences were that in this study, PM2.5 in summer was increasingly affected by those from the north-northwest pathways, whereas PM2.5 in spring and autumn was significantly affected by those from the partially southerly pathways in Zhejiang. Areas of Anhui, Jiangsu, Shandong, and Zhejiang were still the main potential sources of PM2.5 in Zhoushan, with less PM2.5 transported from northern Zhejiang and Jiangsu, and more from northwestern Shandong, southwestern Zhejiang, and the northern coast of Fujian. [ABSTRACT FROM AUTHOR]