Variation in PM2.5 source over megacities on the ancient Silk Road, northwestern China

Due to high-speed and extensive economic development, increasing urbanization, and booming industry in China, there is a growing public concern over PM2.5 pollution. The identification of possible sources of PM2.5 is a basis for studying air pollution. In this paper, the contribution of PM2.5 from both combustion and non-combustion sources is calculated using the selected tracers of SO2, CO and NO2. Changes in the characteristics of natural and anthropogenic PM2.5 sources were analyzed by combining the use of satellite imagery and the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The results showed that the PM2.5 in Xi'an and Lanzhou originated from combustion sources, the contribution of non-combustion sources increased from east to west, high values appeared in Zhangye and Jiuquan (over 70%). In Lanzhou, Zhangye and Jiuquan, PM2.5 was mainly from anthropogenic sources during non-episode periods, and from natural sources (namely, dust storms) during episode days, and the proportion from natural sources increased from east to west. In addition, in our research, although the sources of PM2.5 in the four cities are different, they all face the problem of excessive PM2.5 concentration, and its pollution control problem is worth studying.