Source apportionment of fine particulate matter at different underground sites in the Chengdu metro system in summer

Abstract

With the popularization of subway systems, subway air quality has gradually begun to attract public attention. The removal of PM2.5 based solely on concentration may not be sustainable or effective. Targeted measures directed at the emission sources of PM2.5 are therefore needed to improve removal efficiency. The quantification of the chemical composition of PM2.5 is the basis for source apportionment analysis. In this study, PM2.5 samples were collected from tunnels, carriages, platforms, and outdoor environments. The composition of PM2.5 was detected. PM2.5 sources were determined using positive matrix factorization. The average PM2.5 concentrations at subway sites followed the decreasing sequence of tunnel > carriage > platform, and were higher than those outdoors. Iron was the most abundant element in PM2.5 in the subway system. The five PM2.5 sources at subway sites, included train movement, vehicle emission, mixed source (secondary sulfate and coal combustion), secondary nitrate, and industrial emission. After analyzing the differences in PM2.5 sources at various subway sites, train movement and vehicle emission were identified as priority sources to control if we are to improve subway air quality. They are selected in particular mainly owing to their important contributions to PM2.5 release (20.4 %–33.3 % and 18.9 %–32.9 %, respectively). Overall, these findings provide unique insights for the development of targeted strategies to control subway air pollutants, thus helping to achieve healthy and sustainable subway environments.