Characteristics of PM(2.5) and Black Carbon Exposure Among Subway Workers

This study aimed to assess the characteristics of exposure to both PM(2.5) and black carbon (BC) among subway workers. A total of 61 subway workers, including 26, 23, and 12 subway station managers, maintenance engineers, and train drivers, respectively, were investigated in 2018. Real-time measurements of airborne PM(2.5) and BC were simultaneously conducted around the breathing zones of workers. Maintenance engineers had the highest average levels of exposure to both PM(2.5) and BC (PM(2.5), 76 µg/m(3); BC, 9.3 µg/m(3)), followed by train drivers (63.2 µg/m(3), 5.9 µg/m(3)) and subway station managers (39.7 µg/m(3), 2.2 µg/m(3)). In terms of the relationship between mass concentrations of PM(2.5) and BC, train drivers demonstrated the strongest correlation (R = 0.72), indicating that the proportion of BC contained in PM(2.5) is relatively steady. The average proportion of BC in PM(2.5) among maintenance engineers (13.0%) was higher than that among train drivers (9.4%) and subway station managers (6.4%). Univariate and mixed effect multiple analyses demonstrated the type of task and worksite to be significant factors affecting exposure levels in maintenance engineers and subway station managers. The use of diesel engine motorcars in tunnel maintenance was found to be a key contributor to PM(2.5) and BC exposure levels among subway workers.