Commuter exposure to particulate matter at underground subway stations in Philadelphia

Abstract

We present the first report of exposure to particulate matter by commuters at 12 underground subway stations in Philadelphia, Pennsylvania, USA. Particle measurements were taken during two springtime periods: March 4 to 9, 2018 and February 1 to April 12, 2019. Particle concentrations were variable across the subway stations and demonstrated high temporal variability (daily and yearly) at the underground subway stations with mean PM2.5 and PM10 concentrations of 54.6 ± 34.1 and 61.6 ± 38.9 μg/m3, respectively in 2018, and 45.1 ± 27.8 and 53.6 ± 32.7 μg/m3, respectively, in 2019. Compared to the mean aboveground street levels, the mean underground subway stations' PM2.5 levels were 5.1 times and 2.6 times higher in 2018 and 2019, respectively. The structure and ventilation system within the subway station likely influenced the variations among the subway stations. Subway stations designed with more direct access to the outside environment showed lower PM concentrations than the station with less direct access. In comparison to off-peak hours, higher levels were found during peak subway hours in 3 of the 6 subway stations for PM2.5, and 5 of the 8 subway stations for PM10. Overall, there is high level of PM exposure for commuters at Philadelphia subway stations. Based on the findings in this study, improvements in station design and preventive control measures are recommended to maximize ventilation and reduce PM exposure for Philadelphia's subway passengers and workers.