The impact of coal trains on PM2.5 in the San Francisco Bay area

Abstract

Exposure to fine particulate matter (PM_2.5) is associated with adverse health effects, including mortality, even at low concentrations. Rail conveyance of coal, accounting for one-third of American rail freight tonnage, is a source of PM_2.5. However, there are limited studies of its contribution to PM_2.5, especially in urban settings where residents experience higher exposure and vulnerability to air pollution. We developed a novel artificial intelligence-driven monitoring system to quantify average and maximum PM_2.5 concentrations of full and empty (unloaded) coal trains compared to freight and passenger trains. The monitor was close to the train tracks in Richmond, California, a city with a racially diverse population of 115,000 and high rates of asthma and heart disease. We used multiple linear regression models controlling for diurnal patterns and meteorology. The results indicate coal trains add on average 8.32 µg/m³ (95% CI = 6.37, 10.28; p < 0.01) to ambient PM_2.5, while sensitivity analysis produced midpoints ranging from 5 to 12 µg/m³. Coal trains contributed 2 to 3 µg/m³ more of PM_2.5 than freight trains, and 7 µg/m³ more under calm wind conditions, suggesting our study underestimates emissions and subsequent concentrations of coal train dust. Empty coal cars tended to add 2 µg/m³. Regarding peak concentrations of PM_2.5, our models suggest an increase of 17.4 µg/m³ (95% CI = 6.2, 28.5; p < 0.01) from coal trains, about 3 µg/m³ more than freight trains. Given rail shipment of coal occurs globally, including in populous areas, it is likely to have adverse effects on health and environmental justice.