Diesel particulate matter and coal dust from trains in the Columbia River Gorge, Washington State, USA

Abstract

We examined the emissions of diesel particulate matter (DPM) and coal dust from trains in the Columbia River Gorge (CRG) in Washington State by measuring PM1, PM2.5, CO2, and black carbon (BC) during the summer of 2014. We also used video cameras to identify the train type and speed.During the two-month period, we identified 293 freight trains and 74 coal trains that gave a PM2.5 enhancement of more than 3.0 μg/m3. We found an average PM2.5 enhancements of 8.8 and 16.7 μg/m3, respectively, for freight and coal trains. For most freight trains (52%), and a smaller fraction of coal trains (11%), we found a good correlation between PM2.5 and CO2. Using this correlation, we calculated a mean DPM emission factor (EF) of 1.2 gm/kg fuel consumed, with an uncertainty of 20%.For four coal trains, the videos revealed large plumes of coal dust emanating from the uncovered coal cars. These trains also had the highest peak PM2.5 concentrations recorded during our study (53–232 μg/m3). Trains with visible coal dust were observed for 5.4% of all coal trains, but 10.3% when the effective wind speed was greater than 90 km/h. We also found that nearly all coal trains emit coal dust based on (1) statistically higher PM2.5 enhancements from coal trains compared to freight trains; (2) the fact that most coal trains showed a weak correlation between PM2.5 and CO2, whereas most freight trains showed a strong relationship; (3) a statistically lower BC/PM2.5 enhancement ratio for coal trains compared to freight trains; and (4) a statistically lower PM1/PM2.5 enhancement ratio for coal trains compared to freight trains. Our results demonstrate that, on average, passage of a diesel powered open-top coal train result in nearly twice as much respirable PM2.5 compared to passage of a diesel-powered freight train.