Fuel-based fine particulate and black carbon emission factors from a railyard area in Atlanta

Railyards have the potential to influence localfine particulate matter (aerodynamic diameter < or = 2.5 microm; PM2.5) concentrations through emissions from diesel locomotives and supporting activities. This is of concern in urban regions where railyards are in proximity to residential areas. Northwest of Atlanta, Georgia, Inman and Tilford railyards are located beside residential neighborhoods, industries, and schools. The PM2.5 concentrations near the railyards is the highest measured amongst the state-run monitoring sites (Georgia Environmental Protection Division, 2012; http://www.georgiaair.org/amp/report.php). The authors estimated fuel-based black carbon (BC) and PM2.5 emission factors for these railyards in order to help determine the impact of railyard activities on PM2.5 concentrations, and for assessing the potential benefits of replacing current locomotive engines with cleaner technologies. High-time-resolution measurements of BC, PM2.5, CO2, and wind speed and direction were made at two locations, north and south of the railyards. Emissions factors (i.e., the mass of BC or PM2.5 per gallon of fuel burned) were estimated by using the downwind/upwind difference in concentrations, wavelet analysis, and an event-based approach. By the authors' estimates, diesel-electric engines used in the railyards have average emission factors of 2.8 +/- 0.2 g of BC and 6.0 +/- 0.5 g of PM2.5 per gallon of diesel fuel burned. A broader mix of railyard supporting activities appear to lead to average emission factors of 0.7 +/- 0.03 g of BC and 1.5 +/- 0.1 g of PM2.5 per gallon of diesel fuel burned. Railyard emissions appear to lead to average enhancements of approximately 1.7 +/- 0.1 microg/m3 of PM2.5 and approximately 0.8 +/- 0.01 microg/m3 of BC in neighboring areas on an annual average basis. Uncertainty not quantified in these results could arise mainly from variability in downwind/upwind differences, differences in emissions of the diverse zones within the railyards, and the influence of on-road mobile source emissions.