Measurement of Black Carbon, Particle Number and Mass, and Lung-Deposited Surface Area Emission Factors from in-Use Locomotive

Abstract:

As pollutant emissions from motor vehicles have vastly decreased over the last decades, the relative contribution from non-road sources has increased. There is a serious lack of real-world emissions measurements for many non-road sources including locomotives. As such, uncertainties in emissions from these sources is high. Locomotives contribute to human exposure of diesel pollutants near ports, railyards, and rail lines. Reducing uncertainty in current estimates of locomotive emissions is needed for enhancing the accuracy of emission inventories with corresponding improvements in health risk, air pollution, and climate assessments.

Particulate matter emissions from a large sample (N=88) of in-use freight locomotives were measured in the Alameda Corridor, located near the port of Los Angeles. Emission factors for black carbon (BC), particle number (PN), fine particulate mass (PM_2.5), and lung-deposited surface area (LDSA) were computed based on 1 Hz measurements of the rise and fall of particulate emissions and CO₂ concentrations as the locomotives passed the sampling location. Mean emission factors ± standard deviations were 0.9 ± 0.5 g kg^-1 of fuel consumed for BC, (2.1 ± 1.5)x10¹⁶ # kg^-1 for PN, 1.6 ± 1.3 g kg^-1 for PM_2.5, and (2.2 ± 1.7)x10¹³ µm² kg^-1 for LDSA. Emission factors for individual trains were slightly skewed, with the dirtiest 10% of locomotives responsible for 20%, 24%, 28%, and 27% of total BC, PN, PM_2.5, and LDSA emissions, respectively. BC versus LDSA emissions from individual locomotives were found to be anti-correlated, suggesting that the highest emitters of black carbon may in fact result in less particle lung-deposited surface area than lower BC emitters. Using results presented here along with previous measurements, we compare for freight trains versus diesel trucks the amount of BC emissions associated with pulling an intermodal freight container over a given distance.

Emission factors for locomotives presented here establish a baseline prior to reductions that are anticipated as a result of Federal regulation and state control efforts in 2015.