Measurement of black carbon emissions from in-use diesel-electric passenger locomotives in California. (August 2015)

• Record Type: Journal Article
• Authors: Tang, Nicholas W.; Apte, Joshua S.; Martien, Philip T.; Kirchstetter, Thomas W.
• Is Part Of: Atmospheric environment. Volume 115(2015)
• Page Start: 295
• Page End: 303
• Publication Date: 2015-08
• Subjects: Locomotive emissions -- Black carbon -- Particulate matter -- Emission standards -- Carbon footprint; Air -- Pollution -- Periodicals; Air -- Pollution -- Meteorological aspects -- Periodicals; 551.51
• DOI: 10.1016/j.atmosenv.2015.05.001
• Languages: English
• ISSNs: 1352-2310

Abstract

Abstract: Black carbon (BC) emission factors were measured for a California commuter rail line fleet of diesel-electric passenger locomotives (Caltrain). The emission factors are based on BC and carbon dioxide (CO2 ) concentrations in the exhaust plumes of passing locomotives, which were measured from pedestrian overpasses using portable analyzers. Each of the 29 locomotives in the fleet was sampled on 4–20 separate occasions at different locations to characterize different driving modes. The average emission factor expressed as g BC emitted per kg diesel consumed was 0.87 ± 0.66 g kg −1 (±1 standard deviation, n = 362 samples). BC emission factors tended to be higher for accelerating locomotives traveling at higher speeds with engines in higher notch settings. Higher fuel-based BC emission factors (g kg −1 ) were measured for locomotives equipped with separate "head-end" power generators (SEP-HEPs), which power the passenger cars, while higher time-based emission factors (g h −1 ) were measured for locomotives without SEP-HEPs, whose engines are continuously operated at high speeds to provide both head-end and propulsion power. PM10 emission factors, estimated assuming a BC/PM10 emission ratio of 0.6 and a typical power output-to-fuel consumption ratio, were generally in line with the Environmental Protection Agency's locomotive exhaust emission standards. Per passenger mile, diesel-electric locomotives in this study emit only 20% of the CO2 emitted by typical gasoline-powered light-duty vehicles (i.e., cars). However, the reduction in carbon footprint (expressed in terms of CO2 equivalents) due to CO2 emissions avoidance from a passenger commuting by train rather than car is appreciably offset by the locomotive's higher BC emissions. Highlights: Passenger locomotive emission factors of black carbon (BC) were measured. The average emission factor was 0.87 ± 0.66 g BC emitted per kg diesel consumed. Estimated PM10 emissions were in line with EPA's exhaust emission standards. Per commuter mile, locomotives emit 20% of the CO2 but ten times more BC than emitted by cars. BC emissions dramatically increase the carbon footprint of locomotive travel.