Study finds “markedly” high levels of diesel exhaust present in commuter trains powered by locomotives in pull-mode
Diesel-powered commuter trains may expose their passengers to elevated levels of certain black carbon and ultrafine particles, especially in the coach directly behind the locomotive, according to a new study from researchers at the University of Toronto. A paper on the study is published in the journal Atmospheric Environment.
Professor Greg Evans (ChemE), director of the Southern Ontario Centre for Atmospheric Aerosol Research (SOCAAR) and Dr. Cheol-Heon Jeong, a senior research associate at SOCAAR, measured the ultrafine particle (UFP), black carbon (BC) and lung deposited surface area (LDSA) concentrations during 42 trips on diesel-powered commuter trains. When the passenger coaches were pulled by a locomotive, the geometric mean concentrations of UFP, LDSA, and BC were 18, 10, and 6 times higher than the exposure levels when the locomotive pushed the coaches, respectively. UFP, LDSA, and BC concentrations in pull-trains were 5, 3, and 4 times higher than concentrations measured while walking on city sidewalks, respectively.
Exposure to these pollutants was most elevated in the coach located closest to the locomotive: geometric means were 126,000# cm-3for UFP, 249 μm2 cm−3 for LDSA, and 17,800 ng m−3 of BC; these concentrations are much higher than those previously reported for other modes of public transportation.
Imagine yourself driving down a busy highway in a convertible, and spending your entire commute sitting behind a very large diesel truck. That’s comparable to the levels we see here.—Greg Evans
Studies have linked both BC and UFP to detrimental health effects, although evidence is still emerging and not conclusive. However, both measurements also act as proxies for the complex mixture of gases in diesel exhaust, which is an established carcinogen and associated with respiratory, cardiovascular and reproductive health effects.
In prior research, Evans and his team have found elevated levels of BC and UFP next to busy streets and highways. One day, Jeong left the sensors turned on during his morning commute on the train—it wasn’t until he saw the data that he and Evans realized how high the numbers were inside cars pulled by diesel locomotives.
Over the course of 43 trips, the team gathered more data from inside commuter train cars. They also took measurements while walking along busy streets in downtown Toronto for comparison. Among their findings:
Cars being pulled by diesel trains and located directly behind the locomotive had an average of nine times the levels of BC and UFP compared to air next to a busy city street.
Cars being pushed by diesel trains during a return trip had air that was generally cleaner than that next to busy city streets.
When being pulled, cars in the middle of the trains had levels three times lower than the front-most cars. The average BC and UFP concentrations across all pulled cars was about five times higher than on city streets.
Greg Percy, Chief Operating Officer for Metrolinx, said that Metrolinx is taking a number of steps to address the issue, such as installing high-efficiency filters in the ventilation systems of its train cars. The organization is also moving to locomotives with improved emissions standards and to electrified service on key routes, which will eliminate the diesel emissions altogether.
Evans and his team are currently working with Metrolinx and SNC Lavalin to test the new improved filters for the air intake vents. Preliminary results are positive. Installing the higher grade filters did produce a marked improvement, with an 80% reduction in the levels of black carbon, said Evans.
Cheol-Heon Jeong, Alison Traub, Greg J. Evans (2017) “Exposure to ultrafine particles and black carbon in diesel-powered commuter trains,” Atmospheric Environment doi: 10.1016/j.atmosenv.2017.02.015