Mercury Emissions from Motor Vehicles

The U.S. Environmental Protection Agency initiated a pilot program in 2002 with researchers at the University of Michigan Air Quality Laboratory to investigate motor vehicle mercury emissions. The program included exhaust emissions characterization of vapor and particulate phase mercury from three light-duty gasoline vehicles, one diesel vehicle and mercury analysis of fuel, lubricating oil, engine coolant, brake rotors and brake pads. Mercury was detected in all samples collected. Emission factors for elemental, vapor-phase mercury plus particulate mercury for the light-duty gasoline vehicles ranged from 0.31 to 1.4 ng/mi and for the diesel vehicle from 6.3 to 11.0 ng/mi. Results of the pilot program provide evidence of a mobile source contribution to environmental mercury. The data suggest that some of the factors influencing mercury emissions from mobile sources include oil consumption, driving conditions (including brake wear), and fuel consumption. Limitations of this study include: reactive gasphase mercury was not measured, vehicles were not tested under cold start conditions, and few vehicles and fuels were tested. In addition, the nationwide fleet is not characterized by the few vehicles studied and emissions from non-road engines have not been measured. Further research is needed in order to estimate mobile source mercury contributions to the national mercury inventory.