Increases in the number of winter visitors to Yellowstone National Park during the past decade have raised concerns over the environmental impacts of snowmobiling in the park. During the 1998-99 season, more than 62000 snowmobile and 1300 snow coach trips entered the park. Using the University of Denver's vehicle exhaust remote-sensing equipment, 1385 measurements of carbon monoxide (CD) and hydrocarbon (HG) emissions were collected from in-use snowmobiles at the west and south entrances to the park. Overall means of 392 ± 4 g CD and 237 ± 1 g HG were observed per kilogram of fuel consumed. In addition, using an ultraviolet monochromator, 460 measurements of toluene emissions were collected with a mean of 39 ±1 g toluene/kg of fuel. Using these data, a mobile source emissions inventory based on fuel use for Yellowstone National Park shows that snowmobiles account for 27 of the annual emissions of carbon monoxide and 77 of annual emissions of hydrocarbons using an equivalent best estimate for the summer mobile source emissions. Use of oxygenated fuels in snowmobiles was found to reduce CD emissions by 13.2 ± 6.5 without an observed effect on HG emissions. Liquid-cooled sleds were found to have HG emissions 9.5 ± 2.2 higher than those from fan-cooled sleds because of the increased intake and exhaust port sizes required in the larger liquid-cooled engines, which increases blow by in the 2-stroke engines.
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