Snowmobiles (sleds) have become a very popular way for visitors to explore Yellowstone National Park during its winter season with more than 60000 visits during the 1997-1998 season. In-use emissions data are very limited, and only a small number of sleds tested under controlled conditions have had their measurements reported. Snowmobiles are currently manufactured and marketed in the U.S. by four companies: Arctic Cat, Bombardier (Ski-Doo), Polaris, and Yamaha. Using the University of Denver's nondispersive infrared remote sensing equipment carbon monoxide (CO) and hydrocarbon (HC) emission measurements were collected on 1210 sleds at the West Yellowstone, MT park entrance during 4 days in February 1998. Mean emissions for the measurements were 5.56 plus or minus 0.07 CO and 2.58 plus or minus 0.02 HC (as propane). Using a carbon to hydrogen molar ratio of 1:2 for the fuel, the emissions are 460 plus or minus 6 g CO and 331 plus or minus 2 g HC per kilogram of fuel consumed. This is in large part because snowmobiles utilize conventional two-stroke engine designs which cannot avoid extensive blowby (the exhaust port and intake port being open at the same time) of the unburned fuel, oil, and air mixture which is also poorly regulated by simple carburetors.
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