Snowmobiles operate in cold weather. Like any internal combustion engine, these machines like to run rich in the cold, producing high amounts of carbon monoxide. Cold, stable atmospheric conditions combined with unfavorable topographical features like mountain valleys can "trap" snowmobile emissions, causing high atmospheric concentrations of pollution in areas with high snowmobile usage.

Traditional snowmobiles:

• Utilize a two-stroke engine.
• Are tuned to run "rich" (with excess fuel) for easier starting and reliable operation. (This results in incomplete combustion and the emission of high amounts of unburned hydrocarbons and carbon monoxide.)
• Have recently been regulated but not required to use exhaust after treatment (such as catalysts) to reduce emissions.

Two stroke engines:

• Feature a high power to weight ratio and good cold-start characteristics. However, they are inherently "dirty" engines.
• Between 20 and 50 percent of the fuel, air, and oil mix can be emitted, unburned, from a two-stroke engine due to "short-circuiting" of the fuel-air mixture. (Short circuiting is when both the fuel injection and exhaust ports are open at the same time. There are no valves on a two-stroke engine.)
• Partial combustion of traditional two-stroke oils results in visible particulate pollution

Most snowmobile tour operators replace their snowmobile rental fleet annually.