The Influence of Snowmobile Emissions on Air Quality and Human Health

Scenes of Yellowstone Park Rangers wearing gas masks brought national attention to snowmobile pollution. In Yellowstone (YNP) where the cleanest air in the nation should be found, levels of pollution often exceeded those of downtown Los Angeles (Rodes et al. 1998). Studies were quickly initiated and two-stroke snowmobiles were banned from the Park. Elsewhere, millions of snowmobilers still rev up these engines each winter and head into the snow-covered wildlands. No federal laws regulate snowmobile exhaust (outside Yellowstone) and accordingly they are not equipped with any pollution control devices. Air pollution from snowmobiles is well documented and can result in a number of health problems. This paper reviews current research on the extent of snowmobile pollution and its impacts on human health.

Snowmobile emissions

Snowmobiles first gained popularity in the 1960s. At that time, the 6 horsepower machines reached speeds of 35 mph. Powered by lightweight, high-power engines, today’s snowmobiles boast up to 225 horsepower (4 times a Harley) and can exceed 120 mph. While technological advances have also produced cleaner four-stroke engines, the vast majority of snowmobiles are still two-stroke engines, which are as polluting as their 1960s era predecessors.

Two-stoke engines are highly polluting. The lubricating oil is mixed with the fuel, and 20% to 33% of this mixture is emitted unburned into the air and snowpack (MDEQ 2004). Also, the combustion process itself is relatively ineffi cient and results in high emissions of air pollutants (NPS 2000). Because of these two reasons, two-stroke snowmobiles emit very large amounts of carbon monoxide (CO), unburned hydrocarbons (HC) and smoke (MDEQ 2004).

Extensive research on snowmobile pollution has been conducted in Yellowstone National Park (YNP; e.g., Ingersoll et al. 1997, White and Carroll 1998, Ingersoll 1999, Morris et al. 1999, Bishop et al. 1999, NPS 2000, Bishop et al. 2001, Cain and Coefi eld 2001, Kado et al. 2001, Sive et al. 2002, Janssen and Schettler 2003, Bishop et al. 2006). While the most recent Winter Use Plan has banned the use of two-stoke engines in YNP (replacing them with limited numbers of cleaner burning four-stroke engines), these studies are the best available science for measuring the effects of snowmobiles outside the Park where two-stroke engines still dominate.

The scale of the pollution documented in YNP was remarkable. Snowmobiles were responsible for 68% to 90% of HC emissions and 35% to 68% of CO emissions each year (NPS 2000), but make up only 6% of the total vehicles entering the park annually. On a peak day in YNP, snowmobiles released approximately 20 tons of hydrocarbons (HC) and 54 tons of carbon monoxide (CO) into the air (NPS 2000). For comparison, in an average day in July, cars in YNP emit 2.5 tons of HC and 17.9 tons of CO (NPS 2000). While the snowmobile season usually only lasts three months in YNP (mid-December to mid-March), their emissions equaled or exceeded the total annual emissions for CO and HC from other mobile sources combined (cars, buses, and snow coaches).

The effects of snowmobile emissions on health

Emissions from snowmobiles have been found to contribute to serious health problems. Large numbers of snowmobiles in one area (such as parking lots), cold stable weather conditions, and low wind speed all increase the accumulation of toxins and increase the risk of adverse health effects (NPS 2000). Additionally, riding in groups of snowmobiles exposes the rider to emissions from the snowmobiles in front of them. Below are some of the potential health effects from inhaling HC, CO, and particulate matter (PM) emitted from snowmobiles.

Hydrocarbons (HC)

Hydrocarbons are volatile organic compounds that include benzene, toluene, ethylbenzene, and xylenes. Kado et al. (2001) found high levels of exposure of benzene for various employees in YNP. They found that workers at the West Entrance were exposed to benzene concentrations of 100 to 300 μg/m3, mobile patrol employees 100 to 200 μg/m3, and a mechanic working indoors 500 μg/m3. The mechanic level of exposure exceeded the National Institute for Occupational Safety and Health recommended exposure level for benzene (320 μg/m3). While these compounds can cause dizziness, headaches, and loss of consciousness, the EPA has also identifi ed benzene as a carcinogen, and those exposed to benzene have an increased incidence of leukemia.

Carbon Monoxide (CO)

Snook Fussell (1997) quantifi ed carbon monoxide releases in Grand Teton National Park and concluded that tourists are exposed to signifi cant and dangerous levels of CO. This is compounded by the fact that most tourists travel in large groups (eight on average, Machlis 1995), snowmobile trails force travel directly behind other snowmobiles, most trails are at high elevation (increasing susceptibility to adverse effects), and many trips require several hours of driving. CO binds to the hemoglobin in blood and inhibits the transportation of oxygen in the body. High levels of CO exposure have been shown to lead to visual impairment, reduced work capacity and mental dexterity, poor learning, nausea, headaches, dizziness, and even death (EPA 1991).

Particulate Matter (PM)

Particulate matter, also found in snowmobile emissions, is detrimental in fi ne and coarse forms as it accumulates in the respiratory system and can lead to decreased lung function, respiratory disease and even death (Janssen and Schettler 2003). Of the pollutants emitted by snowmobiles, particulates are of special concern because their small size makes them easily respirable and thus delivered directly into the lungs, causing any number of the aforementioned maladies (NPS 2000).

Ways to reduce emissions

With the negative health impacts of snowmobiles well established, several strategies for minimizing pollution have been identifi ed. These include using oxygenated fuels (such as ethanol-based fuels), direct-injection two-stroke engines, and four-stroke engines. However, only four-stroke engines have been found to signifi cantly reduce emissions. Electric snowmobile prototypes that produce no emissions have been developed, but are not commercially available.

The University of Denver tested the benefi ts of using oxygenated fuels in snowmobiles in Yellowstone (Morris et al. 1999, Bishop et al. 2001). Oxygenated fuels allow for more effi cient combustion and hence, reduced pollution. Although they found a 3% to 11% reduction of CO, there was no reduction in hydrocarbon emissions. Direct-injection two-stroke engines have been shown to decrease hydrocarbon emissions from snowmobiles by 70% to 75% when compared with conventional two-stroke engines, but had similar emissions for other pollutants (NPS 2000). However, neither oxygenated fuels nor direct-injection two-stroke engines were shown to signifi cantly reduce emissions.

Several studies have recommended replacing two-stroke engines with four stroke engines to signifi cantly reduce emissions and noise (Snook Fussell 1997, Miers et al. 2000, Kado et al. 2001, Eriksson et al. 2003). Banning two-stroke engines in YNP has resulted in a 60% reduction in CO and a 96% reduction in HC emissions (Bishop et al. 2006). Additionally, Bishop et al. (2006) found improved fuel effi ciency, reduction in visible exhaust plumes, odor, and noise.

Conclusion

While YNP has banned two-stroke engines, the vast majority of snowmobilers in the U.S. use the out-dated twostroke technology. Two-stoke engines are very polluting and the risk to human health has been well documented. If land managers are concerned about air pollution and its effects on human health, snowmobile use should be limited and/or transitioned to less polluting four-stroke engines.

— Adam Switalski is Science Coordinator for Wildlands CPR.

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