Visionary Science, Ethics, Law and Action in the Public Interest

Health Implications of Snowmobile Use In Yellowstone National Park

(N.B. The link initiates the download of a 32-page paper in MS Word format.)
By Sarah Janssen, M.D., Ph.D. and Ted Schettler, M.D., MPH

Executive Summary – The National Park Service recently announced a major change in how it plans to manage winter visitation in Yellowstone and Grand Teton National Parks. Instead of phasing out the use of snowmobiles, the agency said it intends to restrict the numbers and types of snowmobiles permitted within the parks, protecting environmental and human health through careful limits.

The agency noted that its plan to continue snowmobile use would provide less protection for air quality and human health than an earlier decision to replace snowmobile use with a transportation system of snowcoaches.

The agency also reported that its plan would reduce snowmobile emissions significantly but not enough to remove a likelihood of adverse health effects for employees and visitors susceptible to respiratory and other health problems.

These two acknowledgements seemed at odds with Yellowstone’s designation by Congress as a Class 1 airshed, a place intended to have the cleanest air in the nation.

This report grew out of a strong interest on the part of organizations concerned about public health to better understand the human health implications of this change in policy.

Specifically, the report was undertaken to assess:

  • The pollution levels predicted by the National Park Service;
  • Peer-reviewed literature on the health effects of pollutants prevalent in snowmobile emissions; and
  • Assumptions used by the National Park Service in modeling snowmobile emissions and the agency’s resulting conclusions about the effects on air quality and human health.

The assessment highlights significant omissions and discrepancies in the National Park Service’s analysis. It appears that risks to human health under the Preferred Alternative would likely be greater than the National Park Service has acknowledged, particularly for children, pregnant women, seniors, asthmatics, and people with other respiratory and cardiovascular diseases. Some of these risks are not accurately described in the National Park Service’s analysis. Others are overlooked entirely.

This report details concerns about data both used and not incorporated by the National Park Service in development of its plans to change winter use in Yellowstone. At present, the agency is using flawed analysis to make a decision, which, as a result, is unlikely to be fully protective of employee or public health:

  • The National Park Service has predicted pollution levels with a continuation of snowmobile use that would clearly pose health risks for particular populations. Individuals with asthma and other respiratory and cardiovascular diseases, pregnant women, children, and the elderly would face a higher level of risk than under a snowmobile phase-out. These groups comprise a large percentage of the general public. Yet the National Park Service did not analyze their elevated risk.
  • Many employees and visitors in Yellowstone are exposed to concentrations of snowmobile emissions that are much higher than those measurable as ambient pollution. Examples include employees working in areas of concentrated snowmobile traffic, snowmobilers trailing large groups of machines, or children riding on the backs of snowmobiles. Studies have demonstrated that in these circumstances exposure to harmful pollutants can increase dramatically. The National Park Service’s most recent analysis did not model for these circumstances. As a result there would likely be frequent discrepancies between predicted pollution levels and actual exposure to air contaminants.
  • Recent health studies have identified airborne particulate matter less than 2.5 microns in size (PM2.5) as causing many of the health effects attributed to particulate matter, including respiratory disease, lung damage, cancer, and premature death. Even modest levels of PM2.5 have been associated with adverse health effects. Virtually all particulate matter emissions from snowmobile engines are PM2.5 or smaller yet the National Park Service did not model specifically for PM2.5 in its most recent analysis. Nor did the agency discuss potential health effects of acute and chronic exposure to PM2.5 in its analysis.
  • Visitors not acclimated to Yellowstone’s high elevation are likely to be more susceptible than local residents to adverse health effects from carbon monoxide exposure. CO enters the bloodstream from the lungs, binds to hemoglobin in red blood cells, and forms carboxyhemoglobin (COHb). COHb impairs oxygen delivery throughout the body. For individuals who travel from low elevation to Yellowstone’s average elevation of more than 7,000 feet, the resultant decrease in oxygen delivery to tissues and organs could be highly significant. People who already suffer from compromised oxygen delivery are especially sensitive to changes in elevation and CO exposure. Individuals with cardiac disease are more likely to experience arrhythmia or angina when exposed to CO at high elevations than when exposed to the same concentration of CO at lower elevations. These factors are likely to apply to many of Yellowstone’s winter visitors. However, the National Park Service analysis does not discuss this potential health consequence of permitting higher levels of carbon monoxide than are achievable through a snowmobile phaseout.
  • The National Park Service has overstated benefits to air quality from its plan to cap numbers of snowmobiles and require that all machines be “Best Available Technology” (BAT). In predicting total snowmobile emissions, the agency used data from a snowmobile that is significantly less polluting than the new definition of BAT. The Park Service defines BAT as snowmobiles that emit 90 percent fewer hydrocarbons (HC) than a standard 2-stroke snowmobile and 70 percent less carbon monoxide (CO). The agency’s modeling of future air quality used emissions data from a snowmobile with 95 to 98 percent less HC and 85 percent less CO.
  • The National Park Service has stated that its plan to allow continued snowmobile use is one that assures dramatic reductions in snowmobile emissions. But the agency has failed to make clear that cutting emissions is not the same as cutting pollution. During the winter, Yellowstone frequently experiences stable air masses and/or inversions that limit dispersion of emissions. When emissions accumulate, pollution levels rise. Pollution levels can remain high hours after peak snowmobile traffic has subsided. This is a critical distinction because pollution levels, not emissions from individual snowmobiles, are the relevant factor for human health. By not making this distinction clear, the National Park Service analysis reflects a distorted view of air quality and health benefits associated with its plan to continue snowmobile use. For example, carbon monoxide emissions would be reduced by some 70 percent per snowmobile. But modeling indicates that peak carbon monoxide pollution levels would drop by just 51 percent at Old Faithful, and only 26 percent at the West Entrance where fresh air is piped into work booths and employees still experience symptoms of CO toxicity, including headaches, dizziness, and nausea.
  • The National Park Service plan for continued snowmobile use hinges upon several disputed assumptions regarding “Best Available Technology” (BAT). These include whether the agency has the authority to require emissions reduction more stringent than the Environmental Protection Agency and whether snowmobiles meeting these requirements would be readily available and affordable to the public. It is also unclear how the National Park Service would ensure that all private snowmobiles would be BAT when the machines are not clearly labeled as such by the manufacturers and can be modified, resulting in higher emissions and more noise.

In summary, the evidence presented here demonstrates that serious public health risks from pollution would remain under the National Park Service plan to continue snowmobile use in Yellowstone and Grand Teton national parks. The agency did not use the best available data in its most recent analysis. Air pollution and health effects from snowmobiles have been underestimated, poorly depicted, and, in some cases, not analyzed at all. For these reasons, actual exposure and health risks for park employees and potentially tens of thousands of winter visitors would be greater than the National Park Service has reported. The aim of this report is to convey these concerns, and the large body of peer-reviewed science upon which they are based, to the National Park Service and the public so that more informed decisions can be made. More than 60 published studies referred to throughout this report are listed on pages 26-29.
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