Concerns - Air Quality

Overview

Snowmobiles

Air quality is a measure of pollution in the outdoor air that most people breathe.  Air quality standards have been developed for compounds known to harm human health. The Clean Air Act requires the U.S. Environmental Protection Agency  to set National Ambient Air Quality Standards for pollutants considered harmful to public health and the environment. States also have their own air quality standards. 

Air quality standards for ambient air are generally distinguished from personal exposure standards that govern employees in work areas.

Air quality standards for vehicle emissions (including snowmobiles) include carbon monoxide (CO), unburned hydrocarbons (HC), particulate matter (PM), and oxides of nitrogen (NOx).  CO interferes with the oxygen-carrying capacity of blood, while PM can accumulate in the respiratory system, causing breathing problems. Some air pollutants are known or probable human carcinogens, while others cause neurological problems. 

As they are currently designed, two-stroke engines - whether in a snowmobile or any other kind of vehicle or device - emit significant amounts of air pollution. One reason is that 20-33% of the fuel goes through the engine and out the tailpipe unburned. Another factor is that in standard two-stroke engines lubricating oil must be mixed with fuel. So lube oil makes up part of the exhaust, including most of the visible haze that snowmobiles produce. Snowmobiles are usually tuned "rich," meaning that there is a high ratio of fuel to oxygen. This improves cold starts and throttle response, but also contributes to emission problems. [For more detail, see Two-Stroke Engine Principles.]   Winter air is often stagnant  in low areas such as  mountain valleys, limiting dispersion of emissions.  Heavy snowmobile traffic in congested areas also contributes to emissions causing air quality concerns.

Selected Links

There is a large body of technical literature on engine emissions, air quality, and related health concerns. Included here are only works with direct relevance to the topic of snowmobiles. Go to the Publications and Links section for a more complete list, including related or overlapping topics.

The National Park Service Air Resources Division has completed an overview of air quality issues in the National Parks.

The National Park Service Air Quality Program attempts to protect the National Parks from air pollution problems, and provides a wealth of air quality information for Yellowstone and many other National Parks.

In the winter of 1999, the University of Denver completed a remote sensing study of snowmobile emissions in Yellowstone National Park:

Morris, Jerome A., Bishop, Gary A., Stedman, Donald H. August 1999. Real-time Remote Sensing of Snowmobiles Emissions at Yellowstone National Park: An Oxygenated Fuel Study, 1999. (42 pages)

In 1999, Southwest Research Institute completed a study of particulate matter in snowmobile emissions:

Carroll, James N.,White, Jeff J.,Khalek, Imad A.,Kado, Norman. June 1999. Characterization of Snowmobile Particulate Emissions (8 pages, 485k pdf file).

The Monitoring and Data Management Bureau of the Montana Department of Environmental Quality (DEQ) completed a modeling analysis to estimate the carbon monoxide concentrations from vehicle emissions near the roadways at the West Entrance to Yellowstone National Park:

Cain, Cyra J and Coefield, John. December 1999. Preliminary Air Dispersion Modeling Analysis of Yellowstone National Park West Entrance: Wintertime Carbon Monoxide Emissions. (78k pdf file)

DEQ has prepared a graph (19k pdf file) comparing carbon monoxide levels at the West Entrance to Yellowstone with National Park Service counts of the number of snowmobiles using this entrance between December 2000 and January 2001.

The Office of Transportation and Air Quality at the U. S. Environmental Protection Agency (EPA) provides an overview of air quality and regulatory issues for snowmobiles and other land-based recreational vehicles.

EPA also publishes fact sheets showing health effects of a wide variety of air pollutants:

Health Effects Notebook for Hazardous Air Pollutants. Air Risk Information Center, Research Triangle Park, North Carolina.

EPA promulgates the National Ambient Air Quality Standards (NAAQS) on the basis of scientific information. An air quality criteria document for carbon monoxide (CO) was completed by EPA in 1991: Air Quality Criteria for Carbon Monoxide.

Supported jointly by the U.S. Environmental Protection Agency (EPA) and industry, the Health Effects Institute (HEI) is an independent, nonprofit corporation chartered in 1980 to provide high-quality, impartial, and relevant science on the health effects of pollutants from motor vehicles and from other sources in the environment. Along with EPA, HEI maintains the searchable Particulate Matter Research Activities website.