Condensed from a 1999 Bluewater Network document.

According to snowmobile emissions data, in one hour, a single snowmobile produces more smog-forming pollution than a modern car creates in one year; one hundred snowmobiles can create the equivalent carbon monoxide of more than 100,000 cars.

Two-stroke engines deliver a lot of power but also a lot of exhaust; they spit 100 times more carbon monoxide and 300 times more hydrocarbons than automobiles, according to a report compiled from studies performed by several state and federal agencies and the University of Denver.

The EPA has determined that two-stroke engines release between 25% and 30% of their unburned gas and oil mixture directly into the environment.

For particulate matter concentration, the federal limit is a concentrate of 60. As an example, at Yellowstone National Park's west entrance on Feb. 13 and Feb. 14, 1997, the concentrations were 116 and 122, respectively. "To put this in perspective, the maximum 24-hour particulate matter concentration in the Los Angeles suburb of Azusa in 1997 was 68," the report states.

These engines create dangerous levels of airborne toxins including nitrogen oxides, carbon monoxide, ozone, particulate matter, aldehydes, 1,3 butadiene, benzenes, and extremely persistent polycyclic aromatic hydrocarbons (PAH). EPA lists several of these compounds as “known or probable” human carcinogens. Benzene, for instance, is a "known" human carcinogen. And several aldehydes including butadiene are classified as "probable human carcinogens." All are believed to cause deleterious health effects in humans and animals well short of fatal doses (EPA 1993).

Two‑stroke engines also discharge 25‑30% of their fuel mixture, unburned, directly into the environment. Unburned fuel contains many toxic compounds including benzene, toluene, xylene and the extremely persistent suspected human carcinogen MTBE. Two‑strokes are one of the largest unchecked sources of pollution nationwide. Charles Emmett, an engineer with the California Air Resources Board, says that snowmobiles are "extremely, extremely dirty compared to anything else ... [s]nowmobiles are the worst there is." (McMillion 1994).

A. Polycyclic Aromatic Hydrocarbons (PAHs)

PAHs are by‑products of fuel combustion found in high concentrations in unregulated two‑stroke emissions. They are particularly hazardous because they are both carcinogenic and mutagenic, and are extremely persistent in the environment.

B. Noxious Air Emissions

Dangerous levels of carbon monoxide (CO) and particulate matter (PM) are a primary concern. CO is extremely dangerous to humans (discussed below), and particulate matter is a recently confirmed human carcinogen by the EPA. Snowmobiles emit dangerously high levels of carbon monoxide. A study conducted for the National Park Service in 1997 concluded that a single snowmobile produces 500‑1000 times more carbon monoxide than a 1988 passenger car (Fussell‑Snook 1997). Notably, comparisons to a current model‑year passenger vehicle would increase this figure significantly.

C. Human Health Risks Associated with Carbon Monoxide

The blue haze found trailing behind snowmobiles contains not only dangerous levels of airborne toxins, but can lead to the formation of additional ground level ozone from the photochemical reaction of released nitrogen and hydrocarbons. Health risks associated with exposure to smog and nitrogen include respiratory complications such as coughing, chest pain, heart problems, asthma, concentration lapses and shortness of breath. Elderly individuals and children are particularly sensitive to ground level ozone and nitrogen.

Carbon monoxide is particularly dangerous because it binds to the hemoglobin in blood (forming carboxyhemoglobin) and renders hemoglobin incapable of transporting oxygen (Snook‑Fussell 1997). Elevated levels of carboxyhemoglobin can cause neural‑behavioral effects at lower levels (2‑3 percent), headaches and fatigue (10 percent), and respiratory failure and death at higher levels. And the general consensus among medical professionals is that the health risk from CO increases at high altitude ‑‑ a risk exacerbated by richer fuel mixtures common at higher elevations.