The National Park Service is trying to determine whether there is a link between the exhaust fumes of snowmobiles and heightened reports of illness by employees at the west entrance to Yellowstone National Park.
Employees have complained of headaches and say they can taste oil in the air from exhausts of the twocycle snow machines.
On a busy winter day, up to 1,200 snowmobilers enter the park at the west entrance. At times, between 50 and 70 snowmobiles are waiting in line with engines running.
The results of the study, which began in October, may help the park service decide if changes in winter use are necessary, said park spokesperson Cheryl Matthews.
Bob Seibert, district ranger, said snowmobile industry data indicate the exhaust from one snowmobile can produce the same volume of hydrocarbons and nitrous oxides as 1,000 cars and carbon monoxide emissions equivalent to between 250 and 500 automobiles.