Emissions from these same types of large, industrial sources also account for much of the visibility impairment in the West. Visibility varies with the season and is generally worse during the humid summer months. In our nation's scenic areas, the visual range has been substantially reduced. In eastern parks, average visual range has decreased from 90 miles to 15-25 miles. In the West, visual range has decreased from 140 miles to 35-90 miles.
Haze conditions vary across the country.
Eastern U.S. areas have more haze due to higher pollutant and humidity levels.