The network is the largest in the country devoted to fully characterizing visibility. It also provides information for determining the types of pollutants and sources primarily responsible for reduced visibility. Visibility impairment is generally worse in the rural East compared to most of the West. This is primarily due to higher concentrations of man-made pollution, slightly higher background levels of fine particles, and higher relative humidity levels in the East. The chart below shows the relative levels of pollutants that contribute to visibility impairment in the Eastern and Western parts of the United States.
Sulfates are generally the largest contributor in the East and West.
Great Smoky Mountains under a range of visibility conditions. These plans will include emission management strategies to improve visibility over time in national parks, particularly for the worst visibility days. States will be required to periodically track progress and revise any strategies as necessary. Because fine particles are frequently transported hundreds of miles, pollution that occurs in one state may contribute to the visibility impairment in another state. Other air quality programs are expected to lead to emission reductions that will improve visibility in certain regions of the country.