Interagency Monitoring of Protected Visual Environments (IMPROVE)

Measuring the impact of air pollution on visibility in United States National Parks

National Park Service (NPS), U.S. Environmental Protection Agency (EPA)

Whether you are setting your eyes on the chiseled canyons of Arizona, the lush mountains of North Carolina, or the Great Sand Dunes of Colorado, the visual magnificence of our National Parks plays a vital role in their value and our impetus as a nation to preserve these natural resources.

Reductions in visibility, usually caused by a uniform or layered haze comprised of particles in the air, can diminish the grandeur of some of the country’s most stunning scenery. The haze causes colors to appear less vibrant and the land to appear less varied in texture.

In 1977 Congress passed the Clean Air Act, which included a provision to prevent future impairment and remedy existing visual impairment to Class 1 National Park and Wilderness areas. To implement that legislation, the National Park Service (NPS) and U.S. Environmental Protection Agency (EPA) initiated a program known as Interagency Monitoring of Protected Visual Environments (IMPROVE).

Our scientists have helped protect the integrity of that visibility for nearly three decades as part of our support for the IMPROVE program.

Consistent, High-Quality Measurement of Air Quality

Our chief role is to measure concentrations of airborne particles—whether naturally occurring or from manmade sources—that can inhibit visibility at parks throughout the United States.

We track sulfate, nitrate, nitrite, chloride, and other analytes that are important for measuring air quality. As monitoring technology evolved over the decades, along with our understanding of some compounds (such as secondary organic aerosols), we maintained—and continue to maintain—the highest data quality and consistency in data collection needed to accurately depict trends and changes occurring in an area across years, or even decades.    

By documenting long-term trends, our work enables federal and state agencies to assess progress towards national visibility goals, as well as to develop plans for establishing critical limits. The long-term trend data also helps to assess the impacts of regulatory changes and industry practices, and in turn to inform future policy.

For example, a decrease in overall concentrations of sulfate, a substance that may present risks to human health, was attributed to lower emissions from power plants regulated by the EPA.

Similarly, in the Midwest and upper East Coast regions, increased concentrations of nitrate and ammonia in recent years is likely the result of over-fertilizing in agriculture and animal operations.

With this information, policymakers can make informed decisions and allocate resources to addressing the source of pollutants that lower the air quality in our national parks and present risks to human and environmental health.

Characterizing Effects of Compounds on Environmental Health

Our scientists also work with NPS to conduct studies characterizing secondary organic aerosols in the environment and their effects on increased levels of nitrogen in park ecosystems.

In addition to the impact of our work on policy, regulation, and the science of air quality measurement, the positive influence of our work supporting IMPROVE can be seen in the dramatic improvement in visibility documented in photos over the years and preserved in the memories of visitors to U.S. national parks.

In August of 2016, the National Park Service awarded us with a five-year contract to continue this work. The consistency of data collection methods will help our scientists to continue providing accurate evaluations of visibility in support of U.S. goals to preserve these important national treasures.