• Delicate Arch, Arches National Park, Utah. Credit: Scott Copeland

  • Yosemite National Park, California. Credit: Crocker Lab Staff

  • Power plant in Wyoming. Credit: Scott Copeland

  • East of Angel Pass, Fitzpatrick Wilderness, Wyoming. Credit: Scott Copeland

  • Aerosol sampler, Moosehorn National Wildlife Refuge, Maine. Credit: Crocker Lab Staff

Since the late 1970s, Crocker Nuclear Laboratory has been a leader in the characterization and analysis of the microscopic airborne particles that cause regional haze, the kind of air pollution that impairs visibility over widespread areas.

Sources of regional haze are notoriously difficult to pinpoint because this kind of pollution is almost always caused by an accumulation of emissions from numerous sources scattered over a broad region. By developing equipment, procedures and programs to collect, characterize, measure and analyze levels of particulate matter that contribute to regional haze, Crocker has been making important advances in global efforts to reduce this serious problem.

Crocker launched its first large air quality project in 1979, designing and installing 40 particulate matter sampling stations in eight states. This pioneering effort, funded by the Environmental Protection Agency, helped establish baseline levels for airborne particles at numerous sites. In addition, Crocker’s analyses of trace elements in the collected samples supported efforts to associate visibility degradation at each site with specific types of pollution-emitting sources.

In 1985, when the EPA initiated IMPROVE, a much larger air quality project, it turned to Crocker for the design, operation and quality assurance for the work. Since the program’s inception, Crocker has been the only contractor for this nationwide effort to monitor visibility impairment in the country’s national parks and wilderness areas.


San Gorgonio wildernessAerosol sampling station in San Gorgonio Wilderness,
California. Credit: Scott Copeland

Over the past quarter century, the Crocker air quality team has installed its IMPROVE aerosol sampling modules—and overseen their operation—at some 170 sites in the U.S., Canada and South Korea, while continually upgrading and refining the instrumentation and data analysis aspects of the IMPROVE program.

While data generated by the aerosol samplers are primarily used to monitor long-term trends in visibility, others have made use of the wealth of information made available by IMPROVE for a variety of investigations. These include searching for the sources of emissions that are causing air pollution at specific sites, and correlating meteorological data with statistical models and maps of IMPROVE data to track the long-range movement of pollutants from large emitters such as power plants and refineries.