Field Sites

In 1987, IMPROVE’s first aerosol samplers — designed here at UC Davis — were installed at the program’s first 20 sites including Acadia, Big Bend, Hawaii Volcanoes, and Yellowstone national parks. Since then, the team has outfitted approximately another 150 sites with its IMPROVE samplers.

With the program’s demonstrated success in visibility monitoring and steady advances in instrumentation and data analysis, it has been joined by a number of agencies and groups not affiliated with Class 1 areas. Of the approximately 160 currently active IMPROVE sites, about 60 are hosted by such groups, while the remainder are associated with Class 1 areas.

In the past five years, the program has expanded internationally as well, with the AQRC team installing IMPROVE aerosol samplers and providing training to groups in Canada and South Korea.

With its 25 years of experience designing, improving and refining core components of the IMPROVE program, the AQRC holds a unique vantage point in the field of monitoring and analysis of airborne particles. Agencies or organizations interested in establishing airborne particle monitoring programs should contact Nicole Hyslop, principal investigator of the IMPROVE program.

Aerosol Samplers

Image: Outdoor IMPROVE aerosol sampler during a gray, rainy day.
AQRC’s IMPROVE aerosol samplers are designed for outdoor use, even in extreme weather. This sampler on Baengnyeong Island in South Korea is subjected to subfreezing temperatures,50 inches of annual precipitation and nearly continual levels of humidity above 60 percent. Credit: NIER—Korea.

Special features

Since the 1970s, the Air Quality Research Center has been improving the design of the equipment used to collect airborne particulate matter for the IMPROVE program. A number of special design features have been incorporated into AQRC’s aerosol samplers, including:

  • Higher air intake flow rates and smaller filters to concentrate particles. This enables better detection of small amounts of particulate matter and ensures that an adequate supply is collected for analysis from the relatively clean air in the national parks and wilderness areas where these samplers are deployed.
  • A streamlined and rugged design to allow the equipment to be mounted in the open, even in harsh environments.
  • In the late 1990s the samplers were redesigned to include continuous electronic data recording onto memory cards.
  • Bar coding on every filter to ensure accuracy in the data stream.

The team is currently developing controllers with the capacity to remotely transmit information about the equipment’s status via satellite or cell phone networks.

Image: a UCD staff member works on an open module at a sampler site visit.
UC Davis staff visit each sampler site every two years and are available year-round to solve problems. Credit: Air Quality Research Center staff.


The IMPROVE sampler consists of four sampling modules housed in metal cases, each equipped with a long inlet stack that extends about five feet into the air.

A fifth box contains the controller unit, which serves both as a data recorder and timer. Every third day it activates a pump—programmed to run continuously for 24 hours—which draws ambient air through the stacks and across specialized filters in each module.

While the filters in modules A, B and C all capture particles smaller than 2.5 micrometers in diameter, the design of each filter allows a specific set of analyses to be run on the particles it collects. The filter in module D captures particles smaller than 10 micrometers in diameter.

Referred to as PM2.5 and PM10, this fine and coarse particulate matter collected from the air is not only the main ingredient in regional haze, but has also been clearly linked to respiratory and cardiovascular illness.

Filter collection and processing

Image: illustration of IMPROVE sampler station with four sampling modules.
IMPROVE aerosol samplers house four modules, each for a different aerosol component. Credit: Chuck McDade and Nicole Hyslop.

Local operators at each field site—in many cases a park ranger, firefighter, or rancher—inspect the samplers and exchange filters weekly, shipping all exposed filters back to AQRC every three weeks. Each month, the program’s 160 field sites generate about 7,000 filters, which are processed in AQRC’s laboratories by staff members and a dozen UC Davis students working part-time.

The team analyzes the particles using a variety of tests, including gravimetric mass measurements to measure fine and total aerosol mass, carbon, optical absorption, and X-ray fluorescence (XRF) to determine elemental composition.

Until 2013, AQRC staff visited each of the IMPROVE aerosol samplers annually to conduct routine maintenance and calibration, make repairs and install equipment upgrades. With recent budget cuts, visits now take place every two years.


Site Maps

Interactive map of IMPROVE Sites

IMPROVE Site Map with Affiliated Agencies

Image: Improve site map with affiliated agencies.