A History

In 1972, under the Project Clean Air contract (#PCA-038), an Aerosol Analysis System was designed, built, and utilized at Crocker Nuclear Laboratory, University of CA — Davis, in conjunction with the California Air Resources Board. The purpose of this novel system was to develop techniques in performing elemental analysis of atmospheric particulate samples using accelerator beams, and resulted in the first light element detection of scattering accelerator beams for smog samples. The UCD-ARB joint effort began a state-level air quality monitoring and analysis network that would set precedent for future monitoring programs, as well as grow over the years and merge into the national networks run today.

Five years later, the Clean Air Act was enacted by Congress in 1977 with the goal of identifying the cause of regional haze and how to decrease visible pollution.  With the Clean Air Act in legislation, the Environmental Protection Agency (EPA) organizes the Interagency Monitoring of Protected Visual Environments (IMPROVE) in 1985 again with UC Davis. Aerosol researchers and engineers designed and deployed the first aerosol sampling stations, and 20 sites were in operation by 1987.  As the network expanded, so did the need for a cohesive, collaborative Air Quality group to develop and run analyses, as well as maintain and operate sites on a long-term scale. 2005 saw the inception of the Air Quality Research Center of UC Davis (AQRC).


AQRC maintains and operates two national networks monitoring the air quality across the country: CSN (Chemical Speciation Network) and IMPROVE. The map below shows monitoring locations for both national networks, plus collocated sites. 

Image: Map of the US with CSN & IMPROVE Sites marked. Map inserts show sites located in Alaska, South Korea, Hawaii, and Puerto Rico.
IMPROVE and CSN site locations

Currently, the AQRC monitoring laboratory is equipped for efficient handling and analysis of the large volume of filters generated in the IMPROVE network, comparable in size to CSN. All IMPROVE polytetrafluoroethylene (PTFE) filter analyses are performed on-site at UC Davis, including gravimetric mass, elements by Energy Dispersive X-ray Fluorescence (EDXRF), and light absorption by hybrid integrating plate and sphere (HIPS) analysis. Over the years, we have developed and applied improvements to our analytical techniques and procedures, designed to enhance data quality.

Image: a photo of San Gorgonio Wilderness Aerosol Sampling Station.
Aerosol sampling station in San Gorgonio Wilderness, California. Credit: Scott Copeland

UC Davis offers outstanding expertise in EDXRF of PM samples. We have conducted extensive tests on our PANalytical Epsilon 5 instruments to characterize them fully for elemental analysis of IMPROVE filters. We have informed PANalytical of idiosyncrasies with their instruments that had escaped the notice of their engineers and others using their instrument for PM filter analysis. In recent years, we have produced EDXRF calibration standards that are (a) specially formulated for the low PM concentrations observed on IMPROVE samples, (b) produced by collecting known particle concentrations onto the filters used in the network, (c) prepared using the same samplers used to load these filters in the field, and (d) made with loadings similar to those observed on CSN filters.

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.

Image: a flow chart depicting the Air Quality Research Center's Organization.