Clearing the Air: Battelle Addresses Regional Haze Issues

The U.S. Environmental Protection Agency (EPA) has designated 156 Federal Class I areas in the U.S. on the basis of their scenic beauty. The Class I areas consist of national parks and wilderness areas, such as Yosemite National Park and the Florida Everglades. To protect the beauty of such areas, the 1977 Clean Air Act set forth a national goal for the “prevention of any future, and the remedying of any existing, impairment of visibility in Federal Class I areas which impairment results from manmade air pollution.” Although both natural and manmade factors can reduce visibility in scenic areas, a key factor is the regional haze of tiny airborne particles caused by widespread air pollution sources. In 1999, EPA implemented the Regional Haze Rule to begin the restoration of visibility in scenic areas to a natural level. Specifically, the Rule requires that by the year 2064 natural background visibility conditions be achieved in Class I areas.

Guiding States in Responding to Regional Haze

Under support of EPA’s Office of Air Quality Planning and Standards, staff from Battelle's Atmospheric Science and Applied Technology department are preparing two guidance documents to aid states in developing State Implementation Plans (SIPs) for responding to the Regional Haze Rule. One document addresses the estimation of the natural background visibility conditions, which is the goal of the Rule, the other addresses how to track progress toward attainment of the visibility goals. These guidance documents highlight the key requirements and milestones of the Regional Haze Rule, define the methods for calculating visibility reduction, summarize procedures for handling pollution data, and offer procedures for comparing five-year periods to evaluate changes in visibility impairment.

Key Topics in the Regional Haze Rule Guidance Documents: Methods for calculating light extinction from the data on particulate matter components measured in the IMPROVE (Interagency Monitoring for Protected Visual Environments) ambient monitoring network, How to take into account the effect of relative humidity on light extinction calculations, Steps to take when the data for a particulate matter component is missing from a sample, Data completeness requirements for calculating annual averages or values for the 20 percent worst visibility or 20 percent best visibility days at a monitoring site, Methods for selecting the 20 percent worst visibility and 20 percent best visibility days, Procedures for calculating baseline visibility for the 2000-2004 period, Procedures for calculating current visibility conditions for successive five year periods, and Procedures for comparing successive periods in order to evaluate progress.

The guidance documents are designed to provide relevant agencies with a consistent way to evaluate changes in visibility impairment in Class I areas. However, the information provided is guidance only, and users are encouraged to develop alternative procedures if they provide improved assessments of visibility. Currently, states are in the initial 2000-2004 baseline period of the Regional Haze Rule. For this phase, monitoring data is used to establish current baseline visibility conditions, in order to plan how rapid an improvement is needed to achieve natural background conditions by 2064. The improvement in visibility is to be judged by comparing the 20 percent worst visibility days, over successive five-year periods.

The guidance documents are currently undergoing final revision after successive rounds of public and scientific peer review and will be released by EPA later this year. For more information contact Thomas Kelly at (614) 424-3495, kellyt@battelle.org.

Regional Haze Source Apportionment

Regional haze can partially be assessed based on reconstructed light extinction, a measure which includes the light scattering contributions of measured sulfate, nitrate, organic carbon, soil particles, coarse particles, and the light absorption by aerosol. Properly weighted for relative scattering efficiencies and including the effect of relative humidity, this calculation provides a consistent metric for tracking visibility at monitoring sites. Source apportionment represents one manner to identify pollution emission sources and to quantify their contributions to regional haze.

A recent report (May 2002) prepared by members of Battelle’s Statistics and Data Analysis Systems department for the Mid-Atlantic/Northeast Visibility Union and Midwest Region Planning Organization addressed the problem of identifying emission sources and quantifying their contribution to fine particulate matter (PM2.5) and regional haze. In response to the guidelines set forth by the Regional Haze Rule, the study’s goals were to identify the 20 best and 20 worst visibility days in non-urban portions of the midwestern and eastern U.S. based on receptor observations.

The study focused on 10 sites from the IMPROVE network and six sites from the Clean Air Status and Trends Network (CASTNET). Secondary goals of the study included evaluating and screening available ambient measurements for modeling air pollution with receptor models, evaluating existing emissions databases for use in identifying output from the models, and assessing output from the models.

After performing necessary data quality and assurance activities, the data from each site, along with monthly relative humidity factors, were used to calculate reconstructed light extinction. Two state-of-the-art source apportionment models (Positive Matrix Factorization {PMF} and UNMIX) then were used to attempt to identify contributors to the regional haze. Preliminary identifications were assigned to most of the sources detected with PMF. At each site, a “secondary sulfate source” was determined to be the largest contributor to regional haze during the 20 percent worst days. In some cases, a “secondary organic compound” also was found to be strongly associated with the 20 percent worst days. For more information, contact David Wendt at (614) 424-7653 or wendtd@battelle.org.