Under the Clean Air Act, special protection from adverse

air quality impacts is afforded certain national parks and

wilderness areas, through the Prevention of Significant

Deterioration (PSD) program. These areas have been designated

as Class I areas, and as such, increases of pollutant levels in

these areas are strictly limited. Furthermore, the Federal

Land Manager (FLM) of the Class I area is given an affirmative

responsibility to ensure that Air Quality Related Values

(AQRVs) are not adversely impacted. [The FLMs of the Class I

areas are the U.S. Forest Service (USFS), the National Park

Service (NPS), and the U.S. Fish and Wildlife Service (FWS).]

Air quality models are one of the primary tools used to assess

the impacts from sources of air pollution on both the

established PSD increments and the AQRVs. Steady-state models

are generally used for PSD analyses, however, as the PSD

program has developed, the need for more sophisticated models

to assess air quality impacts in Class I areas, from sources at

relatively greater distances from the Class I areas, has

arisen. In some areas, the FLMs have asserted that Class I

areas have been adversely affected by air pollution and that

new sources of pollution over a broad area are further harming

the resource. The absence of any recommended long range

modeling techniques has left permitting authorities without the

means to assess the assertions of the FLMs. The Environmental

Protection Agency (EPA) and the FLMs have undertaken various

model development efforts to address the air quality impacts of

pollution transported over relatively long distances. The

Interagency Workgroup for Air Quality Modeling (IWAQM) was

formed to coordinate the independent modeling efforts of the

EPA and the FLMs so that a consistent, technically credible

approach can be recommended and used.


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