Summary: Pursuant to a congressional request, GAO examined the Environmental Protection Agency's (EPA) use of pollution concentration estimates obtained from air quality dispersion models in carrying out its responsibilities under the Clean Air Act, focusing on whether EPA policies: (1) on ambient air quality resulted in approval of increased emissions; and (2) ensured the consistent use of air quality models in regulatory decisions.
GAO found that: (1) the EPA policy that defined ambient air as that portion of the atmosphere, external to buildings, which had public access, resulted in higher emissions limits than otherwise permitted; (2) EPA did not consider any air above company-controlled property as ambient air and exempted it from Clean Air Act requirements for air quality standards; (3) EPA stretched some policy decisions to allow some sources to increase emissions by acquiring additional land and restricting public access to it; and (4) there were four instances of noncompliance with EPA-recommended modelling policies and procedures, since EPA guidelines pertaining to model calibration were not sufficiently detailed to promote consistent understanding among model personnel.
