The 5 Worst Environmental Threats To Their Health, ' Natural Resources Defense Council, 1997. Clean Air Act Issues in the 107th Congress, ' Congressional Research Service, bulky June 3, 2002, by James E. McCarthy, Resources, Science, and Industry Division, Library of Congress. Final Report: ' major Air Quality Trends. Environmental Protection Agency, ' Prepared for the Foundation for Clean Air Progress by Meszler Engineering Services, Abingdon, MD, September 1, 2004. National Ambient Air Quality Standards ', Sierra Club, seen October 2006.