1. Air Quality A ct of 1967 Public Law 90- 148.
2. Air Quality Criteria Staff Report Prepared for the use of the Subcommittee on Air and Water Pol
3. lution Committee on Public Works United States Senate 1968.
4. "Air Quality Criteria for Particulate Matter " U.S. Public Health Service National Air Pollution
5. Control Administration Publication No . A P-49.