This paper evaluates and interprets the available scientific and technical information that the EPA staff believes is most relevant to the review of primary (health) and secondary (welfare) National Ambient Air Quality Standards for Particulate Matter (PM) and presents staff recommendations on alternative approaches to revising the standards. The assessment is intended to bridge the gap between the scientific review in the EPA criteria document for particulate matter and sulfur oxides and the judgements required of the Administrator in setting ambient air quality standards for particulate matter. The major recommendations of the staff paper include the following: (1) that TSP be replaced by a new particle indicator that includes only those particles less than a nominal 10 micrometers (thoracic particles or PM(10)); (2) that the levels of both 24-hour and annual standards be revised; (3) that the statistical form of the standard should be changed; (4) consideration of a fine particle (less than 2.5 micrometers) secondary standard recognizing the advantages of combining any action with later decisions on acid deposition programs; and (5) consideration of secondary standards related to soiling and nuisance.

"January, 1982." "EPA/450-5-82-001."