Federal reference and equivalent methods for measuring fine particulate matter

In the national ambient air quality standards specified by the U.S. Environ mental Protection Agency in the Code of Federal Regulations, new standards were established for particulate matter on July 18, 1997. The new particula te matter standards specify mass concentration as the indicator for fine pa rticulate matter (aerodynamic diameter of 2.5 mum or less). Ambient measure ments for the new particulate standard must be performed by a new federal r eference method as specified in the Code of Federal Regulations or by an al ternative measurement method that has been designated by the Environmental Protection Agency as an equivalent method. The new particulate reference me thod is a 24 h integrated sample collected from the ambient air and analyze d gravimetrically. The reference method is explicitly specified using a com bination of design- and performance-based criteria. Additional requirements listed in the Code of Federal Regulations address conditioning, handling, and weighing of the sample filter, which are performed manually. For altern ative measurement techniques that do not meet the qualifications of the ref erence method, the Environmental Protection Agency defines three classes of candidate PM2.5 equivalent methods based on the measurement technique used and its degree of similarity to the reference method specifications.