# National Ambient Air Quality Standards for Particulate Matter
> **Rule** · Final rule. · Published 1998-02-05 · 63 FR 6032
## Document
- **Document number:** 98-2878
- **Category:** air-emissions
- **Federal Register citation:** 63 FR 6032
- **CFR reference:** 40 CFR 50
- **Publication date:** 1998-02-05
- **EPA docket:** AD-FRL-5961-6
## Abstract

On July 18, 1997, EPA announced a supplemental comment period for the limited purpose of taking comments on certain field and laboratory test results associated with the development of the reference method (Appendix L of 40 CFR Part 50) for measuring particles with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers (PM<INF>2.5</INF>) in the ambient air. In the announcement, EPA indicated that upon the close of the comment period it would decide whether any further action would be appropriate. Having carefully assessed the comments received, EPA has determined that no further action is necessary.

## Source
- [Federal Register document](https://www.federalregister.gov/documents/1998/02/05/98-2878/national-ambient-air-quality-standards-for-particulate-matter)
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