# National Ambient Air Quality Standards for Particulate Matter
> **Rule** · Final rule; extension of supplemental public comment period. · Published 1997-08-15 · 62 FR 43642
## Document
- **Document number:** 97-21697
- **Category:** air-emissions
- **Federal Register citation:** 62 FR 43642
- **CFR reference:** 40 CFR 50
- **Publication date:** 1997-08-15
- **EPA docket:** AD-FRL-5875-8
## Abstract

EPA is announcing an extension of the supplemental comment period that was first announced on July 18, 1997 for the limited purpose of taking comment on certain laboratory and field test data and related reports associated with the development of the reference method (Appendix L of 40 CFR part 50) for measuring PM<INF>2.5</INF> in the ambient air.

## Source
- [Federal Register document](https://www.federalregister.gov/documents/1997/08/15/97-21697/national-ambient-air-quality-standards-for-particulate-matter)
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