CFR›Title 40›Chapter I›Part 58›Subpart C ContainsSection 58.20CorpusDaily eCFRDisplayed edition2026-04-27Last updated2026-04-27 Subpart C—Special Purpose Monitors Sections 58.20 § 58.20 Special purpose monitors (SPM). Source71 FR 61302, Oct. 17, 2006, unless otherwise noted. Previous B Subpart B—Monitoring Network Next D Subpart D—Comparability of Ambient Data to the NAAQS