This final rule revises the 40 CFR part 58 ambient air quality surveillance regulations to include provisions for PM<INF>2.5</INF> (particulate matter with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers), as measured by a new reference method being published in 40 CFR part 50, Appendix L, elsewhere in this issue of the Federal Register or by an equivalent method designed in accordance with requirements being promulgated in 40 CFR part 53. In addition, this rule also revises existing ambient air quality monitoring requirements for PM<INF>10</INF> (particles with an aerodynamic diameter less than or equal to 10 micrometers). These revisions address network design and siting, quality assurance (QA) and quality control (QC), operating schedule, network completion, system modifications, data reporting, and other monitoring subjects.