C.F.R. » Title 40 » CHAPTER I—ENVIRONMENTAL PROTECTION AGENCY › SUBCHAPTER C—AIR PROGRAMS › PART 50—NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY STANDARDS

40 C.F.R. § 50.18

National primary ambient air quality standards for PM2.5

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(a) The national primary ambient air quality standards for PM2.5 are 12.0 micrograms per cubic meter (µg/m 3) annual arithmetic mean concentration and 35 µg/m 3 24-hour average concentration measured in the ambient air as PM2.5 (particles with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers) by either:

(1) A reference method based on appendix L to this part and designated in accordance with part 53 of this chapter; or

(2) An equivalent method designated in accordance with part 53 of this chapter.

(b) The primary annual PM2.5 standard is met when the annual arithmetic mean concentration, as determined in accordance with appendix N of this part, is less than or equal to 12.0 µg/m 3.

(c) The primary 24-hour PM2.5 standard is met when the 98th percentile 24-hour concentration, as determined in accordance with appendix N of this part, is less than or equal to 35 µg/m 3.

[78 FR 3277, Jan. 15, 2013]
Notes of Decisions
Cited in 4 cases (1 in the last 5 years), 2014–2024 · leading case: Nucor Steel-Arkansas v. Pruitt
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Nucor Steel-Arkansas v. Pruitt (2017) dcd “Big River Steel has attempted to participate in this lawsuit in several respects.”
Sierra Club v. Envtl. Prot. Agency (2019) cadc “" 40 C.F.R. § 50.18 (a) ; see also id. pt. 50, app.”
City of Brockton v. Energy Facilities Siting Board (No. 1) (2014) mass “See 40 C.F.R. § 50.18 (2013); 78 Fed. Reg. 3,086 -01 (2013).”
Maryland Chapter of the Sierra Club v. Federal Highway Adminstration (2024) mdd “14) (citing AR 196544-55; 40 C.F.R. § 50.18 ). The Furthermore, the Agencies are not required to show that the Preferred Alternative has the least amount of adverse impact on EJ communities.”
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