eCFR Reference Browser

---

title: "40 CFR §51.150"

source: "https://www.ecfr.gov/current/title-40/section-51.150"

title_number: "40"

volume_number: "2"

chapter_number: "Unknown"

subchapter_code: "C"

subchapter_subject: "AIR PROGRAMS"

part_code: "51"

part_subject: "REQUIREMENTS FOR PREPARATION, ADOPTION, AND SUBMITTAL OF IMPLEMENTATION PLANS"

subpart_code: "H"

subpart_subject: "Prevention of Air Pollution Emergency Episodes"

section_number: "51.150"

section_subject: "Classification of regions for episode plans."

cfr_reference: "40 CFR 51.150"

title_name: "Title 40"

title_subject: "Protection of Environment"

parts_covered: "Parts 50 to 51"

revised_date: "Revised as of July 1, 2019"

publication_date: "As of July 1, 2019"

contains_description: "Containing a codification of documents of general applicability and future effect"

publication_info: "Published by the Office of the Federal Register National Archives and Records Administration as a Special Edition of the Federal Register"

---

(a)This section continues the classification system for episode plans. Each region is classified separately with respect to each of the following pollutants: Sulfur oxides, particulate matter, carbon monoxide, nitrogen dioxide, and ozone.

(b)Priority I Regions means any area with greater ambient concentrations than the following:

(1)Sulfur dioxide—100 µg/m3 (0.04 ppm) annual arithmetic mean; 455 µg/m3 (0.17 ppm) 24-hour maximum.

(2)Particulate matter—95 µg/m3 annual geometric mean; 325 µg/m3 24-hour maximum.

(3)Carbon monoxide—55 mg/m3 (48 ppm) 1-hour maximum; 14 mg/m3 (12 ppm) 8-hour maximum.

(4)Nitrogen dioxide—100 µg/m3 (0.06 ppm) annual arithmetic mean.

(5)Ozone—195 µg/m3 (0.10 ppm) 1-hour maximum.

(c)Priority IA Region means any area which is Priority I primarily because of emissions from a single point source.

(d)Priority II Region means any area which is not a Priority I region and has ambient concentrations between the following:

(1)Sulfur Dioxides—60-100 µg/m3 (0.02-0.04 ppm) annual arithmetic mean; 260-445 µg/m3 (0.10-0.17 ppm) 24-hour maximum; any concentration above 1,300 µg/m3 (0.50 ppm) three-hour average.

(2)Particulate matter—60-95 µg/m3 annual geometric mean; 150-325 µg/m3 24-hour maximum.

(e)In the absence of adequate monitoring data, appropriate models must be used to classify an area under paragraph (b) of this section, consistent with the requirements contained in § 51.112(a).

(f)Areas which do not meet the above criteria are classified Priority III.

§51.150 - Classification of regions for episode plans.