40 CFR § 51.150 - Classification of regions for episode plans.
(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/m 3 (0.04 ppm) annual arithmetic mean; 455 µg/m 3 (0.17 ppm) 24-hour maximum.
(2) Particulate matter—95 µg/m 3 annual geometric mean; 325 µg/m 3 24-hour maximum.
(3) Carbon monoxide—55 mg/m 3 (48 ppm) 1-hour maximum; 14 mg/m 3 (12 ppm) 8-hour maximum.
(4) Nitrogen dioxide—100 µg/m 3 (0.06 ppm) annual arithmetic mean.
(5) Ozone—195 µg/m 3 (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/m 3 (0.02–0.04 ppm) annual arithmetic mean; 260–445 µg/m 3 (0.10–0.17 ppm) 24-hour maximum; any concentration above 1,300 µg/m 3 (0.50 ppm) three-hour average.
(2) Particulate matter—60–95 µg/m 3 annual geometric mean; 150–325 µg/m 3 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.