Section 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 [MICRO]g/m3 (0.04 ppm) annual arithmetic mean; 455 [MICRO]g/m3 (0.17 ppm) 24-hour maximum.(2) Particulate matter-95 [MICRO]g/m3 annual geometric mean; 325 [MICRO]g/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 [MICRO]g/m3 (0.06 ppm) annual arithmetic mean.(5) Ozone-195 [MICRO]g/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 [MICRO]g/m3 (0.02-0.04 ppm) annual arithmetic mean; 260-445 [MICRO]g/m3 (0.10-0.17 ppm) 24-hour maximum; any concentration above 1,300 [MICRO]g/m3 (0.50 ppm) three-hour average.(2) Particulate matter-60-95 [MICRO]g/m3 annual geometric mean; 150-325 [MICRO]g/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 FR 40668, Nov. 7, 1986, as amended at 58 FR 38822, July 20, 1993