Each plan for a Priority I region must include a contingency plan which must, as a minimum, provide for taking action necessary to prevent ambient pollutant concentrations at any location in such region from reaching the following levels:
Sulfur dioxide-2.620 [MICRO]g/m3 (1.0 ppm) 24-hour average.
PM10-600 micrograms/cubic meter; 24-hour average.
Carbon monoxide-57.5 mg/m3 (50 ppm) 8-hour average; 86.3 mg/m3 (75 ppm) 4-hour average; 144 mg/m3 (125 ppm) 1-hour average.
Ozone-1,200 ug/m3 (0.6 ppm) 2-hour average.
Nitrogen dioxide-3.750 ug/m3 (2.0 ppm) 1-hour average; 938 ug/m3 (0.5 ppm) 24-hour average.
40 C.F.R. §51.151