Section 243.123  Carbon Monoxide

a)         The 1971 eight-hour and one-hour primary NAAQS for carbon monoxide are as follows:

1)         An eight-hour average concentration of 9 ppm (10 mg/m³), not to be exceeded more than once per year; and

2)         A one-hour average concentration of 35 ppm (40 mg/m³), not to be exceeded more than once per year.

b)         The levels of carbon monoxide in the ambient air must be measured by a method that fulfills either of the following requirements:

1)         An FRM based on appendix C of 40 CFR 50, incorporated by reference in Section 243.108, and designated by USEPA and listed in the List of Designated Methods, incorporated by reference in Section 243.108; or

2)         An FEM designated by USEPA and listed in the List of Designated Methods, incorporated by reference in Section 243.108.

c)         An eight-hour average concentration must be considered valid if at least 75 percent of the hourly average for the eight-hour period is available.  In the event that only six-hour (or seven-hour) averages are available, the eight-hour average must be computed on the basis of the hours available using six (or seven) as the divisor.

d)         When summarizing data for comparison with the standards, averages must be stated to one decimal place.  Comparison of the data with the levels of the standards in ppm must be made in terms of integers with fractional parts of 0.5 or greater rounded up.

BOARD NOTE:  Derived from 40 CFR 50.8.

(Source:  Amended at 44 Ill. Reg. 14223, effective August 18, 2020)