Rule 17.8.212 - AMBIENT AIR QUALITY STANDARDS FOR CARBON MONOXIDE(1) No person shall cause or contribute to concentrations of carbon monoxide in the ambient air which exceed any of the following standards: (a) Hourly average: 23 ppm, hourly average, not to be exceeded more than once per year.(b) Eight-hour average: 9 ppm, eight-hour average, not to be exceeded more than once per year.(2) Measurement method: For determining compliance with this rule, carbon monoxide shall be measured by the nondispersive infrared method, as more fully described in 40 CFR Part 50, Appendix C (1979), or by an approved equivalent method.NEW, 1980 MAR p. 2399, Eff. 8/15/80; TRANS, from DHES, 1996 MAR p. 2285.75-2-111, 75-2-202, MCA; IMP, 75-2-202, MCA;