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Carbon Monoxide (CO) Pollution in Outdoor Air

Table of Historical Carbon Monoxide (CO) National Ambient Air Quality Standards (NAAQS)

History of the National Ambient Air Quality Standards for CO
Final Rule/Decision Primary/ Secondary Indicator (1) Averaging Time Level (2) Form

1971

36 FR 8186
Apr 30, 1971

Primary and Secondary CO 1-Hour period 35 ppm Maximum, not to be exceeded more than once in a year (3)
8-hour period 9 ppm Maximum, not to be exceeded more than once in a year

1985

50 FR 37484
Sept 13, 1985

Primary standards retained, without revision; secondary standards revoked.

1994

59 FR 38906
Aug 1, 1994

Primary standards retained, without revision.

2011

76 FR 54294
Aug 31, 2011

Primary standards retained, without revision.

(1)  CO=Carbon Monoxide

(2) Units of measure are in parts per million (ppm).

(3) Second highest, non-overlapping 8-hour average concentration.

Learn more about setting and reviewing standards to control CO pollution.