EPA signed a proposed rule on January 31, 2011, that would increase monitoring of carbon monoxide (CO) near busy roadways while retaining existing CO air quality standards, which the agency maintains “provide the requisite protection of public health with an adequate margin of safety . . . .” The proposed rule would, when finalized, revise 40 C.F.R. Parts 50, 53 and 58. The primary, health-based standards for CO, set in 1971, are 9 parts per million (ppm) averaged over eight hours and 35 ppm averaged hourly. There are no secondary CO air quality standards.

The proposed rule would expand monitoring for CO along busy roadways in urban areas with populations of 1 million or more. EPA estimates that the rule would add 77 monitors near roadways in 53 cities. The proposed rule would also allow the agency’s regional administrators to require additional monitoring on a case-by-case basis in areas affected by large stationary CO sources or meteorological or topographical factors that increase the pollutant’s concentrations. EPA will accept comments on the proposed rule for 60 days after it is published in the Federal Register.