On August 31, 2011, the EPA promulgated a rule retaining the current primary national ambient air quality standard (“NAAQS”) for carbon monoxide (“CO”).  Review of National Ambient Air Quality Standards for Carbon Monoxide, 76 Fed. Reg. 54,294 (August 31, 2011) (to be codified at 40 C.F.R. pts. 50, 53 & 58).  The EPA has also declined to set a secondary standard.  Thus the CO NAAQS remains the same as when it was first created in 1971—9 ppm with an 8 hour averaging time, and 35 ppm with a 1 hour averaging time, neither to be exceeded more than once a year.  This rule review was conducted under EPA’s program of periodically reviewing the NAAQS.  An August deadline was set for the rule by a court order.  

EPA also made “editorial” changes to the “Federal Reference Method” for CO analyzers.  These changes are not intended to be be substantive, but rather reflect improvements to analysis devices that have occurred since the rule was promulgated in the 1970s.  The EPA is also making changes to the monitoring network.  It will require CO monitors at near-road locations where it has already required NO2 monitors.