Since 1971, EPA has maintained two standards for carbon monoxide: 35 parts per million (ppm) averaged over one hour and 9 ppm averaged over eight hours - not to be exceeded more than once per year. If design values are at or below the standard, then an area is in compliance. Design values correspond to an annual average of eight-hour concentrations and one-hour concentrations. 

Preliminary one-hour CO data from sites, parts per million, CST
Preliminary eight-hour CO data from sites, parts per million, CST
Air Quality Analysis for Carbon Monoxide - Quarterly Report
Air Pollutant Design Values - Quarterly Report
Flags in Air Monitoring Data

Technical issues can affect ability to deliver quality data. Access a table of symbols with explanation of the problems they represent.