Carbon monoxide (CO) a colorless and odorless gas, which at high levels can be harmful to humans by impairing the amount of oxygen transported in the bloodstream to critical organs. Although high concentrations of CO are more of a concern indoors, emissions outdoors, particularly in developing countries can be high. New evidence also reveals that long-term exposure to low concentrations is also associated with a wide range of health effects. The main sources of ambient CO include motor vehicle exhaust and machinery that burn fossil fuels.


Carbon Monoxide

Time-weighted average

10,000 (8.1) - 40,000 (32) µg/Nm3 (ppm)

Averaging time

8 hours - 1 hour

Time –weighted average Averaging Time Number of allowable exceedances
32 ppm 1-hour None
8.1 ppb 8-hour None
Number of allowable exceedances