Carbon monoxide, CO, is a highly toxic gas that can form during incomplete combustion. CO is colorless, odorless, and extremely harmful to the respiratory system. Overexposure to carbon monoxide can cause headache, dizziness, and sometimes death. It is of the greatest importance to measure CO emissions to maintain safety. During combustion most of the carbon burned reacts to form carbon dioxide, however some of the carbon stays in the intermediary stage as carbon monoxide. Excess levels of CO can be created due to incomplete combustion, poor burner design, bad firing conditions, or a leaky furnace. Motor vehicles, industries, and incomplete combustion are the primary producers of manmade CO.
As discussed earlier, some of the NOx reduction methods used in boilers bring with them an increase of CO emissions that may be regulated by the federal, state, and/or local environmental regulatory agencies.
This graph shows a traditional correlation between the NOx and CO emissions at different relative combustion temperatures.