Carbon monoxide (CO) is a colorless and odorless gas that can be lethal in high concentrations.
The National Ambient Air Quality Standards (NAAQS) for CO is 9 parts per million (ppm) on an eight-hour average or 35 ppm on a one-hour averaging period. CO occurs naturally by the decomposition of organic matter. The primary man-made source of CO is the incomplete combustion of fuels such as gasoline, natural gas, and wood. CO forms when there is insufficient oxygen present for complete combustion. The image, below, summarizes CO emissions for the counties that were former nonattainment and maintenance areas.
Carbon Monoxide Emissions Summary for Former Nonattainment and Maintenance Areas
The concentration of CO in the ambient air depends primarily on local weather conditions. High levels of CO can have acute health effects on humans by reducing the supply of oxygen in the bloodstream. Normally, blood cells transport oxygen to, and remove carbon dioxide from, every cell in the body. The blood cells are more attracted to CO than to oxygen. Therefore, exposure to high levels of CO results in oxygen deprivation to various parts of the body. CO exposure can aggravate existing conditions such as heart and lung diseases. At high levels, CO exposure can be fatal. Nationally, a few hundred fatalities a year occur due to high concentrations of CO, usually in poorly ventilated buildings, idling parked cars with faulty exhaust systems and residential fires. The danger from CO is greatest in unborn and newborn infants, the elderly, and those suffering from chronic illnesses.
- View the Health Impacts of CO.
Carbon Monoxide Standard Status
Salt Lake City, Ogden, and Provo were at one time designated as nonattainment areas for carbon monoxide. Due primarily to improvements in motor vehicle technology, Utah has been in compliance with carbon monoxide standards since 1994. Salt Lake City, Ogden, and Provo were redesignated to attainment status in 1999, 2001, and 2006 respectively. Redesignated areas are required to complete two 10-year maintenance periods to demonstrate the ability to maintain attainment of the standard. The maintenance period for Salt Lake City ended in 2019 and in 2021, Ogden completed its maintenance period, leaving only Provo in maintenance for carbon monoxide until 2026.
Carbon Monoxide Trends
CO maximum values tend to occur during wintertime inversions. In order to establish trends, we compare network maximum values to the frequency of wintertime inversions. CO pollution levels have significantly decreased over the past 20 years.
The 8-hour CO NAAQS(9 ppm) allows one exceedance of the standard per year. The calculation of the network maximum value (as shown in the plots) and the calculation of the NAAQS for each pollutant are not identical and differences between these measures should be noted.