Carbon monoxide is an odorless, colorless gas resulting from incomplete combustion of fossil fuel burning. It is a product of the incomplete burning of carbon in fuels from automobiles, buses, trucks, small engines, boilers and some industrial processes. High concentrations can be found in confined spaces such as parking garages, poorly ventilated tunnels, or traffic intersections, especially during peak hours.
Connecticut has been redesignated to attainment for the National Ambient Air Quality Standard (NAAQS) for carbon monoxide statewide since 1999. Previously, three regions had been designated nonattainment, including the Hartford, New Haven and Fairfield County regions. The Hartford Region was officially redesignated to attainment effective January 2, 1996; the New Haven region became attainment December 4, 1998; while the Fairfield County region (i.e., the CT portion of the New York/New Jersey/Connecticut area) became attainment effective May 10, 1999. The remaining regions of the State continue to be designated as attainment.