Abstract
Carboxyhemoglobin (COHb) levels in blood are principally due to inhalation of carbon monoxide, although a low level (approximately 0.3%) of COHb is endogenous. A carboxyhemoglobin level above 1.5 % in non-smokers indicates exposure to CO in excess of the 10 mg/m3 air quality standard established under the Clean Air Act Amendments of 1970.
In most major U.S. cities, automobile emissions constitute the principal source of CO; in Chicago, according to EPA estimates,1 light duty vehicles are responsible for 69.3% of all CO emissions. Thus as new automobiles incorporating emission controls enter the automotive fleet and older, emission-uncontrolled automobiles are phased out, ambient CO concentrations should decline and corresponding reductions in blood carboxyhemoglobin levels of nonsmokers can be expected.