Carbon monoxide levels in microenvironment types of four U.S. cities

Portable monitors were used to measure time-averaged personal exposure (10–30 min) to carbon monoxide. Data were collected from January through March 1981 in four cities where ambient carbon monoxide levels have been reported in excess of National Ambient Air Quality Standards: Stamford, CT; Los Angeles, CA; Phoenix, AZ; and Denver, CO. In each city, personal exposure were measured in three common microenvironment types (indoor, commuting, and residential driving) near fixed stations monitoring ambient levels of carbon monoxide. Measurements recorded at urban-residential fixed monitoring stations (excluding one station in Stamford) underrepresented the time-weighted mean of commuting and residential driving exposures by factors of 0.4 to 0.7. The highest mean commuting and residential driving exposures were found in Los Angeles (16.1 and 7.6 μL/L, respectively). Fixed monitoring stations in Los Angeles, Phoenix, and one station in Stamford overrepresented the time-weighted mean of indoor exposures by factors of 1.1 to 1.3. However, in Denver and another station in Stamford, urban stations underrepresented the mean of indoor exposures by factors of 0.4 to 0.8. The highest mean indoor exposure, 5.9 μL/L, was in Denver. In all four cities, regressing personal exposures on concurrent fixed-site concentrations for all recorded values and for values recorded during 8-h NAAQS exceedance time periods revealed no conclusive linear relationships.