Measurement of carbon monoxide concentrations in indoor and outdoor locations using personal exposure monitors

Abstract

On 15 dates, 5000 measurements of carbon monoxide (CO) were made in downtown commercial settings in four California towns and cities (San Francisco, Palo Alto, Mountain View, and Los Angeles), using personal exposure monitoring (PEM) instruments. Altogether, 588 different commercial settings were visited, and indoor and outdoor locations were sampled at each setting. On 11 surveys, two CO PEM's were carried about 0.15–6 m apart, giving 1706 pairs of observations that showed good agreement: the correlation coefficient was r = 0.97 or greater, and the average difference was less than 1 ppm (μL/L) by volume. Of 210 indoor settings (excluding parking garages), 204 (97.1%) had average CO concentrations less than 9 ppm (μL/L); of 368 outdoor settings, 356 (96.7%) had average CO concentrations less than 9 ppm (μL/L). For a given date and commercial setting, CO concentrations were found to be relatively stable over time, permitting levels to be characterized by making only brief visits to each setting. The data indicate that most commercial settings experience CO concentrations above zero indoors, because CO tends to seep into buildings from vehicular emissions outside. Levels in these locations usually are not above 5 ppm (μL/L) and seldom are higher than the U.S. health-related ambient air quality standards for CO. However, indoor garages and buildings with attached indoor parking areas are exceptions and can experience relatively high CO concentrations.