Carbon monoxide in the urban atmosphere: hazards to the pedestrian and the street-worker.

The carbon monoxide (CO) concentrations encountered by pedestrians and workers in the streets of a large metropolis were monitored by a reliable and sensitive portable detector (the Ecolyzer). Up to 1,000 observations per day were collected for several months during the summer and fall of 1973. The CO levels ranged from 10 to 50 ppm (varying with wind speed and direction, atmospheric stability, traffic density, and the height of nearby buildings). Much higher average concentrations were found in such adverse sites as poorly ventilated underpasses and underground garages. Street closures for a pedestrian mall reduced levels on the mall to around the general urban background withoug large increases in readings on adjoining streets. Many street-workers have little medical supervision, and for this reason the urban eight-hour CO ceilings may be a more appropriate air quality target than the usual industrial figure of 50 ppm. However, even the latter is sometimes exceeded on busy city streets.