The impact of urban street canyons on population exposure to traffic-related primary pollutants

The relationship between emissions and population exposures to traffic-related air pollutants is a necessary component of any assessment of mobile source control strategies. In this analysis, part of the New York Metropolitan Exposure to Traffic Study (NYMETS), we simulated atmospheric dispersion and population exposure in densely populated street canyons in mid-town Manhattan. We estimated population exposure using the concept of an intake fraction (iF), defined as the fraction of material released from a source that is eventually inhaled or ingested by a population. We applied the Operational Street Pollution Model (OSPM) for inert pollutants (e.g., CO, PM2.5), reactive pollutants (e.g., NO and NO2), and ultrafine particles. Concentrations were linked with different subpopulations, including residents, workers, and pedestrians, incorporating time-activity patterns and differential breathing rates. For the base case scenario, the total iF for a 100-m-long street canyon including the contribution of different subpopulations is on the order of 10−3. Daytime office workers and pedestrians contribute most to the overall iF, together contributing over 80% for all pollutants. Univariate sensitivity analyses show that iFs are sensitive to the street configuration and slightly sensitive to traffic volume, speed, and percent of trucks. Our iF estimates are similar in magnitude to those found for indoor environmental tobacco smoke and are substantially higher than previous mobile source estimates, mainly due to the higher population density in street canyons. Our findings emphasize the importance of controlling emissions in urban street canyons, and the need to study high-resolution near-source exposures for primary pollutants in urban settings to inform cost–benefit analyses.