Travelers real-time exposure levels of fine particles in terms of mass and number concentrations were assessed across various transportation-related micro-environments in New York City. Travel modes and locations included cars, subways, intermodal facilities such as ground and underground transfer stations, urban street-sides, and parks. Both PM metrics were observed to be subject to substantial variations, introduced likely by direct exhaust from vehicles. Comparisons of PM2.5 exposure levels across location categories presented a significant discrepancy between the mass and number concentration in the same category. Specifically: (1) the highest particlenumber concentration occurred on urban street-side (60629#/cm3), where the PM2.5 mass concentration (29.60µg/m3) was below average level; (2) the PM2.5 mass concentration on subway trains was the second highest (39.36µg/m3), while the corresponding mean fine particle number concentration was the lowest (17416#/cm3) among locations studied. Mixed effect regression models for PM2.5 mass and fine particle number concentrations confirmed the statistical significance of such discrepancy. The correlation between Fine PM number and PM 2.5 mass concentration significantly varied across different types of locations, from as high as 0.7227(in-vehicle) and 0.4179(on-board subway train) to 0.0493(underground stations). This study showed thatfine particle number concentration can add an important dimension in understanding the effect of mobile source emission on travelers exposure to PM pollution.
Abstract