Vertical Distributions of Particulate Air Pollution and Potentially Exposed Populations near urban Highways: Implications for Exposure Assessment

Abstract

Background: Due to data collection challenges, the vertical variation in population and particulate air pollution are typically not accounted for in exposure assessments, which may lead to misclassification of exposures based on height of residency. Aims: The objective of this work was to assess the vertical distribution of exposed populations and their relative potential exposures to air pollutants. Methods: The vertical distribution of the potentially highly exposed population (PHEP), defined as all residents within the 100-m buffer zone of the above-ground highways or the 200-m buffer zone of a tunnel exit, was estimated by four floor categories in Boston’s Chinatown (MA, USA) using a three-dimensional digital geography (3DIG) methodology. Vertical profiles of particle number concentration (7-1000 nm; PNC) and PM2.5 mass concentration were measured by hoisting instruments up the vertical face of an 11-story (35-m) building near the study area on multiple days. The concentrations from all the profiles (n=23) were averaged together for each floor category. PHEP was multiplied by the average PNC at each floor category to assess the exposures for near-highway populations. Results: As measurement height increased from 0 to 35 m PNC decreased by 7.7%, compared to 3.6% for PM2.5. PHEP was multiplied by the average PNC at each floor category to assess the exposures for near-highway populations. This result of PHEP multiplied by PNC (residents × particles/cm3) suggested that adding vertical air pollution data could help to better define exposures for near-highway populations during certain meteorological conditions. Conclusion The results show that adding temporally-averaged vertical air pollution data had only a small effect on residential ambient exposures for our study population. Greater differences were observed when winds were from the northeast (off the highways).