AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Rethinking Near-road PM2.5 in US Cities
RAJ LAL, Anu Ramaswami, Armistead G. Russell, Georgia Institute of Technology
Abstract Number: 14 Working Group: Urban Aerosols
Abstract Emissions from mobile sources have historically been an important anthropogenic contributor to ambient air pollution leading to high levels of air pollution near major roadways. The US EPA recently implemented the Near-Road (monitoring) Network to measure NO2 concentrations by high-traffic roadways in urban centers throughout the US, as these locations were believed to characterize worst-case human exposures to traffic-related pollutants. Many near-road sites also include CO and PM2.5 measurements, which along with the NO2 observations, were compared against companion non-near-road monitors located within a 10 mile (~city scale) radius. Unexpectedly, we found no statistical difference (α = 0.05) in PM2.5 concentrations between the near-road and non-near-road urban sites (δ = 0.33 (-0.08-0.74) µg m-3, n=80 comparisons), while NO2 and CO levels, on average were significantly higher at the near-road sites versus the non-near-road urban sites by 5.5 (4.2-6.7) ppb and 0.10 (0.05-0.12) ppm, respectively. The average PM2.5 difference (~4%) is considerably lower than previously found, and in 31 of the 80 monitor comparisons PM2.5 is actually higher at the non-near-road urban sites relative to its near-road pair. Cleaner vehicle fleets, decreased formation rates in the near-road environment, the prevalence of other non-vehicular sources of emissions, the displacement of non-mobile sources in the near-road environment, and reactive PM transport wherein formation of secondary PM from on-road emissions occurs further downwind (i.e., away from the road) are likely responsible for this finding. Given that PM2.5 concentrations dominate air pollution-related health risks, these findings across 22 major US cities suggest we rethink our assumptions about elevated PM-related health risk exposures in the near-road environment.