Influence of roadway emissions on near-road PM2.5: Monitoring data analysis and implications

Abstract

Transportation projects must undergo a transportation conformity hot-spot analysis if they are designated as projects of local air quality concern (POAQC). We examined particulate matter 2.5 µm in aerodynamic diameter or smaller (PM2.5) concentrations measured in 2017 from 48 near-road monitoring sites across the U.S. Annual average PM2.5 increments, the difference between near-road and background PM2.5, were between 0.1 ± 0.2 µg/m3 and 2.0 ± 0.2 µg/m3 for sites without noted confounding factor(s). The highest PM2.5 increment from monitors 10 or more meters from the roadway was 1.4 ± 0.2 µg/m3. Using modeled national average exhaust emissions, and associated near-road contribution to PM2.5, the upper bound of2.0 ± 0.2 µg/m3 isprojected to decrease 30% from 2017 to2040, for the types of highways assessed here, assuming a roadway with 8% heavy-duty vehicles and constant traffic volumes. These results can help inform transportation conformity POAQC designations.