Ultrafine particle number concentrations and size distributions around an elevated highway viaduct

High-traffic roadways substantially contribute to UFP number concentrations and size distributions within many urban areas and may contribute to excess urban mortality and morbidity. A number of previous studies have quantified near-road concentrations of UFP and the decay with horizontal displacement from highways and indicated rapid decreases to near background levels within 300 m of the line-source. However, the majority of those previous studies have focused on ground-level highways and so herein we present data from sampling perpendicular to an elevated highway viaduct. Measurements taken during morning rush hour and non-rush hour periods using a bicycle-mounted TSI Nanoscan scanning mobility particle sizer within distances of 200-300 m from the freeway are lower than those from previous studies of ground-level highways, but the decay of UFP number concentrations with distance from the highway is more gradual. A linear mixed-effects model indicates only distance from I-81 and air temperature are significant predictors of near I-81 UFP concentrations, but wind speed and direction and vehicle counts on the street where the measurements were conducted exhibit the expected sign of dependence.