Vertical and horizontal concentration distributions of ultrafine particles near a highway

Assessment of human health effects associated with particles requires knowledge of their emission factors and dispersion characteristics. A field experiment was recently conducted to determine the vertical and horizontal dispersion of particles emitted from highway vehicles. The measurements were conducted near the highway I-90 in Liverpool (NY) over a flat terrain, where the predominant dispersion mechanisms were atmospheric turbulence and traffic-produced turbulence (TPT). Real-time vertical number concentration measurements were made using several identical water condensation particle counters (WCPCs) over nine heights up to 10 m. Three sites (at distances of 15, 50, and 100 m from the highway) were selected to study the concentration profiles. As previously observed at other sites, particle concentrations decay with increasing distance from highways. At the site closest to the highway, the highest concentration was observed under a downwind condition with the average wind speed similar to 1 ms(-1). Under conditions of low wind speed, particles from the highway are observed even at locations upwind of the highway. The vertical profiles of particle concentrations at different measurement locations varied with wind speed, wind direction and distance to the highway. The correlation coefficients of particle concentrations at different elevations reveal the characteristics of the plume dispersion and its development in the horizontal and vertical directions. The experimental results suggest the need for three-dimensional modeling of particle plumes from highways and the importance of considering TPT for accurate prediction of particle dispersion near roadways. (C) 2011 Elsevier Ltd. All rights reserved.