Concentrations of submicrometre particles from vehicle emissions near a major road

As part of a program of study to assess the exposure risks related to particulate matter in the outdoor environment, number concentrations of particles from vehicle emissions were measured at increasing distances from a major road. Particles in the size range from 0.015 to 0.697 μm were measured with the scanning mobility particle sizer (SMPS) and in the size range from 0.5 to 20 μm, with the aerodynamic particle sizer (APS). In addition to number concentration measurements, an approximation of PM2.5 fraction was obtained using a DustTrak (simple photometer). The measurements conducted at distances from the road ranging from 15 to 375 m showed, that for conditions where the wind is blowing directly from the road, the concentration of fine and ultrafine particles decays to around half of the maximum (measured at the closest point to the road) at a distance of approximately 100–150 m from the road. For the wind blowing parallel to the road, the reduction to half of the concentration occurs at 50–100 m. There is no effect on total particle number concentration at a distance greater than 15 m from the road when the wind is blowing towards the road and away from the sampling points. Total number concentrations of larger particles measured were not significantly higher than the average values for the urban environment, and decrease with distance from the road, reaching about 60% at 150 m from the road for wind from the road. PM2.5 levels also decrease with distance to around 75% for wind from the road and to 65% for wind parallel to the road, at a distance of 375 m.