Atmospheric particle number concentration and size distribution in a traffic–impacted area

This study measured ambient particle number concentrations (PNC) and the particle number distributions (PND) in the urban area of Porto Alegre, Rio Grande do Sul, Brazil. The samples were analyzed using a NanoScan model 3910 from TSI (diameters between 10 and 420 nm) and were taken from sites with high density of vehicular traffic, including two roadsides, two traffic intersections, one street canyon and one urban background. Association of meteorological variables (temperature, relative humidity, solar radiation, wind direction, and wind speed) on nanoparticle concentrations was examined. The results indicated PNC averages between 4.85×104 cm–3 and 1.80×105 cm–3 for locations affected by vehicular traffic, wherein highest concentrations were observed at sites corresponding to traffic intersections. In addition, all sites studied showed a trimodal average PND, with the modes centered at ~14 nm, ~30 nm, and ~105 nm. PND was dominated by nucleation (44.9%) and Aitken (42.0%) modes being representative at the studied sites of the pollution originating from urban traffic, except at the urban background. Meteorological parameters and synoptic meteorological conditions contributed to the variation in the results between the sampled days in the same location.