Vertical distribution of aerosol particles and NO x close to a motorway

Abstract: In May 2001, the large-scale field project BAB II was performed at the highly frequented motorway BAB (Bundesautobahn) A656 with two traffic lanes in each direction between the German cities Heidelberg and Mannheim. Extensive measurements of air pollutants were carried out on both sides of the motorway. In a distance of 60m (north side) and 84m (south side) to the traffic lanes, two 52-m-high towers were installed, at which electrically powered elevators were fixed. In these elevators, two NO x analysers, an Electrical Low Pressure Impactor (ELPI; measurement of the particle number size distribution in the diameter range between 30nm and 10μm) and a Diffusion Charger (DC; measuring the particle surface area concentration), were operated to record continuous vertical profiles from 5 to 50m above the earth''s surface. On the upwind side, particle number and surface area concentration as well as NO x values were constant over the entire height profile. On the downwind side, increased concentrations appeared in the near-ground range: in the forenoon, a monotonous decrease in pollutant concentrations with increasing height was found, while around noon the concentration maximum of the particles was slightly shifted to 10m above ground. This height dependence was found for two different size ranges, i.e., for particles with (consisting of soot particles and nucleation mode particles formed by condensation as a result of cooling of the exhaust gas after emission), and for coarse particles (, abrasion and resuspension products). In the size range between 300 and 700nm, no height dependence was found, corroborating the fact that motor traffic emits only few particles in this size range. On the downwind side of the motorway, only background concentrations were measured above 25m. The results of the profile measurements were confirmed by stationary measurements of particle size distributions with Scanning Mobility Particle Sizers (SMPS) at various heights. A good correlation between particle surface area and NO x concentration was observed. Vehicle emission factors were determined for the particle surface area, number and volume of several size ranges. [Copyright &y& Elsevier]