In situ measurements of particle number concentration, chemically resolved size distributions and black carbon content of traffic-related emissions on German motorways, rural roads and in city traffic

In-situ measurements of various properties of traffic-related aerosol particles have been performed with a mobile laboratory. The measured aerosol quantities include particle chemical composition (sulfate, nitrate, total organic matter, ammonium, black carbon) as well as particle size distributions covering diameters from 10 to 300 nm, and total particle number density. Additionally, gas phase emissions (CO2, NO, NO2) were monitored. We performed six measurement drives in the vicinity of the city of Aachen (population ca. 260,000) at 50.8°N, 6.1°E in Germany on motorways, rural roads, and in the inner city of Aachen in June 2005. The results indicate that the main influence of traffic on the aerosol properties results in soot particles coated with organic matter, having a modal diameter around 100 nm (“soot mode”). The abundance of these particles was found to be highest in the inner city traffic. Nucleation mode particles (around 30 nm) have been observed occasionally during truck chasings on motorways. These particles consisted mainly of organic compounds but included possibly also a sulfuric acid core. Data observed under “motorway background” conditions were similar to the rural regional road data. Highest number concentrations have been observed during truck chasings. Comparison between non-refractory (here with respect to 600 °C) and total particle volume indicated a higher contribution of refractory material under all traffic-influenced conditions compared to rural road data. Fuel specific emission ratios were derived for a subset of 18 truck-chasing experiments, yielding (8.3±5.8)×1015 kg−1 for particle number, 224±136 mg kg−1 for black carbon, 125±125 mg kg−1 for organic matter, 17±12 g kg−1 for NO and 18±14 g kg−1 for NOx (mean values and standard deviations).