Dispersion of traffic-related exhaust particles near the Berlin urban motorway – estimation of fleet emission factors

Abstract

Abstract. Atmospheric particle number size distributions of airborne particles (diameter range 10-500 nm) were collected over ten weeks at three sites in the vicinity of the A100 urban motorway in Berlin, Germany. The A100 carries about 180 000 vehicles on a weekday. The roadside particle distributions showed a number maximum between 20 and 60 nm clearly related to the motorway emissions. The average total number concentration at roadside was 28 000 cm −3 with a total range of 1200-168 000 cm −3 . At distances of 80 and 400 m from the motorway the concentrations decreased to mean levels of 11 000 and 9000 cm −3 , respectively. An obstacle-resolving dispersion model was applied to simulate the 3-D flow field and traffic tracer transport in the urban environment around the motorway. By inverse modelling, vehicle emission factors were derived that are representative of a fleet with a relative share of 6% lorry-like vehicles, and driving at a speed of 80 km h −1 . Three different calculation approaches were compared, which differ in the choice of the experimental winds driving the flow simulation. The average emission factor per vehicle was 2.1 (±0.2) · 10 14 km −1 for particle number and 0.077 (±0.01) · 10 14 cm 3 km −1 for particle volume. Regression analysis suggested that lorry-like vehicles emit 123 (±28) times more particle number than passenger car-like vehicles, and lorry-like vehicles account for about 91% of particulate number emissions on weekdays. Our work highlights the increasing applicability of 3-D flow models in urban microscale environments and their usefulness for determining traffic emission factors.

Size Resolved Particle Number Emission Factors of Motorway Traffic Differentiated between Heavy and Light Duty Vehicles

“…Only two other studies (Birmili et al, 2009;Wang et al, 2010) conducted similar analyses of emissions factors of HDV and LDV at motorways as conducted in this study. For HDV a steep increase of the emission factor for particles < 50 nm was detected with the highest emission factor at the lowest particle diameter around 15 nm.…”

“…The first mode is below the lower detectable particle size with the SMPS (< 14 nm), the second mode around 50-70 nm, and the third mode around 200 nm. Comparable modes were found by Jamriska and Morawska (2001), Zhu et al (2002), Rosenbohm et al (2005), Birmili et al (2009) andWang et al (2010). Zhu et al (2002) measured the particle size distribution in the size range 6-220 nm at different distances (from 17 m to 300 m) to the motorway Interstate 710 in Downey, California.…”

“…Only a few studies are available calculating particle size dependent emission factors (Birmili et al, 2009, Wang et al, 2010. The determination of size dependent real world EF allows the calculation of particle size dependent traffic emission contributions and its linkage to toxicological and epidemiological studies.…”

“…Most studies which calculated number emission factors were conducted in tunnel systems and the tunnel ventilation was used to calculate dilution conditions (Kirchstetter et al, 1999;Gidhagen et al, 2003;Kristensson et al, 2004;Geller et al, 2005;Ban-Weiss et al, 2010). Furthermore, different model systems were applied for the calculation of the dilution of the exhaust emissions (Jamriska and Morawska 2001;Corsmeier et al, 2005;Birmili et al, 2009;Wehner et al, 2009) or the NO x tracer method was used for the calculation of the dilution, like by Imhof et al (2005) and Wang et al (2010).…”

Transport impacts on atmosphere and climate: Land transport

“…Size resolved measurement data reveal that about 90% of these particles have an aerodynamic diameter below 0.5 mm (e.g. Birmili et al, 2009;Ketzel et al, 2004Ketzel et al, , 2007Samaras et al, 2005) and hence are in the health relevant size segment. Vehicle emissions of air pollutants strongly depend on the exhaust emission control devices and their operation efficiency in a given year.…”