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

W Birmili,B Alaviippola,T Tuch,A Schacht,J Borken-Kleefeld,O Knoth,D Hinneburg

doi:10.5194/acp-9-2355-2009

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) · 1014 km−1 for particle number and 0.077 (±0.01) · 1014 cm3 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.

Highlights

Clear associations have been found between ambient particular matter (PM) and adverse health effects in humans (Kunzli et al, 2000; Pope et al, 2002)
It is a hypothesis that the health effects observed in broad parts of the population may be caused by a particular sub-fraction of PM rather than total PM mass (HEI, 2002)
A number of arguments point towards the possible induction of health effects by traffic aerosols: The mere small size of ultrafine particles could lead to a deep penetration into the lung, and subsequent irritations in the alveolar region, where ambient air is in exchange with the blood circulation (Seaton et al, 1995)

Summary

Introduction

Clear associations have been found between ambient particular matter (PM) and adverse health effects in humans (Kunzli et al, 2000; Pope et al, 2002). A number of arguments point towards the possible induction of health effects by traffic aerosols: The mere small size of ultrafine particles could lead to a deep penetration into the lung, and subsequent irritations in the alveolar region, where ambient air is in exchange with the blood circulation (Seaton et al, 1995). Particulate traffic emissions contain high numbers of insoluble particles, such as diesel soot (Weingartner et al, 1997; Rose et al, 2006). Such particles are only poorly removed from the lung. Engine emissions tend to contain organic toxins (PAHs) and a myriad of other so far unidentified micropollutants (e.g., Spurny, 1999; Gelencser, 2004)

Methods

Findings

Discussion

Conclusion