Measurements of spatial variability of sub-micron particle number concentrations perpendicular to a main road in a built-up area.

A six-week field study was conducted to determine spatial and temporal variability of sub-micron (diameter range 10-1000 nm) particles perpendicular to a main road in the city of Berlin, Germany. Measurements were carried out on 17 days with overall 72 runs along a 250m almost untraveled footpath. Particle number concentration (PNC) as well as the share of local sources were analyzed in relation to the distance to the road, wind speed and wind direction. This study aims to detect patterns of PNC dispersal along the footpath with increasing distance from the road in a built-up urban environment and to identify impact factors. In the majority of cases, results can be expressed well in terms of an exponential decrease of PNC with increasing distance from the road. Traffic flow along the main road has a substantial impact on concentration levels. About 30% of the PNC at the roadside and 15% at a distance greater than 100m can be attributed to traffic. Variations in background concentrations, however, contribute the largest share to concentration levels. [ABSTRACT FROM AUTHOR]