Final Activity Report Summary - PURAT (Particles in the urban atmosphere: behaviour of fine and ultrafine particles, their spatial variation, and relationships with local policy action)
During the experiment PURAT-1, ambient size distributions were collected at a total of eleven observation sites, revealing differences in ultrafine particle number concentration of up to two orders of magnitude within the same city. Particle number concentrations in the size range 100-400 nm correlated well between different urban background sites. However, the correlation degraded for ultrafine particles, and when correlations to roadside sites were considered. During the three-month experiment PURAT-2 in the vicinity of the Berlin urban motorway, concentrations of ultrafine particles were measured that range among the highest that have been reported in Germany.
A three-dimensional emission and transport simulation confirmed the spatial patterns of aerosol dispersion around the motorway. Results from PURAT-3 and 4 in Leipzig, confirmed that the particle size distribution is far from spatially homogeneous in the microscale environment around a densely built-up street canyon. The general result is that the number of ultrafine particles tends to be far less homogeneously distributed than particle mass concentrations. The data collected will be of considerable importance for future works, such as an assessment of urban residents' exposure to ultrafine particles, the determination of vehicle emission factors as well as the validation of urban microscale dispersion models.