Variability of aerosol particles in the urban atmosphere of Dresden (Germany): Effects of spatial scale and particle size

The spatial distribution of atmospheric particles in urban atmospheres is of significant concern for public health. However, the concentrations especially of ultrafine particles (diameter < 100 nm) are difficult to predict due to the presence of numerous diffuse particle sources and the generally inhomogeneous terrain in urban roughness layers. This study examines the spatial variability of sub-mu m particle number size distributions (diameter range 5-800 nm) in the urban atmosphere of Dresden, Germany, using multiple site measurements between December 2009 and May 2010. A main result is that particles in the accumulation mode size range (300-800 nm) showed only minor spatial variability. These particles form a rather homogeneous regional background of aerosol that changes only slightly with time. Particle concentrations in the size range 5-300 nm, however, proved to be significantly influenced by the local urban sources and showed an increasing variability with decreasing particle size. Besides the apparently highly variable field of traffic-related particles, a photochemical source of ultrafine particles was identified that showed an unexpectedly high spatial homogeneity across the entire city. The spatial gradients of particle concentrations also depended on wind direction, wind speed, and temperature inversions. The results confirm the high relevance of spatially resolved ultrafine particle measurements for the assessment of health-related exposure and strategies for their monitoring in urban atmospheres.