Particle size distribution and particle mass measurements at urban,near-city and rural level in the Copenhagen area and Southern Sweden

Particle size distribution (size-range 3-900 nm) and PM10 was measured simultaneously at an urban back- ground station in Copenhagen, a near-city background and a rural location during a period in September-November 2002. The study investigates the contribution from urban versus re- gional sources of particle number and mass concentration. The total particle number (ToN) and NOx are well cor- related at the urban and near-city level and show a distinct diurnal variation, indicating the common traffic source. The average ToN at the three stations differs by a factor of 3. The observed concentrations are 2500 # cm 3 , 4500 # cm 3 and 7700 # cm 3 at rural, near-city and urban level, respectively. PM10 and total particle volume (ToV) are well correlated between the three different stations and show similar con- centration levels, in average within 30% relative difference, indicating a common source from long-range transport that dominates the concentrations at all locations. Measures to reduce the local urban emissions of NOx and ToN are likely to affect both the street level and urban background concentrations, while for PM10 and ToV only measurable effects at the street level are probable. Taking into account the supposed stronger health effects of ultrafine particles reduction measures should address particle number emissions. The traffic source contributes strongest in the 10-200 nm particle size range. The maximum of the size distribution shifts from about 20-30 nm at kerbside to 50-60 nm at ru- ral level. Particle formation events were observed in the 3- 20 nm size range at rural location in the afternoon hours, mainly under conditions with low concentrations of pre- existing aerosol particles. The maximum in the size distribution of the "traffic con- tribution" seems to be shifted to about 28 nm in the urban