ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-4-281-2004 Particle size distribution and particle mass measurements at urban,near-city and rural level in the Copenhagen area and Southern Sweden Ketzel M. 1 2 Wåhlin P. 1 Kristensson A. 2 Swietlicki E. 2 Berkowicz R. 1 Nielsen O. J. 3 Palmgren F. 1 Department of Atmospheric Environment, National Environmental Research Institute, Roskilde, Denmark Division of Nuclear Physics, Physics Department, Lund University, Lund, Sweden Department of Chemistry, University of Copenhagen, Denmark 13 02 2004 4 1 281 292 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/4/281/2004/acp-4-281-2004.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/4/281/2004/acp-4-281-2004.pdf

Particle size distribution (size-range 3-900nm) and PM10 was measured simultaneously at an urban background 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 regional sources of particle number and mass concentration. <P style="line-height: 20px;"> The total particle number (ToN) and NO<sub>x</sub> are well correlated 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<IMG WIDTH="20" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" src="acp-4-281-img1.gif" ALT="$^{-3}$">, 4500#cm<IMG WIDTH="20" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" src="acp-4-281-img1.gif" ALT="$^{-3}$"> and 7700#cm<IMG WIDTH="20" HEIGHT="18" ALIGN="BOTTOM" BORDER="0" src="acp-4-281-img1.gif" ALT="$^{-3}$"> at rural, near-city and urban level, respectively. <P style="line-height: 20px;"> PM10 and total particle volume (ToV) are well correlated between the three different stations and show similar concentration levels, in average within 30% relative difference, indicating a common source from long-range transport that dominates the concentrations at all locations. <P style="line-height: 20px;"> Measures to reduce the local urban emissions of NO<sub>x</sub> 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. <P style="line-height: 20px;"> The traffic source contributes strongest in the 10-200nm particle size range. The maximum of the size distribution shifts from about 20-30nm at kerbside to 50-60nm at rural level. Particle formation events were observed in the 3-20nm size range at rural location in the afternoon hours, mainly under conditions with low concentrations of pre-existing aerosol particles. <P style="line-height: 20px;"> The maximum in the size distribution of the "traffic contribution" seems to be shifted to about 28nm in the urban location compared to 22nm at kerbside. Assuming NO<sub>x</sub> as an inert tracer on urban scale allows to estimate that ToN at urban level is reduced by 15-30% compared to kerbside. Particle removal processes, e.g. deposition and coagulation, which are most efficient for smallest particle sizes (<IMG WIDTH="15" HEIGHT="29" ALIGN="MIDDLE" BORDER="0" src="acp-4-281-img2.gif" ALT="$&lt;$">20nm) and condensational growth are likely mechanisms for the loss of particle number and the shift in particle size.