ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-5991-2010 CityFlux perfluorocarbon tracer experiments Petersson F. K. 1 3 Martin D. 1 White I. R. 1 Henshaw S. J. 1 Nickless G. 1 Longley I. 2 4 Percival C. J. 2 Gallagher M. 2 Shallcross D. E. 1 School of Chemistry, University of Bristol, Bristol, UK SEAS, University of Manchester, Manchester, UK now at: Ionicon Analytik Gesellschaft mbH, Innsbruck, Austria now at: National Institute of Water and Atmospheric Research, Auckland, New Zealand 05 07 2010 10 13 5991 5997 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/10/5991/2010/acp-10-5991-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/5991/2010/acp-10-5991-2010.pdf

In June 2006, two perfluorocarbon tracer experiments were conducted in central Manchester UK as part of the CityFlux campaign. The main aim was to investigate vertical dispersion in an urban area during convective conditions, but dispersion mechanisms within the street network were also studied. Paired receptors were used in most cases where one receptor was located at ground level and one at roof level. One receptor was located on the roof of Portland Tower which is an 80 m high building in central Manchester. Source receptor distances in the two experiments varied between 120 and 600 m. <br><br> The results reveal that maximum concentration was sometimes found at roof level rather than at ground level implying the effectiveness of convective forces on dispersion. The degree of vertical dispersion was found to be dependent on source receptor distance as well as on building height in proximity to the release site. <br><br> Evidence of flow channelling in a street canyon was also found. Both a Gaussian profile and a street network model were applied and the results show that the urban topography may lead to highly effective flow channelling which therefore may be a very important dispersion mechanism should the right meteorological conditions prevail. <br><br> The experimental results from this campaign have also been compared with a simple urban dispersion model that was developed during the DAPPLE framework and show good agreement with this. <br><br> The results presented here are some of the first published regarding vertical dispersion. More tracer experiments are needed in order to further characterise vertical concentration profiles and their dependence on, for instance, atmospheric stability. The impact of urban topography on pollutant dispersion is important to focus on in future tracer experiments in order to improve performance of models as well as for our understanding of the relationship between air quality and public health.

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