CityFlux perfluorocarbon tracer experiments 1School of Chemistry, University of Bristol, Bristol, UK
2SEAS, 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
Received: 30 September 2009 – Published in Atmos. Chem. Phys. Discuss.: 05 January 2010 Abstract. 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.
Revised: 17 May 2010 – Accepted: 28 May 2010 – Published: 05 July 2010
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.
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.
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.
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.
Citation: Petersson, F. K., Martin, D., White, I. R., Henshaw, S. J., Nickless, G., Longley, I., Percival, C. J., Gallagher, M., and Shallcross, D. E.: CityFlux perfluorocarbon tracer experiments, Atmos. Chem. Phys., 10, 5991-5997, doi:10.5194/acp-10-5991-2010, 2010.