Atmos. Chem. Phys. Discuss., 10, 23739-23780, 2010
© Author(s) 2010. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Controls of carbon dioxide concentrations and fluxes above central London
C. Helfter1, D. Famulari1, G. J. Phillips1,4, J. F. Barlow2, C. R. Wood2, C. S. B. Grimmond3, and E. Nemitz1
1Centre for Ecology and Hydrology (Edinburgh Research Station), Penicuik, EH26 0QB, UK
2Department of Meteorology, University of Reading, Reading, RG6 6BB, UK
3Department of Geography, King's College London, London, UK
4National Centre for Atmospheric Science, University of Leeds, LS2 9JT, UK

Abstract. Eddy-covariance measurements of carbon dioxide fluxes were taken semi-continuously between October 2006 and May 2008 at 190 m height in central London (UK) to quantify emissions and study their controls. Inner London, with a population of 8.2 million (~5000 inhabitants per km2) is heavily built up with 8% vegetation cover within the central boroughs. CO2 emissions were found to be mainly controlled by fossil fuel combustion (e.g. traffic, commercial and domestic heating). The measurement period allowed investigation of both diurnal patterns and seasonal trends. Diurnal averages of CO2 fluxes were found to be highly correlated to traffic. However changes in heating-related natural gas consumption and, to a lesser extent, photosynthetic activity that controlled the seasonal variability. Despite measurements being taken at ca. 22 times the mean building height, coupling with street level was adequate, especially during daytime. Night-time saw a higher occurrence of stable or neutral stratification, especially in autumn and winter, which resulted in data loss in post-processing. No significant difference was found between the annual estimate of net exchange of CO2 for the expected measurement footprint and the values derived from the National Atmospheric Emissions Inventory (NAEI), with daytime fluxes differing by only 3%. This agreement with NAEI data also supported the use of the simple flux footprint model which was applied to the London site; this also suggests that individual roughness elements did not significantly affect the measurements due to the large ratio of measurement height to mean building height.

Citation: Helfter, C., Famulari, D., Phillips, G. J., Barlow, J. F., Wood, C. R., Grimmond, C. S. B., and Nemitz, E.: Controls of carbon dioxide concentrations and fluxes above central London, Atmos. Chem. Phys. Discuss., 10, 23739-23780, doi:10.5194/acpd-10-23739-2010, 2010.
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