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Trace Gas Flux Measurements at the Landscape Scale Using Boundary-Layer Budgets [and Discussion]

T. W. Choularton, M. W. Gallagher, K. N. Bower, D. Fowler, M. Zahniser, A. Kaye, J. L. Monteith, R. J. Harding


Methane effluxes from wetland areas of Scotland were estimated by using the boundary-layer budget method by collecting air samples with an aircraft upwind and downwind of an area of extensive peatland. Nocturnal local area methane fluxes were also estimated at a peat bog site, Loch More, located at 58 degrees 24$^{\prime}$ N 03 degrees 36$^{\prime}$ W, using the concentration build up under the nocturnal inversion and from profiles of methane concentration using a tethered balloon. The mean daytime flux for the Loch More case studies in 1993 was found to be 128 $\pm $ 57 $\mu $ mol m$^{-2}$ h$^{-1}$ for the NE region of Scotland, comparable to but generally larger than those obtained for the same region one year earlier. The fluxes are smaller than those obtained in Caithness by the same technique. In 1993 the nocturnal fluxes were found to be 38 $\pm $ 7 $\mu $mol m$^{-2}$ h$^{-1}$, significantly smaller than those found during 1992. The daytime fluxes measured by the aircraft were generally larger than fluxes measured by micrometeorological techniques at the same time. These differences can be explained in terms of the significant heterogeneity in surface fluxes that exist on scales of a few hundred metres or less and the possibility of additional sources other than peatland in this region.

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