The Control of SO2 Dry Deposition on to Natural Surfaces by NH3 and its Effects on Regional Deposition |
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Authors: | Fowler D. Sutton M. A. Flechard C. Cape J. N. Storeton-West R. Coyle M. Smith R. I. |
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Affiliation: | (1) Centre for Ecology and Hydrology (Edinburgh), Bush Estate, Penicuik, Midlothian, U.K. |
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Abstract: | Two years of continuous measurements of SO2deposition fluxes to moorland vegetation are reported. The mean flux of 2.8 ng SO2 m-2 s-1 is regulated predominantly by surface resistance (rc) which, even for wet surfaces, was seldom smaller than 100 s m-1. The control of surface resistance is shown to be regulated by the ratio of NH3SO2 concentrations with an excess of NH3 generating the small surface resistances for SO2. A dynamic surface chemistry model is used to simulate the effects of NH3 on SO2 deposition flux and is able to capture responses to short-term changes in ambient concentrations of SO2, NH3 and meteorological conditions. The coupling between surface resistance and NH3/SO2 concentration ratios shows that the deposition velocity for SO2 is regulated by the regional pollution climate. Recent long-term SO2 flux measurements in a transect over Europe demonstrate the close link between NH3/SO2 concentrations and rc (SO2). The deposition velocity for SO2 is predicted to have increased with time since the 1970s and imply a 40% increase in vd at a site at which the annual mean ambient SO2 concentrations declined from 47 to 3 g m-3 between 1973 and 1998. |
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Keywords: | canopy resistance deposition non-linearity SO2 velocity |
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