A simple model which predicts some non-linear features between atmospheric sulphur and sulphur emissions |
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Authors: | Hadley Adam Toumi Ralf |
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Affiliation: | Department of Physics, Imperial College of Science, Technology and Medicine, London, UK. al.hadley@ic.ac.uk |
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Abstract: | This paper develops a simple model and suggests a plausible chemico-physical mechanism for a non-linear response between atmospheric sulphur and sulphur emissions. It contains simplified representations of transport, deposition and conversion processes and uses a proxy in-cloud oxidant-limited reaction along a pathway connecting an emission source with a receptor site. Individual pathway responses to emissions show linear behaviour above a threshold. However, by averaging the values of SO2 at the receptor site from different pathways a continuous non-linear relationship is obtained. As emissions reduce, distant emission sources become less significant contributors of sulphur dioxide at a receptor site but their emissions are still counted in an emission inventory, leading to an apparent non-linearity. Sulphate is always found to contribute a signal to the receptor site total. This model goes someway to explaining a proposed 'crossover' between observed proportions of wet and dry deposited sulphur in the UK as emissions have been reduced. |
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