title: A simple model which predicts some non-linear features between atmospheric sulphur and sulphur emissions.
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.
authors.affiliation: Department of Physics, Imperial College of Science, Technology and Medicine, London, UK. al.hadley@ic.ac.uk
authors.forename: Adam
authors.initials: A
authors.lastname: Hadley
authors.forename: Ralf
authors.initials: R
authors.lastname: Toumi
mesh_terms: D000392:Air Movements; D000393:Air Pollutants / Q000032:analysis / Q000737:chemistry*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004784:Environmental Monitoring / Q000379:methods; D008956:Models, Chemical; D017711:Nonlinear Dynamics; D013458:Sulfur Dioxide / Q000032:analysis / Q000737:chemistry*
chemical_list: D000393:Air Pollutants; D013458:Sulfur Dioxide