It's pretty bad as about a third of the city is now an air quality management area. The sea breezes don't help as the salt particles contribute. We've certainly not got the same problems as London though, where 7-9% of deaths are directly attributable to air pollution.
Happy to go into great detail with regard to NOx concentrations and dispersion factors but I charge quite a high rate. I'm a member of the institute of air quality management and the institute of environmental science if that helps.
As an air quality consultant, I can say with some certainty that it's a bloody stupid idea. More people in Brighton WILL die as a result of the increased air pollution than will be saved by the reduced speed limit.