The magnitude and extent of elevated ozone concentrations around the coasts of the British Isles

The marked decreases in ozone concentrations that occur over level ground at night do not occur over open water surfaces. Thus during on-shore flow coastal regions experience higher concentrations than further inland. The magnitude and spatial extent of this enhanced exposure are quantified by analysis of data from monitoring sites in the coastal zone during periods of on-shore flow and by application of a multi-layer, Lagrangian, diffusion model. Observations show that, with on-shore winds, the daily-mean concentration at the coast is 5–7 ppbv greater than at inland sites. Combining these increased concentrations with statistics on flow direction indicates enhanced daily-mean concentrations at the coast typically of 3 ppbv, but up to 5 ppbv in some locations, compared to locations inland. Model studies indicate that the spatial extent of these increased concentrations is restricted to a coastal band of only a few kilometres in width.