Tropospheric layering of ozone in regions of urbanized complex and/or coastal terrain: a review

Exchange of pollutants between the atmospheric boundary layer and free trop osphere is an important (yet often neglected) process that tends to produce distinct layers of pollution in the lower troposphere. These layers repres ent a potential sink for pollutants from the boundary layer, have the poten tial to be mixed to ground and likely influence tropospheric chemistry and the global climate system. Factors influencing the vertical distribution of ozone in the troposphere are outlined as a prelude to a more specific disc ussion of elevated layers and myriad meteorological processes responsible f or their development. Evidence from a range of geographical settings sugges ts that these phenomena are ubiquitous. A rich data set from the Lower Fras er Valley, British Columbia, is used to provide an inventory of layer struc tures and to highlight their diverse origins and histories. Approaches used to assess the impact of down-mixing of pollutants from elevated layers on ground-level concentrations of ozone are outlined and future research prior ities recommended.