DAYTIME PHOTOCHEMICAL POLLUTANT TRANSPORT OVER A TRIBUTARY VALLEY LAKE IN SOUTHWESTERN BRITISH-COLUMBIA

Tethersonde, lidar, aircraft, and surface chemistry measurements from an intensive field campaign (Pacific '93) in the Lower Fraser Valley ( LFV) demonstrate the daytime advection of pollutants into a lake-fille d valley adjoining a broad urbanized coastal valley. On three separate days (immediately before, during, and after a pollutant episode), ele vated concentrations of ozone (O-3) in the narrow tributary valley cou ld be attributed to the advection of pollutants northward from sources in the LFV (primarily metropolitan Vancouver). On 5 August, the highe st concentrations of O-3 observed in the region during the entire epis ode were observed over the tributary lake. Simple Lagrangian mass budg et calculations suggest that the unusually high concentrations observe d on 5 August over the lake were physically reasonable and consistent with the known chemistry of the air advected into the valley. They als o indicate that reductions in O-3 flux divergence during the overlake trajectory in the Pitt Valley, primarily as a result of reduced surfac e deposition, may contribute to the relatively high concentrations obs erved in the tributary valley. Observations immediately after the epis ode show that chemically aged polluted air masses can persist within t he tributary valleys from the previous day. These results have implica tions for the understanding of air pollution in other regions of compl ex terrain ana show that the predominance of daytime upvalley pollutan t transport in such tributary valleys is likely to have significant im pacts on the local ecology and visibility.