A Numerical Study of Recirculation Processes in the Lower Fraser Valley (British Columbia, Canada)

The Lower Fraser Valley (LFV, Figure 1) spanning the Canada/USA border at 49° N is a roughly triangular valley with its westward end being the shoreline of the Strait of Georgia. The LFV contains the city of Vancouver, and its satellite communities with a total population of two million persons, mostly in the Canadian part of the valley. In the last two decades, the LFV has experienced several air pollution episodes. Primary as well as secondary pollutant concentrations are unusually high for such relatively small population. Several experimental campaigns (Pacific93, Pacific2001, Steyn et al. 1997), have been organized to investigate the physical mechanisms responsible for such elevated air pollutant levels. It has been hypothesized that the particularly low boundary layer height in the valley and the recirculation processes, induced by mesoscale circulations, play an important role.