Synoptic and local meteorology influences on aerosol concentrations

Particulate concentrations are both a health and visibility concern in valley communities of the interior of British Columbia. Sources of these pollutants are generally local, and their concentrations are influenced by both synoptic scale flow and the small-scale meteorology that is unique to each valley location. There is a wide variation in particulate concentrations between communities and under different synoptic situations. In order to better understand the role of valley meteorology in air quality, this paper examines the links between meteorology and particulate concentrations in a small community in the southern interior of British Columbia. It suggests that concentrations of both PM2.5 and the coarse fraction of PM10 often respond to changes in synoptic and local meteorological forcing in opposite ways. Shallow overnight inversions, produced by diurnal cooling, restrict the stronger winds aloft from penetrating into the valley. This allows local particulate sources such as domestic heating or industrial activity to increase PM2.5 concentrations as light surface winds redistribute the particulate but confine it to the local valley site. Diurnal heating breaks down these inversions, with the subsequent stronger winds reducing the PM2.5 concentrations by dispersing and diluting the fine particulate though a deeper atmospheric column. At the same time, the concentration of the coarse fraction of the PM10 is increased as these stronger winds re-suspend dust and crustal material from sources both inside and outside the community. Larger-scale synoptic patterns play a significant role in this pattern. Strong inflow from the coast can restrict the depth of valley inversions and the length of time that they exist. A stable atmosphere and weak flow at higher levels can, on the other hand, increase the depth, intensity and duration of these inversions. Synoptic scale flow can therefore influence the concentrations of the two components of PM2.5 and the coarse fraction of PM10, in different ways.