Simulation of a Recent Regional Windblown Dust Event on the Columbia Plateau

A regional, windblown dust modeling system, developed for the Columbia Plateau PM10 Program (CP), was employed to simulate a regional dust storm that occurred during Sept 23 25, 1999. Observed hourly PM10 concentrations exceeded 1000 ug m at downwind urban receptors and extremely poor visibility due to blowing dust in northeastern Oregon caused a fifty car pile-up with the loss of seven lives. To simulate the emission of PM10 due to windblown soil erosion, a detailed emission model has been developed for the CP region. However, in initial applications of the model to historical dust events, the model significantly underestimated observed PM10 concentrations, and a calibrated emission constant was required to yield agreement between observed and predicted PM10 concentrations. For the 1999 event, new analyses of the dust content of CP soils were incorporated into the emission model. Results from the simulation showed that the predicted PM10 concentrations in Spokane, WA were in relatively good agreement (within 30%) with the observed concentrations in terms of the onset and magnitude of elevated concentrations. This good agreement did not require any adjustment of the emission model. However, in Kennewick, WA the predicted concentrations were significantly higher (by a factor of three or more) than the observed concentrations. To investigate the source areas responsible for the PM10 predicted for Spokane and Kennewick, a novel back trajectory source footprint method was employed. This technique indicates that during high wind speeds accompanying a dust storm, emissions affecting the urban receptors are within approximately 40 km of the receptor.