1 Simultaneous Wind Erosion and PM 10 Fluxes Keith Saxton, Larry Stetler, and David Chandler Introduction With the advent of the 1990 Clean Air Act came the responsibility to monitor and control particulates less than 10 micron aerodynamic diameter (PM 10 ). The basis for this legislation was research findings which indicate that exposure to high aerosol concentrations of PM 10 contributes to respiratory problems. Urban areas on the Columbia Plateau of Eastern Washington, Northern Oregon and the Idaho Panhandle have exceeded the PM 10 standard numerous times since measurements were started in 1985, with several of these occasions occurring on days of obvious regional agricultural wind erosion. Although the physical processes contributing to wind erosion and its control through agricultural practices are reasonably well understood, the predictive methods currently in use were not designed to estimate dust emissions. Thus, the Columbia Plateau was chosen as a primary region to study relationships between PM 10 particulate pollution and agricultural field erosion. Historically, wind erosion prediction technology has been based on empirically derived relationships between the major factors found to cause or control wind erosion. The wind erosion equation (WEQ) based on the work of Chepil (Woodruff and Siddoway, 1965), expresses that wind erosion results from interactions between wind forces and field conditions in terms of soil characteristics, surface roughness, vegetative cover and the upwind erodible field length in the direction of wind travel. The equation estimates the average annual mass of soil transported off the downwind edge of an agricultural field. This approach does not allow the total erosive soil loss to be partitioned either spatially between categories of soil transport mechanisms (creep, saltation and suspension) or temporally between individual wind erosion events. Similarly, no clear relationships have been developed between suspended particle concentration and that portion which is PM 10 -sized. A primary objective of the Columbia Plateau PM 10 Project was to develop an empirical model to predict the contribution of dust emissions from wind erosion of agricultural fields to regional PM 10 concentrations. To dovetail prediction efforts with existing urban PM 10 measurements, erosion and dust emission predictions were to be made on an event basis. To achieve this objective, a two-step model was developed. The model was derived to first predict the horizontal flux of eroded soil from factors known to cause and control wind erosion, then subsequently calculate a corresponding vertical flux of PM 10 for the erosion event. An empirical equation was first developed to predict Q t , the streamwise (horizontal) flux of eroded soil on an event basis. Similar in form to the WEQ (Woodruff and Siddoway, 1965), the calculated flux was based on the major conditions known to control an erosion event: Q t = f(W, EI, SC, K, WC) (1) where Q t = eroded soil W = erosive wind energy EI = soil erodibility SC = surface cover K = surface roughness WC = soil moisture and crusting