W ith the advent of the 1990 Clean Air Act came the responsibility to monitor and control fugitive dust particulates less than 10 micron aerodynamic diameter (PM 10 ) in urban regions. The basis for this legislation was research findings which indicated that exposure to high 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. Several of these occasions occurred during days of obvious regional agricultural wind erosion (Saxton, 1995a). 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 fine suspendible dust emissions. Thus, the Columbia Plateau was chosen as a region to study relationships between PM 10 emissions and wind erosion from agricultural fields. Historically, wind erosion prediction technology has been based on empirically derived relationships among the major variables found to influence wind erosion. The wind erosion equation (WEQ) 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 (Chepil, 1941; Woodruff and Siddoway, 1965). 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 . 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 (Saxton, 1995b). A two-step model was developed which first predicts the horizontal flux of eroded soil from factors known to cause and control wind erosion, then estimate a corresponding vertical flux of PM 10 for the erosion event. An empirical equation was first developed to predict Q e , the streamwise (horizontal) flux of eroded soil on an event basis (Saxton et al., 1996). Similar in form to the WEQ, the calculated horizontal erosion flux, Q e , was based on the major variables known to effect an erosion event defined as: Q e = f(W e , SE, SC, K, WC) (1) where Q e = event eroded soil W e = event wind energy SE = soil erodibility SC = vegetative surface cover K = soil surface roughness WC = soil surface wetting and crusting WIND EROSION AND FUGITIVE DUST FLUXES ON AGRICULTURAL LANDS IN THE P ACIFIC NORTHWEST K. Saxton, D. Chandler, L. Stetler, B. Lamb, C. Claiborn, B.-H. Lee ABSTRACT. With recent emphasis of agricultural wind erosion and associated dust emissions impacting downwind air quality, there is an increased need for a prediction method to estimate dust emissions and ambient particle concentrations on a wind event basis. Most current wind erosion methods predict average annual or seasonal erosion amounts, and only very approximate estimates of suspended dust emissions are available. A project in the Columbia Plateau of eastern Washington State was initiated to develop an empirical method to estimate dust emissions for this region. Field measurements, wind tunnel tests, and laboratory analyses were combined to provide an empirical wind erosion equation and a related vertical flux dust emission model. While based on measured data, the model has not been independently verified. When combined with a transport-dispersion model and calibrated, estimates of downwind particulate concentrations compared reasonably with those measured. Keywords. Wind erosion, Wind tunnel, Dust, Emission, PM10, Columbia Plateau. Article was submitted for publication in March 1999; reviewed and approved for publication by the Soil & Water Division of ASAE in February 2000. Presented as ASAE Paper No. 98-2058. Use of commercial names is only for the need of scientific documentation and implies no endorsement or preference. The authors are Keith Saxton, ASAE Fellow Engineer, Research Agricultural Engineer, and David Chandler, Research Agricultural Engineer, USDA/ARS, Smith Hall-WSU, Pullman, Washington; Larry Stetler, Assistant Professor, South Dakota School of Mines and Technology, Rapid City, South Dakota; Brian Lamb, Professor, Candis Claiborn, Associate Professor, and Bu-Hyun Lee, Research Associate, Washington State University, Civil and Environmental Engineering Department, Pullman, Washington. Corresponding author: Dr. Keith Saxton, USDA/ARS, Washington State University, Smith Hall, Pullman, WA 99164-6120, phone: 509.335.2724, fax: 509.335.7786, e-mail: <ksaxton@wsu.edu>. Transactions of the ASAE 2000 American Society of Agricultural Engineers 623 VOL. 43(3): 623-630 sw 3418 ms 7/9/01 9:24 AM Page 623