Numerical modeling of windblown dust in the Pacific Northwest with improved meteorology and dust emission models

Abstract

Soil erosion by wind is a serious consequence of dry land agriculture in eastern Washington, where the main adverse effects are loss of nutrient‐rich soil, reduced visibility during dust storms and degradation of air quality. A multidisciplinary research effort to study windblown dust in central and eastern Washington was initiated under the Columbia Plateau PM10 (CP3) program, which involved measuring wind erosion and windblown dust emissions at sites throughout the region and developing a transport and dispersion model for the area. The modeling system includes the prognostic meteorological model, Mesoscale Metorological Model Version 5 (MM5), coupled with the CALMET/CALGRID Eularian modeling pair and a new dust emission module (EMIT‐PM). Improvements to the modeling system included employing higher spatial resolutions for the meteorological models and improved parameterizations of emission factors in EMIT‐PM. Meteorological fields, dust emissions and the resulting dust concentrations were simulated for six historical regional dust storms: 23 November 1990, 21 October 1991, 11 September 1993, 3 November 1993, 30 August 1996 and 23–25 September 1999. For all the simulated events, with the exception of the August 1996 event, ratios of observed to predicted concentrations were favorable, within a range of 0.5–6.0 without calibration of the dust emission model; PM10 emissions averaged 22 Gg per 24‐hour event, representing approximately 1% of the daily dust flux on a global basis. These results showed that the model performed best for large, strong dust storms but did not simulate smaller storms as well.