Soil and PM10 flux above an eroding agricultural field during high winds.
Brenton Sharratt, USDA-ARS, 213 LJ Smith Hall, WSU, Pullman, WA 99164-6120 and Guanglong Feng, Department of Biological Systems Engineering, Washington State University, LJ Smith Hall, Pullman, WA 99164.
Winter wheat - summer fallow is the conventional cropping system employed on >1.5 million ha in eastern Washington and northern Oregon. Wind erosion contributes to high PM10 (particulate matter ≤10 µm in aerodynamic diameter) concentrations and thus poor air quality in the region. Soil and PM10 flux was assessed from a silt loam in eastern Washington during 2003. Our field site was maintained in fallow using conventional tillage practices and instrumented to assess horizontal soil flux and PM10 concentrations at the leeward position in the field (>225 m fetch) during high wind events. Soil flux was measured using creep and airborne sediment collectors while PM10 concentration was measured using high volume PM10 samplers and E-samplers. A major dust storm occurred on 28 October 2003 when the National Ambient Air Quality Standard for PM10 was exceeded at several locations in eastern Washington. Winds in excess of 17.5 m s-1 resulted in a horizontal soil flux of 22.5 kg m-1 and a maximum 5-m PM10 concentration of 8500 µg m-3 at our field site. The vertical distribution of eroded sediment and PM10 above the field was best described by a power function. For the duration of the 14-h event, PM10 concentration at 0.1 and 5 m above the soil surface was respectively 17000 and 500 µg m-3. This study suggests that high PM10 concentrations above eroding agricultural fields contributes to poor air quality in eastern Washington and northern Oregon and thus the need for alternative tillage practices or cropping systems to reduce PM10 emissions in the region.