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[1] The Portable In situ Wind ERosion Lab (PI-SWERL) was developed to measure dust emissions from soil surfaces. This small, portable unit can test the emissivity of soils in areas that are difficult to access with a field wind tunnel, and can complete a larger number of tests in less time. The PI-SWERL consists of a cylindrical enclosure containing an annular flat blade that rotates at different speeds, which generates shear stress upon the surface. The shear stress generated by PI-SWERL results in the entrainment of particles including dust. PI-SWERL was developed to provide an index of dust emission potential comparable to the field wind tunnel. The PI-SWERL dust emission results were compared against those obtained from a $12 m long, 1 m wide, 0.75 m high straight line suction-type portable field wind tunnel by conducting collocated tests at 32 distinct field settings and soil conditions in the Mojave Desert of southern California. Clay-to sand-rich soils that displayed a range of crusting, gravel cover, and disturbance were tested. The correspondence between dust emissions (mg m À2 s À1 ) for the two instruments is nearly 1:1 on most surfaces. Deviation between the two instruments was noted for densely packed gravel surfaces. For rough surfaces a correction can be applied to the PI-SWERL that results in comparable dust emission data to the wind tunnel. PI-SWERL can be used to complement research efforts in aeolian geomorphology aimed to quantify spatial and temporal patterns of dust emissions as well as air quality research related to dust emissions.

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Excluding windblown dust, unpaved road dust PM 10 emissions in the US EPA's 2002 National Emission Inventory account for more than half of all PM 10 emissions in the arid states of the western U.S. (i.e., CA, AZ, NV, NM, and TX). Despite the large size of the source, substantial uncertainty is associated with both the vehicle activity (i.e., number of kilometers traveled at a particular speed) and the emission factors (i.e., grams of PM 10 per kilometer traveled). In this study, emission factors were measured using the flux tower method for both tracked and wheeled military vehicles at three military bases in the Western U.S. Test vehicle weights ranged from 2400 kg to 60,000 kg. Results from both previously published and unpublished field studies are combined to link emission factors to three related variables: soil type, vehicle momentum, and tred type (i.e., tire or track). Current emission factor models in US EPA's AP-42 Emission Factor Compendium do not factor both speed and weight into unpaved road emission factor calculations. Tracked vehicle emission factors from Ft. Carson, CO, and Ft. Bliss, TX were related to vehicle momentum (speed * mass) with ratios ranging from 0.004-0.006 (g-PM vkt −1 )/(kg m s −1 ). For similar vehicle momentum, wheeled vehicles emitted approximately 2 to 4 times more PM 10 than tracked vehicles. At Yakima, WA, tracked vehicle PM 10 emission factors were substantially higher (0.38 (g-PM vkt −1 )/(kg m s −1 )) due to the unique volcanic ash soil characteristics (48% silt). Results from PI-SWERL, a portable wind tunnel surrogate, are presented to assess its utility to predict unpaved road dust emissions without the deployment of flux tower systems. PI-SWERL showed only a factor of 6 variation between We would like to acknowledge the logistical and financial support provided by the National Guard MATES facilities at Yakima Training Center, Yakima, Washington and Ft. Carson, Colorado. Special thanks to the MATES personnel who operated the vehicles for us as well as their flexibility in accommodating our demands. We would also like to thank Yakima Training Center and Ft. Carson for hosting our field measurement campaigns and the SERDP Sustainable Infrastructure program (projects CP-1191 and SI-1399) for their continued support of this research.

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Crusted surfaces can be major sources of mineral dust emission. Quantitative understanding of dust emission from crusted surfaces is limited, because (1) theories on dust emission are not well tested for such surfaces; and (2) modelling is hampered by a lack of input data sufficient to describe the surface conditions. Combining detailed field measurements with physics-based numerical modelling, we present new insights into dust emission from crusted surfaces. Our measurements confirm that crust erodibility and dust-emission intensity can increase or decrease after previous erosion events. To support interpretation of the measurements and to test the applicability of a state-of-the-art parameterisation to simulate dust emission from crusted surfaces, we apply the dust emission scheme of Shao (2004). Saltation flux, which is input to the scheme, is approximated using the parameterisation of Kawamura (1964) and a scaling factor obtained from observations. Limitations of this approach are discussed. Our results show that the dust emission scheme is suitable to estimate dust emission from crusted surfaces if accurate input data and parameters describing the soil-surface condition are provided. The parameters were optimized for each dust event to achieve a best estimate. The variation of the resulting parameter values confirms the observed variability of dust-emission efficiency between the events and provides further evidence that it was caused by variations in crust erodibility. Our study demonstrates that available physics-based dust-emission parameterisations are able to simulate dust emissions under complicated conditions, but also that refined information on the soil-surface conditions are needed as input to the schemes.