A Technique to Measure Fine-dust Emission Potentials During Wind Erosion

Potential aerosol release rates during wind erosion of soils have been quantified by such methods as sandSuspendable-size soil particles are released during wind erosion and blasting aggregates in laboratory settings (Alfaro et al., transported downwind, impacting regional air quality. Of particular concern are those particles with a mean aerodynamic diameter of 1998), measuring concentrations of fine particles during 10 m (PM10 ) and the finer subset of those 2.5 m (PM2.5 ). To wind tunnel experiments (Mirzamostafa et al. 1998; estimate the air quality impact of wind erosion, the potential release Weinan et al., 1998) and by direct field measurements from nondispersed soil of PM10 and PM2.5 particles must be quantified (Gillette et al., 1972, 1997; Nickling, 1978; Saxton et al., for both those readily entrained existing particles and those generated 2000). by aggregate abrasion. A new laboratory technique was devised to Some have attempted to estimate the particulate determine the potential emission of these size particles by both proemission potential by traditional dispersed soil analyses. cesses from nondispersed soil samples. An emission cone in which However, since there is a fundamental difference bethe soil sample was suspended and rotationally abraded in an air tween dispersed and nondispersed approaches to partistream was coupled with a standard measuring instrument for either cle sizing (McCave and Syvitski, 1991), and soils do PM10 or PM2.5. Data of nondispersed soil samples compared with those dispersed showed significantly less emission potentials for the not undergo chemical dispersion during wind erosion nondispersed. The PM2.5 portion of the PM10 values ranged from 30 events, these results are not directly applicable. Saxton to 55% indicating significant air quality impacts by wind erosion in et al. (2000) adapted a simple, single air-burst resuspenthis region based on either standard. Results from Washington State sion procedure to estimate the mass percentage of PM10 showed spatial patterns closely related to soil morphology, and a linear available for suspension from a soil (D). This resuspenrelationship between dispersed and self-abrader PM10, but not PM2.5. sion method did not include particles released during aggregate abrasion, an important processes during wind erosion (Alfaro et al., 1998), and thus significantly unD release rates of aerosol-size particuderestimated the particulate emission potentials of the lates from disturbed soils during wind erosion tested soils (Table 1). events is a critical step needed to incorporate air quality A new laboratory method was developed to provide prediction into wind erosion models. Particulate aeroestimates of D for both PM10 and PM2.5. The first objecsols arise from the soil surface when it is abraded by tive was to develop a technique that did not require saltating aggregates and mineral grains and by direct chemical dispersion and accounts for both preexisting entrainment from the soil surface because of turbulent particles and those released by aggregate abrasion. The eddies in surface winds (Kind, 1992; Loosmore and results would need to discriminate among the wide variHunt, 2000). Wind erosion prediction models generally ety of soils found across the study region of the Columconsider the aerosols generated by these processes as a bia Plateau. A second objective was to evaluate potenportion of the suspension component of the eroded soil tial relationships between these nondispersed results (Mirzamostafa et al., 1998). with those of traditional dispersed-size fractions to proParticulate aerosols of primary concern to air quality vide a broader based estimating method utilizing existare PM10 and PM2.5. Ambient concentrations of PM10 ing soil data bases. and PM2.5 have been selected as air quality indicators and are the bases of federal air quality regulation in the MATERIALS AND METHODS USA (USEPA, 1990b, 1997). During high wind events, A new laboratory measurement technique was designed, large quantities of PM10 and PM2.5 may be released from calibrated, and used for a wide variety of soils to determine eroding source areas and transported long distances PM10 and PM2.5 emission potentials of nondispersed soil. This downwind as a fraction of the suspension component equipment consisted of a newly designed and constructed of the eroded soil (Stetler and Saxton, 1996). emitting cone coupled with a standard particulate monitoring The particle-size distribution of aerosols arising from instrument. The particles generated in the emitting cone were wind erosion has been measured by several means (Gilaspirated by the particulate monitor intake. The emission cone lette et al., 1974; Gillette and Walker, 1977; McTainsh et suspended both preexisting aerosol-size particles and abraded the aggregates as the soil sample tumbled and self-abraded, al., 1997) and modeled mathematically (Shao et al.,1993; to provide additional particles. Marticorena and Bergametti, 1995; Zobeck et al., 1999). The particulate measurement instrument was a Tapered Element Oscillating Microbalance (TEOM) 1400a Monitor David G. Chandler, Dep. of Plants, Soils and Biometeorology, Utah (Rupprecht & Patashnick Co., Inc., Albany, NY). The TEOM State Univ., Logan, UT 84322; K.E. Saxton, USDA-ARS, L.J. Smith is a Federal Reference Method (USEPA, 1990a) for monitorHall-Washington State Univ., Pullman, WA 99164; J. Kjelgaard, Bioing PM10 and PM2.5 in ambient conditions and commonly used logical Systems Engineering Dep., Washington State Univ., Pullman, WA 99164; A.J. Busacca, Deps. of Crop and Soil Sciences and GeolAbbreviations: ARD, Arizona road dust; D, mass percentage of PM10 ogy, Washington State Univ., Pullman, WA 99164. Received 24 July available for suspensions from a soil; PM2.5, particles 2.5 m; PM10, 2001. *Corresponding author ([email protected]). particles 10 m; TEOM, Tapered Element Oscillation Microbalance. Published in Soil Sci. Soc. Am. J. 66:1127–1133 (2002).