Fine Particulates (Pm10 and Pm2.5) Generated by Breakage of Mobile Aggregates During Simulated Wind Erosion

Wind erosion of soils generates fine particulates that are health hazards (PM10 and PM2.5) by three majorprocesses: entrainment (emission) of loose mobile aggregates from the surface, abrasion from immobile clods/crusts, andbreakage of mobile saltation/creep aggregates. To improve prediction of PM10 generation in erosion models, parameters mustbe established for these processes. The objectives of this research were to measure relative breakage fractions of saltation-sizeaggregates to suspension-size and the fractions of PM10 and PM2.5 generated by the breakage process for a range of soils.Soil samples were collected from nine states (Arizona, California, Nevada, Colorado, Kansas, Nebraska, New Mexico,Oklahoma, and Texas). Sub-samples of the soils were used to determine organic matter and calcium carbonate fractions.Other sub-samples were dispersed to determine sand, silt, and clay fractions. The breakage process was simulated in thelaboratory by repeated impacts of saltation-size aggregates in an enclosed chamber. Relative breakage fractions averaged0.044 for aggregates with saltation-size sand/clay ratios between 0.1 and 10. Fractions for aggregates with either large clayor saltation-size sand fractions were significantly less, averaging 0.015. The fraction of PM10 in the suspension componentcreated by breakage (SF10bk) averaged 0.049 over all soils. The SF10bk was inversely proportional to both clay content andannual precipitation. Average SF10bk was 0.069 with clay fraction <0.1, but significantly lower (0.030) with clay fraction>0.1. The average ratio of PM2.5/PM10 was 0.154, but increased with saltation-size sand/clay ratio and decreased withprecipitation. The predicted values ranged from about 0.1 to 0.3 (R2 = 0.53).