SALTATING PARTICLES, PLAYA CRUSTS AND DUST AEROSOLS AT OWENS (DRY) LAKE, CALIFORNIA

As part of the multinational Lake Owens Dust Experiment (LODE), we hav e studied the generation of dust storms on the south sand sheet of Owe ns (dry) Lake, California, an anthropogenically desiccated playa repor ted to be the single greatest source of particulate matter in North Am erica. During March 1993, we performed an intensive field study includ ing eight significant dust storms, building on our prior work (1978-19 84) and preliminary studies (1991-1992). We studied sources and magnit ude of coarse saltating particles, the meteorological conditions that allow them to become mobile across the flat playa of Owens (dry) Lake, and how the motion of saltating particles across different types of p laya surfaces results in the generation of PM(10) dusts (aerosol parti cles smaller than 10 mu m aerodynamic diameter). Saltating grains of l acustrine sand and broken crust abrade and disaggregate the playa surf ace into fine aerosols, and the resulting PM(10) concentrations record ed during major dust storms are among the highest ever recorded in Nor th America. On 23 March 1993, we measured a 2 h concentration on the p laya of 40620 mu g m(-3), as far as we can determine the highest ambie nt PM(10) value ever recorded in the U.S.A. Abrasion of salt-silt-clay crusts by saltation is shown to be responsible for all but a small pa rt of one dust storm. The quantity 'sand run', saltating particle tran sport multiplied by wind run, is shown to be very closely correlated w ith dust aerosol concentration. Finally, we have established that on-l ake bed studies are essential for quantitative prediction of dust even ts on the Owens (dry) Lake bed, despite the difficult conditions encou ntered.