ORGANIC COMPONENT OF WIND-BLOWN SOIL AEROSOL AS A FUNCTION OF WIND VELOCITY

Wind-blown soil aerosol, generated during 3 dust storms in March 1974, was collected at 1.5 m above the surface in Plains, Texas [USA] during periods of different wind velocities. A cascade impactor permitted separation into 5 size-fractions, 4 of them covering the range of particle radii 0.21-3.4 .mu.m. The total organic C (TOC) in each size range was determined by a wet oxidation method that measures the resultant CO2 in an IR cell. For the aerosol, the mass distribution of TOC decreases with increasing particle size at all 3 wind velocities studied (7.3 m s-1, 9.3 m s-1 and 11.4 m s-1). The percentage of TOC in each size fraction decreases with increasing wind velocity although the corresponding particulate concentrations increase. Moreover the aerosol is enriched in TOC compared with the bulk parent soil, the amount of enrichment being greatest for the smallest particle size. The enrichment factor, integrated over all sizes, varies between 1 and 10 depending upon wind velocity. These data are consistent with results obtained at 3.5 m using a different sampling and sizing method. Microscopic examination of the aerosol reveals vegetative residue in all fractions although its contribution to the TOC appears to be small.