Abstract
Tropospheric aerosols from major dust storms (visibility <11 km) originating in cultivated areas of the High Plains in west central Texas and adjacent areas of New Mexico, Oklahoma and Colorado, were sampled by ground-based airturbine samplers with stacks 1 to 6 m high, by membrane filters, by airplane-borne dust samplers and by a static ground-level sampler. The particle size distributions of the aerosol dust obtained by airplane sampling fell mainly between 1 and 30 μm diameter. A bimodal size distribution occurred for the dust from ground samplers, with large concentrations in the 40 to 80 μm range as well as in the 1 to 30 μm range. The concentration of dust 2 to 5 km above the ground, measured by both the filtering and impactor methods, ranged from 0.1 to 0.4 mg m−3 for four intense dust storms in Texas during April of 1972 and 1973. The vertical flux for dust storms over the four-year period ranged from 0.25 × 10−7 to 2.2 × 10−8 g cm−2 s−1.
Oxygen isotopic ratio values of 1 to 10 μm quartz isolated from 17 dusts collected by ground-based samplers ranged from 16.4 to 19.5‰ (mean, 18.35 ± 0.77‰); three dusts from the airplane samplers averaged 18.2 ± 1.1‰. The Texas dusts arose largely from 13 wind-eroding soil mapping units and erodibility classes of sandy to clayey texture in the four states; the δ18O values of the 1 to 10 μm quartz of these soils averaged 19.55 ± 0.28‰ (reported elsewhere). Abrasion by wind-induced inter-particle impact may have introduced a small amount of coarser quartz into the 1 to 10 μm aerosol fraction. Quartz from the coarser fractions of the dusts had δ18O values ranging from 16.9 to 13.9‰ with the lower values applying to the preponderantly sand sizes (>53 μm). The fine silt from eroding sandy soils, derived not only from weathering but also possibly from eolian deposition, serves as a reservoir for long-range aerosol minerals, in addition to that from shales.
