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[1] The problem of dust emissions from playa sources is an important one both in terms of human health and in terms of global dust issues, distribution of loess, and mineral cycling. A refined method of modeling atmospheric dust concentrations due to wind erosion was developed using real-time saltation flux measurements and ambient dust monitoring data at Owens Lake, California. This modeling method may have practical applications for modeling the atmospheric effects of wind erosion in other areas. Windblown dust from the Owens Lake bed often causes violations of federal air quality standards for particulate matter (PM 10 ) that are the highest levels measured in the United States. The goal of this study was to locate dust source areas on the exposed lake bed, estimate their PM 10 emissions, and use air pollution modeling techniques to determine which areas caused or contributed to air quality violations. Previous research indicates that the vertical flux of PM 10 (F a ) is generally proportional to the total horizontal saltation flux (q) for a given soil texture and surface condition. For this study, hourly PM 10 emissions were estimated using F a = K 0 Â m 15 , where m 15 is the measured sand flux at 15 cm above the surface, and K 0 was derived empirically by comparing air quality model predictions to monitored PM 10 concentrations. Hourly sand flux was measured at 135 sites (1 km spacing) on the lake bed, and PM 10 was monitored at six off-lake sites for a 30 month period. K 0 was found to change spatially and temporally over the sampling period. These changes appeared to be linked to different soil textures and to seasonal surface changes. K 0 values compared favorably with other F a /q values measured at Owens Lake using portable wind tunnel and micrometeorological methods. Hourly trends for the model-predicted PM 10 concentrations agreed well with monitored PM 10 concentrations. Dust production was estimated at 7.2 Â 10 4 t of PM 10 for a 12 month period. A single storm accounted for 9% of the annual dust emissions at 6.5 Â 10 3 t. The modeling results were used to identify 77 km 2 of dust-producing areas on the lake bed that will be controlled to attain the federal air quality standard for PM 10 .

A joint United States/Russian/French collaborative experiment was undertaken in March 1993 and March 1996. Projects LODE I and II (Lake Owens Dust Experiments) took place on the anthropogenically desertified playa (dry lakebed) and surrounding regions of Owens Lake, in east-central California. One of the five parts of Project LODE was to determine relationships between optical depth and flux of dust emitted from the dry lake. Project LODE II included subsequent dust plume measurements and size distributions obtained through April 1996, to further refine the flux measurements for distinct mineral aerosol source regions at Owens Lake.Size distributions of dust aerosol were determined and aerosol optical depths were calculated from sunphotometer solar extinction measurements taken downwind in plumes coming from the emissive areas of Owens Lake. This source was visually observed for 10 measured dust storms. The plume mass was calculated to be 1Á5 Â 10 9 g using ground-based measurements and !1Á6 Â 10 9 g from satellite data. Project LODE II results were found to be consistent with LODE I results for the south end of the playa, but flux values were found to be reduced for the northeastern portion of the playa by comparison. Vertical flux values estimated by sunphotometry were found to be consistent with values estimated via a micrometeorological method.

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