Atmospheric Environment Vol. 27A, No. 16, pp. 2539-2544, 1993. 0004--6981/93 $6.00+0.00 Printed in Great Britain. © 1993 Pergamon Pr¢~ Ltd.

A COMPARISON OF CHARACTERISTICS OF AEROSOL FROM DUST STORMS IN CENTRAL ASIA WITH SOIL-DERIVED DUST FROM OTHER REGIONS

LAURENT GOMES* Laboratoire de Physico-Chimie de rAtmosphrre, Universit6 Paris VII, UA CNRS 1404, 2 place Jussieu,

75251 Paris, France

and

DALE A. GILLETTE

Air Resources Laboratory, NOAA/ERL, 325 Broadway, Boulder, CO 80303, U.S.A.

(First received 2 July 1992 and in final form 12 December 1992)

Abstract--Aerosol samples from dust storms were collected in Tadzhikistan (Soviet Central Asia) during September 1989, as a part of the joint U.S.S.R.-U.S. Dust Experiment. Physico-chemical characteristics of deposited dust were compared with those of soil-derived dust collected in other regions. Particle mass-size distributions appear to be characterized by a common log-normal mode between 1 and 10/~m. Chemical composition of the sampled material shows that the dust is particularly rich in calcium and silicon and poor in iron. Estimated mineral composition of dust indicates that this enrichment in Ca and Si for the Soviet Asian dust must be related to high contents of carbonate and quartz, respectively. Different Fe/A1 also suggest a specific chemical composition for clay minerals in the Asian dust.

Key word index: Aerosols, soil-derived dust, chemistry, mineralogy, Soviet Central Asia.

I N T R O D U C T I O N

Mineral dust in the atmosphere can be observed in many geographical regions of the Earth. For this aerosol, the size fraction of particles < 20/tm has the capability of being transported over thousands of kilometers, mainly from the arid and semi-arid regions of continents. In the Northern Hemisphere, the main deserts are the Asian (Chinese, Arabian, Persian) and the North American arid and semi-arid areas which are mostly at about 40°N + 10 °, and the Sahara desert at about 25°N + 10 °. Soils constitute huge sources for mineral dust in these regions. During its transport, airborne dust is involved in many physico-chemical processes of the atmosphere, the hydrosphere and the geosphere. After their deposition, eolian mineral par- ticles strongly contribute to the composition of the sediments, both on the continents and in oceans (Prospero, 1981). The great loess areas are good ex- amples of past eolian deposits. Eolian sedimentation also provides a significant paleoclimatic record be- cause the dust concentration and composition in cores are linked to past climates of the source area. Such data can also provide information on atmospheric circulation.

* Present address: Air Resources Laboratory, NOAA/ERL, 325 Broadway, Boulder, CO 80303, U.S.A.

For an adequate understanding of the impact of geological sources of aerosol, it is necessary to com- pare their chemical and mineral characteristics. For that, source markers are needed to identify the actual sources for the dust transported in adjacent and distant deposition areas.

Because mineral dust consists of many inert com- pounds, elemental tracer and typical elemental ratios are known to serve as markers for aerosol transport studies (see for example Bergametti et al. (1989) and Tomadin and Lenaz (1989) for the Sahara). Minera- logical components of dust can also be considered.

A comparative investigation was undertaken to describe the geochemical nature of mineral aerosol < 20 gm generated from some major dust source areas of Africa, Asia, and North America. As a part of the joint U.S.S.R.-U.S. Dust Experiment, the elemental and mineral composition of the soil-derived aerosols for the Soviet Central Asian region is presented here and compared.

EXPERIMENTAL PROCEDURES

Aerosol samples from dust storms were obtained near the village of Shaartuz (37°07'N, 68°0YE) in southern Tadzhik, S.S.R., Soviet Central Asia, during September 1989. Filter sampling was used for measuring aerosol concentration. Also, high-volume inertial impactor sampling was employed for measuring the size distribution of airborne particles.

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