HR: 1340h
AN: A33A-0870    [Abstracts]
TI: Dust Particles in the Troposphere Over the UAE and Their Impact on Cloud Formation and Precipitation
AU: * Kojima, T
EM: tkojima@sci.kumamoto-u.ac.jp
AF: Department of environmental Sceinces, Kumamoto University, 2-39-1, Kurokami, Kumamoto, 860-8555 Japan
AU: Kishikawa, Y
EM: 057d8522@sci.stud.kumamoto-u.ac.jp
AF: Department of environmental Sceinces, Kumamoto University, 2-39-1, Kurokami, Kumamoto, 860-8555 Japan
AU: Bruintjes, R T
EM: roelof@ucar.edu
AF: National Center for Atmospheric Research, P.O.Box 3000, Boulder, CO 80307 United States
AU: Salazar, V
EM: vidal@ucar.edu
AF: National Center for Atmospheric Research, P.O.Box 3000, Boulder, CO 80307 United States
AU: Buseck, P R
EM: pbuseck@asu.edu
AF: Departments of Geological Sciences and Chemistry/Biochemistry, Arizona State University, ASU, Tempe, AZ 85287 United States
AB: Airborne aerosol sampling was performed in the UAE during the 2002 winter campaign (February-April) at altitudes ranging from 150 to 4000 m. Aerosol particles were collected using a pair of three-stage cascade impactors (50% cut-off sizes: 2.0, 0.3 and 0.05 μm). Ca-coated TEM grids were used for sampling at cloud bases to test for the presence of water droplets. We used TEM and SEM to examine the physical and chemical properties and mixing states of individual aerosol particles. The coarse-grained fraction (0.3 - 10 μm diameter) consists largely of Ca carbonate and sulfate (35 - 50 % by number) and Mg-, Al-, and K-rich silicates (20 - 40 %). These minerals are major constituents of the eolian sediments in the nearby desert area, so their abundance can be attributed to the desert dust. Na chloride, sulfate, and nitrate occur in variable amounts (5 - 35%) depending on sampling location and date. Other constituents include ammonium sulfate (2 - 8 %), soot (3 - 10 %), and organic material (1 - 5 %). On the other hand, more than 90 % of the fine-grained particles (0.05 - 0.3 μm diameter) are ammonium sulfate that probably resulted from gas-to-particle conversion of SO₂ emitted from the oil fields. The coarse-grained desert-dust particles are commonly attached to Na-salt particles, forming aggregates as large as 15 μm across. Such aggregation might have occurred through cloud processing or through evaporation in salt flats near the sampling locations. TEM observations revealed that some dust particles are covered with fine-grained ammonium sulfate particles. Desert-dust particles are generally considered to be inefficient CCN, but those aggregated with hygroscopic Na salts and ammonium sulfate could act as giant CCN and affect cloud formation and precipitation processes. Samples collected onto Ca-coated grids show many traces of water droplets (1 - 15 μm diameter on the grids) that contain dust particles in the center, suggesting that the particles were hygroscopic and deliquesced.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0320 Cloud physics and chemistry
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 4801 Aerosols (0305, 4906)
DE: 4906 Aerosols (0305, 4801)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005