TY - JOUR
T1 - Interactions of mineral dust with pollution and clouds
T2 - An individual-particle TEM study of atmospheric aerosol from Saudi Arabia
AU - Pósfai, Mihály
AU - Axisa, Duncan
AU - Tompa, Éva
AU - Freney, Evelyn
AU - Bruintjes, Roelof
AU - Buseck, P R
N1 - Funding Information:
The authors gratefully acknowledge the major contribution by the aircraft pilot Ronnie Edwin Chambless. Mr. Chambless skillfully flew the aircraft directly into the dust storm to obtain these measurements. We acknowledge the NOAA Air Resources Laboratory (ARL) for the HYSPLIT transport and dispersion model and READY website ( http://www.arl.noaa.gov/ready.php ) used in this publication. This study was supported by the Presidency of Meteorology and Environment (PME) in Saudi Arabia through a contract with Weather Modification Incorporated of Fargo, North Dakota and by an NSF grant. Supplementary support was provided by NSF grant ATM-0531926 . We gratefully acknowledge the use of TEMs within the LeRoy Eyring Center for Solid State Science at Arizona State University.
PY - 2013/3
Y1 - 2013/3
N2 - Aerosol particles from desert dust interact with clouds and influence climate on regional and global scales. The Riyadh (Saudi Arabia) aerosol campaign was initiated to study the effects of dust particles on cloud droplet nucleation and cloud properties. Here we report the results of individual-particle studies of samples that were collected from an aircraft in April 2007. We used analytical transmission electron microscopy, including energy-dispersive X-ray spectrometry, electron diffraction, and imaging techniques for the morphological, chemical, and structural characterization of the particles.Dust storms and regional background conditions were encountered during four days of sampling. Under dusty conditions, the coarse (supermicrometer) fraction resembles freshly crushed rock. The particles are almost exclusively mineral dust grains and include common rock-forming minerals, among which clay minerals, particularly smectites, are most abundant. Unaltered calcite grains also occur, indicating no significant atmospheric processing. The particles have no visible coatings but some contain traces of sulfur. The fine (submicrometer) fraction is dominated by particles of anthropogenic origin, primarily ammonium sulfate (with variable organic coating and some with soot inclusions) and combustion-derived particles (mostly soot). In addition, submicrometer, iron-bearing clay particles also occur, many of which are internally mixed with ammonium sulfate, soot, or both. We studied the relationships between the properties of the aerosol and the droplet microphysics of cumulus clouds that formed above the aerosol layer. Under dusty conditions, when a large concentration of coarse-fraction mineral particles was in the aerosol, cloud drop concentrations were lower and droplet diameters larger than under regional background conditions, when the aerosol was dominated by submicrometer sulfate particles.
AB - Aerosol particles from desert dust interact with clouds and influence climate on regional and global scales. The Riyadh (Saudi Arabia) aerosol campaign was initiated to study the effects of dust particles on cloud droplet nucleation and cloud properties. Here we report the results of individual-particle studies of samples that were collected from an aircraft in April 2007. We used analytical transmission electron microscopy, including energy-dispersive X-ray spectrometry, electron diffraction, and imaging techniques for the morphological, chemical, and structural characterization of the particles.Dust storms and regional background conditions were encountered during four days of sampling. Under dusty conditions, the coarse (supermicrometer) fraction resembles freshly crushed rock. The particles are almost exclusively mineral dust grains and include common rock-forming minerals, among which clay minerals, particularly smectites, are most abundant. Unaltered calcite grains also occur, indicating no significant atmospheric processing. The particles have no visible coatings but some contain traces of sulfur. The fine (submicrometer) fraction is dominated by particles of anthropogenic origin, primarily ammonium sulfate (with variable organic coating and some with soot inclusions) and combustion-derived particles (mostly soot). In addition, submicrometer, iron-bearing clay particles also occur, many of which are internally mixed with ammonium sulfate, soot, or both. We studied the relationships between the properties of the aerosol and the droplet microphysics of cumulus clouds that formed above the aerosol layer. Under dusty conditions, when a large concentration of coarse-fraction mineral particles was in the aerosol, cloud drop concentrations were lower and droplet diameters larger than under regional background conditions, when the aerosol was dominated by submicrometer sulfate particles.
KW - Cloud microphysics
KW - Desert dust
KW - Individual aerosol particles
KW - Smectite
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U2 - 10.1016/j.atmosres.2012.12.001
DO - 10.1016/j.atmosres.2012.12.001
M3 - Article
AN - SCOPUS:84872423198
SN - 0169-8095
VL - 122
SP - 347
EP - 361
JO - Atmospheric Research
JF - Atmospheric Research
ER -