Atmos. Chem. Phys. Discuss., 8, 19249-19272, 2008
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Observation of nitrate coatings on atmospheric mineral dust particles
W. J. Li1,2 and L. Y. Shao1
1State Key Laboratory of Coal Resources and Safe Mining & Department of Resources and Earth Science, China University of Mining and Technology, Beijing, China
2School of Earth and Space Exploration & Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ, USA

Abstract. Nitrate compounds have recently received much attention because of their ability to alter the hygroscopic properties and cloud condensation nuclei (CCN) activity of mineral dust particles in the atmosphere. However, very little is known about specific characteristics of nitrate-coated mineral particles in an individual particle scale in field study. The sample collection was conducted during brown haze and dust episodes occurred between 24 May and 21 June 2007 in Beijing, northern China. The sizes, morphologies, and compositions of mineral dust particles together with their coatings were analyzed using transmission electron microscopy (TEM). 92% of the internally mixed mineral particles analyzed are covered with Ca-, Mg-, and Na-rich coatings, and 8% are associated with K- and S-rich coatings. The major coatings contain Ca, Mg, O, and N with minor amounts of S and Cl, suggesting that they are possibly nitrates mixed with less sulfates and chlorides. These nitrate coatings strongly relate with the presence of alkaline mineral components (e.g., calcite and dolomite) within individual mineral particles. Calcium sulfate particles with the diameter from 10 to 500 nm were also detected within Ca(NO3)2 and Mg(NO3)2 coatings. Our results indicate that mineral particles in brown haze episodes were involved in atmospheric heterogeneous reactions with two or more acidic gases (e.g., SO2, NO2, HCl, and HNO3). Mineral particles that acquire hygroscopic coatings tend to be more spherical and larger. Such changes enhance their light scattering and CCN activity, both of which have cooling effects on the climate.

Citation: Li, W. J. and Shao, L. Y.: Observation of nitrate coatings on atmospheric mineral dust particles, Atmos. Chem. Phys. Discuss., 8, 19249-19272, doi:10.5194/acpd-8-19249-2008, 2008.
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