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| Titel |
Observation of nitrate coatings on atmospheric mineral dust particles |
| VerfasserIn |
W. J. Li, L. Y. Shao |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 9, no. 6 ; Nr. 9, no. 6 (2009-03-17), S.1863-1871 |
| Datensatznummer |
250007080
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| Publikation (Nr.) |
 copernicus.org/acp-9-1863-2009.pdf |
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| Zusammenfassung |
| Nitrate compounds have 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 ambient nitrate-coated mineral
particles on an individual particle scale. In this study, sample collection
was conducted during brown haze and dust episodes between 24 May and 21 June
2007 in Beijing, northern China. Sizes, morphologies, and compositions of
332 mineral dust particles together with their coatings were analyzed using
transmission electron microscopy (TEM) coupled with energy-dispersive X-ray
(EDX) microanalyses. Structures of some mineral particles were verified
using selected-area electron diffraction (SAED). TEM observation indicates
that approximately 90% of the collected mineral particles are covered by
visible coatings in haze samples whereas only 5% are coated in the dust
sample. 92% of the analyzed mineral particles are covered with Ca-,
Mg-,
and Na-rich coatings, and 8% are associated with K- and S-rich coatings.
The majority of coatings contain Ca, Mg, O, and N with minor amounts of S
and Cl, suggesting that they are possibly nitrates mixed with small amounts
of sulfates and chlorides. These nitrate coatings are strongly
correlated with the presence of alkaline mineral components (e.g., calcite
and dolomite). CaSO4 particles with diameters from 10 to 500 nm were
also detected in the coatings including Ca(NO3)2 and
Mg(NO3)2. 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 nitrate coatings tend to be more
spherical and larger, enhancing their light scattering and CCN activity,
both of which have cooling effects on the climate. |
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