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| Titel |
Sea salt, sulfate, nitrate, chloride in Asian dust particles observed in Japan: results of individual particle analysis |
| VerfasserIn |
Daizhou Zhang, Maromu Yamada, Yutaka Tobo, Hiroko Ogata, Kazutaka Hara, Tetsuji Nagatani, Atsushi Matsuki, Yasunobu Iwasaka, Kirsten Lieke |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250033666
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| Zusammenfassung |
| Atmospheric particles were collected in Japan during Asian dust storm events from 2000 to
2007. Dust particles were analyzed by using electron microscopes and the mixture
state of individual dust particles with sea salt, sulfate, nitrate and chloride were
investigated. About 60~85% of dust particles were internally mixed with sea salt,
91% or more dust particles contained sulfate, and 27% or less contained nitrate.
Besides the coagulation of sea-salt and dust particles, chlorine could deposit onto dust
particles through the absorption of chlorine-containing gases when the particles
passed through the marine atmosphere between China and Japan. The quantitative
estimation revealed that the chlorine deposition on many particles was not negligible
compared to sulfur deposition. The preferential formation of chloride in Ca-rich dust
particles in cases when the particles contain little or no sulfate was found. Most of the
particles were in an amorphous state and nearly spherical even under high vacuum,
implying the potential enhancement of dust hygroscopicity. Comparisons of the relative
weight ratios of sodium, sulfur and chlorine in mixture particles and in sea salt
particles showed that mineral materials could enhance particulate sulfate and nitrate
formation and restrain chlorine depletion from the sea salt components in mixture
particles.
Size distributions of the particles segregated by the mixture degrees of mineral and sea
salt in different dust storm events were similar and all distributions showed a diameter range
of 1~8 μm with maximum mode around 3 μm. Out of 1~8 μm, dust particles were rarely
detected. It is confirmed that the size increase of dust particles had a strong correlation with
their sea salt content but was independent from their non-sea-salt sulfur content, suggesting
that the growth of dust particles in size during their dispersion in the marine atmosphere was
dominated by the combination with sea salt rather than by other processes such as surface
uptake of sulfate. Estimates of size shift of dust particles due to sea salt adhering
indicated that mixing with sea salt had caused their size distributions to shift to
larger ranges approximately by 0.4 ~ 0.8 μm during the particles passed the marine
atmosphere between China and Japan. Since size and density of a particle are two key
parameters in determining its settling velocity, it is expected that the combination
of dust particles with sea salt might largely change the settling velocity of dust
particles to the surface and consequently the sedimental flux of mineral dust to sea
surface in the marine atmosphere. Estimates with the observational data from six
dust events revealed that, due to sea salt adhering, the gravitational settling flux
of mineral dust increased approximately 14 ~ 17% in well-mixed events and 4
~ 6% in less-mixed events, indicating the importance of considering this effect
in the schemata of particle gravitational settling when mapping dust flux to the
ocean.
This presentation provides the data of Asian dust to the presentation (by K. Lieke et al.)
about the comparison of African dust and Asian dust observed at islands close to the
continents where they were originated. |
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