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| Titel |
Wet and dry deposition of mineral dust particles in Japan: factors related to temporal variation and spatial distribution |
| VerfasserIn |
K. Osada, S. Ura, M. Kagawa, M. Mikami, T. Y. Tanaka, S. Matoba, K. Aoki, M. Shinoda, Y. Kurosaki, M. Hayashi, A. Shimizu, M. Uematsu |
| 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 ; 14, no. 2 ; Nr. 14, no. 2 (2014-01-29), S.1107-1121 |
| Datensatznummer |
250118325
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| Publikation (Nr.) |
 copernicus.org/acp-14-1107-2014.pdf |
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| Zusammenfassung |
Recent ground networks and satellite remote-sensing observations have
provided useful data related to spatial and vertical distributions of
mineral dust particles in the atmosphere. However, measurements of temporal
variations and spatial distributions of mineral dust deposition fluxes are
limited in terms of their duration, location, and processes of deposition.
To ascertain temporal variations and spatial distributions of mineral dust
deposition using wet and dry processes, weekly deposition samples were
obtained at Sapporo, Toyama, Nagoya, Tottori, Fukuoka, and Cape Hedo
(Okinawa) in Japan during October 2008–December 2010 using automatic wet
and dry separating samplers. Mineral dust weights in water-insoluble residue
were estimated from Fe contents measured using an X-ray fluorescence
analyser. Wet and dry deposition fluxes of mineral dusts were both high in
spring and low in summer, showing similar seasonal variations to frequency
of aeolian dust events (Kosa) in Japan. For wet deposition, highest and lowest
annual dust fluxes were found at Toyama (9.6 g m−2 yr−1) and at
Cape Hedo (1.7 g m−2 yr−1) as average values in 2009 and 2010.
Higher wet deposition fluxes were observed at Toyama and Tottori, where
frequent precipitation (> 60% days per month) was observed
during dusty seasons. For dry deposition among Toyama, Tottori, Fukuoka, and
Cape Hedo, the highest and lowest annual dust fluxes were found respectively
at Fukuoka (5.2 g m−2 yr−1) and at
Cape Hedo (2.0 g m−2 yr−1)
as average values in 2009 and 2010. The average ratio of wet and
dry deposition fluxes was the highest at Toyama (3.3) and the lowest at Hedo
(0.82), showing a larger contribution of the dry process at western sites,
probably because of the distance from desert source regions and because of
the effectiveness of the wet process in the dusty season.
Size distributions of refractory dust particles were obtained using
four-stage filtration: > 20, > 10, > 5, and > 1 μm diameter. Weight fractions of the sum of
> 20 μm and 10–20 μm (giant fraction) were
higher than 50% for most of the event samples. Irrespective of the
deposition type, the giant dust fractions generally decreased with increasing
distance from the source area, suggesting the selective depletion of larger
giant particles during atmospheric transport. Based on temporal variations of
PMc (2.5 < D < 10 μm),
ground-based lidar, backward air trajectories, and vertical profiles of
potential temperatures, transport processes of dust particles are discussed
for events with high-deposition and low-deposition flux with high
PMc. Low dry dust depositions with high PMc
concentrations were observed under stronger (5 K km−1) stratification
of potential temperature with thinner and lower (< 2 km)
dust distributions because the PMc fraction of dust particles
only survived after depletion of giant dust particles by rapid gravitational
settling at the time they reach Japan. In contrast, transport through a
thicker (> 2 km) dust layer with weak vertical gradient of
potential temperature carry more giant dust particles to Japan. Because giant
dust particles are an important mass fraction of dust accumulation,
especially in the North Pacific, which is known as a high-nutrient,
low-chlorophyll (HNLC) region, the transport height and fraction of giant
dust particles are important factors for studying dust budgets in the
atmosphere and their role in biogeochemical cycles. |
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