Faculty Profiles - OSADA, Kazuo

Papers - OSADA, Kazuo

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Maritime aerosol optical thickness measured during Antarctic research cruises of R V Umitaka-Maru

Hiroshi Kobayashi, Toru Hirawake, Masanori Yabuki, Sayako Ueda, Kazuo Osada, Masataka Shiobara, Mitsuo Fukuchi

Vol. 54 ( 0 ) page： 465-473 2010.12

Language：English Publishing type：Research paper (scientific journal)

東京海洋大学[海鷹丸]の南極海研究航海において,大気エアロゾルの光学的厚さ(AOT)の観測を実施した.南極海インド洋セクターでの500 nmでのAOTは,0.02-0.12の範囲であった.南極大陸沿岸域でのAOTは比較的低く,0.02前後であった.40-60゜Sの海域では,0.1以上の値を示すことがあった.インド洋低中緯度帯でのAOTは,0.05-0.15の範囲であった.風速とAOTとに正の相関がみられたことから,南極海では光学的に海塩粒子が卓越し,風速がAOTに影響を及ぼしていると考えられる.AOTが高くなるにつれ,オングストローム指数は減少した.AOTの波長スペクトルにおいて,380 nmと870 nmのAOTはべき関数からずれる傾向がみられた.レイリーの光学的厚さの算出方法を比較したところ,ずれが大幅に改善される可能性が示された.今後,より観測精度を高めていくためには,機器定数の精度を把握するとともに,レイリーの光学的厚さの算出方法の見直しなどが必要である.Aerosol optical thickness (AOT) was measured during Antarctic research cruises of R V Umitaka-Maru. The measured AOTs at 500 nm in the Indian sector of the Antarctic Ocean ranged from 0.02 to 0.12. In Antarctic coastal waters, the AOTs were as low as around 0.05. On the other hand, the some AOTs were higher than 0.1 from 40゜S to 60゜S. In middle and low latitude regions of the Indian Ocean, the AOTs ranged from 0.05 to 0.15. The AOTs were correlated with wind speed. It is indicated that sea-salt particles, generated by wind, dominated optically and wind speed affected the AOT in the Antarctic Ocean. Angstro¨m exponent decreased with increasing AOT. In the AOT wavelength spectra, some AOTs in 380 nm and 870 nm tended to deviate from the power function. Comparing calculation methods of Rayleigh optical thickness suggested a possibility of reducing the deviations of these AOTs. In the future, accuracy check of the instrument constant and review of the calculation method of Rayleigh optical thickness are recommended to enhance the accuracy of maritime AOT measurement.

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Monitoring of aerosol concentration at Syowa Station

Hayashi Masahiko, Osada Kazuo, Hara Keiichiro, Yabuki Masanori, Kobayashi Hiroshi, Ihara Satoshi, Wada Makoto, Yamanouchi Takashi, Hashida Gen, Shiobara Masataka

Antarctic record Vol. 54 ( 0 ) page： 474-486 2010.12

Language：English Publishing type：Research paper (scientific journal)

Concentrations of condensation nuclei (>0.01 μm in diameter) and of aerosol particles larger than 0.3 μm in diameter were monitored at Syowa Station from February, 1996. Number concentrations of condensation nucleus were high in summer and low in winter. Concentrations increased at the rate of several partcles cm^3 per year. On the other hand, the concentrations of fine particles (>0.3 μm) and coarse particles (>1.0 μm) were low in summer and high in winter. Concentrations of fine particles 0.3 μm and larger after July were double those before July.

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沖縄辺戸岬における大気中のアンモニア/アンモニウム濃度の変動と分配 Reviewed

高見昭憲、長田和雄、定永靖宗、坂東博、

エアロゾル研究 Vol. 掲載決定 2010.12

Seasonal variation of size distribution of submicrometer aerosol particles at Syowa Station, Antarctica

Osada Kazuo, Nishita-Hara Chiharu, Hara Keiichiro, Yabuki Masanori, Shiobara Masataka, Wada Makoto, Yamanouchi Takashi, Hayashi Masahiko

Antarctic record Vol. 54 ( 0 ) page： 530-540 2010.12

Language：English Publishing type：Research paper (scientific journal)

Number-size distributions (5-168 nm in diameter) of atmospheric aerosol particles were measured at Syowa Station, Antarctica from February 2004 to January 2005. Size distributions in winter consisted of 1 to 2 modes larger than 50 nm in diameter, whereas 2 to 3 modes contributed to the size distributions in October to March with mode diameters between 20 and 80 nm. Size distribution with a valley at around 50 nm was often observed in summer to fall when the open ocean was located near Syowa Station. From September to March, concentration of ultra fine particles (<20 nm) was occasionally high. Associated with local wind pattern after vertical mixing of boundary layer air in late afternoon, high concentrations of ultra fine particles were observed for several days in late November.

Observations of atmospheric aerosol particles over the Antarctic ocean by ocean research vessels

Osada Kazuo, Hara Keiichiro, Yabuki Masanori, Nishita-Hara Chiharu, Kobayashi Hiroshi, Miura Kazuhiko, Ueda Sayako, Hayashi Masahiko, Hashida Gen, Shiobara Masataka, Wada Makoto, Yamanouchi Takashi

Antarctic record Vol. 54 ( 0 ) page： 449-464 2010.12

Language：English Publishing type：Research paper (scientific journal)

To investigate spatial and temporal variation of number-size distribution of atmospheric aerosol particles in the Antarctic Ocean, atmospheric observations were conducted on research vessels: Hakuho-maru, Tangaroa, and Umitaka-maru. Concentrations of ionic constituents in aerosols and precursor gases (SO_2 and NH_3) were also measured during the cruises. Concentrations of nucleation mode particles (<20 nm in diameter) were often high under the conditions of very low number concentrations of preexisting aerosol particles larger than 0.1 μm in diameter, when the ocean was calm. Nucleation mode particles did not appear when concentrations of preexisting aerosols were high. Major ionic concentrations of aerosols at Lutzow-Holmbukta observed by Umitaka-maru in January 2005 were almost the same as average values of those in January at Syowa Station. Especially for short-term increasing events in condensation nucleus concentration, large differences were found for number size-distributions of nucleation and Aitken mode particles between Syowa Station and Umitaka-maru in Lutzow-Holmbukta.

Electroconductivity of fallen and drifting snow at Syowa Station, Antarctica

Osada Kazuo, Hara Keiichiro, Yabuki Masanori, Adachi Masaki

Antarctic record Vol. 54 ( 0 ) page： 697-703 2010.12

Language：English Publishing type：Research paper (scientific journal)

Samples of fallen snow, drifting snow and deposited snow were obtained at Syowa Station from April 2003 to October 2006. Electroconductivity of the meltwater was measured. The electroconductivities of the samples for the fallen snow under weak wind condition were mostly below several tens of μS cm, whereas much higher values were obtained for the drifting snow samples under strong wind condition with seasonal variation: maximum (several hundred to thousands) in April to July, then decreasing to a few hundred after September. Higher electro conductivities of the drifting snow samples correlated well with breakup of sea ice windward of Syowa Station. Lower values were obtained after snow accumulated on sea ice at Kita-no-ura, windward bay area north-east and offshore of Syowa Station. These suggest that brine from sea ice changes the electroconductivity of drifting snow.

Seasonal variation of coarse aerosol particle concentration at Syowa Station, Antarctica

Osada Kazuo, Hayashi Masahiko, Hara Keiichiro, Yabuki Masanori, Wada Makoto, Shiobara Masataka, Yamanouchi Takashi, Fujita Kouji

Antarctic record Vol. 54 ( 0 ) page： 487-497 2010.12

Language：English Publishing type：Research paper (scientific journal)

Number-size distributions (D_p>0.3 μm) of atmospheric aerosol particles were measured at Syowa Station, Antarctica, from February 2004 to January 2006. Volume concentrations of coarse particles (D_p 1.0-5.0 μm) were low in December to January and high in the rest of the year. To identify factors controlling the seasonal variation of coarse particle concentrations at Syowa Station, seasonal variations of wind speed distribution over the Southern Ocean, sea ice extent, wind speed at the edge of sea ice and at Syowa Station, and seasonal patterns of backward air trajectories were compared with the volume concentrations of coarse particles. Patterns of backward air trajectories and changes in size distributions of coarse particles associated with sea ice extent suggest changes in major source areas of sea salt particles observed at Syowa Station: coastal areas near Syowa in February and March, but far north of the sea ice edge, around 60゜ south, in October.

Seasonal variation of carbonaceous and metal compositions of atmospheric aerosols at Syowa Station, Antarctica in 2001

Kobayashi Hiroshi, Hara Keiichiro, Shiobara Masataka, Yamanouchi Takashi, Osada Kazuo, Ohta Sachio

Antarctic record Vol. 54 ( 0 ) page： 554-561 2010.12

Language：English Publishing type：Research paper (scientific journal)

Antarctic aerosols collected at Syowa Station in 2001 were analyzed to investigate their seasonal variations and long-range transport of anthropogenic aerosols. The measured chemical species were elemental carbon and organic carbon, and metals such as Al, V, Cr, Mn, Fe, Co, Ni, Zn and Pb. Concentration of elemental carbon was relatively low in April-June and was high in March, October and November. The concentrations of Al, V, Co, Ni and Pb were sometimes lower than the detection limits. Spikes of the highest concentrations of V, Cr, Fe, Co, Ni, Zn and Pb were recorded in August-October. The enrichment factors were high during blizzards. This indicates that air masses containing anthropogenic aerosols were transported to Antarctica by low-pressure system perturbation.

Haze episodes at Syowa Station, Antarctica

Hara Keiichiro, Osada Kazuo, Yabuki Masanori, Hashida Gen, Yamanouchi Takashi, Hayashi Masahiko, Shiobara Masataka, Nishita-Hara Chiharu, Wada Makoto

Antarctic record Vol. 54 ( 0 ) page： 593-622 2010.12

Language：English Publishing type：Research paper (scientific journal)

During our aerosol measurement program at Syowa Station, Antarctica in 2004-2007, some low visibility (haze) phenomena were observed under conditions with weak wind and without drifting snow and fog in winter-spring. In the "Antarctic haze" phenomenon, the number concentration of aerosol particles and black carbon concentration increased by one-two orders higher relative to background conditions at Syowa Station, while surface O_3 concentration simultaneously dropped especially after polar sunrise. Major aerosol constituents in the haze phenomenon were sea-salts (e.g., Na^+ and Cl^-). From the trajectory analysis and NAAPS model, the plumes from biomass burning in South America and southern Africa were transported to Syowa Station, Antarctic coast, during eastward (occasionally westward) approach of cyclones in the Southern Ocean. Thus, poleward flow of the plume from mid-latitudes and injection of sea-salt particles during the transport may lead to the Antarctic haze phenomenon at Syowa Station. The difference of O_3 concentration between the background and the haze conditions tended to be larger in spring (polar sunrise) relative to that in winter. Because enhancement of sea-salt particles can play an important role as an additional source of reactive halogen species, the haze episodes might make a significant contribution to surface O_3 depletion during the polar sunrise on the Antarctic coast.

Seasonal variation and volatility of ultra-fine particles in coastal Antarctic troposphere

Hara Keiichiro, Osada Kazuo, Nishita-Hara Chiharu, Yabuki Masanori, Hayashi Masahiko, Yamanouchi Takashi, Wada Makoto, Shiobara Masataka

Antarctic record Vol. 54 ( 0 ) page： 541-553 2010.12

Language：English Publishing type：Research paper (scientific journal)

The Size distribution and volatility of ultrafine aerosol particles were measured at Syowa Station during the 46-47 Japanese Antarctic Research Expeditions. During the summer, most of the ultrafine particles were volatile particles, which were composed of H_2SO_4, CH_3SO_3H and sulfates bi-sulfates. The abundance of non-volatile particles was 〜 20% during the summer, increasing to>90% in winter-spring. Non-volatile particles in winter were dominantly sea-salt particles. Some ultrafine sea-salt particles might be released from sea-ice. When air mass was transported from the free troposphere over the Antarctic continent, the abundance of non-volatile particles dropped to<30% even in winter.

Seasonal variations and vertical features of aerosol particles in the Antarctic troposphere

Hara Keiichiro, Osada Kazuo, Nishita-Hara Chiharu, Yamanouchi Takashi, Hayashi Masahiko

Antarctic record Vol. 54 ( 0 ) page： 731-759 2010.12

Language：English Publishing type：Research paper (scientific journal)

Tethered balloon-borne aerosol measurements were carried out at Syowa Station, Antarctica during the 46th Japanese Antarctic Research Expedition. CN concentration had a maximum in the summer, whereas the number concentrations of fine particles (D_p>0.3 μm) and coarse particles (D_p>2.0 μm) increased during the winter-spring. The range of CN concentration was 30-2200 cm^<-3> near the surface (surface-500 m) and 7-7250 cm^<-3> in the lower free troposphere (>1500 m). During the austral summer, higher CN concentration was often observed in the lower free troposphere. Frequent appearance of higher CN concentration in the free troposphere relative to the surface measurements strongly suggests that new particle formation in the Antarctic regions occurs in the lower free troposphere. Single particle analysis indicated that most of the aerosol particles during the winter were composed of Mg-enriched sea-salt particles originated from sea-salt fractionation on the sea-ice and their modified particles by NO_3^<-> and SO_4^<2->. This suggests that sea-salt fractionation on sea-ice and modification of sea-salt particles were affected greatly by aerosol hygroscopicity during the winter. Antarctic haze layer was observed not only in the boundary layer but also in the lower free troposphere.

Chemistry of sea-salt particles and sea-salt fractionation in Antarctic region

Hara Keiichiro, Osada Kazuo, Hayashi Masahiko, Yabuki Masanori, Hashida Gen, Yamanouchi Takashi

Antarctic record Vol. 54 ( 0 ) page： 668-696 2010.12

Language：English Publishing type：Research paper (scientific journal)

Observations of aerosol constituents and acidic gases were carried out at Syowa Station (1997-1998 and 2003-2006; JARE-38〜 39, and JARE-44〜 47) and Dome Fuji Station (1997, JARE-38). Seasonal variations and size distribution of sea-salt particles were compared between coastal and inland stations. Seasonal variations of the concentrations of sea-salt particles showed a minimum in the austral summer and higher during the winter at both stations due to strong winds and long-range transport. Sea-salt particles were mostly distributed in fine (D_p: 0.2-2.0 μm) and ultra-fine (D_p<0.2 μm) modes at Syowa Station. Particulate Cl^- and Br^- are liberated preferentially from sea-salt particles through the heterogeneous reactions at Syowa and Dome Fuji Stations in the summer. The molar ratio of Cl^- Na^+ and Br^- Na^+ at Syowa Station decreased to ca. 0.5 and 〜0, respectively, in summer. Fewer sea-salt particles were modified at Syowa Station during the winter, whereas sea-salt particles were modified through the year at Dome Fuji Station. In particular, sea-salt particles were modified with NO_3^- and its precursors at Dome Fuji Station during the winter. The concentrations of gaseous inorganic chlorine species (mostly HCl) and bromine species at Syowa Station were 0.2-9.4 nmol m^<-3> and below the detection limit (BDL)-1.5 nmol m^<-3>, respectively. Sea-salt fractionation (SO_4^<2-> depletion) due to Mirabilite formation was identified not only at Syowa Station but also at Dome Fuji Station. Seasonal variation of molar ratio of Mg^<2+> Na^+ showed higher ratios at lower temperature. The range and temperature dependence of Mg^<2+> Na^+ strongly suggested that other sea-salt fractionation (e.g., formation of gypsum and hydrohalite) occurred in the Antarctic coasts in addition to Mirabilite formation. Because of different seasonal variation and range of Mg^<2+> Na^+ between Dome Fuji and Syowa Stations, sea-salt fractionation may proceed even in the inland area.

Black carbon at a coastal Antarctic station (Syowa Station): Seasonal variation and transport processes

Hara K., Osada K., Yabuki M., Hayashi M., Yamanouchi T., Shiobara M., Wada M.

Antarctic Record Vol. 54 ( SPEC. ISSUE ) page： 562 - 592 2010.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Antarctic Record

Measurement of atmospheric black carbon (BC) was carried out at Syowa Station Antarctica (69°00′S, 39°35′E) from February 2004 until January 2007. The BC concentration at Syowa Station ranged from below detection to 176 ng m -3. Higher BC concentrations were observed frequently from April until October. Increase of BC concentration may be associated with poleward flow due to the approach of a cyclone and/or blocking event during winter-spring. The BC-rich air masses traveled through the lower troposphere from the Atlantic and Indian Oceans to Syowa (Antarctic coast). During the summer (November-February), the BC concentration showed a diurnal variation together with surface wind speed and increased in the presence of katabatic wind from the Antarctic continent. Considering the low BC source strength over the Antarctic continent, the higher BC concentration in the continental air (katabatic wind) might be caused by long range transport of BC via the free troposphere from mid-and low-latitudes. The seasonal variation of BC at Syowa Station had a maximum in July-September, while at the other coastal stations (Halley, Neumayer, and Ferraz) and a continental station (Amundsen-Scott), the maximum occurred in October. This difference may result from different transport pathways, significant contribution of source regions and scavenging of BC by precipitation during the transport from the source regions. During the austral summer, long-range transport of BC via the free troposphere is likely to make an important contribution to the ambient BC concentration along the Antarctic coasts. © 2010 National Institute of Polar Research.

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Chemistry of sea-salt particles and sea-salt fractionation in Antarctic region Reviewed

Hara K., Osada K., Hayashi M., Yabuki M., Hashida G., Yamanouchi T.

Antarctic Record Vol. 54 ( SPEC. ISSUE ) page： 668 - 696 2010.12

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Antarctic Record

Observations of aerosol constituents and acidic gases were carried out at Syowa Station (1997-1998 and 2003-2006; JARE-38∼39, and JARE-44∼47) and Dome Fuji Station (1997, JARE-38). Seasonal variations and size distribution of sea-salt particles were compared between coastal and inland stations. Seasonal variations of the concentrations of sea-salt particles showed a minimum in the austral summer and higher during the winter at both stations due to strong winds and long-range transport. Sea-salt particles were mostly distributed in fine (D p: 0.2-2.0 μm) and ultra-fine (D p<0.2μm) modes at Syowa Station. Particulate Cl - and Br - are liberated preferentially from sea-salt particles through the heterogeneous reactions at Syowa and Dome Fuji Stations in the summer. The molar ratio of Cl -/Na + and Br -/Na + at Syowa Station decreased to ca. 0.5 and ≈0, respectively, in summer. Fewer sea-salt particles were modified at Syowa Station during the winter, whereas sea-salt particles were modified through the year at Dome Fuji Station. In particular, sea-salt particles were modified with NO 3- and its precursors at Dome Fuji Station during the winter. The concentrations of gaseous inorganic chlorine species (mostly HC1) and bromine species at Syowa Station were 0.2-9.4 nmol m -3 and below the detection limit (BDL)-1.5 nmol m -3, respectively. Sea-salt fractionation (SO 42- depletion) due to Mirabilite formation was identified not only at Syowa Station but also at Dome Fuji Station. Seasonal variation of molar ratio of Mg 2+/Na + showed higher ratios at lower temperature. The range and temperature dependence of Mg 2+/Na + strongly suggested that other seasalt fractionation (e.g., formation of gypsum and hydrohalite) occurred in the Antarctic coasts in addition to Mirabilite formation. Because of different seasonal variation and range of Mg 2+/Na + between Dome Fuji and Syowa Stations, sea-salt fractionation may proceed even in the inland area. © 2010 National Institute of Polar Research.

Scopus

Monitoring of aerosol concentration at Syowa Station

Hayashi M., Osada K., Hara K., Yabuki M., Kobayashi H., Ihara S., Wada M., Yamanouchi T., Hashida G., Shiobara M.

Antarctic Record Vol. 54 ( SPEC. ISSUE ) page： 474 - 486 2010.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Antarctic Record

Concentrations of condensation nuclei (>0.01 μm in diameter) and of aerosol particles larger than 0.3 μm in diameter were monitored at Syowa Station from February, 1996. Number concentrations of condensation nucleus were high in summer and low in winter. Concentrations increased at the rate of several partcles/cm 3 per year. On the other hand, the concentrations of fine particles (>0.3μm) and coarse particles (>1.0μm) were low in summer and high in winter. Concentrations of fine particles 0.3 μm and larger after July were double those before July. © 2010 National Institute of Polar Research.

Scopus

Maritime aerosol optical thickness measured during antarctic research cruises of R/V Umitaka-Maru Reviewed

Kobayashi H., Hirawake T., Yabuki M., Ueda S., Osada K., Shiobara M., Fukuchi M.

Antarctic Record Vol. 54 ( SPEC. ISSUE ) page： 465 - 473 2010.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Antarctic Record

Aerosol optical thickness (AOT) was measured during Antarctic research cruises of R/V Umitaka-Maru. The measured AOTs at 500 nm in the Indian sector of the Antarctic Ocean ranged from 0.02 to 0.12. In Antarctic coastal waters, the AOTs were as low as around 0.05. On the other hand, the some AOTs were higher than 0.1 from 40°S to 60°S. In middle and low latitude regions of the Indian Ocean, the AOTs ranged from 0.05 to 0.15. The AOTs were correlated with wind speed. It is indicated that sea-salt particles, generated by wind, dominated optically and wind speed affected the AOT in the Antarctic Ocean. Angström exponent decreased with increasing AOT. In the AOT wavelength spectra, some AOTs in 380 nm and 870 nm tended to deviate from the power function. Comparing calculation methods of Rayleigh optical thickness suggested a possibility of reducing the deviations of these AOTs. In the future, accuracy check of the instrument constant and review of the calculation method of Rayleigh optical thickness are recommended to enhance the accuracy of maritime AOT measurement. © 2010 National Institute of Polar Research.

Scopus

Electroconductivity of fallen and drifting snow at Syowa Station, Antarctica Reviewed

Osada K., Hara K., Yabuki M., Adachi M.

Antarctic Record Vol. 54 ( SPEC. ISSUE ) page： 697 - 703 2010.12

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：Antarctic Record

Samples of fallen snow, drifting snow and deposited snow were obtained at Syowa Station from April 2003 to October 2006. Electroconductivity of the meltwater was measured. The electroconductivities of the samples for the fallen snow under weak wind condition were mostly below several tens of μS/cm, whereas much higher values were obtained for the drifting snow samples under strong wind condition with seasonal variation: maximum (several hundred to thousands) in April to July, then decreasing to a few hundred after September. Higher electro conductivities of the drifting snow samples correlated well with breakup of sea ice windward of Syowa Station. Lower values were obtained after snow accumulated on sea ice at Kita-no-ura, windward bay area north-east and offshore of Syowa Station. These suggest that brine from sea ice changes the electroconductivity of drifting snow. © 2010 National Institute of Polar Research.

Scopus

Mixing states of cloud interstitial particles between water-soluble and insoluble materials at Mt. Tateyama, Japan: effects of meteorological conditions Reviewed

Ueda, S., K. Osada, K. Okada

Vol. 掲載決定 2010.10

Haze episodes at Syowa Station, coastal Antarctica: Where did they come from?

Hara K., Osada K., Yabuki M., Hashida G., Yamanouchi T., Hayashi M., Shiobara M., Nishita C., Wada M.

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 115 ( 14 ) 2010.7

Deposition processes of ionic constituents to snow cover

Osada K., Shido Y., Iida H., Kido M.

ATMOSPHERIC ENVIRONMENT Vol. 44 ( 3 ) page： 347-353 2010.1

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Papers - OSADA, Kazuo