報告書番号

T86093

タイトル（和文）

降雨による火山噴出物質の洗浄作用

タイトル（英文）

WET DEPOSITION OF VOLCANIC GAS AND ASH AROUND THE SAKURAJIMA VOLCANO

概要 （図表や脚注は「報告書全文」に掲載しております）

桜島からの水平距離が３０ｋｍ以内の６地点で７カ月にわたって実施した降雨／降下塵の観測データなどをもとに，降雨による噴煙の洗浄作用について，検討を行った。湿性沈着の効果を考慮した長期平均濃度式導出し，風速と洗浄係数の比で定義される係数をこれらに導入することにより，周辺地域での沈着フラックスを調べた。その結果，噴煙の湿性沈着量は各成分の物理・化学的性質に大きく依存することが明らかになった。ＳＯ４，ＣＩ，Ｆなどの溶解性物質を表面に付着した火山塵粒子は，粒経分布の中心がミクロン領域にあたるため雨滴が完全吸収体とみなせる火山ガスの分布特性もこれと同様である。これに対してＳＯ４は，噴煙に共存するＨＣｌやＨＦの影響により雨滴内での酸化速度が低下するため，これらの物質と比較すると海上へ流出する割合が大きくなる。噴煙の流出経路は，上層風系の影響を受けるため季節的に相違するが，年間を通してみると太平洋海域へ

概要 （英文）

MOUNT SAKURAJIMA IS ONE OF THE MAJOR VOLCANOES IN JAPAN. ESTIMATED EMISSION RATE OF SULFUR DIOXIDE ASSOCIATED WITH ITS ACTIVITY RANGS FROM 55 TO 1750 MGS/DAY. OUR LABORATORY SELECTED MOUNT SAKURAJIMA AS A MODEL VOLCANO AND OPERATED A MONITORING NETWORK FOR MEASURING WET AND DRY DEPOSITION IN ITS VICINTY FROM SEPTEMBER 1985 TO MARCH 1986. IN THIS PAPER,THESE MONITORING DATA WERE USED AS A BASIS FOR EXAMINATION OF CLEASING FUNCTION OF PRECIPITATION FOR VOLCANIC GAS AND ASH IN ERUPTION CLOUDS AROUND THE VOLCANO. TRANSPORT,TRANSFORMATION AND REMOVAL PROCESSES OF VOLCANIC EMISSIONS IN THE LOWER ATMOSPHERE ARE AFFECTED BY THE WIND DIRECTION AT AN ALTITUDE OF 1000 TO 2000 METERS. WET ONLY DEPOSITION SAMPLES COLLECTED WITHIN A 30KM DOWNWIND DISTANCE FROM THE VOLCANO AT 15 DAY INTERVALS HAD A PH RANGE OF 3.5 TO 5.2. THE RANK OF ANIONS AS THE BLANCHING H WAS EXCL>EXSO4>F>NO3 WITH THE INFLUENCEOF CL AND F DECREASING WITH DISTANCE FROM THE VOLCANO. HIGH LEVELS OF FE AND AL CONCENTRATION WERE FOUND IN THE WET-ONLY SAMPLES,AND IT WAS THOUGHT THAT THESE CATIONS WERE DISSOLVED FROM VOLCANIC ASH PARTICLES TONEUTRALIZE ACIDIC MATERIALS OF VOLCANIC ORIGIN. WASHOUT COEFFICIENTS FOR VARIOUS VOLCANIC EMISSIONS WERE CALCULATED BASED ON THE CLIMATOLOGICAL ATMOSPHERIC DIFFUSION MODEL. THE RESIDENCE TIME ESTIMATED FROM THESECALCULATIONS SHOWED THAT HC,HF(GASES)AND SULFATE(PARTICULATE)DEPOSITEDRELATIVELY CLOSE TO THE VOLCANO. ON THE OTHER HAND,SULFUR DIOXIDE WAS THOUGHT TO BE TRANSPORTED OVER TO A WIDE AREA OF THE FAR EAST.

報告者

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