Atmospheric transport and deposition of Indonesian volcanic emissions

[摘要] A regional climate model has been used to study the transport and deposition ofsulfur (SO₂ and SO₄^2-) and PbCl₂ emissionsfrom Indonesian volcanoes. The sensitivity of the atmospheric loss of thesetrace species to meteorological conditions and their solubility was examined.Two experiments were conducted: 1) volcanic sulfurreleased as primarily SO₂ and subject to transport, deposition, andoxidation to SO₄^2-; and 2) PbCl₂ released as an infinitelysoluble passive tracer subject to only transport and deposition. The first experimentwas used to calculate SO₂ loss rates from each active Indonesian volcanoproducing an annual mean loss rate for all volcanoes of 1.1×10^-5 s^-1,or an e-folding rate of approximately 1 day. SO₂ loss rate was found tovary seasonally, be poorly correlated with wind speed, and uncorrelated withtemperature or relative humidity. The variability of SO₂ loss rates is found tobe correlated with the variability of wind speeds, suggesting that it is much moredifficult to establish a "typical'' SO₂ loss rate for volcanoes that are exposedto changeable winds. Within an average distance of 70 km away from theactive Indonesian volcanoes, 53% of SO₂ loss is due to conversion toSO₄^2-, 42% due to dry deposition, and 5% due to lateraltransport away from the dominant direction of plume travel. The solubility ofvolcanic emissions in water is shown to influence their atmospheric transport anddeposition.High concentrations of PbCl₂ are predicted to be deposited near tothe volcanoes while volcanic S travels further away until removal fromthe atmosphere primarily via the wet deposition of H₂SO₄. Theratio of the concentration of PbCl₂ to SO₂ is found toexponentially decay at increasing distance from the volcanoes. The more rapidremoval of highly soluble species should be considered when observingSO₂ in an aged plume and relating this concentration to othervolcanic species. An assumption that the ratio between the concentrations ofhighly soluble volcanic compounds and SO₂ within a plumeis equal to that observed in fumarolic gases is reasonable at small distances fromthe volcanic vent, but will result in an underestimation of the emission flux of highlysoluble species.

[学科分类] 大气科学