The impact of anthropogenic chlorine emissions, stratospheric ozone change and chemical feedbacks on stratospheric water

[摘要] Mixing ratios of water (H₂O) in the stratosphere appear to increase dueto increased input of H₂O and methane from the troposphereand due to intensified oxidation of CH₄ in the stratosphere, but many of theunderlying mechanisms are not yet understood. Here we identify and quantifythree chemical mechanisms which must have led to more efficient oxidation ofCH₄ in the stratosphere over the past several decades: 1) The increase instratospheric chlorine levels due to anthropogenic CFC emissions, 2) the thinning of thestratospheric ozone column and 3) enhanced OH levels in the stratosphere dueto increasing H₂O levels themselves. In combination with the increasein tropospheric CH₄ mixing ratios and with solar cycle relatedvariations of upper stratospheric ozone, these effects can explain about50% of the additional conversion of CH₄ to H₂O as observedthroughout the stratosphere. The relative contributions from the individualprocesses have varied over the past decades.

[学科分类] 大气科学