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

• Main Authors: T. Röckmann, J.-U. Grooß, R. Müller
• Format: Article
• Language: English
• Published: Copernicus Publications 2004-01-01
• Series: Atmospheric Chemistry and Physics
• Online Access: http://www.atmos-chem-phys.net/4/693/2004/acp-4-693-2004.pdf
• ISSN: 1680-7316; 1680-7324

Mixing ratios of water (H₂O) in the stratosphere appear to increase due to increased input of H₂O and methane from the troposphere and due to intensified oxidation of CH₄ in the stratosphere, but many of the underlying mechanisms are not yet understood. Here we identify and quantify three chemical mechanisms which must have led to more efficient oxidation of CH₄ in the stratosphere over the past several decades: 1) The increase in stratospheric chlorine levels due to anthropogenic CFC emissions, 2) the thinning of the stratospheric ozone column and 3) enhanced OH levels in the stratosphere due to increasing H₂O levels themselves. In combination with the increase in tropospheric CH₄ mixing ratios and with solar cycle related variations of upper stratospheric ozone, these effects can explain about 50% of the additional conversion of CH₄ to H₂O as observed throughout the stratosphere. The relative contributions from the individual processes have varied over the past decades.