Implication of hydrogen isotope measurements of CH4 and H2 for investigation of their atmospheric processes

Abstract

Earth's atmosphere contains a variety of trace gases emitted by natural and anthropogenic processes. Some of these gases critically influence the global climate and human health, suggesting the importance of understanding the life cycle of these gases. Stable isotope analysis opens a window to find or to refine the sources of these trace gases associated with their characteristic isotope ratios, and to understand atmospheric processes taking place in the atmosphere by the use of isotope effects. Here I present how to utilize hydrogen isotope analyses of CH4 and H2 to investigate a various processes in the troposphere, the stratosphere, and the mesosphere. CH4 is produced on Earth's surface dominantly by biological processes, emitted into the atmosphere from a various sources, and oxidized by the reaction with radicals ending up with CO2, H2O, and HCl. H2 is produced by high temperature processes and photochemical reactions of CH4 and other hydrocarbons, and disappears on soils by biotic uptake and/or by the reaction with radicals in the atmosphere. CH4 is a unique source of stratospheric H2 except import from the troposphere. In the mesosphere, photolysis of H2O produces H2. The aforementined source emissions and photochemical and biological processes of CH4 and H2 leave their trails of isotopic ratios, which provide valuable information to understand various aspects of the natural processes occurring in the atmosphere.