[A-AS11] Atmospheric Chemistry

[AAS11-13] Contribution of chemical budget of δD-CH₄ on δD-H₂O in the equatorial lower stratosphere

*Takayoshi Yamada¹, Futa Saito^1,2, Seidai Nara¹, Tomohiro Sato¹, Kaley Walker³, Yukio Nakano², YASUKO KASAI¹ (1.National Institute of Information and Communications Technology, 2.Tokyo Gakugei University, 3.University of Toronto)

Water vapor plays a key role in determining the radiative cooling effect in the upper atmosphere (UA). Methane is the most abundant hydrocarbon, and its amount is rising in UA due to anthropogenic emissions from the surface. The water vapor in UA is produced through the oxidation reaction of CH₄ + OH → H₂O + CH₃. In general, the isotopic ratio is a strong tracer of the molecular history such as source, sink, and processes. We have confirmed how much the contribution of CH₄ oxidation on H₂O formation by global satellite observation of δD-CH₄ and δD-H₂O from space.
We used the version 4.0 data of Atmospheric Chemistry Experiment - Fourier Transform Spectrometer (ACE-FTS) (launched in 2003 and still in operation) onboard SciSat-1 developed by the Canadian government. The vertical resolution of the ACE-FTS solar occultation observation is 3 km, and observation wavenumber ranges 750 – 4400 cm^-1 including H₂O, HDO, CH₄, and CH₃D lines.
The scatter plot between δD-H₂O and δD-CH₄ showed a linear relationship by using the observed data at altitudes of 20 – 30 km and latitudes of 15^oS – 15^oN. The result of least-squares linear regression shows that the coefficient of determination is over 0.8 and δD-H₂O increased linearly with the decrease of about 64% of δD-CH₄. We will present the contribution of the chemical budget of δD-CH₄ on δD-H₂O in the lower stratosphere.