New Atmospheric O₂/N₂ Ratio Measurements over the Western North Pacific Using a Cargo Aircraft C-130H

抄録

Air samples collected over the western North Pacific using a cargo aircraft C-130H have been analyzed for O₂/N₂ ratio (δ(O₂/N₂)), Ar/N₂ ratio (δ(Ar/N₂)), δ¹⁵N of N₂, δ¹⁸O of O₂ and δ⁴⁰Ar since May 2012. The relationships of δ(Ar/N₂), δ¹⁸O and δ⁴⁰Ar with δ¹⁵N indicate a significant artificial fractionation due to thermal diffusion during the air sample collection. The observed δ(O₂/N₂) and the atmospheric potential oxygen (APO = O₂ + 1.1 × CO₂), corrected for the artificial fractionation, show clear seasonal cycles at all altitudes over Minamitorishima, with amplitudes decreasing with height. Both the seasonal amplitude of the mid-tropospheric APO and its ratio to the surface value are found to decrease significantly from the mid-latitude to the subtropical region. The amplitude of the mid-tropospheric CO₂ seasonal cycle does not change significantly meridionally in a latitude band.