Isotopic Composition of Atmospheric Moisture

Abstract

The main factor controlling the fractionation of isotopic species in surface waters is the difference in the saturated vapor between various water molecules: ${{P}_{{{\text{H}}_{2}}^{16}\text{O}}}>{{P}_{{{\text{H}}_{2}}^{18}\text{O}}}>{{P}_{\text{HDO}}}$. The fractionation factor in isotopic species of water molecules under equilibrium conditions is determined by the ratio of the saturated vapor pressure of light (p) and heavy (р′) components: α = р/р′. The fractionation factor α at 20°С is 1.08 for HDO and 1.009 for Н₂ ¹⁸О. In this case, the vapor in equilibrium with water will be depleted in deuterium (D) by 80‰ and in oxygen-18 (¹⁸О) by 9‰. The isotopic composition of the vapor is R _v  = R _w /α.