Measurements of Isotopic Composition of Water Vapor Using CIMS From the NASA DC-8 During TC4

Measurements of the isotope ratio of water vapor in the tropical troposphere were performed from the NASA DC-8 aircraft platform during the TC4 campaign in 2007. Measurements were conducted in-situ using a chemical ionization tandem mass spectrometry system. Using the global meteoric relationship, the data are used to calculate the ratio of HDO to H2O and δD in the water vapor. The tropospheric δD observations are discussed in the context of a simple model for Rayleigh fractionation. The data are also compared to data from two water isotope measurements aboard the high altitude NASA WB-57 aircraft, providing a surface-to-stratosphere profile of δD as well as an opportunity for instrument intercomparison.