Time-multiplexed open-path TDLAS spectrometer for dynamic, sampling-free, interstitial H218O and H216O vapor detection in ice clouds
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- Kühnreich, B., Wagner, S., Habig, J.C. et al. Appl. Phys. B (2015) 119: 177. doi:10.1007/s00340-015-6074-4
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An advanced in situ diode laser hygrometer for simultaneous, sampling-free detection of interstitial H216O and H218O vapor was developed and tested in the aerosol interaction and dynamics in atmosphere (AIDA) cloud chamber during dynamic cloud formation processes. The spectrometer to measure isotope-resolved water vapor concentrations comprises two rapidly time-multiplexed DFB lasers near 1.4 and 2.7 µm and an open-path White cell with 227-m absorption path length and 4-m mirror separation. A dynamic water concentration range from 2.6 ppb to 87 ppm for H216O and 87 ppt to 3.6 ppm for H218O could be achieved and was used to enable a fast and direct detection of dynamic isotope ratio changes during ice cloud formation in the AIDA chamber at temperatures between 190 and 230 K. Relative changes in the H218O/H216O isotope ratio of 1 % could be detected and resolved with a signal-to-noise ratio of 7. This converts to an isotope ratio resolution limit of 0.15 % at 1-s time resolution.