Development and Deployment of Optical Instruments to Measure Trace Atmospheric Species: I. Water Isotopologues; II. Glyoxal; III. Iodine Monoxide

Abstract

Understanding future climate requires observations of trace species that can significantly influence the chemical or radiative properties of the atmosphere. The development of optical instruments, utilizing laser-systems as high-resolution light sources, for making in situ observations of trace species from either airborne- or ground-based platforms and results from field campaigns are presented. Glyoxal, the smallest \(\alpha\)-dicarbonyl, is a common product during the oxidation of volatile organic compounds. An instrument using the technique of laser-induced phosphorescence was developed to measure glyoxal at the part per trillion by volume (pptv) level from a tower in a forest canopy. The instrument was deployed as part of the Community Atmosphere-Biosphere INteractions EXperiment. The instrumental limit of detection is 3 pptv with a 1-minute acquisition time. Nearly continuous measurements of glyoxal ranging between 5 – 75 pptv were acquired throughout the campaign and vertical gradients in the forest canopy were found to be driven by elevated temperature. A sensitive instrument using laser-induced fluorescence detection was developed and deployed into remote marine environments to measure iodine monoxide (IO) where the mixing ratio is on the order of 1 – 5 pptv. The challenges and solutions of operating in this environment and results from the field and laboratory are discussed. Laboratory experiments show that IO can be generated from Laminaria digitata, a subtidal kelp species, in the presence of ozone. Observations of the isotopic composition of condensed and vapor water above a large summertime tropical convective system obtained by Hoxotope and ICOS instruments during the TC4 campaign are used to analyze the role of convection in the lower tropical transition layer (TTL). Regions of ice that are characteristic of either convective lofting or in situ condensation are encountered above an active deep tropical convective system. Ice is an important component of water transport models in the TTL, yet its isotopic composition is a relatively unconstrained parameter. The implications from the direct observations of the isotopic composition of ice during convection is explored with respect to transport models of water in the TTL.