Open-Path IR Absorption for Airborne Measurements of Stratospheric Trace Gases

Infrared absorption, using tunable diode lasers from aircraft and balloon platforms measures stratospheric trace gas. The goal of this project is to develop a new open-path absorption cell suitable for in situ measurements of reactive trace species from an aircraft platform. The open-path design, in which the laser beam undergoes multiple reflections between two mirrors located on the wing and the fuselage, is preferable to more commonly used enclosed path sampling cells because reactive gases may be perturbed by sampling inlets and surfaces. This project will test a multipass cell that uses a novel astigmatic mirror system which can obtain sufficient path length (600 m) with relatively small diameter mirrors (¿10 cm). This cell will minimize size, weight, and aerodynamic perturbations and will make the system particularly suitable for deployment on small, unmanned aircraft being developed for stratospheric research. Phase I research would optimize the design of the mirrors, develop an automated alignment method, and evaluate the applicability of the open-path absorption system for detecting target stratospheric trace gases such as HNO3, HOCl, HCl, ClONO2, and the HO2 radical.