Proposal Title: Next Generation Technologies for the in situ Detection of NOx Radicals and Their Reservoirs from Aircraft and Balloons
Atmospheric nitrogen oxide radicals (NOx=NO+NO2) regulate the abundance of stratospheric ozone, are the major source of tropospheric ozone and may have a strong effect on the rate of carbon uptake by the terrestrial biosphere. Uncertainties in our understanding of the distribution of nitrogen oxide radicals remain unacceptably large because the factors that control NOx are complex and because we lack accurate and precise observations. Measurements are needed at a variety of spatial and temporal scales to test specific mechanistic hypotheses and to determine the extent to which modern photochemical-dynamical models incorporating these hypotheses are capable of representing the distribution of nitrogen oxides and their reservoirs on regional and global scales. We propose to develop technology to enable routine, in situ, measurements of NO2 using laser-induced fluorescence (LIF). NO will be detected by chemical conversion to NO2 followed by LIF, and labile rese! ! rvoirs of NOx including N2O5 and peroxynitrates will be detected by thermal conversion to NO2 followed by LIF detection of NO2. Our goal is to develop an instrument that is accurate, sensitive, specific, smaller than 0.1m3, weighs less than 20kg, uses less than 500W of power, and is capable of fully autonomous operation for weeks to months. These goals represent manifold improvements over existing instrumentation with comparable sensitivity (20ppt/10sec), especially with respect to size, weight and reliability. During this project we will investigate variations on the design of our recently developed LIF instruments. The results of these initial experiments will then be used to develop a prototype for a new instrument that meets the objectives outlined above. We plan to incorporate simpler solid-state lasers, pulsed supersonic expansions, novel photon counting detectors, and newly developed high reflectivity optics into this new sensor. The completion of this project will enab! ! le us to propose 1) deploying NOx instruments on commercial aircraft, 2) establishing a regular program of NOx detection from small balloons, analogous to the current O3, H2O and aerosol observations, and 3) implementing a cost effective approach to accurate and precise measurements in urban environs. These are measurements that will provide new insights into global and regional atmospheric chemistry, making possible for the first time in situ observations of the global distribution of tropospheric NOx and greatly increasing the probability that a consortium of techniques will be assembled that is capable of detecting trends in the distribution of NOx throughout the atmosphere. In addition, the measurements will enhance the capability for ground truth and intercomparison of measurements of stratospheric and tropospheric NOx from instruments that are a part of NASA's EOS payloads, including SAGE III and TES.