A Balloon-Borne Open-Path Cavity Ringdown Spectrometer for Measuring Atmospheric Extinction and Validating Remote Sensing Products

Aerosol extinction measurements are crucial to understanding the effects of atmospheric particles on ozone depletion (stratosphere), radiation (stratosphere and troposphere), visibility (troposphere) and public health (boundary layer).nbsp; Despite the acute need, no existing instrument can measure direct, in situ aerosol extinction profiles from the ground to the mid-stratosphere.nbsp; Satellite-based instruments, including NASArsquo;s new Stratospheric Aerosol and Gas Experiment III-ISS, report extinction globally but are currently validated by indirect measurements with ~40% uncertainty. nbsp;This uncertainty could be eliminated by measuring extinction directly with the balloon-borne Open-path Cavity Ringdown Spectrometer (BOPCRDS) we will develop in this project.nbsp; The BOPCRDS (expected precision is 0.05 Mm-1) will cost lt;$25,000, and its open-path configuration will enable it to measure ambient extinction (rather than extinction from dried particles or estimated from size distribution measurements) from 0-30 km altitude, thereby significantly advancing the current state-of-the-art.nbsp; During Phase I we will (1) design and build the BOPCRDS, (2) test it at -60 degrees Celsius and on a vibration table, (3) compare measurements against theory using gases with known extinction cross-sections, (4) deploy it during a SAGE III-ISS overpass and demonstrate its utility for satellite validation by comparing its measurements against the current state-of-the-art instruments. nbsp;In Phase II, we will develop a multi-wavelength, miniature BOPCRDS with expanded dynamic range and target price of $5,000.nbsp; Increased dynamic range could make the BOPCRDS useful for measuring stratospheric aerosol during volcanically active periods and tropospheric profiles in polluted regions.