Open AccessOpen-path cavity ring-down spectroscopy for trace gas measurements in ambient air
Author(s) -
Laura E. McHale,
A. Hecobian,
Azer P. Yalin
Publication year - 2016
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.24.005523
Subject(s) - cavity ring down spectroscopy , trace gas , optics , spectroscopy , methane , materials science , absorption (acoustics) , path length , stray light , noise (video) , optical path , absorption spectroscopy , physics , chemistry , computer science , meteorology , organic chemistry , quantum mechanics , artificial intelligence , image (mathematics)
The present work used a near-infrared methane cavity ring-down spectroscopy (CRDS) sensor to examine performance and limitations of open-path CRDS for atmospheric measurements. A simple purge-enclosure was developed to maintain high mirror reflectivity and allowed >100 hours of operation with mirror reflectivity above 0.99996. We characterized effects of aerosols on ring-down decay signals and found the dominant effect to be fluctuations by large super-micron particles. Simple software filtering approaches were developed to combat these fluctuations allowing noise-equivalent sensitivity of ~6x10 -10 cm -1 HJ Hz -1/2 within a factor of ~3 of closed-path systems (based on stability of the absorption baseline). Sensor measurements were validated against known methane concentrations in a closed-path configuration, while open-path validation was performed by side-by-side comparison with a commercial closed-path system.