Stratospheric HCl observations are important for evaluating catalytic chemistry that can impact the ozone layer. We report in situ observations of stratospheric HCl employing an off-axis integrated cavity output spectrometer (ICOS) fitted with a third mirror called a re-injection mirror (RIM). This is the first time that 1) stratospheric HCl measurements have been obtained with ICOS, and 2) any three-mirror cavity enhanced instrument has been tested in-flight. Implementation of a RIM increases the photon flux onto the detector by a factor of 10, resulting in a 30-second precision of 26 parts per trillion by volume. The HCl instrument acquired measurements on a balloon-borne descent between 29-18 km altitude in August 2018. Simultaneous measurements of ambient pressure, temperature and ozone were obtained with additional instrumentation aboard the balloon gondola. The observations agreed with nearby satellite measurements (NASA Microwave Limb Sounder) within 10 % on average. Our test flight demonstrates that RIM-ICOS can function outside of the laboratory setting and provides robust results that compare favorably with established HCl instruments in sensitivity, response time, and precision.

Balloon-borne observations of stratospheric HCl using three-mirror integrated cavity output spectroscopy

ACS Spring Meeting 2021

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