HOCl retrievals from the Atmospheric Chemistry Experiment

HOCl is a chlorine reservoir molecule found in the stratosphere and in the marine boundary layer. In the stratosphere, it originates from anthropogenic emissions of long-lived chlorine-containing molecules as chlorofluorocarbons (CFCs). HOCl is also a key species in polar ozone destruction and the formation of the Antarctic ozone hole. A new HOCl retrieval has been developed using solar occultation spectra recorded by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) from orbit. Altitude-latitude volume mixing ratio (VMR) distributions of HOCl are presented for the entire mission (2004-2020) and for four seasonal quarters. A time series of quarterly averages for the region 60 degrees S-60 degrees N, 35.5-39.5 km altitude shows a marginally significant trend of -0.23 +/- 0.11 ppt/year consistent with the success of the Montreal Protocol. (C) 2021 Elsevier Ltd. All rights reserved.