Phosgene in the Upper Troposphere and Lower Stratosphere: A Marker for Product Gas Injection Due to Chlorine-Containing Very Short Lived Substances

Phosgene in the atmosphere is produced via the degradation of carbon tetrachloride, methyl chloroform, and a number of chlorine-containing very short lived substances (VSLS). These VSLS are not regulated by the Montreal Protocol even though they contribute to stratospheric ozone depletion. While observations of VSLS can quantify direct stratospheric source gas injection, observations of phosgene in the upper troposphere/lower stratosphere can be used as a marker of product gas injection of chlorine-containing VSLS. In this work we report upper troposphere/lower stratosphere measurements of phosgene made by the ACE-FTS (Atmospheric Chemistry Experiment Fourier Transform Spectrometer) instrument and compare with results from the TOMCAT/SLIMCAT three-dimensional chemical transport model to constrain phosgene trends over the 2004–2016 period. The 13-year ACE-FTS time series provides the first observational evidence for an increase in chlorine product gas injection. In 2016, VSLS accounted for 27% of modeled stratospheric phosgene, up from 20% in the mid-2000s.