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

Jeremy J Harrison,Sandip Dhomse,Christopher D Boone,Peter F Bernath,Wuhu Feng,Ryan Hossaini,Martyn P Chipperfield

doi:10.1029/2018gl079784

Abstract

AbstractPhosgene 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.

Highlights

The majority of chlorine (Cl) in the atmosphere has arisen from anthropogenic emissions of organic species such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs)
In this work we report upper troposphere/lower stratosphere measurements of phosgene made by the Atmospheric Chemistry Experiment Fourier transform spectrometer (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
In this work we report measurements of phosgene in the upper troposphere/lower stratosphere made by the ACE-FTS (Atmospheric Chemistry Experiment Fourier Transform Spectrometer) instrument

Summary

Introduction

The majority of chlorine (Cl) in the atmosphere has arisen from anthropogenic emissions of organic species such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). Smaller contributions to the phosgene budget are known to arise from the atmospheric degradation of very short lived substances (VSLS), species with tropospheric lifetimes under 6 months, such as dichloromethane (CH2Cl2), chloroform (CHCl3), and tetrachloroethene (C2Cl4) These VSLS can degrade in the troposphere to produce phosgene, some of which is directly transported into the stratosphere via so-called product gas injection (PGI). Whereas the concentrations of the VSLS source gases near the tropopause can be measured straightforwardly and to high precision, for example, by the National Aeronautics and Space Administration (NASA) Airborne Tropical Tropopause Experiment (ATTREX; e.g., Navarro et al, 2015), the product gas phosgene is only measured (to a lower precision) by spectroscopic remote-sensing instruments, for example, located on satellite platforms This makes the PGI of phosgene somewhat harder to quantify than SGI and has led to its relative neglect in studies of VSLS-derived chlorine entering the stratosphere. For the present work, detailed stratospheric phosgene chemistry is included in the TOMCAT/SLIMCAT scheme for the first time

Satellite Observations of Phosgene

Model Simulations of Phosgene

Results and Discussion

Conclusions