Aircraft-Based Observations of Ozone-Depleting Substances in the Upper Troposphere and Lower Stratosphere in and Above the Asian Summer Monsoon

Karina E. Adcock*, Paul J. Fraser, Brad D. Hall, Ray L. Langenfelds, Geoffrey Lee, Stephen A. Montzka, David E. Oram, Thomas Röckmann, Fred Stroh, William T. Sturges, Bärbel Vogel, Johannes C. Laube

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

Recent studies show that the Asian summer monsoon anticyclone (ASMA) transports emissions from the rapidly industrializing nations in Asia into the tropical upper troposphere. Here, we present a unique set of measurements on over 100 air samples collected on multiple flights of the M55 Geophysica high altitude research aircraft over the Mediterranean, Nepal, and Northern India during the summers of 2016 and 2017 as part of the European Union project StratoClim. These air samples were measured for 27 ozone-depleting substances (ODSs), many of which were enhanced above expected levels, including the chlorinated very short-lived substances, dichloromethane (CH2Cl2), 1,2-dichloroethane (CH2ClCH2Cl), and chloroform (CHCl3). CH2Cl2 mixing ratios in the tropopause region were 65–136 parts per trillion (ppt) in comparison to previous estimates of mixing ratios in the tropical tropopause layer of 30–44 ppt in 2013–2014. Backward trajectories, calculated with the trajectory module of the chemistry-transport model CLaMS and driven by the ERA5 reanalysis, indicate possible source regions of CH2Cl2 in South Asia. We derived total equivalent chlorine (ECl), and equivalent effective stratospheric chlorine (EESC) and found that these quantities were substantially higher than previous estimates in the literature. EESC at mean age-of-air of 3 years based on the 2016 measurements was 1,861–1,872 ppt in comparison to a previously estimated EESC of 1,646 ppt. Our findings show that the ASMA transports larger than expected mixing ratios of long-lived and very short-lived ODSs into the upper troposphere and lower stratosphere, likely leading to an impact on the stratospheric ozone layer.

Original languageEnglish
Article numbere2020JD033137
Pages (from-to)1-18
Number of pages18
JournalJournal of Geophysical Research: Atmospheres
Volume126
Issue number1
DOIs
Publication statusPublished - 16 Jan 2021

Bibliographical note

Funding Information:
We are grateful for the contributions of Michel Bolder, Carina van der Veen (both Utrecht University), and the Geophysica team (sample collection and campaign organization), Guus Velders and Andreas Engel (EESC comparisons), Elinor Tuffnell (data processing) and the NOAA Global Monitoring Division (surface halocarbon data). We thank the staff at the Cape Grim station and at CSIRO GASLAB Aspendale for collecting and maintaining the Cape Grim air archive and preparing the UEA flasks and sub‐samples. We also acknowledge CSIRO and the Bureau of Meteorology for funding these activities. The StratoClim flights were funded by the European Commission (FP7 project Stratoclim‐603557, www.stratoclim.org ). This work was supported by the Natural Environment Research Council through the EnvEast Doctoral Training Partnership (grant number NE/L002582/1) as well as the ERC project EXCITE (EXC3ITE‐678904‐ERC‐2015‐STG). Johannes C. Laube received funding from the UK Natural Environment Research Council (Research Fellowship NE/I021918/1. 3

Publisher Copyright:
© 2021. The Authors.

Copyright:
Copyright 2021 Elsevier B.V., All rights reserved.

Funding

We are grateful for the contributions of Michel Bolder, Carina van der Veen (both Utrecht University), and the Geophysica team (sample collection and campaign organization), Guus Velders and Andreas Engel (EESC comparisons), Elinor Tuffnell (data processing) and the NOAA Global Monitoring Division (surface halocarbon data). We thank the staff at the Cape Grim station and at CSIRO GASLAB Aspendale for collecting and maintaining the Cape Grim air archive and preparing the UEA flasks and sub‐samples. We also acknowledge CSIRO and the Bureau of Meteorology for funding these activities. The StratoClim flights were funded by the European Commission (FP7 project Stratoclim‐603557, www.stratoclim.org ). This work was supported by the Natural Environment Research Council through the EnvEast Doctoral Training Partnership (grant number NE/L002582/1) as well as the ERC project EXCITE (EXC3ITE‐678904‐ERC‐2015‐STG). Johannes C. Laube received funding from the UK Natural Environment Research Council (Research Fellowship NE/I021918/1. 3

Keywords

  • Asian summer monsoon
  • ozone depletion
  • ozone-depleting substances
  • stratosphere

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