Articles | Volume 17, issue 19
Atmos. Chem. Phys., 17, 11929–11941, 2017
Atmos. Chem. Phys., 17, 11929–11941, 2017

Research article 12 Oct 2017

Research article | 12 Oct 2017

A growing threat to the ozone layer from short-lived anthropogenic chlorocarbons

David E. Oram1,2, Matthew J. Ashfold3, Johannes C. Laube2, Lauren J. Gooch2, Stephen Humphrey2, William T. Sturges2, Emma Leedham-Elvidge2,8, Grant L. Forster1,2, Neil R. P. Harris4, Mohammed Iqbal Mead4,5, Azizan Abu Samah5, Siew Moi Phang5, Chang-Feng Ou-Yang6, Neng-Huei Lin6, Jia-Lin Wang7, Angela K. Baker8, Carl A. M. Brenninkmeijer8, and David Sherry9 David E. Oram et al.
  • 1National Centre for Atmospheric Science, School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK
  • 2Centre for Ocean and Atmospheric Sciences, School of Environmental Sciences, University of East Anglia, Norwich, UK
  • 3School of Environmental and Geographical Sciences, University of Nottingham Malaysia Campus, 43500 Semenyih, Malaysia
  • 4Centre for Atmospheric Informatics and Emissions Technology, School of Energy, Environment and Agrifood/Environmental Technology, Cranfield University, Cranfield, UK
  • 5Institute of Ocean and Earth Sciences, University of Malaya, Kuala Lumpur, Malaysia
  • 6Department of Atmospheric Sciences, National Central University, Taoyuan, Taiwan
  • 7Department of Chemistry, National Central University, Taoyuan, Taiwan
  • 8Max Planck Institute for Chemistry, Air Chemistry Division, Mainz, Germany
  • 9Nolan Sherry & Associates, Kingston upon Thames, London, UK

Abstract. Large and effective reductions in emissions of long-lived ozone-depleting substance (ODS) are being achieved through the Montreal Protocol, the effectiveness of which can be seen in the declining atmospheric abundances of many ODSs. An important remaining uncertainty concerns the role of very short-lived substances (VSLSs) which, owing to their relatively short atmospheric lifetimes (less than 6 months), are not regulated under the Montreal Protocol. Recent studies have found an unexplained increase in the global tropospheric abundance of one VSLS, dichloromethane (CH2Cl2), which has increased by around 60 % over the past decade. Here we report dramatic enhancements of several chlorine-containing VSLSs (Cl-VSLSs), including CH2Cl2 and CH2ClCH2Cl (1,2-dichloroethane), observed in surface and upper-tropospheric air in East and South East Asia. Surface observations were, on occasion, an order of magnitude higher than previously reported in the marine boundary layer, whilst upper-tropospheric data were up to 3 times higher than expected. In addition, we provide further evidence of an atmospheric transport mechanism whereby substantial amounts of industrial pollution from East Asia, including these chlorinated VSLSs, can rapidly, and regularly, be transported to tropical regions of the western Pacific and subsequently uplifted to the tropical upper troposphere. This latter region is a major provider of air entering the stratosphere, and so this mechanism, in conjunction with increasing emissions of Cl-VSLSs from East Asia, could potentially slow the expected recovery of stratospheric ozone.

Short summary
We have observed large amounts of man-made chlorine compounds in E and SE Asia and in the upper tropical troposphere. These relatively short-lived compounds are not controlled by the Montreal Protocol, but if significant quantities were able to reach the stratosphere, the long-term recovery of stratospheric ozone would be delayed. We have also identified an important atmospheric transport mechanism that can rapidly transport these chemicals from E Asia to the upper troposphere via the tropics.
Final-revised paper