Articles | Volume 16, issue 5
Atmos. Chem. Phys., 16, 3345–3368, 2016

Special issue: Limb observations of the middle atmosphere by space- and airborne...

Atmos. Chem. Phys., 16, 3345–3368, 2016

Research article 15 Mar 2016

Research article | 15 Mar 2016

Global HCFC-22 measurements with MIPAS: retrieval, validation, global distribution and its evolution over 2005–2012

M. Chirkov1, G. P. Stiller1, A. Laeng1, S. Kellmann1, T. von Clarmann1, C. D. Boone2, J. W. Elkins3, A. Engel4, N. Glatthor1, U. Grabowski1, C. M. Harth5, M. Kiefer1, F. Kolonjari6, P. B. Krummel7, A. Linden1, C. R. Lunder8, B. R. Miller3, S. A. Montzka3, J. Mühle5, S. O'Doherty9, J. Orphal1, R. G. Prinn10, G. Toon11, M. K. Vollmer12, K. A. Walker2,6, R. F. Weiss5, A. Wiegele1, and D. Young9 M. Chirkov et al.
  • 1Karlsruhe Institute of Technology (KIT), Institute for Meteorology and Climate Research (IMK), Karlsruhe, Germany
  • 2University of Waterloo, Department of Chemistry, Waterloo, Ontario, Canada
  • 3NOAA/ESRL Climate Monitoring Division, Boulder, Colorado, USA
  • 4Goethe-Universität Frankfurt, Experimental Atmospheric Research Institute for Atmospheric and Environmental Sciences, Frankfurt, Germany
  • 5Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA
  • 6University of Toronto, Department of Physics, Toronto, Ontario, Canada
  • 7CSIRO Oceans & Atmosphere Flagship, Aspendale, Victoria, Australia
  • 8Norwegian Institute for Air Research, Kjeller, Norway
  • 9Atmospheric Chemistry Research Group, School of Chemistry, University of Bristol, Bristol, UK
  • 10Center for Global Change Science, MIT, Cambridge, MA, USA
  • 11Jet Propulsion Laboratory and California Institute of Technology, Pasadena, California, USA
  • 12Laboratory for Air Pollution and Environmental Technology, Empa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland

Abstract. We report on HCFC-22 data acquired by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) in the reduced spectral resolution nominal observation mode. The data cover the period from January 2005 to April 2012 and the altitude range from the upper troposphere (above cloud top altitude) to about 50 km. The profile retrieval was performed by constrained nonlinear least squares fitting of modelled spectra to the measured limb spectral radiances. The spectral ν4-band at 816.5 ± 13 cm−1 was used for the retrieval. A Tikhonov-type smoothing constraint was applied to stabilise the retrieval. In the lower stratosphere, we find a global volume mixing ratio of HCFC-22 of about 185 pptv in January 2005. The rate of linear growth in the lower latitudes lower stratosphere was about 6 to 7 pptv year−1 in the period 2005–2012. The profiles obtained were compared with ACE-FTS satellite data v3.5, as well as with MkIV balloon profiles and cryosampler balloon measurements. Between 13 and 22 km, average agreement within −3 to +5 pptv (MIPAS – ACE) with ACE-FTS v3.5 profiles is demonstrated. Agreement with MkIV solar occultation balloon-borne measurements is within 10–20 pptv below 30 km and worse above, while in situ cryosampler balloon measurements are systematically lower over their full altitude range by 15–50 pptv below 24 km and less than 10 pptv above 28 km. MIPAS HCFC-22 time series below 10 km altitude are shown to agree mostly well to corresponding time series of near-surface abundances from the NOAA/ESRL and AGAGE networks, although a more pronounced seasonal cycle is obvious in the satellite data. This is attributed to tropopause altitude fluctuations and subsidence of polar winter stratospheric air into the troposphere. A parametric model consisting of constant, linear, quasi-biennial oscillation (QBO) and several sine and cosine terms with different periods has been fitted to the temporal variation of stratospheric HCFC-22 for all 10°-latitude/1-to-2-km-altitude bins. The relative linear variation was always positive, with relative increases of 40–70 % decade−1 in the tropics and global lower stratosphere, and up to 120 % decade−1 in the upper stratosphere of the northern polar region and the southern extratropical hemisphere. Asian HCFC-22 emissions have become the major source of global upper tropospheric HCFC-22. In the upper troposphere, monsoon air, rich in HCFC-22, is instantaneously mixed into the tropics. In the middle stratosphere, between 20 and 30 km, the observed trend is inconsistent with the trend at the surface (corrected for the age of stratospheric air), hinting at circulation changes. There exists a stronger positive trend in HCFC-22 in the Southern Hemisphere and a more muted positive trend in the Northern Hemisphere, implying a potential change in the stratospheric circulation over the observation period.

Short summary
HCFC-22 global distributions from MIPAS measurements for 2005 to 2012 are presented. Tropospheric trends are in good agreement with ground-based observations. A layer of enhanced HCFC-22 in the upper tropospheric tropics and northern subtropics is identified to come from Asian sources uplifted in the Asian monsoon. Stratospheric distributions provide show seasonal, semi-annual, and QBO-related variations. Hemispheric asymmetries of trends hint towards a change in the stratospheric circulation.
Final-revised paper