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The MLS HCN Product

Contact: Hugh Pumphrey

Basic Information

HCN is a minor constituent of the atmosphere, whose sources are thought to be at the Earth's surface.
The HCN Molecule
HCN molecule visualization

How it is part of MLS Science Objectives

HCN is a "secondary" MLS data product, that can provide new information on the extent to which this tropospheric source molecule reaches the stratosphere and may (or may not) be involved with stratospheric chemistry.

How EOS MLS measures HCN

HCN is produced by the 190 GHz retrieval. The signal from the HCN molecule is not strong, and as a result the HCN product is noisy and will require some form of averaging for most purposes. The spectral line of HCN lies in the lower sideband of the radiometer, at 177 GHz. This spectral region is relatively free of interfering lines, but the double sideband nature of the measurement mixes the HCN signal with much stronger signals from O3 and HNO3 in the upper sideband. This interference makes the retrieval of HCN problematic in the lower stratosphere. Inspection of HCN retrieved from the measured radiances suggests that it is worse than in the simulation.

HCN Information from the Spectroscopy Database

Quick Product Information for data version v4.2

  • Swath Name: HCN
  • Status Flag: Only use profiles for which the Status field is an even number.
  • Useful Range: 21 - 0.1 hPa
  • DAAC Short Name: ML2HCN
  • Precision: Only use values for which the estimated precision is a positive number.
  • Quality Threshold: >0.2
  • Convergence Threshold: <2.0
Download EOS Aura MLS HCN v4.2 data

Publications related to the MLS HCN data product


  1. Santee, M.L., G.L. Manney, N.J. Livesey, M.J. Schwartz, J.L. Neu, W.G. Read, "A comprehensive overview of the climatological composition of the Asian summer monsoon anticyclone based on 10 years of Aura Microwave Limb Sounder measurements", Journal of Geophysical Research: Atmospheres 122, doi:10.1002/2016jd026408, 2017. reprint


  1. Schoeberl, M.R., A.E. Dessler, T. Wang, M.A. Avery, E.J. Jensen, "Cloud formation, convection, and stratospheric dehydration", Earth and Space Science 1, 1-17, doi:10.1002/2014EA000014, 2014. reprint


  1. Pumphrey, H.C., M.L. Santee, N.J. Livesey, M.J. Schwartz, W.G. Read, "Microwave Limb Sounder observations of biomass-burning products from the Australian bush fires of February 2009", Atmospheric Chemistry and Physics 11, 2, 6285-6296, doi:10.5194/acp-11-6285-2011, 2011. reprint


  1. Pommrich, R., R. Mueller, J.U. Grooss, G. Gunther, P. Konopka, M. Riese, A. Heil, M. Schultz, H.C. Pumphrey, K.A. Walker, "What causes the irregular cycle of the atmospheric tape recorder signal in HCN?", Geophysical Research Letters 37, L16805, doi:10.1029/2010GL044056, 2010. reprint


  1. Li, Q., P.I. Palmer, H.C. Pumphrey, P. Bernath, E. Mahieu, "What drives the observed variability of HCN in the troposphere and lower stratosphere?", Atmospheric Chemistry and Physics 9, 8531-8543, doi:10.5194/acp-9-8531-2009, 2009. reprint


  1. Pumphrey, H.C., C. Boone, K.A. Walker, P. Bernath, N.J. Livesey, "The tropical tape recorder observed in HCN", Geophysical Research Letters 35, L05801, doi:10.1029/2007GL032137, 2008. reprint


  1. Cofield, R.E., P.C. Stek, "Design and field-of-view calibration of 114-660 GHz optics of the Earth Observing System Microwave Limb Sounder", IEEE Transactions on Geoscience and Remote Sensing 44, no. 5, 1166-1181, doi:10.1109/TGRS.2006.873234, 2006. reprint
  2. Pumphrey, H.C., C.J. Jimenez, J.W. Waters, "Measurement of HCN in the middle atmosphere by EOS MLS", Geophysical Research Letters 33, L08804, doi:10.1029/2005GL025656, 2006. reprint

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