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THE MLS HCl PRODUCT

Contact: Lucien Froidevaux


Basic Information

HCl in the stratosphere (from 15 to 50 km altitude) is a gas that results from the decomposition (by UV radiation) of tropospheric sources gases, mainly chlorofluorocarbons (CFCs). Most of the chlorine that is released from CFCs are stored in this HCl reservoir at high altitudes (near 50 km), and HCl in the upper stratosphere provides a measure of the total chlorine content of the atmosphere (an abundance close to 3.5 parts per billion by volume). The chemistry that leads to ozone depletion at high latitudes largely comes from the more reactive forms of gaseous chlorine (mainly as ClO or chlorine monoxide, also measured by MLS), which makes up all or a large fraction of the atmospheric chlorine content in the lower stratosphere (near 20 km altitude) during polar winter and spring. Some chlorine at high altitude (near 40 km) is also in the form of ClO, which participates in ozone depletion as well. HCl is converted to ClO at high altitude, mainly by reaction with the OH radical; methane (CH4) reacting with chlorine atoms reforms HCl. A steady-state balance in the concentrations of active and reservoir chlorine molecules is achieved. Chlorine nitrate (ClONO2) also plays a role as a temporary chlorine reservoir, usually with lower abundances than HCl.
The HCl Molecule
 HCl molecule visualization


How it is part of MLS Science Objectives

One of the objectives for MLS and the Aura mission is to understand and follow changes in the chemistry and atmospheric composition that can affect stratospheric ozone. HCl in the upper stratosphere has now been decreasing (since about the turn of the century), based on expectations from measurements of CFCs at the ground as well as past satellite HCl data and column HCl measurements from ground-based infrared data. MLS is observing the global decrease in upper stratospheric HCl, which confirms that international agreements to limit the production of CFCs is having an impact in the region where ozone depletion has occurred, during the past two decades. In the lower stratosphere during polar winter and spring, the MLS measurements of HCl and ClO provide important information about the partitioning of chlorine products critical to ozone depletion.


How EOS MLS measures HCl

The standard product for HCl is taken from the 640 GHz (Core+R4A) retrieval. Simulations indicate excellent closure for HCl, typically to better than ~1%. Systematic biases (usually positive) tend to increase to 0.1 ppbv or more at the lowermost pressure (147 hPa); this can amount to more than 30% for the small abundances often found at this altitude. This, and the fact that the random error also increases significantly there leads us to be cautious about HCl below 100 hPa, except possibly at high latitudes where larger abundances can be found.

Sample HCl observation map
(map from 2005d264)
HCl Information from the Spectroscopy Database


Quick Product Information for data version v3.3

  • Swath Name: HCl
  • Vertical Resolution:
    ~3km lower stratosphere
    4-5 km at 1hPa and higher
  • Useful Range: 100 - 0.32 hPa
  • DAAC Short Name: ML2HCL
  • Precision:
    0.4-0.2 ppbv at 100-10 hPa
    0.2-0.7 ppbv at 10-0.5 hPa
  • Quality Threshold: 1.2

The RMS scatter about the 'truth' (for noisy retrievals) is slightly (20%) lower than the estimated precision in the lower stratosphere and up to 50% lower in the lower mesosphere. Clouds tend to cause some (mostly positive) biases, but mainly at 147 hPa where the estimated precision is also increasing; therefore the effect on real data will not be obvious. Some profiles incur vertical oscillations at high latitudes, although this is usually within the estimated noise of the measurements.



v3.3 HCl Averaging Kernel
HCl averaging kernel diagrams

colored lines are individual kernels; thick dashed line is full width at half maximum, thick solid is integrated kernel value

Publications related to the MLS HCl data product

2011

  1. de Laat, A.T.J., "The 2010 Antarctic ozone hole: Observed reduction in ozone destruction by minor sudden stratospheric warmings", vol 10.1038/srep00038, num 1, pgs. 38, 2011. Preprint
  2. Feng, W., "Modelling the effect of denitrification on polar ozone depletion for Arctic winter 2004/2005", num 11, 2011. Preprint
  3. Jones, A., "Analysis of HCl and ClO time series in the upper stratosphere using satellite data sets", num 11, 2011. Preprint
  4. Manney, G.L., "Unprecedented Arctic ozone loss in 2011", vol doi:10.1038/nature10556, num 478, 2011. Preprint
  5. Santee, M.L., "Trace gas evolution in the lowermost stratosphere from Aura Microwave Limb Sounder measurements", vol 10.1029/2011JD015590, num 116, 2011. Preprint

2010

  1. Mebarki, Y., "More evidence for very short-lived substance contribution to stratospheric chlorine inferred from HCl balloon-borne in situ measurements in the tropics", num 10, 2010. Reprint Preprint
  2. Minschwaner, K., "The photochemistry of carbon monoxide in the stratosphere and mesosphere evaluated from observations by the Microwave Limb Sounder on the Aura satellite", vol doi:10.1029/2009JD012654, num 115, 2010. Reprint Preprint

2009

  1. Kawa, S.R., "Sensitivity of polar stratospheric ozone loss to uncertainties in chemical reaction kinetics", num 9, 2009. Preprint
  2. Nedoluha, G.E., "Water vapor measurements in the mesosphere from Mauna Loa over solar cycle 23", vol doi:10.1029/2009JD012504, num 114, 2009. Preprint

2008

  1. Coffey, M.T., "Airborne Fourier transform spectrometer (FTS) observations in support of EOS Aura validation", vol doi:10.1029/2007JD008833, num 113, 2008. Reprint Preprint
  2. Considine, D.B., "Noncoincident validation of Aura MLS observations using the Langley Research Center Lagrangian chemistry and transport model", vol doi:10.1029/2007JD008770, num 113, 2008. Reprint Preprint
  3. Froidevaux, L., "Validation of Aura Microwave Limb Sounder HCl measurements", vol doi:10.1029/2007JD009025, num 113, 2008. Reprint Preprint
  4. Lary, D.J., "Space-based measurements of HCl: Intercomparison and historical context", vol doi:10.1029/2007JD008715, num 113, 2008. Reprint Preprint
  5. Mahieu, E., "Validation of ACE-FTS v2.2 measurements of HCl, HF, CCl3F and CCl2F2 using space-, balloon- and ground-based instrument observations", num 8, pgs. 20, 2008. Preprint
  6. McConnell, J.C., "Stratospheric Ozone Chemistry", vol doi:10.3137/ao.460104, num 46, pgs. No. 1, 2008. Reprint Preprint
  7. Santee, M.L., "A study of stratospheric chlorine partitioning based on new", vol doi:10.1029/2007JD009057, num 113, 2008. Reprint Preprint
  8. Schoeberl, M.R., "QBO and Annual Cycle Variations in Tropical Lower Stratosphere Trace Gases from HALOE and Aura MLS Observations", vol doi:10.1029/2007JD008678, num 113, 2008. Reprint Preprint

2007

  1. Lary, D.J., "Variations in Stratospheric Inorganic Chlorine Between 1991 and 2006", vol doi:10.1029/2007GL030053, num 34, 2007. Reprint Preprint
  2. Manney, G.L., "Solar Occultation Satellite Data and Derived Meteorological Products: Sampling Issues and Comparisons with Aura MLS", vol doi:10.1029/2007JD008709, num 112, 2007. Reprint Preprint

2006

  1. Cofield, R.E., "Design and field-of-view calibration of 114-660 GHz optics of the Earth Observing System Microwave Limb Sounder", num 44, pgs. no. 5, 2006. Preprint
  2. Froidevaux, L., "Early validation analyses of atmospheric profiles from EOS MLS on the Aura satellite", num 44, pgs. no. 5, 2006. Preprint
  3. Froidevaux, L., "Temporal decrease in upper atmospheric chlorine", vol doi:10.1029/2006GL027600, num 33, 2006. Preprint Abstract
  4. Hilsenrath, E., "Early Data from Aura and Continuity from UARS and TOMS", vol doi:10.1007/s11214-006-9074-1, num 125, 2006. Reprint Preprint
  5. Schoeberl, M.R., "Chemical Observations of a Polar Vortex Intrusion", vol doi:10.1029/2006JD007134, num 111, 2006. Reprint Preprint

2005

  1. Manney, G.L., "EOS Microwave Limb Sounder Observations of the Antarctic Polar Vortex Breakup in 2004", vol doi:10.1029/2005GL022823, num 32, 2005. Preprint
  2. Santee, M.L., "Polar processing and development of the 2004 Antarctic ozone hole: First results from Aura MLS", vol doi:10.1029/2005GL022582, num 32, 2005. Preprint

2004

  1. Drouin, B.J., "Temperature Dependent Pressure Induced Lineshape of the HCl J = 1 <- 0 Rotational Transition in Nitrogen and Oxygen", num 83, pgs. Issues 3-4, 2004. Preprint

2003

  1. Mueller, R., "Chlorine activation and chemical loss deduced from HALOE and balloon measurements in the Arctic during the winter of 1999-2000", vol doi:10.1029/2001JD001423, num 108, pgs. D5, 2003. Reprint Preprint

1999

  1. Stachnik, R.A., "Measurements of chlorine partitioning in the winter Arctic stratosphere", num 26, 1999. Preprint

1997

  1. Engel, A., "Partitioning Between Chlorine Reservoir Species Deduced from Observations in the Arctic Winter Stratosphere", num 27, 1997. Preprint

1992

  1. Stachnik, R.A., "Submillimeterwave heterodyne measurements of stratospheric ClO, HCl, O3, and HO2: First results", num 19, 1992. Reprint Preprint




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