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Hydrogen Chemistry
Contact: Shuhui Wang


Summary

The odd-hydrogen radicals, OH and HO2 (collectively known as HOx), play fundamental roles in the middle atmospheric photochemistry due to their ability to destroy odd oxygen (O3 and O). In particular, at altitudes above ~40 km, the major catalytic O3 loss is controlled by reactions involving HOx species. A better understanding of the trend in HOx thus helps to properly identify the recovery of the O3 layer. In this region of the atmosphere, HOx mainly come from the photolysis of O3 (i.e., the break down of O3 by sunlight) followed by reaction with H2O. In addition, chemical destruction of H2 and direct photolysis of H2O are also sources of HOx, especially above 80 km. The distribution of HOx species and the chemistry involved are sensitive to solar forcing such as the diurnal cycle, the seasonal cycle, the solar 11-year and 27-day cycles, and solar proton events (SPEs).

Before the launch of Aura, the investigation of hydrogen chemistry had been greatly limited due to the lack of multi-year systematic observations on a global scale. The only available long-term records were a number of ground-based measurements of OH total column abundance. Large discrepancies among measurements and between model predictions and observations were reported. MLS provides the first global daily measurements of HOx vertical profiles in the stratosphere and the mesosphere, making it possible to resolve some of these discrepancies, and significantly improve our understanding of the chemistry involved and the response to external forcing. In particular, MLS observations will help to investigate the discrepancy between modeled and observed O3 in the upper stratosphere, known as the "O3 deficit", which implies that there could be a gap in the current understanding of hydrogen chemistry. In addition, the magnitude of the solar effects on hydrogen chemistry is currently unclear, given the large discrepancies between observed and modeled response of O3 and OH to the solar cycle.

MLS-related publications concerning stratospheric and mesospheric hydrogen chemistry

2011

  1. Verronen, P.T., "First evidence of mesospheric hydroxyl response to electron precipitation from the radiation belts", vol doi:10.1029/2010JD014965, num 116, 2011. Reprint Preprint

2010

  1. Dyrland, M.E., "Improved estimates for neutral air temperatures at 90 km and 78°N using satellite and meteor radar data", vol doi:10.1029/2009RS004344, num 45, 2010. Reprint Preprint
  2. Englert, C.R., "Spatial Heterodyne Imager for Meospheric Radicals on STPSat-1", vol doi:10.1029/2010JD014398, num 115, 2010. Preprint

2008

  1. Pickett, H.M., "Validation of Aura Microwave Limb Sounder OH and HO2 measurements", vol doi:10.1029/2007JD008775, num 113, 2008. Reprint Preprint
  2. Wang, S., "Validation of Aura Microwave Limb Sounder OH measurements with Fourier Transform Ultra-Violet Spectrometer total OH column measurements at Table Mountain, California", vol doi:10.1029/2008JD009883, num 113, 2008. Reprint Preprint

2007

  1. Kovalenko, L.J., "Observed and Modeled HOCl Profiles in the Midlatitude Stratosphere: Implication for Ozone Loss", vol doi:10.1029/2007GL031100, num 34, 2007. Reprint Preprint
  2. Verronen, P.T., "Latitudinal extent of the January 2005 solar proton event in the Northern Hemisphere from satellite observations of hydroxyl", num 25, 2007. Preprint

2006

  1. Canty, T., "Stratospheric and Mesospheric HOx: Results from Aura MLS and FIRS-2", vol doi:10.1029/2006GL025964, num 33, 2006. Reprint Preprint
  2. Pickett, H.M., "Microwave Limb Sounder THz Module on Aura", num 44, pgs. no. 5, 2006. Preprint
  3. Pickett, H.M., "Observation of Night OH in the Mesosphere", vol doi:10.1029/2006GL026910, num 33, 2006. Preprint
  4. Pickett, H.M., "Validation of Aura MLS HOx measurements with remote-sensing balloon instruments", vol doi:10.1029/2005GL024048, num 33, 2006. Reprint Preprint
  5. Verronen, P.T., "Production of Odd Hydrogen in the Mesosphere During the January 2005 Solar Proton Event", vol doi:10.1029/2006GL028115, num 33, 2006. Reprint Preprint

1996

  1. Pickett, H.M., "Comparison of measured stratospheric OH with prediction", num 101, pgs. D11, 1996. 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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