Sources of upper tropospheric HOx over the South Pacific Convergence Zone: A case study

Céline Mari, Carine Saüt, Daniel J. Jacob, François Ravetta, Bruce Anderson, Melody A. Avery, Donald R. Blake, William H. Brune, Ian Faloona, G. L. Gregory, Brian G. Heikes, Glen W. Sachse, Scott T. Sandholm, Hanwant B. Singh, Robert W. Talbot, David Tan, Stephanie Vay

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Abstract

A zero-dimensional (0-D) model has been applied to study the sources of hydrogen oxide radicals (HOx = HO2 + OH in the tropical upper troposphere during the Pacific Exploratory Mission in the tropics (PEM-Tropics B) aircraft mission over the South Pacific in March-April 1999. Observations made across the Southern Pacific Convergence Zone (SPCZ) and the southern branch of the Intertropical Convergence Zone (ITCZ) provided the opportunity to contrast the relative contributions of different sources of HOx, in a nitrogen oxide radical (NOx)-limited regime, in relatively pristine tropical air. The primary sources of HOx vary significantly along the flight track, in correlation with the supply of water vapor. The latitudinal variation of HOx sources is found to be controlled also by the levels of NOx and primary HOx production rates P(HOx). Budget calculations in the 8- to 12-km altitude range show that the reaction O(1D + H2O is a major HOx source in the cloud region traversed by the aircraft, including SPCZ and the southern branch of the ITCZ. Production from acetone becomes significant in drier region south of 20°S and can become dominant where water vapor mixing ratios lie under 200 ppmv. Over the SPCZ region, in the cloud outflow, CH3 OOH transported by convection accounts for 22% to 64% of the total primary source. Oxidation of methane amplifies the primary HOx source by 1-1.8 in the dry regions.

Original languageEnglish (US)
Pages (from-to)PEM 1-1 PEM 1-9
JournalJournal of Geophysical Research: Atmospheres
Volume108
Issue number2
DOIs
StatePublished - Jan 27 2003

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Palaeontology

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