Bromine and iodine chemistry in a global chemistry-climate model: Description and evaluation of very short-lived oceanic sources

C. Ordóñez, J. F. Lamarque, S. Tilmes, D. E. Kinnison, Elliot L Atlas, D. R. Blake, G. Sousa Santos, G. Brasseur, A. Saiz-Lopez

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Abstract

The global chemistry-climate model CAM-Chem has been extended to incorporate an expanded bromine and iodine chemistry scheme that includes natural oceanic sources of very short-lived (VSL) halocarbons, gas-phase photochemistry and heterogeneous reactions on aerosols. Ocean emissions of five VSL bromocarbons (CHBr3, CH2Br2, CH2BrCl, CHBrCl2, CHBr2Cl) and three VSL iodocarbons (CH 2ICl, CH2IBr, CH2I2) have been parameterised by a biogenic chlorophyll-α (chl-α) dependent source in the tropical oceans (20 °N-20° S). Constant oceanic fluxes with 2.5 coast-to-ocean emission ratios are separately imposed on four different latitudinal bands in the extratropics (20° -50° and above 50 in both hemispheres). Top-down emission estimates of bromocarbons have been derived using available measurements in the troposphere and lower stratosphere, while iodocarbons have been constrained with observations in the marine boundary layer (MBL). Emissions of CH3I are based on a previous inventory and the longer lived CH3Br is set to a surface mixing ratio boundary condition. The global oceanic emissions estimated for the most abundant VSL bromocarbons - 533 Gg yr-1 for CHBr 3 and 67.3 Gg yr-1 for CH2Br2 - are within the range of previous estimates. Overall the latitudinal and vertical distributions of modelled bromocarbons are in good agreement with observations. Nevertheless, we identify some issues such as the reduced number of aircraft observations to validate models in the Southern Hemisphere, the overestimation of CH2Br2 in the upper troposphere - lower stratosphere and the underestimation of CH3I in the same region. Despite the difficulties involved in the global modelling of the shortest lived iodocarbons (CH2ICl, CH2IBr, CH 2I2), modelled results are in good agreement with published observations in the MBL. Finally, sensitivity simulations show that knowledge of the diurnal emission cycle for these species, in particular for CH2I2, is key to assess their global source strength.

Original languageEnglish (US)
Pages (from-to)1423-1447
Number of pages25
JournalAtmospheric Chemistry and Physics
Volume12
Issue number3
DOIs
StatePublished - 2012

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bromine
iodine
climate modeling
stratosphere
troposphere
ocean
boundary layer
halocarbon
photochemistry
mixing ratio
Southern Hemisphere
evaluation
vertical distribution
aircraft
chlorophyll
boundary condition
aerosol
coast
gas
modeling

ASJC Scopus subject areas

  • Atmospheric Science

Cite this

Bromine and iodine chemistry in a global chemistry-climate model : Description and evaluation of very short-lived oceanic sources. / Ordóñez, C.; Lamarque, J. F.; Tilmes, S.; Kinnison, D. E.; Atlas, Elliot L; Blake, D. R.; Sousa Santos, G.; Brasseur, G.; Saiz-Lopez, A.

In: Atmospheric Chemistry and Physics, Vol. 12, No. 3, 2012, p. 1423-1447.

Research output: Contribution to journalArticle

Ordóñez, C, Lamarque, JF, Tilmes, S, Kinnison, DE, Atlas, EL, Blake, DR, Sousa Santos, G, Brasseur, G & Saiz-Lopez, A 2012, 'Bromine and iodine chemistry in a global chemistry-climate model: Description and evaluation of very short-lived oceanic sources', Atmospheric Chemistry and Physics, vol. 12, no. 3, pp. 1423-1447. https://doi.org/10.5194/acp-12-1423-2012
Ordóñez, C. ; Lamarque, J. F. ; Tilmes, S. ; Kinnison, D. E. ; Atlas, Elliot L ; Blake, D. R. ; Sousa Santos, G. ; Brasseur, G. ; Saiz-Lopez, A. / Bromine and iodine chemistry in a global chemistry-climate model : Description and evaluation of very short-lived oceanic sources. In: Atmospheric Chemistry and Physics. 2012 ; Vol. 12, No. 3. pp. 1423-1447.
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AU - Tilmes, S.

AU - Kinnison, D. E.

AU - Atlas, Elliot L

AU - Blake, D. R.

AU - Sousa Santos, G.

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