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| Titel |
On the vertical distribution of boundary layer halogens over coastal Antarctica: implications for O3, HOx, NOx and the Hg lifetime |
| VerfasserIn |
A. Saiz-Lopez, J. M. C. Plane, A. S. Mahajan, P. S. Anderson, S. J.-B. Bauguitte, A. E. Jones, H. K. Roscoe, R. A. Salmon, W. J. Bloss, J. D. Lee, D. E. Heard |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 8, no. 4 ; Nr. 8, no. 4 (2008-02-22), S.887-900 |
| Datensatznummer |
250005673
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| Publikation (Nr.) |
 copernicus.org/acp-8-887-2008.pdf |
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| Zusammenfassung |
| A one-dimensional chemical transport model has been developed to investigate
the vertical gradients of bromine and iodine compounds in the Antarctic
coastal boundary layer (BL). The model has been applied to interpret recent
year-round observations of iodine and bromine monoxides (IO and BrO) at
Halley Station, Antarctica. The model requires an equivalent I atom flux of
~1010 molecule cm−2 s−1 from the snowpack in order to
account for the measured IO levels, which are up to 20 ppt during spring.
Using the current knowledge of gas-phase iodine chemistry, the model
predicts significant gradients in the vertical distribution of iodine
species. However, recent ground-based and satellite observations of IO imply
that the radical is well-mixed in the Antarctic boundary layer, indicating a
longer than expected atmospheric lifetime for the radical. This can be
modelled by including photolysis of the higher iodine oxides
(I2O2, I2O3, I2O4 and I2O5), and
rapid recycling of HOI and INO3 through sea-salt aerosol. The model
also predicts significant concentrations (up to 25 ppt) of I2O5
in the lowest 10 m of the boundary layer. Heterogeneous chemistry
involving sea-salt aerosol is also necessary to account for the vertical
profile of BrO. Iodine chemistry causes a large increase (typically more
than 3-fold) in the rate of O3 depletion in the BL, compared with
bromine chemistry alone. Rapid entrainment of O3 from the free
troposphere appears to be required to account for the observation that on
occasion there is little O3 depletion at the surface in the presence of
high concentrations of IO and BrO. The halogens also cause significant
changes to the vertical profiles of OH and HO2 and the NO2/NO
ratio. The average Hg0 lifetime against oxidation is also predicted to
be about 10 h during springtime. An important result from the model is
that very large fluxes of iodine precursors into the boundary layer are
required to account for the observed levels of IO. The mechanisms which
cause these emissions are unknown. Overall, our results show that halogens
profoundly influence the oxidizing capacity of the Antarctic troposphere. |
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