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| Titel |
What drives the observed variability of HCN in the troposphere and lower stratosphere? |
| VerfasserIn |
Q. Li, P. I. Palmer, H. C. Pumphrey, P. Bernath, E. Mahieu |
| 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 ; 9, no. 21 ; Nr. 9, no. 21 (2009-11-10), S.8531-8543 |
| Datensatznummer |
250007741
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| Publikation (Nr.) |
 copernicus.org/acp-9-8531-2009.pdf |
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| Zusammenfassung |
| We use the GEOS-Chem global 3-D chemistry transport model to investigate the
relative importance of chemical and physical processes that determine
observed variability of hydrogen cyanide (HCN) in the troposphere and lower
stratosphere. Consequently, we reconcile ground-based FTIR column
measurements of HCN, which show annual and semi-annual variations, with
recent space-borne measurements of HCN mixing ratio in the tropical lower
stratosphere, which show a large two-year variation. We find that the
observed column variability over the ground-based stations is determined by a
superposition of HCN from several regional burning sources, with GEOS-Chem
reproducing these column data with a positive bias of 5%. GEOS-Chem
reproduces the observed HCN mixing ratio from the Microwave Limb Sounder and
the Atmospheric Chemistry Experiment satellite instruments with a mean
negative bias of 20%, and the observed HCN variability with a mean negative
bias of 7%. We show that tropical biomass burning emissions explain most of
the observed HCN variations in the upper troposphere and lower stratosphere
(UTLS), with the remainder due to atmospheric transport and HCN chemistry. In
the mid and upper stratosphere, atmospheric dynamics progressively exerts
more influence on HCN variations. The extent of temporal overlap between
African and other continental burning seasons is key in establishing the
apparent bienniel cycle in the UTLS. Similar analysis of other, shorter-lived
trace gases have not observed the transition between annual and bienniel
cycles in the UTLS probably because the signal of inter-annual variations
from surface emission has been diluted before arriving at the lower
stratosphere (LS), due to shorter atmospheric lifetimes. |
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