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| Titel |
Simulation of the diurnal variations of the isotope anomaly (Δ¹⁷O) of reactive trace gases (NOx, HOx) and implications for the Δ¹⁷O of nitrate. |
| VerfasserIn |
Samuel Morin, Rolf Sander, Joel Savarino |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250038605
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| Zusammenfassung |
| The isotope anomaly of secondary atmospheric species such as nitrate (NO3-) has potential
to provide useful constrains on their formation pathways. Indeed, the Î17O of their
precursors (NOx, HOx etc.) differs and depends on their interactions with ozone, which is the
main source of non-zero Î17O in the atmosphere. Interpreting variations of Î17O in
nitrate requires an in-depth understanding of the Î17O of its precursors taking into
account non-linear chemical regimes operating under various environmental settings.
In addition, the role of isotope exchange reactions must be carefully accounted
for.
To investigate the relevance of various assessments of the isotopic signature of nitrate
production pathways that have recently been proposed in the literature, an atmospheric
chemistry box model (MECCA, Sander et al., 2005, ACP)) was used to explicitly compute
the diurnal variations of the isotope anomaly of NOx, HOx under several conditions
prevailing in the marine boundary layer. Î17O was propagated from ozone to other species
(NO, NO2, OH, HO2, RO2, NO3, N2O5, HONO, HNO3, HNO4, H2O2) according to the
classical mass-balance equation applied at each time step of the model (30 seconds
typically).
The model confirms that diurnal variations in Î17O of NOx are well predicted by the
photochemical steady-state relationship introduced by Michalski et al. (2003, GRL) during
the day, but that at night a different approach must be employed (e.g. « fossilization »
of the Î17O of NOx as soon as the photochemical lifetime of NOx drops below
ca. 5 minutes). The model also allows to evaluate the impact on Î17O of NOx
and nitrate of the frequently made simplifying assumption that Î17O(HOx)=0
permil, with and without mass-independent fractionation during the H+O2-HO2
reaction.
Recommendations for the modeling of Î17O of nitrate will be given, based on the
extensive model work carried out. In addition, the link between diurnal variations of the
Î17O of nitrate precursors and seasonal variations of the Î17O of nitrate will be explored.
Perspectives include the implementation of halogen species in this assessment, and
the full incorporation of the developed framework into the CAABA-MECCA box
model. |
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