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| Titel |
Accounting for non-linear chemistry of shipping plumes in the GEOS-Chem global chemistry transport model |
| VerfasserIn |
Geert C. M. Vinken, K. Folkert Boersma, Daniel J. Jacob, Ernst W. Meijer |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250045645
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| Zusammenfassung |
| Current chemistry transport models (CTMs) generally apply instantaneous mixing of
shipping emissions over the model grid cells, thereby neglecting the effects of non-linear,
in-plume chemistry, and overestimating NOx concentrations and subsequent ozone
production over the oceans. In this study, we adapted a Gaussian plume dispersion model
with chemistry, to explicitly simulate NOx decay and ozone production during the early
stages of plume dispersion. By taking non-linear, in-plume chemistry into account, we can
improve ozone simulations over the oceans, but our main goal is to achieve a meaningful
comparison between simulated NOx concentrations and observed tropospheric
NO2 columns from satellite sensors over a number of distinct shipping lanes. In
order to account for the effects of in plume chemistry in the global GEOS-Chem
CTM, we parameterized the dispersion model by constructing a look-up table (LUT)
with the fraction of NOx remaining and the integrated ozone production 5 hours
after initial release and implemented it. The fraction of NOx remaining and the
integrated ozone production are a function of 7 important environmental parameters in
the marine boundary layer: temperature, ozone concentration, CO concentration,
the solar elevation angle at the time of initial and actual release, and photolysis
rate constants for NO2 and O(1D). To our knowledge, this is the first time that the
effects of non-linear, in-plume chemistry are taken into account in a global CTM.
We will show that our improved model simulates NOx concentrations over the
Pacific Ocean that agree best with observational data from the Pacific Exploratory
Mission West-B (PEMWB). Simulations with the popular instant dilution approach
result in NOx concentrations that are a factor 2 too high. The improved model leads
to summertime O3 concentrations that are 2-3 ppbv lower than with the instant
dilution approach over areas with intense ship traffic, but in winter the differences are
small. We found that ship emissions are responsible for up to 90% of surface NOx
concentrations over the North Atlantic. We will show first comparisons of satellite
measured NO2 columns with NO2 columns modelled with the new approach, a
first step towards providing constraints on shipping NOx emissions from space. |
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