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| Titel |
Tropospheric carbon monoxide over the Pacific during HIPPO: two-way coupled simulation of GEOS-Chem and its multiple nested models |
| VerfasserIn |
Y.-Y. Yan, J.-T. Lin, Y. Kuang, D. Yang, L. Zhang |
| 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 ; 14, no. 23 ; Nr. 14, no. 23 (2014-12-02), S.12649-12663 |
| Datensatznummer |
250119201
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| Publikation (Nr.) |
 copernicus.org/acp-14-12649-2014.pdf |
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| Zusammenfassung |
Global chemical transport models (CTMs) are used extensively to study air
pollution and transport at a global scale. These models are limited by
coarse horizontal resolutions that do not allow for a detailed representation of
small-scale nonlinear processes over the pollutant source regions. Here we
couple the global GEOS-Chem CTM and its three high-resolution nested models
to simulate the tropospheric carbon monoxide (CO) over the Pacific Ocean
during five High-performance Instrumented Airborne Platform for
Environmental Research (HIAPER) Pole-to-Pole Observations (HIPPO) campaigns between 2009
and 2011. We develop a two-way coupler, the PeKing University CouPLer (PKUCPL), allowing for the exchange and
interaction of chemical constituents between the global model (at
2.5° long. × 2° lat.) and the three nested
models (at 0.667° long. × 0.5° lat.)
covering Asia, North America, and Europe. The coupler obtains
nested model results to modify the global model simulation within the
respective nested domains, and simultaneously acquires global model results
to provide lateral boundary conditions (LBCs) for the nested models.
Compared to the global model alone, the two-way coupled simulation results
in enhanced CO concentrations in the nested domains. Sensitivity tests
suggest the enhancement to be a result of improved representation of the
spatial distributions of CO, nitrogen oxides, and non-methane volatile
organic compounds, the meteorological dependence of natural emissions, and
other resolution-dependent processes. The relatively long lifetime of CO
allows for the enhancement to be accumulated and carried across the globe.
We found that the two-way coupled simulation increased the global
tropospheric mean CO concentrations in 2009 by 10.4%, with a greater
enhancement at 13.3% in the Northern Hemisphere. Coincidently, the global
tropospheric mean hydroxyl radical (OH) was reduced by 4.2%, resulting in
a 4.2% enhancement in the methyl chloroform lifetime (MCF; via reaction
with tropospheric OH). The resulting CO and OH contents and MCF lifetime are
closer to observation-based estimates.
Both the global and the two-way coupled models capture the general
spatiotemporal patterns of HIPPO CO over the Pacific. The two-way coupled
simulation is much closer to HIPPO CO, with a mean bias of 1.1 ppb (1.4%)
below 9 km compared to the bias at −7.2 ppb (−9.2%) for the global model
alone. The improvement is most apparent over the North Pacific. Our test
simulations show that the global model alone could resemble the two-way
coupled simulation (especially below 4 km) by increasing its global CO
emissions by 15% for HIPPO-1 and HIPPO-3, by 25% for HIPPO-2 and
HIPPO-4, and by 35% for HIPPO-5. This has important implications for
using the global model alone to constrain CO emissions. Thus, the two-way
coupled simulation is a significantly improved model tool for studying the
global impacts of air pollutants from major anthropogenic source regions. |
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