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| Titel |
Improvement and further development in CESM/CAM5: gas-phase chemistry and inorganic aerosol treatments |
| VerfasserIn |
J. He, Y. 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. 17 ; Nr. 14, no. 17 (2014-09-08), S.9171-9200 |
| Datensatznummer |
250119008
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| Publikation (Nr.) |
 copernicus.org/acp-14-9171-2014.pdf |
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| Zusammenfassung |
| Gas-phase chemistry and subsequent gas-to-particle conversion processes such
as new particle formation, condensation, and thermodynamic partitioning
have large impacts on air quality, climate, and public health through
influencing the amounts and distributions of gaseous precursors and secondary
aerosols. Their roles in global air quality and climate are examined in this
work using the Community Earth System Model version 1.0.5 (CESM1.0.5) with
the Community Atmosphere Model version 5.1 (CAM5.1) (referred to as
CESM1.0.5/CAM5.1). CAM5.1 includes a simple chemistry that is coupled with a
7-mode prognostic Modal Aerosol Model (MAM7). MAM7 includes classical
homogenous nucleation (binary and ternary) and activation nucleation
(empirical first-order power law) parameterizations, and a highly simplified
inorganic aerosol thermodynamics treatment that only simulates
particulate-phase sulfate and ammonium. In this work, a new gas-phase
chemistry mechanism based on the 2005 Carbon Bond Mechanism for Global
Extension (CB05_GE) and several advanced inorganic aerosol treatments for
condensation of volatile species, ion-mediated nucleation (IMN), and explicit
inorganic aerosol thermodynamics for sulfate, ammonium, nitrate, sodium, and
chloride have been incorporated into CESM/CAM5.1-MAM7. Compared to the
simple gas-phase chemistry, CB05_GE can predict many more gaseous species,
and thus could improve model performance for PM2.5, PM10, PM
components, and some PM gaseous precursors such as SO2 and NH3 in
several regions as well as aerosol optical depth (AOD) and cloud properties
(e.g., cloud fraction (CF), cloud droplet number concentration (CDNC), and
shortwave cloud forcing, SWCF) on the global scale. The modified condensation and
aqueous-phase chemistry could further improve the prediction of additional
variables such as HNO3, NO2, and O3 in some regions, and new
particle formation rate (J) and AOD on the global scale. IMN can improve the
prediction of secondary PM2.5 components, PM2.5, and PM10
over Europe as well as AOD and CDNC on the global scale. The explicit inorganic
aerosol thermodynamics using the ISORROPIA II model improves the prediction of all
major PM2.5 components and their gaseous precursors in some regions as
well as downwelling shortwave radiation, SWCF, and cloud condensation nuclei
at a supersaturation of 0.5% on the global scale. For simulations of 2001–2005
with all the modified and new treatments, the improved model predicts that on global average, SWCF increases by 2.7 W m−2, reducing the normalized mean bias (NMB) of SWCF
from −5.4 to 1.2%. Uncertainties in emissions can largely explain the
inaccurate prediction of precursor gases (e.g., SO2, NH3, and NO)
and primary aerosols (e.g., black carbon and primary organic matter).
Additional factors leading to the discrepancies between model predictions and
observations include assumptions associated with equilibrium partitioning for
fine particles assumed in ISORROPIA II, irreversible gas/particle mass
transfer treatment for coarse particles, uncertainties in model treatments
such as dust emissions, secondary organic aerosol formation, multi-phase
chemistry, cloud microphysics, aerosol–cloud interaction, dry and wet
deposition, and model parameters (e.g., accommodation coefficients and
prefactors of the nucleation power law) as well as uncertainties in model
configuration such as the use of a coarse-grid resolution. |
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