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| Titel |
Simulating emission and chemical evolution of coarse sea-salt particles in the Community Multiscale Air Quality (CMAQ) model |
| VerfasserIn |
J. T. Kelly, P. V. Bhave, C. G. Nolte, U. Shankar, K. M. Foley |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 3, no. 1 ; Nr. 3, no. 1 (2010-04-08), S.257-273 |
| Datensatznummer |
250000805
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| Publikation (Nr.) |
 copernicus.org/gmd-3-257-2010.pdf |
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| Zusammenfassung |
| Chemical processing of sea-salt particles in coastal environments
significantly impacts concentrations of particle components and gas-phase
species and has implications for human exposure to particulate matter and
nitrogen deposition to sensitive ecosystems. Emission of sea-salt particles
from the coastal surf zone is known to be elevated compared to that from the
open ocean. Despite the importance of sea-salt emissions and chemical
processing, the US EPA's Community Multiscale Air Quality (CMAQ) model has
traditionally treated coarse sea-salt particles as chemically inert and has
not accounted for enhanced surf-zone emissions. In this article, updates to
CMAQ are described that enhance sea-salt emissions from the coastal surf
zone and allow dynamic transfer of HNO3, H2SO4, HCl, and
NH3 between coarse particles and the gas phase. Predictions of updated
CMAQ models and the previous release version, CMAQv4.6, are evaluated using
observations from three coastal sites during the Bay Regional Atmospheric
Chemistry Experiment (BRACE) in Tampa, FL in May 2002. Model updates improve
predictions of NO3−, SO42−, NH4+, Na+, and Cl−
concentrations at these sites with only a 8% increase in run time. In
particular, the chemically interactive coarse particle mode dramatically
improves predictions of nitrate concentration and size distributions as well
as the fraction of total nitrate in the particle phase. Also, the surf-zone
emission parameterization improves predictions of total sodium and chloride
concentration. Results of a separate study indicate that the model updates
reduce the mean absolute error of nitrate predictions at coastal CASTNET and
SEARCH sites in the eastern US. Although the new model features improve
performance relative to CMAQv4.6, some persistent differences exist between
observations and predictions. Modeled sodium concentration is biased low and
causes under-prediction of coarse particle nitrate. Also, CMAQ over-predicts
geometric mean diameter and standard deviation of particle modes at the
BRACE sites. These over-predictions may cause too rapid particle dry
deposition and partially explain the low bias in sodium predictions. Despite
these shortcomings, the updates to CMAQ enable more realistic simulations of
chemical processes in environments where marine air mixes with urban
pollution. The model updates described in this article are included in the
public release of CMAQv4.7 (http://www.cmaq-model.org). |
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