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| Titel |
Modeling atmospheric ammonia and ammonium using a stochastic Lagrangian air quality model (STILT-Chem v0.7) |
| VerfasserIn |
D. Wen, J. C. Lin, L. Zhang, R. Vet, M. D. Moran |
| 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 ; 6, no. 2 ; Nr. 6, no. 2 (2013-03-11), S.327-344 |
| Datensatznummer |
250017794
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| Publikation (Nr.) |
 copernicus.org/gmd-6-327-2013.pdf |
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| Zusammenfassung |
| A new chemistry module that simulates atmospheric ammonia (NH3) and ammonium
(NH+4) was incorporated into a backward-in-time stochastic Lagrangian air
quality model (STILT-Chem) that was originally developed to simulate the
concentrations of a variety of gas-phase species at receptors. STILT-Chem
simulates the transport of air parcels backward in time using ensembles of
fictitious particles with stochastic motions, while accounting for emissions,
deposition and chemical transformation forward in time along trajectories
identified by the backward-in-time simulations. The incorporation of the new
chemistry module allows the model to simulate not only gaseous species, but
also multi-phase species involving NH3 and NH+4. The model was applied
to simulate concentrations of NH3 and particulate NH+4 at six sites in
the Canadian province of Ontario for a six-month period in 2006. The
model-predicted concentrations of NH3 and particulate NH+4 were
compared with observations, which show broad agreement between simulated
concentrations and observations. Since the model is based on back
trajectories, the influence of each major process such as emission,
deposition and chemical conversion on the concentration of a modeled species
at a receptor can be determined for every upstream location at each time
step. This makes it possible to quantitatively investigate the upstream
processes affecting receptor concentrations. The modeled results suggest that
the concentrations of NH3 at those sites were significantly and frequently
affected by Ohio, Iowa, Minnesota, Michigan, Wisconsin, southwestern Ontario and nearby areas. NH3 is
mainly contributed by emission sources whereas particulate NH+4 is mainly
contributed by the gas-to-aerosol chemical conversion of NH3. Dry
deposition is the largest removal process for both NH3 and particulate
NH+4. This study revealed the contrast between agricultural versus forest
sites. Not only were emissions of NH3 higher, but removal mechanisms
(especially chemical loss for NH3 and dry deposition for NH+4) were
less efficient for agricultural sites. This combination explains the
significantly higher concentrations of NH3 and particulate NH+4
observed at agricultural sites. |
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