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| Titel |
Improving the representation of secondary organic aerosol (SOA) in the MOZART-4 global chemical transport model |
| VerfasserIn |
A. Mahmud, K. Barsanti |
| 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. 4 ; Nr. 6, no. 4 (2013-07-18), S.961-980 |
| Datensatznummer |
250017858
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| Publikation (Nr.) |
 copernicus.org/gmd-6-961-2013.pdf |
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| Zusammenfassung |
| The secondary organic aerosol (SOA) module in the Model for Ozone and
Related Chemical Tracers, version 4 (MOZART-4) was updated by replacing
existing two-product (2p) parameters with those obtained from two-product
volatility basis set (2p-VBS) fits (MZ4-C1), and by treating SOA formation
from the following additional volatile organic compounds (VOCs): isoprene,
propene and lumped alkenes (MZ4-C2). Strong seasonal and spatial variations
in global SOA distributions were demonstrated, with significant differences
in the predicted concentrations between the base case and updated model
simulations. Updates to the model resulted in significant increases in
annual average SOA mass concentrations, particularly for the MZ4-C2
simulation in which the additional SOA precursor VOCs were treated. Annual
average SOA concentrations predicted by the MZ4-C2 simulation were
1.00 ± 1.04 μg m−3 in South America, 1.57 ± 1.88 μg m−3
in Indonesia, 0.37 ± 0.27 μg m−3 in the
USA, and 0.47 ± 0.29 μg m−3 in Europe with corresponding
increases of 178, 406, 311 and 292% over the base-case
simulation, respectively, primarily due to inclusion of isoprene. The
increases in predicted SOA mass concentrations resulted in corresponding
increases in SOA contributions to annual average total aerosol optical depth
(AOD) by ~ 1–6%. Estimated global SOA production was 5.8,
6.6 and 19.1 Tg yr−1 with corresponding
burdens of 0.22, 0.24 and 0.59 Tg for the base-case, MZ4-C1 and MZ4-C2
simulations, respectively. The predicted SOA budgets fell well within
reported ranges for comparable modeling studies, 6.7 to 96 Tg yr−1, but
were lower than recently reported observationally constrained values, 50 to
380 Tg yr−1. For MZ4-C2, simulated SOA concentrations at the surface
also were in reasonable agreement with comparable modeling studies and
observations. Total organic aerosol (OA) mass concentrations at the surface,
however, were slightly over-predicted in Europe, Amazonian regions and
Malaysian Borneo (Southeast Asia) during certain months of the year, and
under-predicted in most sites in Asia; relative to those regions, the model
performed better for sites in North America. Overall, with the inclusion of
additional SOA precursors (MZ4-C2), namely isoprene, MOZART-4 showed
consistently better skill (NMB (normalized mean bias) of −11 vs. −26%) in predicting total
OA levels and spatial distributions of SOA as compared with unmodified
MOZART-4. Treatment of SOA formation by these known precursors (isoprene,
propene and lumped alkenes) may be particularly important when MOZART-4
output is used to generate boundary conditions for regional air quality
simulations that require more accurate representation of SOA concentrations
and distributions. |
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