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| Titel |
Exploring the vertical profile of atmospheric organic aerosol: comparing 17 aircraft field campaigns with a global model |
| VerfasserIn |
C. L. Heald, H. Coe, J. L. Jimenez, R. J. Weber, R. Bahreini, A. M. Middlebrook, L. M. Russell, M. Jolleys, T.-M. Fu, J. D. Allan, K. N. Bower, G. Capes, J. Crosier, W. T. Morgan, N. H. Robinson, P. I. Williams, M. J. Cubison, P. F. DeCarlo, E. J. Dunlea |
| 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 ; 11, no. 24 ; Nr. 11, no. 24 (2011-12-15), S.12673-12696 |
| Datensatznummer |
250010272
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| Publikation (Nr.) |
 copernicus.org/acp-11-12673-2011.pdf |
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| Zusammenfassung |
| The global organic aerosol (OA) budget is highly uncertain and past studies
suggest that models substantially underestimate observed concentrations. Few
of these studies have examined the vertical distribution of OA. Furthermore,
many model-measurement comparisons have been performed with different models
for single field campaigns. We synthesize organic aerosol measurements from
17 aircraft campaigns from 2001–2009 and use these observations to
consistently evaluate a GEOS-Chem model simulation. Remote, polluted and
fire-influenced conditions are all represented in this extensive dataset.
Mean observed OA concentrations range from 0.2–8.2 μg sm−3 and
make up 15 to 70% of non-refractory aerosol. The standard GEOS-Chem
simulation reproduces the observed vertical profile, although observations
are underestimated in 13 of the 17 field campaigns (the median observed to
simulated ratio ranges from 0.4 to 4.2), with the largest model bias in
anthropogenic regions. However, the model is best able to capture the
observed variability in these anthropogenically-influenced regions
(R2=0.18−0.57), but has little skill in remote or fire-influenced
regions. The model bias increases as a function of relative humidity for 11
of the campaigns, possibly indicative of missing aqueous phase SOA
production. However, model simulations of aqueous phase SOA suggest a
pronounced signature in the mid-troposphere (2–6 km) which is not supported
in the observations examined here. Spracklen et al. (2011) suggest adding
~100 Tg yr−1 source of anthropogenically-controlled SOA to close
the measurement-model gap, which we add as anthropogenic SOA. This
eliminates the model underestimate near source, but leads to overestimates
aloft in a few regions and in remote regions, suggesting either additional
sinks of OA or higher volatility aerosol at colder temperatures. Sensitivity
simulations indicate that fragmentation of organics upon either
heterogeneous or gas-phase oxidation could be an important (missing) sink of
OA in models, reducing the global SOA burden by 15% and 47%
respectively. The best agreement with observations is obtained when the
simulated anthropogenically-controlled SOA is increased to ~100 Tg yr−1
accompanied by either a gas-phase fragmentation process or a
reduction in the temperature dependence of the organic aerosol partitioning
(by decreasing the enthalpy of vaporization from 42 kJ mol−1 to 25 kJ mol−1).
These results illustrate that models may require both
additional sources and additional sinks to capture the observed
concentrations of organic aerosol. |
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