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| Titel |
In situ vertical profiles of aerosol extinction, mass, and composition over the southeast United States during SENEX and SEAC4RS: observations of a modest aerosol enhancement aloft |
| VerfasserIn |
N. L. Wagner, C. A. Brock, W. M. Angevine, A. Beyersdorf, P. Campuzano-Jost, D. Day, J. A. de Gouw, G. S. Diskin, T. D. Gordon, M. G. Graus, J. S. Holloway, G. Huey, J. L. Jimenez, D. A. Lack, J. Liao, X. Liu, M. Z. Markovic, A. M. Middlebrook, T. Mikoviny, J. Peischl, A. E. Perring, M. S. Richardson, T. B. Ryerson, J. P. Schwarz, C. Warneke, A. Welti, A. Wisthaler, L. D. Ziemba, D. M. Murphy |
| 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 ; 15, no. 12 ; Nr. 15, no. 12 (2015-06-30), S.7085-7102 |
| Datensatznummer |
250119861
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| Publikation (Nr.) |
 copernicus.org/acp-15-7085-2015.pdf |
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| Zusammenfassung |
| Vertical profiles of submicron aerosol from in situ aircraft-based
measurements were used to construct aggregate profiles of chemical,
microphysical, and optical properties. These vertical profiles were collected
over the southeastern United States (SEUS) during the summer of 2013 as part
of two separate field studies: the Southeast Nexus (SENEX) study and the
Study of Emissions and Atmospheric Composition, Clouds, and Climate Coupling
by Regional Surveys (SEAC4RS). Shallow cumulus convection was observed
during many profiles. These conditions enhance vertical transport of trace
gases and aerosol and create a cloudy transition layer on top of the
sub-cloud mixed layer. The trace gas and aerosol concentrations in the
transition layer were modeled as a mixture with contributions from the mixed
layer below and the free troposphere above. The amount of vertical mixing, or
entrainment of air from the free troposphere, was quantified using the
observed mixing ratio of carbon monoxide (CO). Although the median aerosol
mass, extinction, and volume decreased with altitude in the transition layer,
they were ~10 % larger than expected from vertical mixing alone.
This enhancement was likely due to secondary aerosol formation in the
transition layer. Although the transition layer enhancements of the
particulate sulfate and organic aerosol (OA) were both similar in magnitude,
only the enhancement of sulfate was statistically significant. The column
integrated extinction, or aerosol optical depth (AOD), was calculated for
each individual profile, and the transition layer enhancement of extinction
typically contributed less than 10 % to the total AOD. Our measurements
and analysis were motivated by two recent studies that have hypothesized an
enhanced layer of secondary aerosol aloft to explain the summertime
enhancement of AOD (2–3 times greater than winter) over the southeastern
United States. The first study attributes the layer aloft to secondary organic
aerosol (SOA) while the second study speculates that the layer aloft could be
SOA or secondary particulate sulfate. In contrast to these hypotheses, the
modest enhancement we observed in the transition layer was not dominated by
OA and was not a large fraction of the summertime AOD. |
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