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| Titel |
Flow climatology for physicochemical properties of dichotomous aerosol over the western North Atlantic Ocean at Bermuda |
| VerfasserIn |
J. L. Moody, W. C. Keene, O. R. Cooper, K. J. Voss, R. Aryal, S. Eckhardt, B. Holben, J. R. Maben, M. A. Izaguirre, J. N. Galloway |
| 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 ; 14, no. 2 ; Nr. 14, no. 2 (2014-01-22), S.691-717 |
| Datensatznummer |
250118300
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| Publikation (Nr.) |
 copernicus.org/acp-14-691-2014.pdf |
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| Zusammenfassung |
| Dichotomous aerosols (nominal super- and sub-μm-diameter size
fractions) in sectored on-shore flow were sampled daily from July 2006
through June 2009, at the Tudor Hill Atmospheric Observatory (THAO) on the
western coast of Bermuda (32.27° N, 64.87° W) and
analyzed for major chemical and physical properties. FLEXPART retroplumes
were calculated for each sampling period and aerosol properties were
stratified accordingly based on transport from different regions. Transport
from the northeastern United States (NEUS) was associated with significantly
higher (factors of 2 to 3 based on median values) concentrations of bulk
particulate non-sea-salt (nss) SO42-,
NO3-, and NH4+
and associated scattering and absorption at 530 nm, relative to transport
from Africa (AFR) and the oceanic background. These differences were driven
primarily by higher values associated with the sub-μm size fraction
under NEUS flow. We estimate that 75(±3)% of the NEUS nss
SO42- was anthropogenic in origin, while only 25(±9)% of the
AFR nss SO42- was anthropogenic. Integrating over all transport
patterns, the contribution of anthropogenic sulfate has dropped 14.6% from
the early 1990s. Bulk scattering was highly correlated with bulk nss
SO42- in all flow regimes but the corresponding regression slopes
varied significantly reflecting differential contributions to total
scattering by associated aerosol components. Absorption by super-μm
aerosol in transport from the NEUS versus AFR was similar although the
super-μm aerosol size fraction accounted for a relatively greater
contribution to total absorption in AFR flow. Significantly greater
absorption Ångström exponents (AAEs) for AFR flow reflects the
wavelength dependence of absorption by mineral aerosols; lower AAEs for NEUS
flow is consistent with the dominance of absorption by combustion-derived
aerosols. Higher AOD associated with transport from both the NEUS and AFR
relative to oceanic background flow results in a top of atmosphere direct
radiative forcing on the order of −1.6 to −2.5 W m−2,
respectively, showing these aerosols drive cooling. The dominance of
transport from the NEUS on an annual basis coupled with the corresponding
decreases in anthropogenic nss SO42- aerosols since the early 1990s
implies that emission reductions in the US account for a decline in
atmospheric cooling over the western North Atlantic Ocean during this period. |
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