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| Titel |
Black carbon over Mexico: the effect of atmospheric transport on mixing state, mass absorption cross-section, and BC/CO ratios |
| VerfasserIn |
R. Subramanian, G. L. Kok, D. Baumgardner, A. Clarke, Y. Shinozuka, T. L. Campos, C. G. Heizer, B. B. Stephens, B. Foy, P. B. Voss, R. A. Zaveri |
| 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 ; 10, no. 1 ; Nr. 10, no. 1 (2010-01-13), S.219-237 |
| Datensatznummer |
250007902
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| Publikation (Nr.) |
 copernicus.org/acp-10-219-2010.pdf |
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| Zusammenfassung |
| A single particle soot photometer (SP2) was operated on the NCAR C-130
during the MIRAGE campaign (part of MILAGRO), sampling black carbon (BC)
over Mexico. The highest BC concentrations were measured over Mexico City
(sometimes as much as 2 μg/m3) and over hill-fires to the south of
the city. The age of plumes outside of Mexico City was determined using a
combination of HYSPLIT trajectories, WRF-FLEXPART modeling and CMET balloon
tracks. As expected, older, diluted air masses had lower BC concentrations.
A comparison of carbon monoxide (CO) and BC suggests a CO background of
around 65 ppbv, and a background-corrected BC/COnet ratio of 2.89±0.89
(ng/m3-STP)/ppbv (average ± standard deviation). This ratio
is similar for fresh emissions over Mexico City, as well as for aged
airmasses. Comparison of light absorption measured with a particle soot
absorption photometer (PSAP) and the SP2 BC suggests a BC mass-normalized
absorption cross-section (MAC) of 10.9±2.1 m2/g at 660 nm (or
13.1 m2/g @ 550 nm, assuming MAC is inversely dependent on wavelength).
This appears independent of aging and similar to the expected absorption
cross-section for aged BC, but values, particularly in fresh emissions,
could be biased high due to instrument artifacts. SP2-derived BC coating
indicators show a prominent thinly-coated BC mode over the Mexico City
Metropolitan Area (MCMA), while older air masses show both thinly-coated and
thickly-coated BC. Some 2-day-old plumes do not show a prominent
thickly-coated BC mode, possibly due to preferential wet scavenging of the
likely-hydrophilic thickly-coated BC. |
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