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| Titel |
Observations of heterogeneous reactions between Asian pollution and mineral dust over the Eastern North Pacific during INTEX-B |
| VerfasserIn |
C. S. McNaughton, A. D. Clarke, V. Kapustin, Y. Shinozuka, S. G. Howell, B. E. Anderson, E. Winstead, J. Dibb, E. Scheuer, R. C. Cohen, P. Wooldridge, A. Perring, L. G. Huey, S. Kim, J. L. Jimenez, E. J. Dunlea, P. F. DeCarlo, P. O. Wennberg, J. D. Crounse, A. J. Weinheimer, F. Flocke |
| 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 ; 9, no. 21 ; Nr. 9, no. 21 (2009-11-03), S.8283-8308 |
| Datensatznummer |
250007726
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| Publikation (Nr.) |
 copernicus.org/acp-9-8283-2009.pdf |
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| Zusammenfassung |
In-situ airborne measurements of trace gases, aerosol size distributions,
chemistry and optical properties were conducted over Mexico and the Eastern
North Pacific during MILAGRO and INTEX-B. Heterogeneous reactions between
secondary aerosol precursor gases and mineral dust lead to sequestration of
sulfur, nitrogen and chlorine in the supermicrometer particulate size range.
Simultaneous measurements of aerosol size distributions and weak-acid
soluble calcium result in an estimate of 11 wt% of CaCO3 for Asian
dust. During transport across the North Pacific, ~5–30% of the
CaCO3 is converted to CaSO4 or Ca(NO3)2 with an
additional ~4% consumed through reactions with HCl. The 1996 to
2008 record from the Mauna Loa Observatory confirm these findings,
indicating that, on average, 19% of the CaCO3 has reacted to form
CaSO4 and 7% has reacted to form Ca(NO3)2 and ~2%
has reacted with HCl. In the nitrogen-oxide rich boundary layer near Mexico
City up to 30% of the CaCO3 has reacted to form Ca(NO3)2
while an additional 8% has reacted with HCl.
These heterogeneous reactions can result in a ~3% increase in dust
solubility which has an insignificant effect on their optical properties
compared to their variability in-situ. However, competition between
supermicrometer dust and submicrometer primary aerosol for condensing
secondary aerosol species led to a 25% smaller number median diameter for
the accumulation mode aerosol. A 10–25% reduction of accumulation mode
number median diameter results in a 30–70% reduction in submicrometer
light scattering at relative humidities in the 80–95% range. At 80% RH
submicrometer light scattering is only reduced ~3% due to a higher
mass fraction of hydrophobic refractory components in the dust-affected
accumulation mode aerosol. Thus reducing the geometric mean diameter of the
submicrometer aerosol has a much larger effect on aerosol optical properties
than changes to the hygroscopic:hydrophobic mass fractions of the
accumulation mode aerosol.
In the presence of dust, nitric acid concentrations are reduced to <50%
of total nitrate (nitric acid plus particulate nitrate). NOy as a
fraction of total nitrogen (NOy plus particulate nitrate), is reduced
from >85% to 60–80% in the presence of dust. These observations
support previous model studies which predict irreversible sequestration of
reactive nitrogen species through heterogeneous reactions with mineral dust
during long-range transport. |
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