Atmospheric Chemistry and Physics Discussions
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2007
10.5194/acpd-7-11429-2007
http://www.atmos-chem-phys-discuss.net/7/11429/2007/
http://www.atmos-chem-phys-discuss.net/7/11429/2007/acpd-7-11429-2007.html
http://www.atmos-chem-phys-discuss.net/7/11429/2007/acpd-7-11429-2007.pdf
11429
11463
2007-08-03
Capturing vertical profiles of aerosols and black carbon over the Indian Ocean using autonomous unmanned aerial vehicles
C. E. Corrigan
ccorrigan@ucsd.edu
G. C. Roberts
M. V. Ramana
D. Kim
V. Ramanathan
Center for Atmospheric Sciences, Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Dr. m/c 0221, La Jolla, CA, 92093
Measurements of the vertical distribution of aerosol properties provide
essential information for generating more accurate model estimates of
radiative forcing and atmospheric heating rates compared with employing
remotely sensed column averaged properties. A month long campaign over the
Indian Ocean during March 2006 investigated the interaction of aerosol,
clouds, and radiative effects. Routine vertical profiles of aerosol and
water vapor were determined using autonomous unmanned aerial vehicles
equipped with miniaturized instruments. Comparisons of these airborne
instruments with established ground-based instruments and in
aircraft-to-aircraft comparisons demonstrated an agreement within 10%.
<br><br>
Aerosol absorption optical depths measured directly using the unmanned
aircraft differed from columnar AERONET sun-photometer results by only
20%. Measurements of total particle concentration, particle size
distributions, aerosol absorption and black carbon concentrations are
presented along with the trade wind thermodynamic structure from the surface
to 3000 m above sea level. Early March revealed a well-mixed layer up to the
cloud base at 500 m above mean seal level (m a.s.l.), followed by a
decrease of aerosol concentrations with altitude. The second half of March
saw the arrival of a high altitude plume existing above the mixed layer that
originated from a continental source and increased aerosol concentrations by
more than tenfold, yet the surface air mass showed little change in aerosol
concentrations and was still predominantly influenced by marine sources.
Black carbon concentrations at 1500 m above sea level increased from 70 ng/m³ to more than 800 ng/m³ with the arrival of this polluted
plume. The absorption aerosol optical depth increased from as low as 0.005 to as much as 0.035 over the same period. The spectral dependence of the
aerosol absorption revealed an absorption Angstrom exponent of 1.0, which is
typical of an aerosol with most of its absorption attributed to black carbon
and generally indicates the absorbing component originated from fossil fuel
sources and other high-temperature combustion sources. The results indicate
that surface measurements do not represent the aerosol properties within the
elevated layers, especially if these layers are influenced by long range
transport.
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