Highwood, E. J., Northway, M. J., McMeeking, G. R., Morgan, W. T., Liu, D., Osborne, S., Bower, K., Coe, H., Ryder, C. and Williams, P.
Aerosol scattering and absorption during the EUCAARI-LONGREX flights of the Facility for Airborne Atmospheric Measurements (FAAM) BAe-146: can measurements and models agree?
Atmospheric Chemistry and Physics, 12 (15).
To link to this article DOI: 10.5194/acp-12-7251-2012
Scattering and absorption by aerosol in anthropogenically
perturbed air masses over Europe has been measured
using instrumentation flown on the UK’s BAe-146-301
large Atmospheric Research Aircraft (ARA) operated by the
Facility for Airborne Atmospheric Measurements (FAAM)
on 14 flights during the EUCAARI-LONGREX campaign
in May 2008. The geographical and temporal variations of
the derived shortwave optical properties of aerosol are presented. Values of single scattering albedo of dry aerosol at 550 nm varied considerably from 0.86 to near unity, with a campaign average of 0.93 ± 0.03. Dry aerosol optical depths ranged from 0.030 ± 0.009 to 0.24 ± 0.07. An optical properties closure study comparing calculations from composition data and Mie scattering code with the measured properties is presented. Agreement to within measurement uncertainties of 30% can be achieved for both scattering and absorption,but the latter is shown to be sensitive to the refractive indices chosen for organic aerosols, and to a lesser extent black carbon, as well as being highly dependent on the accuracy of the absorption measurements. Agreement with the measured absorption can be achieved either if organic carbon is assumed to be weakly absorbing, or if the organic aerosol is purely scattering and the absorption measurement is an overestimate due to the presence of large amounts of organic carbon. Refractive
indices could not be inferred conclusively due to this
uncertainty, despite the enhancement in methodology compared
to previous studies that derived from the use of the
black carbon measurements. Hygroscopic growth curves derived
from the wet nephelometer indicate moderate water uptake
by the aerosol with a campaign mean f (RH) value (ratio
in scattering) of 1.5 (range from 1.23 to 1.63) at 80% relative humidity. This value is qualitatively consistent with the major chemical components of the aerosol measured by the aerosol mass spectrometer, which are primarily mixed organics and nitrate and some sulphate.
|Date Deposited:||20 Nov 2014 10:51|
|Last Modified:||19 Jan 2017 03:32|
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