Aerosol scattering and absorption during the EUCAARI-LONGREX flights of the Facility for Airborne Atmospheric Measurements (FAAM) BAe-146: can measurements and models agree? 1Department of Meteorology, University of Reading, Reading, UK
09 Aug 2012
2SEAS, University of Manchester, Manchester, UK
3Met Office, Cardington, UK
*now at: Department of Atmospheric Science, Colorado State University, USA
Received: 27 Apr 2011 – Published in Atmos. Chem. Phys. Discuss.: 29 Jun 2011 Abstract. 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.
Revised: 17 Jul 2012 – Accepted: 01 Aug 2012 – Published: 09 Aug 2012
Citation: 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?, Atmos. Chem. Phys., 12, 7251-7267, doi:10.5194/acp-12-7251-2012, 2012.