Andrews, Elizabeth

Bundke, Ulrich

Freedman, Andrew

Hallar, Anna G.

Massoli, Paola

Onasch, Timothy B.

Petzold, Andreas

Juelich Shared Electronic Resources

Optical closure study on light-absorbing aerosols

Geophysical Research AbstractsVol. 16, EGU2014-16644, 2014EGU General Assembly 2014© Author(s) 2014. CC Attribution 3.0 License.Optical closure study on light-absorbing aerosolsAndreas Petzold (1), Ulrich Bundke (1), Andrew Freedman (2), Timothy B. Onasch (2), Paola Massoli (2),Elizabeth Andrews (3), and Anna G. Hallar (4)(1) Forschungszentrum Jülich, Institute of Energy and Climate Research 8: Troposphere, Germany, (2) Aerodyne Research,Inc., Billerica, MA 01821-3976, USA, (3) NOAA/ESRL Global Monitoring Division, Boulder, CO 80305, USA, (4) StormPeak Laboratory, Division of Atmospheric Sciences, DRI, Steamboat Springs, CO 80488, USAThe in situ measurement of atmospheric aerosol optical properties is an important component of quantifyingclimate change. In particular, the in-situ measurement of the aerosol single-scattering albedo (SSA), which is theratio of aerosol scattering to aerosol extinction, is identified as a key challenge in atmospheric sciences and climatechange research. Ideally, the complete set of aerosol optical properties is measured through optical closure studieswhich simultaneous measure aerosol extinction, scattering and absorption coefficients. The recent developmentof new optical instruments have made real-time in situ optical closure studies attainable, however, many of theseinstruments are state-of-the-art but not practical for routine monitoring.In our studies we deployed a suit of well-established and recently developed instruments including the cavityattenuated phase shift (CAPS) method for aerosol light extinction, multi-angle absorption photometer (MAAP)and particle soot absorption photometer (PSAP) for aerosol light absorption, and an integrating nephelometer(NEPH) for aerosol light scattering measurements. From these directly measured optical properties we calculatedlight absorption from extinction minus scattering (difference method), light extinction from scattering plusabsorption, and aerosol single-scattering albedo from combinations CAPS + MAAP, NEPH + PSAP, NEPH +MAAP, CAPS + NEPH. Closure studies were conducted for laboratory-generated aerosols composed of variousmixtures of black carbon (Regal 400R pigment black, Cabot Corp.) and ammonium sulphate, urban aerosol(Billerica, MA), and background aerosol (Storm Peak Lab.).Key questions addressed in our closure studies are: (1) how well can we measure aerosol light absorption byvarious methods, and (2) how well can we measure the aerosol single-scattering albedo by various instrumentcombinations? In particular we investigated (3) whether the combination of a CAPS and NEPH provides areasonable approach for determining aerosol absorption using the difference method, and (4) whether thiscomparison provides any indication that the PSAP and/or MAAP measurements of absorption have artifacts byorganic condensation as suggested in the literature.The results presented here contribute to the ongoing efforts of assessing measurement methods suitable for themonitoring of aerosol optical properties.

http://juser.fz-juelich.de/record/153259/files/FZJ-2014-02909.pdf

Optical closure study on light-absorbing aerosols

Abstract

Similar works

Full text

Available Versions

Juelich Shared Electronic Resources

Juelich Shared Electronic Resources