Generation and Analysis of Organic-Coated Aerosols

PATRICK W. HILLYARD (1), Barbara V. Scarnato (2), Anthony W. Strawa (3), and Thomas W. Kirchstetter (4)

(1) Bay Area Environmental Research Institute, (2) Oak Ridge Associated Universities, (3) NASA Ames Research Center, (4) Lawrence Berkeley National Laboratory

     Abstract Number: 236
     Last modified: April 30, 2010

Abstract
After emission to the atmosphere, black carbon (BC) becomes increasingly internally mixed with other aerosol species through condensation and coagulation. For example, it has been found that in polluted urban air, BC becomes coated on a time scale of about 12 hours with organics and sulfate (1). Multiple studies have demonstrated an increase in the mass absorption efficiency of BC when it becomes internally mixed with non-absorbing organic compounds (2,3).

To quantify this absorption enhancement, we have generated and analyzed uncoated and coated BC and ammonium sulfate aerosols with organic compounds. Black carbon aerosols have been generated by nebulizing aqueous suspensions of soot and with an inverted diffusion flame.

TEM images are used to determine the aerosol mixing state and the morphology of the BC particles. Measurements of the extinction and scattering coefficients of uncoated and coated aerosols with known shell and core diameters are directly and simultaneously measured with the Ames Aerosol Instrument (AAI). AAI uses cavity ring-down spectroscopy to measure absorption coefficient and reciprocal nephelometry to measure scattering coefficient. From these measurements, absorption coefficient and single scattering albedo are obtained. We will present results from these measurements and intercomparisons with other instruments as well as comparisons with theoretical estimates.

References:
1 M. Shiraiwa, Y. Kondo, N. Moteki, N. Takegawa, Y. Miyazaki, and D.R. Blake. Geophys. Res. Lett., 34(16): L16803, 2007.
2 T.C. Bond and R.W. Bergstrom. Aerosol Sci. Tech., 40: 27–67, 2006.
3 L. Liu, M.I. Mishchenko, and W.P. Arnott. J. Quant. Spectrosc. RA., 109: 2656–2663, 2008.