Cooperative Institute for Research in Environmental Sciences

Science Rendezvous > 2009 Posters
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Laboratory Investigation of the Relative Humidity Dependence of Light Extinction by Mixed Organic/Sulfate Particles

Melinda R. Beaver, Tahllee Baynard, Rebecca M. Garland, Christa Hasenkopf, A. R. Ravishankara and Margaret A. Tolbert

Light extinction by atmospheric particles is strongly dependent on the size, chemical composition, and water content of the aerosol. Since light extinction by particles directly impacts climate and visibility, direct measurement of extinction at various relative humidity (RH) conditions is needed. In this work, the optical growth factors, fRH_ext (80%RH, Dry) have been measured using cavity ring-down aerosol extinction spectroscopy for particles of varying organic/sulfate compositions. Specifically, slightly soluble, multifunctional aromatic compounds resulting from biomass burning have been investigated in this work. In general, the organic compounds studied exhibit much smaller optical growth than inorganic compounds such as ammonium sulfate. Also, a linear relationship between mass fraction organic and optical growth has been observed for most organic compounds studied. These results, an exception to the linear relationship, comparisons to growth factor measurements, Gf, refractive index determinations, and implications for climate calculations will be presented.