Field observations linking organic carbon content to optical properties in atmospheric aerosols

Ground and airborne measurements of aerosol optical properties and chemical composition are reported from the fall 2008 Cheju Atmospheric Brown Cloud Plume-Asian Monsoon Experiment (CAPMEX; www-ramanathan.ucsd.edu/capmex.html) and spring 2007 Indirect and Semi-direct Aerosol Campaign (ISDAC; acrf-campaign.arm.gov/isdac/) field campaigns. Correlation between increased short wavelength absorption, measured by a 3-laser photoacoustic soot spectrometer (LANL), and increased brown carbon content, measured by single particle laser ablation aerosol mass spectrometry (PNNL) and filter based thermo-optical methods (UW), are observed in both Asian continental outflow and Arctic Haze aerosols. In both campaigns, we observe significant darkening in single scatter albedo at 405 nm (down to ~0.7) relative to 532 and 781 nm for aerosols with larger brown carbon (soot + organic) mass fractions. We investigate the nature of optical property/composition correlations and their implications for radiative forcing; determination of the wavelength dependence of mass absorption cross sections for brown carbon aerosols; and the utility of diagnosing aerosol sources using the wavelength dependence of their optical properties.