AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Aerosol Optical Hygroscopicity Measurements during the 2010 CARES Campaign
Dean Atkinson, James Radney, JANELL LUM, Christopher Cappa, Katheryn Kolesar, Daniel Cziczo, Mikhail Pekour, Qi Zhang, Ari Setyan, Chen Song, Portland State University
Abstract Number: 233 Working Group: Aerosol Chemistry
Abstract Optical hygroscopicity (the variation in aerosol extinction or scattering with relative humidity) was measured during the 2010 Carbonaceous Aerosols and Radiative Effects Study, CARES. CARES was designed to gather information on aerosol changes during transport; specifically, urban aerosols as they were transported over rural and forested areas with extensive biogenic emissions. Changes in aerosol hygroscopicity, size and composition during atmospheric transport is a major emphasis of current experimental and modeling research. Hygroscopicity is an important property because water uptake changes particle size increasing light scattering (and perhaps absorption depending on particle morphology). This increases the particle’s single-scattering albedo leading to more negative radiative forcing. Increases in hygroscopicity also may change the particle from solid to a water droplet, increasing the potential transformations to include aqueous phase reactions. The distinctly different hygroscopic behavior of salts versus organics and of supermicron (defined here as particles over 800 nm in mobility diameter Dp) and submicron (Dp < 800 nm) particles were incorporated into a model of the extinction or scattering change with relative humidity (RH). The model used measured size distributions and composition and the kappa formalism for hygroscopic growth.
An expectation was that the organic loading on particles would increase during transport. The goal of this poster is to present a model for particle extinction and scattering values for both low and high-RH aerosols that achieved optical hygroscopic closure for the CARES data. It also provides values for the hygroscopicity of the oxidized organic aerosol component characterized by the Aerosol Mass Spectrometer. Evolution in particle composition and hygroscopicity can allow better understanding of particle changes in urban to rural transport. This understanding may help in producing parameterizations of optical hygroscopicity for regional and global climate models.