AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
The Limitations of Electrical Mobility Diameter for Biomass Burning CCN Activation
MICHAEL GIORDANO, Carlos Espinoza, Akua Asa-Awuku, University of California, Riverside
Abstract Number: 116 Working Group: Aerosols, Clouds, and Climate
Abstract Biomass burning is a large contributor of aerosols to the atmosphere. Aerosols can impact the earth’s radiative balance through their ability to activate into cloud condensation nuclei (CCN). Electrical mobility is often used to size-select aerosols to determine their critical activation diameter. The electrical mobility diameter is subsequently used to estimate the volume and moles of solute dissolved in the activated droplet. This approach assumes that a particle is spherical and that the electrical mobility diameter is equivalent to the volume equivalent diameter. In this study we explore the fractal nature of biomass burning aerosol and its influence on CCN activity. Controlled burns were conducted at UC-Riverside’s College of Engineering-Center for Environmental Research and Technology facility to determine the sphericity of the aerosol. Two common southwestern brush species, manzanita and chamise, were burned in a wood stove. The emissions were diluted and injected into a 12 m$^3 Teflon environmental chamber. Emissions were aged with ultraviolet light over 6-8 hours. A Kanomax Aerosol Particle Mass (APM) analyzer in conjunction with a scanning mobility particle sizer (SMPS) determined the effective particle density and fractal dimension of the aerosol. A continuous flow streamwise thermal gradient CCN Counter determined the CCN activation diameters at supersaturations of .2-1%. Results show that biomass burning aerosol can be non-spherical, the degree of which can change with aging (effective densities from .6 to .8 g cm$^(-3) over the experiment). The sensitivity of single parameter estimates of CCN activation, assuming a spherical aerosol, is compared to measurements. Accounting for the sphericity of biomass burning aerosol can be important in predicting CCN activation.