AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
BC Mixing State during CARES 2010: Results from and Limitations of the Single Particle Soot Photometer
R. SUBRAMANIAN, Arthur J. Sedlacek, Rahul Zaveri, Claudio Mazzoleni, Noopur Sharma, RTI International
Abstract Number: 443 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Direct radiative forcing by BC-containing aerosols (BCA) is affected by the relative fraction of non-BC material and the particle morphology – collectively referred to as “mixing state”. In June 2010, as part of the CARES field campaign, DMT single particle soot photometers (SP2) were deployed at two ground sites. T0 was located inside the Sacramento, CA urban area, while T1 was 40 km away in Cool, CA. The SP2 provides BC mass per particle, as well as information on the mixing state at the single-particle-level for a narrow range of aerosol sizes. The SP2s deployed at CARES reported mixing state information for BCA larger than ~170 nm. Preliminary results using Gao et al. (2007)’s Leading Edge Only (LEO) Gaussian fitting technique indicate that at T0, BC cores smaller than 100 nm mass-equivalent diameter are thickly-coated, with a coating thickness between 60-120 nm; a detectable coating was not observed for BC cores larger than 200 nm. The mixing state of BC at T0 was influenced by local sources as well as by a build-up of aged aerosols in the region over June 22-28, when the thickly-coated BCA number fraction reached almost 30% for shell/core diameter ratios over two. For BCA particles with a shell/core diameter ratio over 1.5, the thickly-coated number fraction varied between 40-60%. The effect of SP2 instrument limitations and various optical modeling assumptions will also be explored in this presentation.