AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Real Refractive Indices and Volatility of Secondary Organic Aerosol Generated from Ozonolysis and Photooxidation of Limonene, Alpha-Pinene and Toluene upon Heating
Hwajin Kim, SUZANNE PAULSON, University of California Los Angeles
Abstract Number: 570 Working Group: Aerosol Chemistry
Abstract Recent studies have suggested chamber SOA particles processed with a thermodenuder (TD) result in particles that are more representative of the atmosphere. We generated particles via homogeneous nucleation from toluene, alpha-pinene and limonene using high and low NOx photochemistry and ozonolysis, and monitored both their refractive index (a fundamental optical property) and their volatility over the range 65 - 98 C. Angular scattering was monitored with a polar nephelometer using parallel and perpendicular polarized 532 nm light, and retrievals were performed with a genetic algorithm method using Mie-Lorenz scattering theory and measured particle size distributions. Overall range of retrieved real refractive indices for the SOA was from about 1.35 - 1.62 depending on parent hydrocarbon and oxidation chemistry. Several types of particles exhibit substantial increases in refractive index as the particles grow initially, particularly limonene (1.35 – 1.56) and toluene (1.37 – 1.62) photo-oxidation and to a lesser degree alpha-pinene ozonolysis (1.38 – 1.48) and photooxidation (1.42 – 1.53). Because of the complications of retrievals from particles with rapidly changing size distributions we thermo-denuded particles only after initial rapid growth was complete. Toluene was not affected by heating in the range investigated, while alpha-pinene and limonene SOA was much more volatile, losing 30 – 60 % of their mass depending on parent hydrocarbon, oxidation chemistry and temperature. Generally as the biogenic SOA are heated the size of the particles decrease and the refractive index of the smaller particle returns to about the same value as observed for unheated particles with matched size observed earlier in the experiment, although there are a few exceptions. The possible factors controlling refractive index, its changes upon heating and its relationship with volatility will be discussed.