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| - Gas-Particle Partitioning ofSemivolatile Organic Compounds(SOCs) on Mixtures of Aerosols in aSmog Chamber
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| - The partitioning behavior of a set of diverse SOCs on twoand three component mixtures of aerosols from differentsources was studied using smog chamber experimental data.A set of SOCs of different compound types was introducedinto a system containing a mixture of aerosols fromtwo or more sources. Gas and particle samples weretaken using a filter-filter-denuder sampling system, and apartitioning coefficient Kp was estimated using Kp =Cp/(CgTSP). Particle size distributions were measured usinga differential mobility analyzer and a light scatteringdetector. Gas and particle samples were analyzed usingGCMS. The aerosol composition in the chamber was trackedchemically using a combination of signature compoundsand the organic matter mass fraction (fom) of the individualaerosol sources. The physical nature of the aerosolmixture in the chamber was determined using particlesize distributions, and an aggregate Kp was estimated fromtheoretically calculated Kp on the individual sources.Model fits for Kp showed that when the mixture involvedprimary sources of aerosol, the aggregate Kp of the mixturecould be successfully modeled as an external mixture ofthe Kp on the individual aerosols. There were significantdifferences observed for some SOCs between modelingthe system as an external and as an internal mixture. However,when one of the aerosol sources was secondary, theaggregate model Kp required incorporation of the secondaryaerosol products on the preexisting aerosol for adequatemodel fits. Modeling such a system as an external mixturegrossly overpredicted the Kp of alkanes in the mixture.Indirect evidence of heterogeneous, acid-catalyzed reactionsin the particle phase was also seen, leading to a significantincrease in the polarity of the resulting aerosol mix anda resulting decrease in the observed Kp of alkanes in thechamber. The model was partly consistent with thisdecrease but could not completely explain the reductionin Kp because of insufficient knowledge of the secondaryorganic aerosol composition.
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