AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Enhancements in Secondary Organic Aerosol Formation in the Presence of Preexisting Organic Particles
JIANHUAI YE, Greg J. Evans, Bruce Urch, Arthur Chan, University of Toronto
Abstract Number: 238 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosol (SOA) produced from atmospheric oxidation of organic vapors, comprises a large fraction of ambient particulate matter. Currently, all modeling frameworks make one key assumption that all organic species, including both primary organic aerosol (POA) and SOA form a well-mixed liquid phase. Oxidation products are assumed to partition into POA similarly as into SOA; and it follows that SOA yields (mass of SOA formed per mass of hydrocarbon reacted) are enhanced in the presence of preexisting organic aerosol.
In this work, we study the enhancement in SOA yields from preexisting organic aerosol. SOA formation from alpha-pinene ozonolysis is investigated in the presence of different organic particles, including squalane, hexadecanol, tetraethylene glycol (TEG), citric acid, and erythritol. The seeds were chosen based on their polarity and phase state at room temperature. Yield enhancement is only observed with TEG or citric acid as seed. The lack of enhancement for other seeds is attributed either to their high viscosity (hexadecanol, erthyritol), which inhibits mixing at experimental timescales, or to their low polarity (squalane), leading to immiscibility. Here we develop a method using Hansen solubility framework to determine organic miscibility and predict SOA yield enhancements. This method provides a simple predictive parameter for different types of SOA for use in atmospheric models. We also hypothesize that aerosol liquid water decreases the viscosity, leading to more mixing between organics and increased SOA yields.
In conclusion, there is a strict mixing criterion for organic aerosols in the atmosphere. It is not realistic to simply treat aerosol as a well-mixed liquid phase. Our results highlight the need to fully understand the aerosol phase state in the atmosphere in order to better parameterize SOA formation.