Volatile organic compounds (VOC) are oxidized in the atmosphere and their products contribute to secondary organic aerosol (SOA) formation and growth.  Quantifying these processes is important to predict their impacts on visibility, climate, and human health.  While it is often assumed that particles grow via rapid equilibrium partitioning between liquid particles and gas-phase species, recent work has shown that growth may be better represented by an irreversible, kinetically limited uptake of gas-phase species onto more viscous, tar-like SOA.  However, uptake coefficients for these processes and how they depend on the nature of the gas and the SOA are not known.  The goal of this project is to initiate studies of these relationships by measuring uptake coefficients for amines onto dicarboxylic acids and determining how they vary with the chemical composition of the gas and the condensed phase.  Uptake coefficients were measured using two approaches:  (1) a flow system where the walls of the flow tube were coated with the dicarboxylic acid and the amine introduced via a moveable inlet, and (2) a Knudsen cell.  In both cases, uptake coefficients were derived from the decay in amine measured by mass spectrometry.  The results of this study will contribute to developing a structure-interaction relationship for uptake of gases into SOA that can be implemented into regional and global models.

Measuring uptake coefficients for amines on dicarboxylic acids as models for secondary organic aerosol growth

251st National Meeting (2016)

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