10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Development of a Method for the Measurement of the Henry’s Law Constant Distribution of Atmospheric Organic Aerosol
AIKATERINI LIANGOU, Kerrigan Cain, Petro Uruci, Antonios Tasoglou, Spyros Pandis, University of Patras, Patras, Greece
Abstract Number: 291 Working Group: Aerosol Transport and Transformation
Abstract The Henry’s law constant of organic aerosol (OA) components and their precursors determines their partitioning between the gas and aqueous-phases. It determines their dry deposition velocity, their wet deposition rates, and to a large extent their potential for significant aqueous-phase chemical transformations. The corresponding constants for specific atmospheric organic compounds vary from 10-4 to 1010 M atm-1. There is very little information about the distribution of Henry’s law constants for ambient OA and this creates significant uncertainty in the predictions of CTMs simulating semi-volatile OA.
In this study, an experimental method for the measurement of the Henry’s law constant distribution of atmospheric OA is developed. The method relies on the separation of the OA components based on their volatility and then the measurement of the water solubility distribution of each fraction. The separation by volatility is performed using a thermodenuder (TD) and the volatility distribution is estimated using a TD aerosol dynamics model. The measurement of the solubility distribution is based on the extraction of the water soluble organic carbon from each sample using different amounts of water. The solubility distribution range can be further extended with cloud condensation nuclei (CCN) measurements of both the total OA and the different volatility fractions. The synthesis of the measurements results in the estimation of the Henry’s law constant distribution of each volatility bin in the Volatility Basis Set framework.
The method was tested by measuring the Henry’s law constant distribution of the products of the dark ozonolysis of a-pinene in a smog chamber. The results indicate a wide distribution of properties that can be now used in chemical transport models to improve the description of the removal of the corresponding compounds.