Influence of Organic Compound Functionality on Aerosol Hygroscopicity: Dicarboxylic Acids, Alkyl-Substituents, Sugars and Amino Acids
Aleksandra Marsh1, Rachael E. H. Miles1, Grazia Rovelli1, Alexander G. Cowling1, Lucy Nandy2, Cari S. Dutcher2, and Jonathan P. Reid11School of Chemistry, University of Bristol, Bristol, BS8 1TS, UK 2Department of Mechanical Engineering, University of Minnesota, 111 Church Street SE, Minneapolis, MN 55455, USA
Received: 25 Nov 2016 – Accepted for review: 26 Nov 2016 – Discussion started: 14 Dec 2016
Abstract. Hygroscopic data for 36 organic compounds including amino acids, organic acids, alcohols and sugars is determined using a Comparative Kinetics Electrodynamic Balance (CK-EDB). The CK-EDB employs an electric field to trap charged aqueous droplets in a temperature and relative humidity (RH) controlled chamber. The dual micro dispenser set up allows for sequential trapping of probe and sample droplets for accurate determination of droplet water activities from 0.45 to > 0.99. Here, we validate and benchmark the CK-EDB for the homologous series of straight chain dicarboxylic acids (oxalic – pimelic) with measurements in better agreement with UNIversal quasichemical Functional group Activity Coefficients (UNIFAC) predictions than the original data used to parametrise UNIFAC. Further, a series of increasingly complex organic compounds, with subtle changes to molecular structure and branching, are used to rigorously assess the accuracy of predictions by UNIFAC, which does not explicitly account for molecular structure. We show that the changes in hygroscopicity that result from increased branching and chain length are poorly represented by UNIFAC, with UNIFAC under-predicting hygroscopicity. Similarly, amino acid hygroscopicity is under-predicted by UNIFAC predictions, a consequence of the original data used in the parametrisation of the molecular subgroups. New hygroscopicity data are also reported for a selection of alcohols and sugars.
Marsh, A., Miles, R. E. H., Rovelli, G., Cowling, A. G., Nandy, L., Dutcher, C. S., and Reid, J. P.: Influence of Organic Compound Functionality on Aerosol Hygroscopicity: Dicarboxylic Acids, Alkyl-Substituents, Sugars and Amino Acids, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1051, in review, 2016.