ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-4-1451-2004 A study of the phase transition behavior of internally mixed ammonium sulfate - malonic acid aerosols Braban C. F. 1 Abbatt J. P. D. 2 Centre for Atmospheric Science, Dept. of Chemistry, Lensfield Road, University of Cambridge, Cambridge, CB2 1EW, UK Department of Chemistry, University of Toronto, Toronto, ON, M5S 3H6, Canada 01 09 2004 4 5 1451 1459 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/4/1451/2004/acp-4-1451-2004.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/4/1451/2004/acp-4-1451-2004.pdf

This is a study into the phase transitions of aerosol composed of the ternary system ammonium sulfate (AS) - malonic acid (MA) - water using infrared extinction spectroscopy. Twelve compositions were studied in both deliquescence and efflorescence mode experiments. The presence of a MA fraction, by dry mass, (<i>f</i><sub>MA</sub>) of 0.1 in an AS aerosol altered the relative humidity at which the phase transitions occur in an atmospherically significant manner. For compositions with 0.25<<i>f</i><sub>MA</sub><0.90, no distinct ``deliquescence" was observed, contrary to the observed behavior in the binary systems. The crystallization of both the MA and AS components is suppressed by the presence of the other component in the aerosol. At <i>f</i><sub>MA</sub>=0.9, the crystallization relative humidity of MA was lowered from <i>RH</i>=6% to less than 1%. Similarly, at <i>f</i><sub>MA</sub>=0.4, the AS component did not crystallize. The atmospheric implications of the results are discussed.