HR: 0830h
AN: A51F-0755    [PDF]
TI: Effect of Dicarboxylic Acids on the Phase Transitions of Model Tropospheric Aerosols
AU: * Braban, C
EM: cbraban@chem.utoronto.ca
AF: University of Toronto, Department of Chemistry, 80 St. George St., Toronto, ON M5S 3H6 Canada
AU: Abbatt, J P
EM: jabbatt@chem.utoronto.ca
AF: University of Toronto, Department of Chemistry, 80 St. George St., Toronto, ON M5S 3H6 Canada
AB: The phase of tropospheric aerosol is important in determining its physical and chemical properties. Tropospheric aerosol is chemically mixed and contains a significant organic fraction including dicarboxylic acids such as malonic and oxalic acid. Experiments have been performed using an aerosol flow tube - FT-IR system (AFT) to identify particulate phase transitions. The major part of this paper is a detailed study into the deliquescence and efflorescence phase transitions of aerosol composed of ammonium sulfate (AS) and malonic acid (MA) at 283 and 293 K, respectively. When the fraction of MA by dry mass ({\it f$_{MA}$}) was $<$ 0.1, phase transitions occurred at the deliquescence and efflorescence relative humidity (DRH and ERH) of AS. However between 0.1 $<$ {\it f$_{MA}$} $<$ 0.25 deliquescence occurred at the eutonic DRH for the AS-MA system and the crystallisation RH of AS is lowered. Between 0.25 $<$ {\it f$_{MA}$} $<$ 0.90, no distinct deliquescence or efflorescence was observed, with particles taking up water at all relative humidities. The crystallization of both MA and AS is suppressed by the presence of the other component. The crystallization RH of MA was $<$ 1% when any AS was present. When {\it f$_{MA}$} $>$ 0.25, AS did not crystallise even when RH $<$ 1%. Thus, the presence of the second component increased the range of conditions under which the particles were in the solution phase. This behaviour, should it be widely applicable, will have a large impact on the phase of chemically mixed aerosol in the atmosphere. We have also studied the phase transitions of AS - oxalic acid, AS - ammonium oxalate and other ammoniated dicarboxylic acids. The results from these studies will be summarised and the atmospheric implications of all of the results discussed.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting