Spectro-microscopic characterization of liquid-liquid phase separation in aerosols

 

Authors

Rachel E OBrien — College of William and Mary
Bingbing Wang — Stony Brook University
Alexander Laskin — Purdue University
Allan K Bertram — University of British Columbia
Ryan Moffet — Sonoma Technology Inc.
Mary Gilles — Lawrence Berkeley National Laboratory

Category

Aerosol Properties

Description

The liquid-liquid phase separations of laboratory-generated aerosol particles were investigated using (1) scanning transmission x-ray microscopy/near-edge x-ray absorption fine structure spectroscopy (STXM/NEXAFS) coupled to a relative humidity (RH) controlled in situ cell and (2) environmental scanning electron microscopy (ESEM). In previous work, samples have been prepared by extraction from filter material and subsequent generation of larger particles. The techniques used here, however, are well-suited for analyzing the phase separations of ambient particles with no prior processing. The aerosol particles were comprised of 1:1 and 3:1 HMMA: ammonium sulfate. HMMA is a nine-carbon, aromatic compound that is used as a proxy for water-soluble organic compounds found in atmospheric aerosols. Preliminary results show that liquid-liquid phase separations occur at RHs between the deliquescence and efflorescence points, and that the organic phase surrounds the inorganic phase. The STXM/NEXAFS technique provides insight into the chemical bonding environment in the two phases both before and after separation for atmospherically relevant particles of 1–3 μm diameter.