Impact of palmitic acid coating on the water uptake and loss of ammonium sulfate particles R. M. Garland1, M. E. Wise1,*, M. R. Beaver1, H. L. DeWitt1, A. C. Aiken1, J. L. Jimenez1, and M. A. Tolbert1 1Department of Chemistry and Biochemistry and CIRES, University of Colorado, Boulder, Colorado, USA *now at: Department of Geological Sciences and Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona, USA
Abstract. While water insoluble organics are prevalent in the atmosphere, it is not
clear how the presence of such species alters the chemical and physical
properties of atmospheric aerosols. Here we use a combination of FTIR
spectroscopy, Transmission Electron Microscopy (TEM) and Aerosol Mass
Spectrometry (AMS) to characterize ammonium sulfate particles coated with
palmitic acid. Coated aerosols were generated by atomizing pure ammonium
sulfate, mixing the particles with a heated flow of nitrogen with palmitic
acid vapor, and then flowing the mixture through an in-line oven to create
internally mixed particles. The mixing state of the particles was probed
using the AMS data and images from the TEM. Both of these probes suggest
that the particles were internally mixed. Water uptake by the mixed
particles was then probed at 273 K. It was found that for ammonium sulfate
containing ~20 wt% palmitic acid the deliquescence relative
humidity (DRH) was the same as for pure ammonium sulfate (80±3%
RH). For particles with ~50 wt% palmitic acid however, the mixed
particles began to take up water at relative humidities as low at 69% and
continued to slowly take up water to 85% RH without fully deliquescing.
In addition to studies of water uptake, water loss was also investigated.
Here coatings of up to 50 wt% had no impact on the efflorescence relative
humidity. These studies suggest that even if insoluble substances coat salt
particles in the atmosphere, there may be relatively little effect on the
resulting water uptake and loss.
Citation: Garland, R. M., Wise, M. E., Beaver, M. R., DeWitt, H. L., Aiken, A. C., Jimenez, J. L., and Tolbert, M. A.: Impact of palmitic acid coating on the water uptake and loss of ammonium sulfate particles, Atmos. Chem. Phys., 5, 1951-1961, doi:10.5194/acp-5-1951-2005, 2005.