ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-5-1951-2005 Impact of palmitic acid coating on the water uptake and loss of ammonium sulfate particles Garland R. M. 1 Wise M. E. 1 2 Beaver M. R. 1 DeWitt H. L. 1 Aiken A. C. 1 Jimenez J. L. 1 Tolbert M. A. 1 Department 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 01 08 2005 5 7 1951 1961 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/5/1951/2005/acp-5-1951-2005.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/5/1951/2005/acp-5-1951-2005.pdf

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.