AMT Atmospheric Measurement Techniques AMT Atmos. Meas. Tech. 1867-8548 Copernicus Publications Göttingen, Germany 10.5194/amt-4-2333-2011 Droplet activation, separation, and compositional analysis: laboratory studies and atmospheric measurements Hiranuma N. 1 Kohn M. 2 Pekour M. S. 1 Nelson D. A. 1 Shilling J. E. 1 Cziczo D. J. 1 3 Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, Washington, USA Institute for Atmospheric and Environmental Sciences, Goethe-University Frankfurt am Main, Frankfurt, Germany now at: Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts, USA 26 10 2011 4 10 2333 2343 Copyright: © 2011 N. Hiranuma et al. 2011 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://amt.copernicus.org/articles/4/2333/2011/amt-4-2333-2011.html The full text article is available as a PDF file from https://amt.copernicus.org/articles/4/2333/2011/amt-4-2333-2011.pdf

Droplets produced in a cloud condensation nuclei chamber (CCNC) as a function of supersaturation have been separated from unactivated aerosol particles using counterflow virtual impaction. Residual material after droplets were evaporated was chemically analyzed with an Aerodyne Aerosol Mass Spectrometer (AMS) and the Particle Analysis by Laser Mass Spectrometry (PALMS) instrument. Experiments were initially conducted to verify activation conditions for monodisperse ammonium sulfate particles and to determine the resulting droplet size distribution as a function of supersaturation. Based on the observed droplet size, the counterflow virtual impactor cut-size was set to differentiate droplets from unactivated interstitial particles. Validation experiments were then performed to verify that only droplets with sufficient size passed through the counterflow virtual impactor for subsequent analysis. A two-component external mixture of monodisperse particles was also exposed to a supersaturation which would activate one of the types (hygroscopic salts) but not the other (polystyrene latex spheres or adipic acid). The mass spectrum observed after separation indicated only the former, validating separation of droplets from unactivated particles. Results from ambient measurements using this technique and AMS analysis were inconclusive, showing little chemical differentiation between ambient aerosol and activated droplet residuals, largely due to low signal levels. When employing as single particle mass spectrometer for compositional analysis, however, we observed enhancement of sulfate in droplet residuals.

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