Droplet activation, separation, and compositional analysis: laboratory studies and atmospheric measurements
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Hiranuma-2011-Droplet activation.pdf
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358.44 KB
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Author(s)
Hiranuma, N.
Kohn, M.
Pekour, M. S.
Nelson, D. A.
Shilling, J. E.
Cziczo, Daniel James
Date Issued
October 2011
Journal
Atmospheric Measurement Techniques
Publisher
Copernicus Publications on behalf of the European Geosciences Union
Citation
Hiranuma, N. et al. “Droplet Activation, Separation, and Compositional Analysis: Laboratory Studies and Atmospheric Measurements.” Atmospheric Measurement Techniques 4.10 (2011): 2333–2343. Web.
Version
Final published version
Abstract
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.
MIT Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
Terms of Use
Creative Commons Attribution
Persistent DSpace Link
DOI of Published Version
http://dx.doi.org/10.5194/amt-4-2333-2011
