Atmos. Chem. Phys. Discuss., 8, 4439-4482, 2008
www.atmos-chem-phys-discuss.net/8/4439/2008/
doi:10.5194/acpd-8-4439-2008
© Author(s) 2008. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
CCN activation experiments with adipic acid: effect of particle phase and adipic acid coatings on soluble and insoluble particles
S. S. Hings1, W. C. Wrobel1, E. S. Cross1, D. R. Worsnop2, P. Davidovits1, and T. B. Onasch1,2
1Department of Chemistry, Boston College, Chestnut Hill, MA 02467, USA
2Aerodyne Research Inc., Billerica, MA 01821, USA

Abstract. Slightly soluble atmospherically relevant organic compounds, such as adipic acid, may influence particle CCN activity and therefore cloud formation. The 11 published experimental studies on the CCN activity of adipic acid particles are not consistent with each other nor do they in most cases agree with the Köhler theory. The CCN activity of adipic acid aerosol particles was studied over a significantly wider range of conditions than in any previous single study. The work spans the conditions of the previous studies and also provides alternate methods for producing wet and dry adipic acid particles without the need to produce them by atomization of aqueous solutions. The CCN effect of adipic acid coatings on both soluble and insoluble particles has also been studied. The CCN activation of the small (dm<150 nm) initially dry particles is subject to a deliquescence barrier, while for the larger particles the activation follows the Köhler curve. Adipic acid particles prepared in a wet state follow the Köhler curve over the full range of particle diameters studied. The experiments suggest that the scatter in the previously published CCN measurements is most likely due to the difficulty of producing uncontaminated adipic acid particles by atomization of solutions and possibly also due to uncertainties in the calibration of the instruments. The addition of a hydrophilic soluble compound to dry adipic acid eliminates the effect of particle phase, that is, the effect of the deliquescence barrier to CCN activation. An adipic acid coating on hydrophobic soot yields a CCN active particle. For the relatively small soot particles (dcore=88 and 102 nm) the CCN activity of the coated particles approaches the deliquescence line of adipic acid, suggesting that the total size of the particle determines CCN activation and the soot core acts as a scaffold.

Citation: Hings, S. S., Wrobel, W. C., Cross, E. S., Worsnop, D. R., Davidovits, P., and Onasch, T. B.: CCN activation experiments with adipic acid: effect of particle phase and adipic acid coatings on soluble and insoluble particles, Atmos. Chem. Phys. Discuss., 8, 4439-4482, doi:10.5194/acpd-8-4439-2008, 2008.
 
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