Experimental Verification of Classical Heterogeneous Nucleation Theory with Perfect Wetting, with a Variable Saturation Scanning Condensation Particle Sizer (VSCPS)

LUIS-JAVIER PEREZ-LORENZO, Michel Attoui, Charles Brock, Juan Fernandez de la Mora, Yale University

     Abstract Number: 497
     Working Group: Aerosol Physical Chemistry and Microphysics

Abstract
In the sheathed Variable Saturation Scanning Condensation Particle Sizer of Gallar et al., seed particles sense a well-defined maximal saturation ratio S_max, controlled through the fraction w of a saturator flow combined with a dry flow: S_max=Cw, though C is unknown. We describe recent improvements to both this VSCPS and the uniformity of the test aerosol, resulting in singularly sharp activation curves P(w) for PolyEthylene Glycol (PEG) 3-9 nm particles in n-butanol. We further determine the unknown proportionality constant C by assuming that the largest particles obey classical nucleation theory with perfect wetting. This turns the measured P(w) into P(S) data, which we compare with classical heterogeneous nucleation theory. Besides C, there is only one adjustable parameter K, the preexponential coefficient entering into the nucleation rate. P(S) curves then agree well with theory between 5 and 7nm. Smaller particles depart slightly from the theory, due to the limitations of the macroscopic model used. The measured P(S) is nevertheless unbiased by the VSCPC, and can be used to test other nucleation theories claiming validity below 5 nm. The predicted widths of the P(S) curves decrease with increasing particle size, while measured widths stop steepening above 7 nm. This saturation is apparently due to limited instrument resolution. Measured widths are nevertheless narrow, with reliable critical supersaturation values that agree well with theory.

C. Gallar, C. A. Brock, J. L. Jimenez, C. Simons, A Variable Supersaturation Condensation Particle Sizer, Aerosol Sci. & Techn. 40 (6) (2006) 431–436.