Comment on Kokkola et al. (2008) – Comparisons with analytical solutions from Khvorostyanov and Curry (2007) on the critical droplet radii and supersaturations of CCN with insoluble fractions V. I. Khvorostyanov^{1} and J. A. Curry^{2} ^{1}Central Aerological Observatory, Dolgoprudny, Moscow Region, Russia ^{2}School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia

Abstract. Analytical solutions for the critical radii r_{cr} and
supersaturations s_{cr} of the cloud condensation nuclei with
insoluble fractions were derived by Khvorostyanov and Curry (2007,
hereafter KC07). Similar solutions were found later by Kokkola et
al. (2008, hereafter Kok08); however, Kok08 used the approximation of
an ideal dilute solution, while KC07 used more accurate assumptions
that account for nonideality of solutions. Kok08 found a large
discrepancy with KC07 in the critical supersaturations. Various
possible reasons of this are analyzed. It is shown that the major
discrepancy was caused by a simple mistake in Kok08 in the equation
for the critical supersaturation: erroneous ''plus'' sign between
the Kelvin and Raoult terms instead of correct ''minus'' sign. If
this mistake is corrected, the equations from Kok08 mostly repeat the
equations from KC07, except that Kok08 use the dilute solution
approximation. If the mistake in Kok08 is corrected, then the
differences in the critical radii and supersaturations do not exceed
16–18%, which characterizes the possible errors of an ideal
diluted solution approximation. If the Kok08 scheme is corrected and applied to a nonideal solution, then the difference with KC07 does not exceed
0.4–1%.

Citation: Khvorostyanov, V. I. and Curry, J. A.: Comment on Kokkola et al. (2008) – Comparisons with analytical solutions from Khvorostyanov and Curry (2007) on the critical droplet radii and supersaturations of CCN with insoluble fractions, Atmos. Chem. Phys. Discuss., 9, 9537-9550, doi:10.5194/acpd-9-9537-2009, 2009.