Theory of isotopic fractionation on facetted ice crystals Laucks Foundation Inc. Suite 2100, PMB 174, 1700 Seventh Ave., Seattle, WA 98101, USA
16 Nov 2011
Received: 08 May 2011 – Published in Atmos. Chem. Phys. Discuss.: 21 Jun 2011Abstract. The currently used "kinetic-fractionation" (KF) model of the differential
incorporation of water-molecule isotopologues into vapor-grown ice omits
surface processes on crystal facets that may be important in temperature
reconstructions. This article introduces the "surface-kinetic"
fractionation model, a model that includes such surface processes, and shows
that differences in deposition coefficients for water isotopologues can
produce isotopic fractionation coefficients that significantly differ from
those of KF theory. For example, if the deposition coefficient of
H218O differs by just 5% from that of ordinary water
(H216O), the resulting fractionation coefficient at 20%
supersaturation may deviate from the KF value by up to about ±17‰, and
even more at greater supersaturation. As a result, the surface-kinetic
theory may significantly change how fractionation depends on
supersaturation. Moreover, the model introduces possible new temperature
dependencies from the deposition coefficients. These parameters need to be
constrained by new laboratory measurements.
Revised: 15 Oct 2011 – Accepted: 30 Oct 2011 – Published: 16 Nov 2011
Citation: Nelson, J.: Theory of isotopic fractionation on facetted ice crystals, Atmos. Chem. Phys., 11, 11351-11360, doi:10.5194/acp-11-11351-2011, 2011.