Chemical retention during dry growth riming

Partitioning of volatile chemicals among the gas, liquid, and solid phases during the conversion of liquid water to ice in clouds can impact distributions of chemicals in precipitation and in the poststorm troposphere. In this paper, we extend a theoretical scaling model of chemical retention during hydrometeor freezing to all dry growth riming conditions. We account for spreading of drops upon impact with an ice‐phase hydrometeor using the spread height as the mass and heat transfer length scale. To account for heat loss to the ice substrate, we use an iterative solution to calculate the total freezing time. Using this augmented development, we calculate a theoretical dimensionless retention indicator λ under the conditions of several experimental studies and compare the retention indicator to the measured retention fraction Γ. Experimental retention compares well with the retention indicator. Empirically fitting the retention indicator to the experimental data provides the first parameterization for the retention coefficient, Γ = 1 − exp (−0.002λ), that is applicable to a range of chemicals and dry growth riming conditions. The analysis and model presented in this paper can be used to improve experimental design and parameterization of retention in cloud models.