The Fate of Volatile Chemicals during Wet Growth of a Hailstone

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We develop and apply a mechanistic model for the study and prediction of volatile chemical partitioning during wet growth of a hailstone. The model estimates the fraction of a chemical's mass in the impinging drops that is retained in a two-phase hailstone. It is derived from mass and rate balances over solute and water for steady accretion conditions. We applied the model using a modified Monte Carlo ensemble simulation approach to study the impact of chemical, environmental, and hail-specific input variables on the predicted retention fraction for six atmospherically relevant volatile chemical species, sulfur dioxide, hydrogen peroxide, ammonia, nitric acid, formaldehyde, and formic acid. Individual input variables found to significantly influence retention are the ice–liquid interface supercooling, the liquid water content of the hail, and the effective Henry's constant. The retention fraction increased with increasing values of these variables. Conversely, the ice–liquid distribution coefficient and hail diameter were found to have negligible effects on solute retention. The overall range of simulated retention fraction was from 1 × 10−8 to 1, while ensemble mean retentions for fixed values of individual input variables ranged from 9 × 10−7 to 0.3. No single variable was found to control the extremes; rather they are due to combinations of model input variables.

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Environmental Research Letters, v. 4, no. 1, art. 015001