The role of adsorption of chemical species onto ice and snow in deep convection

The adsorption of gas-phase species onto ice and snow has been documented as an important process for nitric acid in both laboratory (Zondlo et al.,1997) and field studies (Popp et al., 2004). Recent modeling studies (von Kuhlmann and Lawrence, 2006) have indicated that the adsorption of gas-phase nitric acid onto ice reduces the gas-phase concentration of nitric acid in the upper troposphere by 40-60%. Wang (2005) also shows significant nitric acid uptake on ice in the anvil region of a tropical deep convective storm, but only small to negligible amounts of uptake of formaldehyde ontoice.

In this study, numerical model simulations using the Weather Research and Forecast model coupled with gas and aqueous chemistry are analyzed to examine the importance of adsorption of gas species onto ice for a summertime, midlatitude thunderstorm. The analysis focuses on nitric acid, formaldehyde, and peroxides, species that are adsorbed onto ice in varying degrees. Simulations that do not include the uptake of these species onto ice are partitioned ~90% in the gas phase and 10% in the ice phase for the anvil region of the storm. Thus, the role of adsorption of these species onto ice would be to partition these species more to the ice and snow which settle to the mid troposphere where sublimation of the ice releases the species back to the gas phase, allowing the species to participate in mid-tropospheric chemistry rather than upper tropospheric chemistry.