Modeling of the processing and removal of trace gas and aerosol species by Arctic radiation fogs and comparison with measurements

A Lagrangian radiation fog model is applied to a fog event at Summit, Greenland. The model simulates the formation and dissipation of fog. Included in the model are detailed gas and aqueous phase chemistry, and deposition of chemical species with fog droplets. Model predictions of the gas phase concentrations of H 2 O 2 , HCOOH, SO 2 , and HNO 3 as well as the fog fluxes of S(VI), N(V), H 2 O 2 , and water are compared with measurements. The predicted fluxes of S(VI), N(V), H 2 O 2 , and fog water generally agree with measured values. Model results show that heterogeneous SO 2 oxidation contributes to approximately 40% of the flux of S(VI) for the modeled fog event, with the other 60% coming from preexisting sulfate aerosol. The deposition of N(V) with fog includes contributions from HNO 3 and NO 2 initially present in the air mass. HNO 3 directly partitions into the aqueous phase to create N(V), and NO 2 forms N(V) through reaction with OH and the nighttime chemistry set of reactions which involves N 2 O 5 and water vapor. PAN contributes to N(V) by gas phase decomposition to NO 2 , and also by direct aqueous phase decomposition. The quantitative contributions from each path are uncertain since direct measurements of PAN and NO 2 are not available for the fog event. The relative contributions are discussed based on realistic ranges of atmospheric concentrations. Model results suggest that in addition to the aqueous phase partitioning of the initial HNO 3 present in the air mass, the gas phase decomposition of PAN and subsequent reactions of NO 2 with OH as well as nighttime nitrate chemistry may play significant roles in depositing N(V) with fog. If a quasi‐liquid layer exists on snow crystals, it is possible that the reactions taking place in fog droplets also occur to some extent in clouds as well as at the snow surface.