Scavenging of SO2 and NH3 during growth of ice

Scavenging of SO2 and NH3 during ice growth by deposition of water vapour by diffusion was studied in a diffusion chamber at T=−6°C and −15°C. At both temperatures, we observed within the ice an increase of sulphur compounds, expressed as S(VI), for SO2 gas concentrations up to about 3 ppmv. At higher concentrations, saturation was reached in the ice phase. Addition of O3 to the flowing air produced an increase of S(VI) within the ice, at lower SO2 concentrations only. In experiments with NH3, we obtained at T=−15°C nitrogen compound concentrations, expressed as NH4+, regardless of the NH3 concentration in the gas phase in the range of concentrations tested, while at T=−6°C, NH4+ increased with increasing NH3. Concentrations of NH4+ and SO42− turned out to be higher at T=−6°C, compared to −15°C. By considering mixed runs at T=−15°C and −6°C, we observed an increase in both NH4+ and SO42− in the ice phase, compared to experiments at the same temperature, but with separate gases.