Experimental measurements of the heterogeneous reactivity of sulfuric acid‐water mixtures at low temperatures are presented. The kinetic data are combined with a stratospheric aerosol‐loading model and simple chemical models to predict the effect of heterogeneous chlorine and chlorine oxide radical reactions on the stratospheric Cl/HCl ratio at several altitudes. The Cl reactions are found to have little influence, but the ClO reaction reduces the Cl/HCl ratio by about 3% at 20 km (within a factor of 2 at 1 standard deviation). The effect at higher altitudes is smaller. Simulated sunlight was found to have no effect on the heterogeneous reactivities.

The products of the heterogeneous reactions of chlorine atoms and chlorine oxide radicals with acid coated Pyrex walls have been directly determined for the first time. Contrary to the usual assumption that chlorine atoms recombine to form Clz, we find that the major product is HCl, with small amounts of perchlorate also formed. Similarly, C10 radicals form HC1 rather than Clz. The source of hydrogen for these reactions is probably the water always found in this type of vacuum system. These results may change the interpretation of flow tube experiments with chlorine atoms. Application to the H + HC1 reaction is discussed as an example.

Chlorine atom diffusion coefficients in argon were determined using a flowing afterglow system and electron spin resonance detection. Measured values, projected to 1 atm total pressure and 295°K, were 0.26±0.05 cm2/sec. Measurements were also made of oxygen atom diffusion in helium for comparison to previously reported values for the latter system. Diffusion coefficients for oxygen atoms in helium, projected to 1 atm total pressure and 295°K, were found to be 1.08±0.12 cm2/sec in this study, compared to literature values of 1.00 and 0.72 cm2/sec.