Heterogeneous Reaction of HOI with Sodium Halide Salts

The interaction of gaseous HOI with crystalline grains of NaCl and sea-salt and thin films of NaBr crystals has been studied in a wall coated tubular flow reactor coupled to a quadrupole mass spectrometer over a concentration range (0.2−8) × 10 12 molecules cm -3 at 278 and 298 K. On a fresh surface, the uptake coefficients determined were independent of temperature with γ = 0.034 ± 0.009, γ = 0.016 ± 0.004, and γ = 0.061 ± 0.021 for NaBr, NaCl, and sea-salt, respectively. No increase in reactivity was observed on addition of water vapor between 0 and 23% relative humidity at 278 K. It was also shown that the reactivity of the salt surface decreased with time of exposure to HOI and that steady-state uptake was slower on “aged” salt surfaces. Products of the reactions released into the gas phase were IBr, ICl, and IBr + ICl for the reaction of HOI on NaBr, NaCl, and sea-salt surfaces, respectively. The atmospheric implications of the results obtained are briefly discussed.