Heterogeneous chemistry of nitryl halides in relation to tropospheric halogen activation

The heterogeneous chemistry of nitryl chloride and nitryl bromide by salt c ontaining solutions was studied as a function of temperature in the range f rom 275 to 293 K with the wetted-wall flowtube combined with FTIR and mass spectrometry detection. Uptake coefficients and values of the product Hk(1/ 2) on these saline solutions have been determined. For nitryl halides inter acting with NaI: and NaBr solutions, the values of the product Hk(1/2) are respectively 4384.7 +/- 326.7 and 103.1 +/- 18.7 M atm(-1) s(-/12) for nitr yl chloride at 275 K and 544.2 +/- 94.7 and 47.7 +/- 15.2 M atm(-1) s(-1/2) for nitryl bromide at 278 K. When reacting with NaI or NaBr solutions, the se heterogeneous reactions release, as major products, the molecular forms of the halogen i.e., respectively I-2 and Br-2. A simplified reaction schem e explaining the formation of these products is presented and is inserted i nto a model simulating the chemistry in the marine boundary layer. The mode lling effort showed Cl and BrO atoms concentrations up to 5 x 10(4) and 1.8 x 10(6) molecules cm(-3) respectively, which are comparable to values actu ally measured in field campaigns.