HETEROGENEOUS LOSS OF OH ON NACL AND NH4NO3 AT TROPOSPHERIC TEMPERATURES

The uptake coefficients (gamma) for OH radicals on some dry salts of t ropospheric interest (NaCl and NH4NO3) have been investigated as a fun ction of temperature using the flow tube technique combined with an EP R spectrometer as a detection method. The temperature dependence of ga mma-values measured over the temperature range 245-340 K can be expres sed in Arrhenius form: gamma(NaCl)(OH) = (1.2 +/- 0.7) x 10(-5) exp [( 1750 +/- 200)/T] and gamma(NH4NO3)(OH) = (1.4 +/- 0.5) x 10(-4) exp [( 1000 +/- 100)/T]. These Arrhenius expressions lead to very similar gam ma-values (approximate to 4 x 10(-3)) for both salts studied at 300 K. It is shown that the heterogeneous OH sinks on solids aerosol play a very minor role in tropospheric chemistry in comparison with the homog eneous sinks.