Heterogeneous loss of OH on NaCl and NH4NO3 at tropospheric temperatures

The uptake coefficients (gamma) for OH radicals on some dry salts of tropospheric interest (NaCl and NH4NO3) have been investigated as a function of temperature using the flow tube technique combined with an EPR spectrometer as a detection method. The temperature dependence of gamma-values measured over the temperature range 245-340 K can be expressed 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 gamma-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 homogeneous sinks.