Heterogeneous loss of OH on NaCl and NH sub(4) NO sub(3) at tropospheric temperatures

The uptake coefficients ( gamma ) for OH radicals on some dry salts of tropospheric interest (NaCl and NH sub(4) NO sub(3) ) 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 sub(N) sub(a) sub(C) sub(l) super(O) super(H) =(1.2 plus or minus 0.7) x 10 super(-) super(5) exp[(1750 plus or minus 200)/T] and gamma sub(N) sub(H) sub(N) sub(O) super(O) super(H) =(1.4 plus or minus 0.5) x 10 super(-) super(4) exp[(1000 plus or minus 100)/T]. These Arrhenius expressions lead to very similar gamma -values ( identical with 4 x 10 super(-) super(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.