Heterogeneous loss of OH on NaCl and NH4 NO 3 at tropospheric temperatures

The uptake coefficients () 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 -values measured over the temperature range 245–340 K can be expressed in Arrhenius form: ^OH_NaCl=(1.2±0.7)×10⁻⁵exp[(1750±200)/T] and ^OH_NH4NO3=(1.4±0.5)×10⁻⁴exp[(1000±100)/T]. These Arrhenius expressions lead to very similar -values (approx4×10⁻³) 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.