Heterogeneous loss of OH on NaCl and NH₄NO₃ at tropospheric temperatures

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