The uptake of HO2 radicals on synthetic sea salt, NaCl, NaBr and MgCl(2).6H2O dry solid films was studied over the temperature range 240 to 340 K and at 1 Torr pressure of helium using a discharge flow reactor coupled to a modulated molecular beam mass spectrometer. The Arrhenius expressions (calculated with geometric surface area) were obtained for the uptake coefficient of HO2: 3.1x10(-9) exp[(3990+/-200)/T], 2.2x10(-8) exp[(3340+/-180)/T], 1.2x10(-8) exp[(3570+/-180)/T] and 3.8x10(-5) exp[(1710+/-60)/T] on sea salt, NaCl, NaBr and MgCl(2).6H2O, respectively (quoted uncertainty is 2sigma statistical). H2O2 was observed as a main product of HO2 interaction with salt surface indicating a heterogeneous HO2 self reaction mechanism. The results show that the HO2 loss through heterogeneous interaction with salt surface is not sufficiently rapid to explain the observed differences between modeled and measured HO2 concentrations in remote coastal areas.

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The uptake of HNO(3) on aviation kerosene (TC-1) soot was measured as a function of temperature (253-295 K) and the partial pressure of HNO(3), and the uptake of HNO(3) on hexane soot was studied at 295 K and over a limited partial pressure of HNO(3). The HNO(3) uptake was mostly reversible and did not release measurable amounts of gas-phase products such as HONO, NO(3), NO(2) or N(2)O(5). The heat of adsorption of HNO(3) on soot was dependent on the surface coverage. The isosteric heats of adsorption, Delta(0)H(isosteric), were determined as a function of coverage. Delta(0)H(isosteric) values were in the range -16 to -13 kcal mol(-1). The heats of adsorption decrease with increasing coverage. The adsorption data were fit to Freundlich and to Langmuir-Freundlich isotherms. The heterogeneity parameter values were close to 0.5, which suggested that a HNO(3) molecule can occupy two sites on the surface with or without being dissociated and that the soot surface could be nonuniform. Surface FTIR studies on the interaction of soot with HNO(3) did not reveal formation of any minor product such as organic nitrate or nitro compound on the soot surface. Using our measured coverage, we calculate that the partitioning of gas-phase nitric acid to black carbon aerosol is not a significant loss process of HNO(3) in the atmosphere.