The uptake kinetics of ozone (O3) and methyl hydroperoxide (CH3OOH, MHP) by aqueous solutions were studied as a function of temperature using the droplet train technique combined with mass spectrometry detection. The uptake of ozone by pure water was found to be too small to be directly measured. Using NaI as a scavenger increased the uptake coefficient γ from below the detection limit to a range from 0.0037 to 0.0116 for I- activities in the range from 0.3615 to 2.889 at 282 K. From these experiments, we estimated the second-order rate constant for the reaction O3 + I- → products to be in the range 3.2 × 108 to 2.4 × 109 M-1 s-1 for temperature between 275 and 293 K. The activation parameters for this reaction were also estimated. For methyl hydroperoxide, the uptake rate on pure water was fast enough to be directly measured. According to the physicochemical properties of this hydroperoxide, the uptake was mainly due to the diffusion and accommodation processes. It was therefore possible to measure its mass accommodation coefficient α as a function of temperature. The observed values are in the range 0.92 × 10-2 to 2.08 × 10-2 for temperature between 281 and 261 K. The activation parameters for the accommodation were also determined.

The uptake kinetics of N2O5 were studied with the droplet train technique as a function of temperature between 262 and 278 K on different aqueous solutions. No pronounced temperature dependence was observed, and the average uptake coefficient in this temperature range is 0.018 ± 0.003. When interacting with salt solutions (i.e., NaCl, NaBr, or NaI), N2O5 contributes to the formation of ClNO2 and BrNO2. The multiphase chemistry of these nitryl compounds was further investigated using the wetted-wall technique as a function of temperature between 275 and 293 K on different aqueous solutions. The uptake coefficients are reported for both species, and no distinct temperature dependence was observed. Their uptake rate was efficiently enhanced by the presence, in the aqueous phase, of halogenides ions. When reacting with Br- or I-, both nitryl compounds deliver to the gas phase the molecular form of the halogen, i.e., Br2 or I2. A reaction scheme potentially explaining these observations is presented and its importance for the sea-salt aerosol chemistry is discussed.

The uptake kinetics of methanesulfonic acid (CH 3 SO 3 H, MSA) and glyoxal (CHOCHO, ethanedial) by aqueous solutions were studied as a function of temperature using the droplet train technique combined with mass spectrometry and FTIR detection. The measured uptake kinetics for MSA were shown to be independent of the composition of the aqueous phase for NaCl concentrations in the range from 0 to 2 M. The mass accommodation coefficient was determined as a function of temperature between 261 and 283 K. The measured values decreased from 0.16 to 0.1 in this temperature range. The uptake kinetics of glyoxal were studied as a function of temperature between 263 and 283 K and were very close to our detection limit in pure water (i.e., uptake coefficient γ close to 10 -3 ) but were strongly affected by the pH (in the range from 1 to 14) or by sulfite ions (γ increasing to ∼0.02). The rate constant of the reaction between nonhydrated glyoxal and sulfite ions was determined to be ∼7.6 × 10 6 M -1 s -1 at 283 K. The mass accommodation temperature dependence was beyond the sensitivity of the technique employed in this study; therefore, we report an average value of R ) 0.023 for the studied temperature range. The uptake kinetics of CHOCHO were shown to be in agreement with bulk properties for temperatures larger than 273 K but deviate from it below. A surface reaction where glyoxal is protonated prior to accommodation was discussed as a possible explanation for an increased uptake rate in acidic solutions.

Abstract. The uptake kinetics of gaseous ClONO 2 and BrONO 2 on aqueous surfaces were measured, as a function of temperature and liquid composition (pure water and NaCl or NaBr containing solutions) using the droplet train technique coupled to a mass spectrometer. The uptake kinetics are driven by the reactivity of these gases and, for both compounds, the uptake rates on pure water or on NaCl solutions (0.1 M) are comparable. The uptake coefficient γ of ClONO 2 does not depend on the temperature while that of BrONO 2 increases slightly when the temperature is raised from 272 to 280 K. For ClONO 2 and BrONO 2 , the uptake rates increase on NaBr-doped droplets, enabling the estimation of the mass accommodation coefficient α. The corresponding values for α are 0.108±0.033 for ClONO 2 and 0.063±0.021 for BrONO 2 where the statistical errors correspond to ±2σ .The reactions of ClONO 2 and BrONO 2 on NaCl solutions lead respectively to the formation of Cl 2 and BrCl. The uptake of ClONO 2 on NaBr solutions generates BrCl as primary product, which in turn can react with NaBr to produce Br 2 . As expected, the only product of BrONO 2 reaction on NaBr solution is Br 2 .

The uptake kinetics of three different hydrogen halides, i.e., HCl, HBr, and HI, by aqueous surfaces were measured as a function of temperature in the range from 262 to 281 K using the droplet train technique. The reported mass accommodation coefficients (R) were shown to decrease with increasing temperature. For HCl, R decreases from 0.24 to 0.13 when the temperature was raised from 263 to 281 K. In the same temperature range, the mass accommodation of HBr and HI decrease from 0.16 to 0.068 and 0.19 to 0.079, respectively. This temperature trend suggests that the rate-limiting step during the accommodation process is part of the physical solvation process as previously reported for nonreacting gases. The data were accordingly interpreted using a model found in the literature which describes the mass accommodation process as a dynamical nucleation event. The implications for the tropospheric chemistry of these findings are also discussed.