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 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.

The uptake of nitryl chloride C1NO 2 by pure water and NaI solutions was studied as a function of temperature in the range from 268 to 279 K with the droplet train technique. An upper limit of 10 -5 was derived for the uptake on pure water, while the uptake rate was observed to be greatly enhanced in the presence of 10 -3 -10 -2 M iodide, yielding uptake coefficients in the range from 1.1x10 -3 to 6.6x10 -3. This enhancement is a consequence of a reaction between I-and C1NO 2 where we suggest that a transfer of C1 + to iodide is involved. We also suggest that bulk kinetics alone is unable to describe the measured uptake rate which is influenced by surface reactions. These results show that heterogeneous chemistry in concentrated aerosols may play an important role for the fate of C1NO2, and may affect the concentration of atomic chlorine in the marine boundary layer.

The uptake kinetics of nitrosyl chloride (NOCl) by aqueous solutions has been measured as a function of temperature, using two different techniques, i.e., the wetted-wall at atmospheric and reduced pressure and the droplet train flow tubes, both techniques being combined with FTIR and HPLC detection. Uptake coefficients, which were shown to be slightly temperature dependent, range from 0.012 to 0.0058 for temperatures between 273 and 293 K. The production of HONO was observed from the hydrolysis of NOCl, and its yield in the gas phase is in agreement with the Henry's law constant of nitrous acid. The uptake of NOCl was also studied on solutions containing HCl, NaCl, and NaOH. Only the latter affected the uptake kinetics, probably through a nucleophilic reaction with OH-. The observed kinetics are shown to be consistent with a lower limit of 0.03 for the mass accommodation coefficient. These results suggest that heterogeneous removal of NOCl is very efficient, meaning that this compound is not expected to be a significant precursor of atomic Cl in the atmosphere. The Henry's law constant for NOCl was observed to be greater than 0.05 mol L-1 atm-1.

Uptake of Nitrosyl Chloride (NOCl) by Aqueous Solutions.-Kinetic studies on the heterogeneous chemistry of NOCl on aqueous solutions using the wetted-wall flow tube as well as the droplet train technique indicate that NOCl is not a significant precursor of atomic chlorine in the atmosphere. -(SCHEER, V.; FRENZEL, A.; BEHNKE, W.; ZETZSCH, C.; MAGI, L.; GEORGE, CH.; MIRABEL, PH.; J. Phys. Chem. A 101 (1997) 49, 9359-9366; Fraunhofer-Inst. Toxikol. Aerosolforsch., D-30625 Hannover, Germany; EN)