Abstract. The chemistry of N20 5 on liquid NaC1 aerosols or bulk NaC1 solutions was studied at 291 K by aerosol smog chamber and wetted-wall flow tube experiments. The uptake of N20 5 on deliquescent aerosol was obtained to be (3.2 + 0.2) x 10 -2 (lrr error) from the aerosol experiments. In the wetted-wall flow tube we observed that nitryl chloride (C1NO2) is the main product of the reaction at NaC1 concentrations larger than approximately 0.5 M and almost the only product at concentrations larger than I M. The C1NO: yield does not depend linearly on the NaC1 concentration, especially at small sodium chloride concentrations (i.e., smaller than 1 M). It appeared that a simple C1-) is unable to explain the observed concentration dependence of the product yield. We propose that N20 s dissociates to NO•-and NO•-(rate constant k I > 10 • s -•) mainly. The directly hydrolysis of N20 s (k3[H20]) is less than 20% of the total reaction. NO•-reacts with water to form 2H + and NO• (ks) or with C1-to form C1NO 2 (k4).Neglecting the influence of ionic strength we evaluate k4/k s to be 836 __ 32 (lo-error). Using the wetted-wall flow tube technique, we studied the uptake of nitryl chloride by aqueous solutions containing NaC1. We observed that the uptake coetScient 3• decreased from (4.84 +_ 0.13) x 10 -6 on pure water to (0.27 _+ 0.02) x 10 -6 on a 4.6 M NaC1

The heterogeneous reactions leading to formation and loss of BrNO2 on salt solutions as a model substrate for atmospheric sea salt aerosol are investigated. Further to the reaction of ClNO2 with bromide solutions, the reaction of Br2 with nitrite solution was found to be a convenient method for the synthesis of BrNO2. We measured the temperature-dependent lifetime of BrNO2 in a quartz cell and obtained the activation energy E A = 89 ± 9 kJ/mol for the unimolecular decay at atmospheric pressure. The reactive uptake of BrNO2 and ClNO2 on water and aqueous solutions was determined using a wetted-wall flow tube technique. We observed the reactions Br2 + NO2 - ↔ BrNO2 + Br-, Cl2 + NO2 - → ClNO2 + Cl-, and the net reaction ClNO2 + Br- ↔ BrNO2 + Cl-. BrNO2 and ClNO2 both react with NO2 - to release NO2 into the gas phase. Observed concentration profiles in the gas phase and in solution can be described qualitatively by a numerical model of the diffusion and reaction processes in the experimental setup.

The uptake of N2O5 by pure water and NaCl solution was studied as a function of temperature in the range from 262 to 278 K with the droplet train technique, where a highly controlled beam of droplets was exposed to N2O5 in a low-pressure flow tube reactor, and the formation of nitrate in the liquid phase was determined by ion chromatography. The uptake coefficients, y, for N2O5 on pure water are observed to decrease from 0.03 to 0.0 13 with increasing temperature. This behavior corresponds to the expected negative temperature dependence of mass accommodation leading to an enthalpy m o b , = (-9.6 f 1.6) kcal mol-' and to an entropy m o b s = (-43 f 6) cal mol-' K-l for the phase transfer, corresponding to a continuous nucleation process with a critical cluster size N* of about 2.4. A significantly lower yield of nitrate than with pure water is observed in the experiments on NaCl solution (1 mol/L), indicating that nitrogen compounds (such as ClN02) are formed after the uptake of N2O5 by subsequent reactions with NaCl and escape from the droplets. After correction for the known yield for the formation of CIN02, the results exhibit a slight systematic tendency for the uptake coefficient on NaCl solution to be greater than on pure water, indicating that the uptake of N2O5 by these aqueous media might be reaction-controlled. This assumption leads to a lower limit of 800 mol L-I atm-I s-l12 for the product Hk112 from a simple steady state model (where H is the Henry's law constant for N2O5 and k is the first-order hydrolysis rate constant).

The design and performance of a smog chamber for the study of photochemical reactions under simulated environmental conditions is described. The chamber is thermostated for aerosol experiments, and it comprises a gas chromatographic sample enrichment system suitable for monitoring hydrocarbons at the ppbv level. By irradiating NO x/alkane-mixtures rate constants for the reaction of OH radicals with n-alkanes are determined from n-pentane to n-hexadecane to be (k++_2a)/lO -12 cm 3 at 312K. Rate constants, (k _+ 2a)/10 -17 cm 3 s -l , for the reaction of ozone with trans-2-butene (21.2 _+ 1.0), cis-3-methylpentene-(2) (47.2 _+ 1.7), cyclopentene (62.4_+3.5), cyclohexene (7.8 _+0.5), cycloheptene (28.3 _+ 1.5), c~-pinene (8.6 _+ 1.3), and fl-pinene (1.4 _+ 0.2) are determined in the dark at 297 K using cis-2-bntene (13.0) as reference standard.

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