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 formation of the adducts of OH with benzene, toluene and phenol and consecutive reactions of the adducts with NO, NO2 and O2 are investigated in the temperature range from ∼298–374 K employing the flash photolysis/resonance fluorescence technique in Ar at 133 mbar. Biexponential decays of OH can be observed over at least 2 orders of magnitude in the presence of the aromatics, and the three reaction channels: abstraction of H by OH, addition of OH and unimolecular decomposition of the adduct are distinguished in overlapping temperature ranges. Rate constants and preliminary Arrhenius parameters are obtained for these channels for benzene, toluene, and phenol. The reactions of the adducts with NO are very slow and can be neglected (<10−13 cm3 s−1) in all three cases. Values of ∼3·10−11 cm3 s−1 are obtained for the rate constants of the reactions of the adducts with NO2, almost independent of reactant and temperature. Preliminary determinations of the adduct reactivities against O2 ∼ 2 · 10−16 (benzene‐OH) and ∼5 · 10−16 cm3 s−1 (toluene‐OH) near room temperature indicate that this path predominates under tropospheric conditions. The results for O2 are confirmed by direct observations of the adduct benzene‐OH by the cw UV‐laser longpath absorption technique.

Abstract. During the DOMINO (Diel Oxidant MechanismIn relation to Nitrogen Oxides) campaign in southwest Spain we measured simultaneously all quantities necessary to calculate a photostationary state for HONO in the gas phase. These quantities comprise the concentrations of OH, NO, and HONO and the photolysis frequency of NO 2 , j (NO 2 ) as a proxy for j (HONO). This allowed us to calculate values of the unknown HONO daytime source. This unknown HONO source, normalized by NO 2 mixing ratios and expressed as a conversion frequency (% h −1 ), showed a clear dependence on j (NO 2 ) with values up to 43 % h −1 at noon. We compared our unknown HONO source with values calculated from the measured field data for two recently proposed processes, the light-induced NO 2 conversion on soot surfaces and the reaction of electronically excited NO 2 * with water vapour, with the result that these two reactions normally contributed less than 10 % (<1 % NO 2 + soot + hν; and <10 % NO 2 * + H 2 O) to our unknown HONO daytime source. OH production from HONO photolysis was found to be larger (by 20 %) than the "classical" OH formation from ozone photolysis (O( 1 D)) integrated over the day.Correspondence to: M. Sörgel

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