On the stratospheric chemistry of hydrogen cyanide

HCN profiles measured by solar occultation spectrometry during 10 balloon flights of the JPL MkIV instrument are presented. The HCN profiles reveal a compact correlation with stratospheric tracers. Calculations with a 2D-model using established rate coefficients for the reactions of HCN with OH and O(^1D) severely underestimate the measured HCN in the middle and upper stratosphere. The use of newly available rate coefficients for these reactions gives reasonable agreement of measured and modeled HCN. An HCN yield of ∼30% from the reaction of CH_3CN with OH is consistent with the measurements

Temperature-Dependent Kinetics Study of the Reactions of OH with C2H5I, n-C3H7I, and iso-C3H7I

International audienceFlash photolysis (FP) coupled with resonance fluorescence (RE) was used to measure the absolute rate coefficients for the reactions of OH(X-2 Pi) radicals with C2H5I (k(1)), n-C3H7I (k(2)), and iso-C3H7I (k(3)) at temperatures between 297 and 372 K in 188 Torr of He; this represents the first temperature-dependent kinetics studies for the title reactions. The experiments involved time-resolved RE detection of the OH (A(2)Sigma(+) -> X-2 Pi transition at lambda = 308 nm) radicals following FP of H2O/C2H5I/He, H2O/n-C3H7I/He, and H2O/iso-C3H7I/He mixtures. The OH(X-2 Pi) radicals were produced by FP of H2O in vacuum-UV at wavelengths lambda > 120 nm. Decays of OH radicals in the presence of C2H5I, n-C3H7I, and iso-C3H7I were observed to be exponential, and the decay rates were found to be linearly dependent on the C2H5I, n-C3H7I, and iso-C3H7I concentrations. The results are described by the following Arrhenius expressions (units of cm(3) molecule(-1) s(-1)): k(1)(297-372 K) = (5.55 +/- 3.20) x 10(-12) exp[-(830 +/- 90) K/T], k(2)(300-370 K) = (1.65 +/- 0.90) x 10(-11) exp[-(780 +/- 90) K/T] and k(3)(299-369 K) = (7.58 +/- 3.70) x 10(-12) exp[-(530 +/- 80) K/T]. Reported errors in E/R and in the pre-exponential factors are 2 sigma random errors, returned by the weighted (by 1/sigma(2)) least-squares fits to the kinetic data. The implications of the reported kinetic results for understanding both atmospheric and nuclear safety interests of C2H5I, n-C3H7I, and iso-C3H7I are discussed

Evaluation of the reaction artifacts in an annular denuder-based sampler resulting from the heterogeneous ozonolysis of naphthalene

International audienceThe heterogeneous ozonolysis of naphthalene adsorbed on XAD-4 resin was studied using an annular denuder technique. The experiments involved depositing a known quantity of naphthalene on the XAD-4 resin and then measuring the quantity of the solid naphthalene that reacted away under a constant flow of gaseous ozone (0.064 to 4.9 ppm) for a defined amount of time. All experiments were performed at room temperature (26 to 30 A degrees C) and atmospheric pressure. The kinetic rate coefficient for the ozonolysis reaction of naphthalene adsorbed on XAD-4 resin is reported to be (10.1 A +/- 0.4) x 10(-19) cm(3) molecule(-1) s(-1) (error is 2 sigma, precision only). This value is five times greater than the currently recommended literature value for the homogeneous gas phase reaction of naphthalene with ozone. The obtained rate coefficient is used to evaluate reaction artifacts from field concentration measurements of naphthalene, acenaphthene, and phenanthrene. The observed uncertainties associated with field concentration measurements of naphthalene, acenaphthene, and phenanthrene are reported to be much higher than the uncertainties associated with the artifact reactions. Consequently, ozone reaction artifact appears to be negligible compared to the observed field measurement uncertainty results