Showing papers by "A. R. Ravishankara published in 2004"

Kinetic studies of the reactions of O(1D) with several atmospheric molecules

Abstract: The rate coefficients for the removal of O(1D) by N2, O2, N2O, CO2, O3 and n-butane were measured between 210 and 370 K. The appearance of O(3P) was observed following photolytic production of O(1D) in an excess of the reactants. The measured rate coefficients in this study, in units of 10−10 cm3 molecule−1 s−1, are: k1(N2) = (0.195 ± 0.020)exp((125 ± 20)/T); k2(O2) = (0.365 ± 0.023)exp((22 ± 10)/T); k3(N2O) = (1.17 ± 0.20)exp((40 ± 50)/T); k4(CO2) = (0.79 ± 0.07)exp((110 ± 20)/T); k5(O3) = (2.65 ± 0.35)exp((−20 ± 40)/T); k6(n-C4H10) = (5.00 ± 1.55)exp((−10 ± 90)/T). The quoted uncertainties include estimated systematic errors and are at the 95% confidence level. Our results are compared with previous measurements, particularly the very recent data from Strekowski et al. (this issue) and Blitz et al., (this issue), to produce a set of rate coefficients most appropriate for use in atmospheric calculations. The newly recommended rate coefficients, in units of 10−10 cm3 molecule−1 s−1, are: k1(N2) = (0.21 ± 0.02)exp((115 ± 10)/T); k2(O2) = (0.312 ± 0.025)exp((70 ± 10)/T); k3(N2O) = (1.11 ± 0.11)exp((17 ± 40)/T); k4(CO2) = (0.74 ± 0.07)exp((133 ± 40)/T); k5(O3) = (2.37 ± 0.36)exp((6 ± 15)/T); k6(n-C4H10) = (5.35 ± 0.54)exp((−33 ± 32)/T).

Measurement of the rate coefficient for the reaction of O(1D) with H2O and re-evaluation of the atmospheric OH production rate

Abstract: The rate coefficient for the reaction of O(1D) with H2O (Reaction 1), whose value is critical for calculating production rates of the OH radical in the atmosphere, was measured over a range of atmospherically relevant temperatures. The temporal profile of O(3P) following photolytic production of O(1D) in the presence of water vapor was used to determine a temperature dependent value for k1 of (1.45 ± 0.34) × 10−10 exp((89 ± 65)/T) cm3 molecule−1 s−1, where the quoted errors are at the 95% confidence level, include estimated systematic errors and σA = AσlnA. In addition, ratios of rate coefficients for quenching of O(1D) by N2 and O2 (k2 and k3) to that for Reaction 1 were determined to be k2/k1 = (0.13 ± 0.04) and k3/k1 = (0.19 ± 0.09) by measuring the relative OH concentration produced from Reaction 1 in the presence of various concentrations of N2 or O2. Combining our results of this work with previous measurements of k1, we recommend a value for k1 = (1.62 ± 0.27) × 10−10 exp((65 ± 50)/T) cm3 molecule−1 s−1, where the quoted errors are 95% confidence level, include estimated systematic errors and σA = AσlnA. Based on these results, the uncertainty in the calculated atmospheric OH production rate due to the uncertainty in these rate coefficients is reduced from ±50% to ±20%.

Temperature-dependent quantum yields for O(3P) and O(1D) production from photolysis of O3 at 248 nm

Abstract: A pulsed laser photolysis–resonance fluorescence technique was employed independently by two laboratories to measure ΦO3P, the quantum yield for production of O(3P) from O3 photolysis at 248 nm, between 196 and 427 K. The agreement between the two studies is very good, and the combined results are adequately represented by the function ΦO3P= (0.115 ± 0.030) × exp((35 ± 60)/T) where the uncertainties are 2σ. Within experimental uncertainties, the new results are in agreement with previously reported room temperature results as well as with the single previous temperature dependence study, and greatly reduce the uncertainties in ΦO3P(T) and ΦO1D(T) (=1− ΦO3P(T)) especially at temperatures other than room temperature. The yield of O(3P) in the reaction of O(1D) with O3 is shown to be greater than unity at room temperature and below, and to increase slightly with decreasing temperature.