H. I. Schiff

Determination of proton affinities from the kinetics of proton transfer reactions. VII. The proton affinities of O2, H2, Kr, O, N2, Xe, CO2, CH4, N2O, and CO

The flowing afterglow and selected ion flow tube techniques are applied in a room temperature study of the kinetics of proton‐transfer reactions of the type XH++Y?YH++X for X or Y=He, H2, O2, Kr, O, N2, Xe, CO2, CH4, CD4, N2O, OH, and CO, and for the deuteration of O2 by D3+. Equilibrium constants are determined and changes in thermodynamic state properties (ΔG°, ΔH°, ΔS°) are derived for the reactions with X/Y=H2/O2, O2/Kr, H2/Kr, H2/N2, O/N2, N2/Xe, Xe/CO2, CO2/CH4, CH4/N2O, and N2O/CO. Proton affinities are reported for O2, H2, Kr, O, N2, Xe, CO2, CH4, N2O, and CO, together with the heats of formation of their protonated species. Also a correlation is presented between the kinetic and thermodynamic results obtained in this study.

Absolute rate constant determinations for the deactivation of O(1D) by time resolved decay of O(1D) →O(3P) emission

Absolute rate constants for the deactivation of O(1D) atoms by some atmospheric gases have been determined by observing the time resolved emission of O(1D) at 630 nm. O(1D) atoms were produced by the dissociation of ozone via repetitive laser pulses at 266 nm. Absolute rate constants for the relaxation of O(1D) (×10−10 cm3 molecule−1⋅s−1) by N2(0.30±0.01), O2(0.41±0.05), CO2(1.2±0.09), O3(2.4±0.1), H2(1.3±0.05), D2(1.3±0.05), CH4(1.3±0.3), HCl(1.4±0.3), NH3 (3.4±0.3), H2O(2.1±1.0), N2O(1.4±0.1), and Ne (<0.0013) are reported at 298 K. The results obtained are compared with previous relative and absolute measurements reported in the literature.

Temperature dependence of O(1D) rate constants for reactions with O2, N2, CO2, O3, and H2O

Absolute rate constants and their temperature dependencies for the deactivation of O(1D) by five important atmospheric gases are reported. O(1D) atoms are produced by photolysis of ozone at 266 nm and the atoms are directly observed in time resolved decay of the O(1D) →O(3P) radiation at 630 nm. Gases which only quench O(1D) (O2, N2, and CO2) are observed to have a small negative temperature dependence while O3 and H2O, which also have a reactive channel, display no temperature dependence. Arrhenius expressions for the reactions measured are (A in units of 10−10 cm3/molecule⋅ s, E in cal/mole) O2(T=104–354 K) 0.29 exp(134/RT), N2(T=104–354 K) 0.20 exp(214/RT), CO2(T=139–200 K) 1.2 and (T=200–354 K) 0.68 exp(233/RT). The rate constants for O3 and H2O are 2.4×10−10 and 2.3×10−10 cm3/molecule⋅ s over ranges of 103–393 K and 253–353 K, respectively. The results are compared with other energy dependent measurements and with the theories reported in the literature.

Atmospheric concentrations and temporal variations of C1C3 carbonyl compounds at two rural sites in central Ontario

Abstract Measurements of formaldehyde, acetaldehyde, acetone and propionaldehyde concentrations were made at two rural sites in central Ontario. One site (at Egbert, Ont.) is located ≈60 km northwest of Toronto, while the other site (at Dorset, Ont.) is ≈150 km northeast of the Egbert site. Measurements were made using a modified version of a derivatization technique in which sample air is pumped through Teflon tubes packed with silica gel that is coated with 2,4-dinitrophenylhydrazine (DNPH). The product hydrazones were separated and quantified using HPLC. Quantitative determinations of formaldehyde, acetaldehyde and acetone were made for 49 and 47 samples at the Dorset and Egbert sites, respectively, between 25 July and 30 August 1988. The average concentrations determined at the Dorset site for formaldehyde, acetaldehyde, and acetone were 1.6, 0.46 and 1.8 ppb, respectively, and for the Egbert site the corresponding averages were 1.8, 0.57 and 1.6 ppb. A set of 10 samples from the Egbert site were analysed for propionaldehyde yielding an average concentration of 0.03 ppb. The formaldehyde measurements were compared with measurements made at the same time using Tunable Diode Laser Absorption Spectroscopy. The observed concentrations reported here are compared with previously reported measurements of these species and interpreted in terms of atmospheric variables (e.g. meteorology, concentrations of precursor hydrocarbons) influencing their concentrations.

Studies of reactions involving C2Hx+ ions with HCN using a modified selected ion flow tube

Abstract A modified version of the selected ion flow tube is describe. Its application to the study of the reactions of C2Hx+ ions with HCN eliminates the complications encountered with attempts to study some of these reactions with the flowing afterglow technique. Proton transfer is the only process observed for reactions of C2H3+ and C2H5+ and is the dominant channel for the C2H7+ reaction. C2+ reacts exclusively by condensation while C2H+ reacts, with nearly equal probability, by proton and hydrogen atom transfer. The second-order reactions of all the ions, with the exception of C2H2+, occur with probabilities greater than 65% of their theoretical values. Three-body association is the dominant channel for the C2H2+ reaction, with proton transfer and condensation occurring at less than 1% of the theoretical collision rate. Clustering is the only reaction observed for C2H4+ but, in this case, it is the only known exothermic channel.

Temperature dependence of O(1D) rate constants for reactions with N2O, H2, CH4, HCl, and NH3

Absolute rate constants are reported for the deactivation of O(1D) by five trace atmospheric constituents for the temperature range 200–350 K. O(1D) atoms produced by photolyzing ozone with a frequency quadrupled pulse from a Nd‐YAG laser are monitored directly by means of the O(1D) →O(3P) emission at 630 nm. All the gases studied here are thought to deactivate O(1D) primarily through reactive channels. Their rate constants exhibit no detectable temperature dependence. The rate constants are (in units of 10−10 cm3/molecule⋅s) N2O: 1.1,±0.2, H2: 0.99±0.3, HCl: 1.4±0.4, NH3: 2.5±0.5, CH4: 1.4±0.4. The present results and those of our previous studies are compared with rate constants obtained using the time‐resolved attenuation of resonance absorption technique.

Stratospheric Nitrous Oxide Altitude Profiles at Various Latitudes

Abstract A number of N2O profiles obtained in the troposphere and stratosphere at five latitudes are reported. The variability in the reported stratosphere N20 mixing ratios is substantial and indicates a strong dependence on both stratospheric transport and photochemistry. A profile obtained at Panama indicates a relatively large transport of N2O into the stratosphere at low latitudes. This profile represents the first one obtained in the tropics. From the observed data, area-averaged, global vertical eddy diffusion coefficients were derived that were found to be a factor of 1.5 to 3 times larger than those derived by Hunten from data obtained at locations not including the tropics. The derived eddy diffusion profile is heavily weighted by one single profile in the tropics and more observations are needed to substantiate this finding. The estimated flux of N20 into the stratosphere was equal to 15×1012 g(N) per year and the total stratospheric production of NOx was estimated to be 1.6×1012 g(N) per year....

Measurements of formaldehyde in the troposphere by tunable diode laser absorption spectroscopy

Measurements of formaldehyde, HCHO, using tunable diode laser abssrption spectroscopy (TDLAS) are reported for four sites in North America. The TDLAS apparatus and its application to these measurements is described. Detection limits of ca. 0.25 ppbv were obtained with a three-minute time resolution. Two distinct types of diurnal behaviour were observed: in the absence of local pollution sources the HCHO diurnal variation was weak and HCHO is not lost during the night. We conclude that the lifetime of HCHO with respect to dry deposition was greater than 50 h at the least-polluted site. At sites downwind of pollution sources, the HCHO peaks near noon and declines in the afternoon. At the least-polluted location, the most probable value for HCHO was 0.25–0.5 ppbv, while hourly averaged values up to 12 ppbv were observed at the other locations.

Formaldehyde Measurement Methods Evaluation and Ambient Concentrations During the Carbonaceous Species Methods Comparison Study

During the Carbonaceous Species Methods Comparison Study at Glendora, CA, six groups made independent measurements of ambient formaldehyde concentrations during the period August 11–21, 1986. Measurement methods included DNPH-impregnated cartridges, an enzymatic technique, a diffusion scrubber, Fourier transform infrared spectroscopy (FTIR), differential optical absorption spectroscopy (DOAS), and tunable diode laser absorption spectroscopy (TDLAS). Sufficient data were obtained over the 10-day period to assess differences among methods based on hourly averages, 4- and 8-hour time-integrated sampling periods, and 3–5-minute averaging times. Comparison among the three spectroscopic methods (DOAS, FTIR, and TDLAS) showed good agreement, within 15% of the mean of the three methods for 162 hourly values. The enzymatic technique and diffusion scrubber reported concentrations ∼ 25% higher and 25% lower than the spectroscopic mean, respectively, for the entire study period. The DNPH cartridges, the only routine ...

An intercomparison of formaldehyde measurement techniques at ambient concentration

Abstract A study was conducted to evaluate five techniques for determining ambient formaldehyde concentrations. One technique used a spectroscopic determination, and the other four techniques used derivatization followed by fluorometric analysis or high-performance liquid chromatography with detection by u.v. absorption. Formaldehyde was generated by two techniques. In the first technique, zero air was bubbled through a solution of aqueous formaldehyde to produce gas-phase formaldehyde. Various compounds serving as possible interferences were added singly or in combination to these air mixtures. In the second technique, formaldehyde was generated as a product from controlled irradiations of hydrocarbons and nitrogen oxides in a smog chamber operated in a dynamic mode. The study was conducted as a blind intercomparison with no knowledge by the participants of the HCHO concentrations or the interferences added. The data from each of the techniques were compared against mean values in each sampling period. For formaldehyde in zero air, average deviations for each of the techniques ranged between 15 and 30%. At a formaldehyde concentration of 10 ppb, each technique showed no evidence for interferences by O3 (190 ppbv), NO2 (300 ppbv), SO2 (20 ppbv), and H2O2 (7 ppbv). The agreement for formaldehyde concentrations measured for the photochemical mixtures was similar to that of the mixtures in zero air. Ambient measurements were also performed on three evenings and for one 36-h period. Ambient formaldehyde concentrations ranged from 1 to 10 ppbv. Ambient H2O2 measurements were also performed. A strong correlation in the diurnal concentration profile for formaldehyde and H2O2 was observed over the 36-h period.