Gervase I. Mackay

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.

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.

A comparison of three methods for measurement of atmospheric nitric acid and aerosol nitrate and ammonium

Three methods for measuring gaseous ambient nitric acid in the low concentration range 0–15 μ m−3 were compared under field conditions in Southwestern Ontario during 1–14 June 1982. The methods employed were (1) tunable diode laser absorption, (2) a tungstic acid denuder tube and (3) a filter pack containing a Teflon-nylon-W41 filter combination operated over 3-h sampling periods. In general, the three methods measured nitric acid with adequate sensitivity (sub ppb) and they correlated reasonably over the low ambient concentrations considered here. However, there were some notable differences (up to a factor of 2 at night) by the tungstic acid and filter pack methods. During the field comparison, particulate nitrate and ammonium were also measured (0–6 μg m−3 range) by the tungstic acid and filter pack methods. These correlated well but some differences (less than 20%) were observed in the particulate nitrate measurements. In view of the low concentrations measured and the resultant larger experimental error, specific loss or interfering mechanisms could not be unambiguously identified.

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.

Comparison of techniques for measurement of ambient levels of hydrogen peroxide

A study measured hydrogen peroxide (H/sub 2/O/sub 2/) from three sources: (1) zero air in the presence and absence of common interferences; (2) steady-state irradiations of hydrocarbon/NOX mixtures; and (3) ambient air. The techniques employed for measuring H/sub 2/O/sub 2/ included infrared absorption from a diode laser, fluorescence from an enzymatically produced complex, and chemiluminescence from reaction with luminol. Four systems, each of which utilized one of the above techniques, were compared with respect to sensitivity, selectivity, and dynamic range in measuring H/sub 2/O/sub 2/ concentrations ranging from 0.062 to 128 ppbv. There was no indication of interferences for an H/sub 2/O/sub 2/ level of 6 ppbv except in the luminol technique, where a negative interference was caused by SO/sub 2/. Agreement among techniques was much worse for measurement of H/sub 2/O/sub 2/ produced in the photochemical mixtures. Significant concentrations of organic peroxide were measured by the enzymatic technique. During ambient monitoring, the techniques employed showed quantitative agreement.

Alkyl nitrates and their contribution to reactive nitrogen at a rural site in Ontario

Abstract Alkyl nitrates (C3C6), NO, NO2, HNO3 and PAN were measured at a rural site in Ontario from 26 March to 27 April 1990. A series of nine alkyl nitrates were measured daily at this site. The sum of the concentrations of these alkyl nitrates ranged from 29 to 87 ppt. The alkyl nitrates were found to contribute, on average, only 1.8% of the sum of the odd nitrogen species. In this paper, we discuss the observed distribution of the alkyl nitrates in light of the relative formation and removal processes. The observed concentration distribution is consistent with the relative formation rates calculated using the observed alkane concentrations, although it is somewhat skewed toward the lower molecular weight nitrates. The importance of the alkyl nitrates, relative to multifunctional organic nitrates that are produced from OH reaction with alkenes, is discussed.

Comparison of hydroperoxide measurements made during the Mauna Loa Observatory Photochemistry Experiment 2

From the fall of 1991 through the summer of 1992 the Mauna Loa Observatory Photochemistry Experiment 2 (MLOPEX 2) took place in Hawaii. The experiment consisted of four intensive research periods, each approximately 1 month in duration. We report a comparison of measurements of atmospheric hydroperoxide and methylhydroperoxide as measured during MLOPEX 2a (September 16 to October 23, 1991) and MLOPEX 2b (January 15 to February 15, 1992). The analytical techniques used for measuring hydroperoxides included tunable diode laser infrared absorption (TDLAS) and fluorescence from an enzymatically produced dimer. The TDLAS technique measured hydrogen peroxide (H2O2) only. Three different procedures were utilized to distinguish between H2O2 and organic hydroperoxides in the fluorescence analytical techniques. These were high performance liquid chromatographic (HPLC) separation, enzymatic discrimination, and differential aqueous solubility. The measured concentrations ranged from 0 to 2 parts per billion by volume (ppbv) for H2O2 and 0 to ppbv for methylhydroperoxide (CH3OOH). Depending on the time period of measurement, the agreement varied between 20% and a factor of 2 or more for the measurement of H2O2. The discrepancy for the CH3OOH data was larger.

Measurement of atmospheric aerosols and photochemical products at a rural site in SW Ontario

Abstract During 1–15 June 1982, measurements were made of atmospheric aerosol constituents, nitric acid, ammonia, peroxyacetyl nitrate (PAN), O 3 , SO 2 , and C 2 -C 6 speciated hydrocarbons (HCs) at a rural site in southern Ontario. A recently developed tunable diode laser technique was used to measure ambient HNO 3 with a 1-min time resolution and at concentrations down to 0.5 ppb; the tungstic acid method was used to measure particulate NO − 3 and NH − 4 , and gaseous HNO 3 and NH 3 ; a triple filter pack method was used to measure particulate constituents, and gaseous HNO 3 and SO 2 . Pollutant concentrations were correlated with air mass origin: southerly air parcel trajectories generally gave rise to pollutant episodes with peak HNO 3 and PAN concentrations in the range 1–5 ppb and 0.5–1.5 ppb, respectively. There was a strong diurnal variation in the HNO 3 , PAN and O 3 concentrations. The calculated product of the ambient HNO 3 and NH 3 concentration exhibited large scatter about the dissociation constant as calculated for dry NH 4 NO 3 .