Ole John Nielsen

Absolute rate constants for the reaction of NO with a series of peroxy radicals in the gas phase at 295 K

Abstract The rate constants for the reaction of NO with a series of peroxy radicals: CH 3 O 2 , C 2 H 5 O 2 , (CH 3 ) 3 CCH 2 O 2 , (CH 3 ) 3 CC(CH 3 ) 2 CH 2 O 2 , CH 2 FO 2 , CH 2 ClO 2 , CH 2 BrO 2 , CHF 2 O 2 , CF 2 ClO 2 , CHF 2 CF 2 O 2 , CF 3 CF 2 O 2 , CFCl 2 CH 2 O 2 and CF 2 ClCH 2 O 2 were measured at 298 K and a total pressure of 1 atm. The rate constants were obtained using the absolute technique of pulse radiolysis combined with time-resolved UVVIS spectroscopy. The results are discussed in terms of reactivity trends and the atmospheric chemistry of peroxy radicals.

Inhalation anaesthetics and climate change

BACKGROUND Although the increasing abundance of CO(2) in our atmosphere is the main driver of the observed climate change, it is the cumulative effect of all forcing agents that dictate the direction and magnitude of the change, and many smaller contributors are also at play. Isoflurane, desflurane, and sevoflurane are widely used inhalation anaesthetics. Emissions of these compounds contribute to radiative forcing of climate change. To quantitatively assess the impact of the anaesthetics on the forcing of climate, detailed information on their properties of heat (infrared, IR) absorption and atmospheric lifetimes are required. METHODS We have measured the IR spectra of these anaesthetics and conducted calculations of their contribution to radiative forcing of climate change recognizing the important fact that radiative forcing is strongly dependent on the wavelength of the absorption features. RESULTS Radiative efficiencies of 0.453, 0.469, and 0.351 W m(-2) ppb(-1) and global warming potentials (GWPs) of 510, 1620, and 210 (100 yr time horizon) were established for isoflurane, desflurane, and sevoflurane, respectively. CONCLUSIONS On the basis of the derived 100 yr GWPs, the average climate impact per anaesthetic procedure at the University of Michigan is the same as the emission of ∼22 kg CO(2). We estimate that the global emissions of inhalation anaesthetics have a climate impact which is comparable with that from the CO(2) emissions from one coal-fired power plant or 1 million passenger cars.

Absolute rate constants for the reaction of CF3O2 and CF3O radicals with NO at 295 K

Abstract Using a pulse radiolysis UV absorption technique and subsequent simulations of experimental NO 2 and FNO absorption transients, rate constants for reaction between CF 3 O and CF 3 O 2 radicals with NO were determined, CF 3 O 2 + NO→CF 3 O + NO 2 (3), CF 3 O + NO→CF 2 O + FNO (5). k 3 was derived to be (1.68±0.26) × 10 −11 cm 3 molecule −1 s −1 , and k 5 = (5.2±2.7) × 10 −11 cm 3 molecule −1 , s −1 . Results are discussed in the context of the atmospheric chemistry of halocarbons.

Atmospheric chemistry of 3-pentanol: kinetics, mechanisms, and products of Cl atom and OH radical initiated oxidation in the presence and absence of NOX.

Smog chamber/FTIR techniques were used to study the atmospheric chemistry of 3-pentanol and determine rate constants of k(Cl+3-pentanol) = (2.03 +/- 0.23) x 10 (-10) and k(OH+3-pentanol) = (1.32 +/- 0.15) x 10 (-11) cm (3) molecule (-1) s (-1) in 700 Torr of N 2/O 2 diluent at 296 +/- 2 K. The primary products of the Cl atom initiated oxidation of 3-pentanol in the absence of NO were (with molar yields) 3-pentanone (26 +/- 2%), propionaldehyde (12 +/- 2%), acetaldehyde (13 +/- 2%) and formaldehyde (2 +/- 1%). The primary products of the Cl atom initiated oxidation of 3-pentanol in the presence of NO were (with molar yields) 3-pentanone (51 +/- 4%), propionaldehyde (39 +/- 2%), acetaldehyde (44 +/- 4%) and formaldehyde (4 +/- 1%). The primary products of the OH radical initiated oxidation of 3-pentanol in the presence of NO were (with molar yields) 3-pentanone (58 +/- 3%), propionaldehyde (28 +/- 2%), and acetaldehyde (37 +/- 2%). In all cases the product yields were independent of oxygen concentration over the partial pressure range 10-700 Torr. The reactions of Cl atoms and OH radicals with 3-pentanol proceed 26 +/- 2 and 58 +/- 3%, respectively, via attack on the 3-position to give an alpha-hydroxyalkyl radical, which reacts with O 2 to give 3-pentanone. The results are discussed with respect to the literature data and atmospheric chemistry of 3-pentanol.

Pulse radiolysis study of CF3CFHO2 radicals in the gas phase at 298 K

Abstract The ultraviolet absorption spectrum of the CF3CHFO2 radical, and the kinetics of its reaction with NO, have been studied in the gas phase at 298 K. Absorption cross sections were quantified over the wavelength range 220–290 nm. The measured cross section at 220 nm is σCF3CHFO2 (220 nm) = (5.34±1.08)×10−18 cm2 molecule−1. Errors represent statistical (2σ) and our estimate of potential systematic errors (15%). The rate constant for the reaction of CF3CFHO2 radicals with NO was then determined to be k6=(1.28±0.36)×10−11 cm3 molecule−1 s−1. Errors represent statistical (2σ) and our estimate of potential systematic errors (20%). As part of this work the rate constant for the reaction of F atoms with CF3CFH2 was measured and found to be (3.6±0.9)×10 −12 cm3 molecules−1s−1 at 298 K. Errors are 2σ.

Ultraviolet absorption spectra and kinetics of acetonyl and acetonylperoxy radicals

Abstract Acetonyl radicals and acetonylperoxy radicals were produced by pulse radiolysis of gas mixtures with varying concentrations of CH3COCH3 and O2 in 1 atm of SF6 to initiate the reactions (1) F+CH3COCH3→HF+CH3COCH2, (2) 2CH3COCH2 → products, (3) CH3COCH2+O2(+M) → CH3COCH2O2(+M) and (4) 2CH3COCH2O2 → products. The ultraviolet absorption spectrum of the acetonyl radical is composed of a fairly weak band centered at 315 nm and a stronger band in the range of 200–250 nm. The absorption cross section has been determined, σ(310 nm) = (8.73 ± 0.50) × 10−19 cm2 molecule−1. The values k2=(4.8 ± 0.4) × 10−11, k3=(1.5 ± 0.3) × 10−12 and k4=(8.3 ± 1.6) × 10−12 cm3 molecule−1 s−1 at 298 K were derived by computer modelling of the observed kinetic features.

Atmospheric Chemistry of Isoflurane, Desflurane, and Sevoflurane: Kinetics and Mechanisms of Reactions with Chlorine Atoms and OH Radicals and Global Warming Potentials

The smog chamber/Fourier-transform infrared spectroscopy (FTIR) technique was used to measure the rate coefficients k(Cl + CF(3)CHClOCHF(2), isoflurane) = (4.5 ± 0.8) × 10(-15), k(Cl + CF(3)CHFOCHF(2), desflurane) = (1.0 ± 0.3) × 10(-15), k(Cl + (CF(3))(2)CHOCH(2)F, sevoflurane) = (1.1 ± 0.1) × 10(-13), and k(OH + (CF(3))(2)CHOCH(2)F) = (3.5 ± 0.7) × 10(-14) cm(3) molecule(-1) in 700 Torr of N(2)/air diluent at 295 ± 2 K. An upper limit of 6 × 10(-17) cm(3) molecule(-1) was established for k(Cl + (CF(3))(2)CHOC(O)F). The laser photolysis/laser-induced fluorescence (LP/LIF) technique was employed to determine hydroxyl radical rate coefficients as a function of temperature (241-298 K): k(OH + CF(3)CHFOCHF(2)) = (7.05 ± 1.80) × 10(-13) exp[-(1551 ± 72)/T] cm(3) molecule(-1); k(296 ± 1 K) = (3.73 ± 0.08) × 10(-15) cm(3) molecule(-1), and k(OH + (CF(3))(2)CHOCH(2)F) = (9.98 ± 3.24) × 10(-13) exp[-(969 ± 82)/T] cm(3) molecule(-1); k(298 ± 1 K) = (3.94 ± 0.30) × 10(-14) cm(3) molecule(-1). The rate coefficient of k(OH + CF(3)CHClOCHF(2), 296 ± 1 K) = (1.45 ± 0.16) × 10(-14) cm(3) molecule(-1) was also determined. Chlorine atoms react with CF(3)CHFOCHF(2) via H-abstraction to give CF(3)CFOCHF(2) and CF(3)CHFOCF(2) radicals in yields of approximately 83% and 17%. The major atmospheric fate of the CF(3)C(O)FOCHF(2) alkoxy radical is decomposition via elimination of CF(3) to give FC(O)OCHF(2) and is unaffected by the method used to generate the CF(3)C(O)FOCHF(2) radicals. CF(3)CHFOCF(2) radicals add O(2) and are converted by subsequent reactions into CF(3)CHFOCF(2)O alkoxy radicals, which decompose to give COF(2) and CF(3)CHFO radicals. In 700 Torr of air 82% of CF(3)CHFO radicals undergo C-C scission to yield HC(O)F and CF(3) radicals with the remaining 18% reacting with O(2) to give CF(3)C(O)F. Atmospheric oxidation of (CF(3))(2)CHOCH(2)F gives (CF(3))(2)CHOC(O)F in a molar yield of 93 ± 6% with CF(3)C(O)CF(3) and HCOF as minor products. The IR spectra of (CF(3))(2)CHOC(O)F and FC(O)OCHF(2) are reported for the first time. The atmospheric lifetimes of CF(3)CHClOCHF(2), CF(3)CHFOCHF(2), and (CF(3))(2)CHOCH(2)F (sevoflurane) are estimated at 3.2, 14, and 1.1 years, respectively. The 100 year time horizon global warming potentials of isoflurane, desflurane, and sevoflurane are 510, 2540, and 130, respectively. The atmospheric degradation products of these anesthetics are not of environmental concern.

Upper limits for the rate constants of the reactions of CF3O2 and CF3O radicals with ozone at 295 K

Abstract Using the pulse radiolysis UV absorption technique and subsequent simulations of experimental absorption transients at 254 and 276 nm, upper limits of the rate constants for the reactions of CF 3 O 2 and CF 3 O radicals with ozone were determined at 295 K, CF 3 0 2 +O 3 →CF 3 O+2O 2 (4), CF 3 O+O 3 →CF 3 O 2 +O 2 (5). The upper limits were derived as k 4 −14 cm 3 molecule −1 s −1 , and k 5 −13 cm 3 molecule −1 s −1 . Results are discussed in the context of the atmospheric chemistry and ozone depletion by hydrofluorocarbons.

An absolute- and relative-rate study of the gas-phase reaction of OH radicals and Cl atoms with n-alkyl nitrates

Abstract Rate constants for the reaction of OH radicals and Cl atoms with CH3ONO2, C2H5ONO2, n-C3H7ONO2, n-C4H9ONO2, and n-C5H11ONO2 have been determined at 298 ± 2 K and a total pressure of approximately 1 atm. The OH rate data were obtained using both the absolute-rate technique or pulse radiolysis combined with kinetic spectroscopy and a conventional photolytic relative-rate method. The Cl rate constants were measured using only the relative-rate method. Evidence is presented from the kinetic studies that reaction of OH radicals with alkyl nitrates may involve both addition and abstraction pathways. The data show that the —ONO2 group substantially decreases the rate constant for H-atom abstraction by OH radicals from groups bonded to the —ONO2 group and also decreases that for groups in the β position. Similar resuls were found for the reaction of Cl atoms with these compounds. The results are discussed in terms of reactivity trends.

Comparison of the combined monitoring-based and modelling-based priority setting scheme with partial order theory and random linear extensions for ranking of chemical substances

The combined monitoring-based and modelling-based priority setting scheme (COMMPS) used to establish a priority setting list within the EU Water Framework Directive plays a major role in the European environmental policy on chemical substances. The COMMPS procedure can be classified as a so-called scoring method. The applied functional relationship and weight factors are established based on expert judgement, which unfortunately appears to be vulnerable to subjective inputs. In this study an alternative priority setting methods based on partial order theory (POT) and random linear extensions (RLE) is suggested and compared to the COMMPS procedure. The POT/RLE is characterised as being based on fewer assumptions concerning functional relationships and does not apply weighting factors. Using the POT/RLE methodology a different ranking result occur than when using the COMMPS procedure. Eight of the top 20 substances from the COMMPS procedure are not ranked within the top 20 when using POT/RLE. From the viewpoint of environmental protection, especially the substances that have been given low priority in the COMMPS procedure, but a high rank in POT/RLE, are of interest in a regulatory context. These substances are naphthalene, trichloromethane, isoproturon, metolachlor, endosulfan, acenaphthene, alachlor and dichloromethane. An analysis of the ability of the descriptors to separate the single substance discloses that the most significant descriptor is the concentrations detected in the environment. Further, the frequency of detection is not applied as a descriptor in the COMMPS procedure. However, if this descriptor was to be applied the analysis revealed that it would have been the third most significant descriptor.