Atmospheric chemistry of n-C6F13CH2CHO: formation from n-C6F13CH2CH2OH, kinetics, and mechanisms of reactions with chlorine atoms and OH radicals

Smog chamber FTIR techniques were used to measure k(Cl + n-C(6)F(13)CH(2)CHO) = (1.84 +/- 0.22) x 10(-11), k(Cl + n-C(6)F(13)CHO) = (1.75 +/- 0.70) x 10(-12), and k(OH + n-C(6)F(13)CH(2)CHO) = (2.15 +/- 0.26) x 10(-12) cm(3) molecule(-1) s(-1) in 700 Torr of N(2) or air diluent at 296 +/- 2K. The chlorine-atom-initiated oxidation of n-C(6)F(13)CH(2)CH(2)OH in air gives n-C(6)F(13)CH(2)CHO in a molar yield of 99 +/- 8%. The atmospheric fate of n-C(6)F(13)CH(2)C(O) radicals is reaction with O(2), while the fate of n-C(6)F(13)C(O) radicals is decomposition to give n-C(6)F(13) radicals and CO. The results are discussed with respect to the atmospheric chemistry of fluorinated alcohols and the formation of perfluorocarboxylic acids.

Atmospheric chemistry of sulfuryl fluoride: reaction with OH radicals, Cl atoms and O3, atmospheric lifetime, IR spectrum, and global warming potential

Sulfuryl fluoride (SO2F2) is a radiatively active industrial chemical released into the atmosphere in significant (ktonne/ year) quantities. The potential for SO2F2 to contribute to radiative forcing of climate change needs to be assessed. Long path length FTIR/smog chamber techniques were used to investigate the kinetics of the gas-phase reactions of Cl atoms, OH radicals, and O3 with SO2F2, in 700 Torr total pressure of air or N2 at 296 +/- 1 K. Upper limits of k(Cl + SO2F2) < 9 x 10(-19), k(OH + SO2F2) < 1.7 x 10(-14) and k(O3 + SO2F2) < 5.5 x 10(-24) cm3 molecule(-1) s(-1) were determined. Reaction with Cl atoms, OH radicals, or O3 does not provide an efficient removal mechanism for SO2F2. The infrared spectrum of SO2F2 is reported and a radiative efficiency of 0.196 W m(-2) ppbv(-1) was calculated. Historic production data estimates are presented which provide an upper limit for expected atmospheric concentrations. The radiative forcing of climate change associated with emissions of SO2F2 depends critically on the atmospheric lifetime of SO2F2. Further research is urgently needed to define the magnitude of potential nonatmospheric sinks.

Atmospheric chemistry of 2-ethoxy-3,3,4,4,5-pentafluorotetrahydro-2,5-bis[1,2,2,2-tetrafluoro-1-(trifluoromethyl)ethyl]-furan: kinetics, mechanisms, and products of Cl atom and OH radical initiated oxidation

Smog chamber/FTIR techniques were used to study the atmospheric chemistry of the title compound which we refer to as RfOC2H5. Rate constants of k(Cl + RfOC2H5) = (2.70 +/- 0.36) x 10(-12), k(OH + RfOC2H5) = (5.93 +/- 0.85) x 10(-14), and k(Cl + RfOCHO) = (1.34 +/- 0.20) x 10(-14) cm3 molecule(-1') s(-1) were measured in 700 Torr of N2, or air, diluent at 294 +/- 1 K. From the value of k(OH + RfOC2H5) the atmospheric lifetime of RfOC2H5 was estimated to be 1 year. Two competing loss mechanisms for RfOCH(O*)CH3 radicals were identified in 700 Torr of N2/O2 diluent at 294 +/- 1 K; decomposition via C-C bond scission giving a formate (RfOCHO), or reaction with 02 giving an acetate (RfOC(O)CH3). In 700 Torr of N2/O2 diluent at 294 +/- 1 K the rate constant ratio k(O2)/k(diss) = (1.26 +/- 0.74) x 10(-19) cm3 molecule(-1). The OH radical initiated atmospheric oxidation of RfOC2H5 gives Rf0CHO and RfOC(O)CH3 as major products. RfOC2H5 has a global warming potential of approximately 55 for a 100 year horizon. The results are discussed with respect to the atmospheric chemistry and environmental impact of RfOC2H5.

Atmospheric Chemistry of the Z and E Isomers of CF3CFCHF; Kinetics, Mechanisms, and Products of Gas-Phase Reactions with Cl Atoms, OH Radicals, and O3

Smog chamber/FTIR techniques were used to study the atmospheric chemistry of the Z and E isomers of CF3CF=CHF, which we refer to as CF3CF=CHF(Z) and CF3CF=CHF(E). The rate constants k(Cl + CF3CF=CHF(Z)) = (4.36 +/- 0.48) x 10-11, k(OH + CF3CF=CHF(Z)) = (1.22 +/- 0.14) x 10-12, and k(O3 + CF3CF=CHF(Z)) = (1.45 +/- 0.15) x 10-21 cm3 molecule-1 s-1 were determined for the Z isomer of CF3CF=CHF in 700 Torr air diluent at 296 +/- 2 K. The rate constants k(Cl + CF3CF=CHF(E)) = (5.00 +/- 0.56) x 10-11, k(OH + CF3CF=CHF(E)) = (2.15 +/- 0.23) x 10-12, and k(O3 + CF3CF=CHF(E)) = (1.98 +/- 0.15) x 10-20 cm3 molecule-1 s-1 were determined for the E isomer of CF3CF=CHF in 700 Torr air diluent at 296 +/- 2 K. Both the Cl-atom and OH-radical-initiated atmospheric oxidation of CF3CF=CHF give CF3C(O)F and HC(O)F in molar yields indistinguishable from 100% for both the Z and E isomer. CF3CF=CHF(Z) has an atmospheric lifetime of approximately 18 days and a global warming potential (100 year time horizon) of approximately 6. CF3CF=CHF(E) has an atmospheric lifetime of approximately 10 days and a global warming potential (100 year time horizon) of approximately 3. CF3CF=CHF has a negligible global warming potential and will not make any significant contribution to radiative forcing of climate change.

Atmospheric chemistry of 4:2 fluorotelomer alcohol (n-C4F9CH2CH2OH): products and mechanism of Cl atom initiated oxidation in the presence of NOx

Smog chamber/FTIR techniques were used to study the Cl atom initiated oxidation of 4:2 fluorotelomer alcohol (C(4)F(9)CH(2)CH(2)OH, 4:2 FTOH) in the presence of NO(x) in 700 Torr of N(2)/O(2) diluent at 296 K. Chemical activation effects play an important role in the atmospheric chemistry of the peroxy, and possibly the alkoxy, radicals derived from 4:2 FTOH. Cl atoms react with C(4)F(9)CH(2)CH(2)OH to give C(4)F(9)CH(2)C(*)HOH radicals which add O(2) to give chemically activated alpha-hydroxyperoxy radicals, [C(4)F(9)CH(2)C(OO(*))HOH]*. In 700 Torr of N(2)/O(2) at 296 K, approximately 50% of the [C(4)F(9)CH(2)C(OO(*))HOH]* radicals decompose "promptly" to give HO(2) radicals and C(4)F(9)CH(2)CHO, the remaining [C(4)F(9)CH(2)C(OO(*))HOH]* radicals undergo collisional deactivation to give thermalized peroxy radicals, C(4)F(9)CH(2)C(OO(*))HOH. Decomposition to HO(2) and C(4)F(9)CH(2)CHO is the dominant atmospheric fate of the thermalized peroxy radicals. In the presence of excess NO, the thermalized peroxy radicals react to give C(4)F(9)CH(2)C(O(*))HOH radicals which then decompose at a rate >2.5 x 10(6) s(-1) to give HC(O)OH and the alkyl radical C(4)F(9)CH(2)(*). The primary products of 4:2 FTOH oxidation in the presence of excess NO(x) are C(4)F(9)CH(2)CHO, C(4)F(9)CHO, and HCOOH. Secondary products include C(4)F(9)CH(2)C(O)O(2)NO(2), C(4)F(9)C(O)O(2)NO(2), and COF(2). In contrast to experiments conducted in the absence of NO(x), there was no evidence (<2% yield) for the formation of the perfluorinated acid C(4)F(9)C(O)OH. The results are discussed with regard to the atmospheric chemistry of fluorotelomer alcohols.

Atmospheric chemistry of CF3CH=CH2 and C4F9CH=CH2: products of the gas-phase reactions with Cl atoms and OH radicals

FTIR-smog chamber techniques were used to study the products of the Cl atom and OH radical initiated oxidation of CF3CH=CH2 in 700 Torr of N2/O2, diluent at 296 K. The Cl atom initiated oxidation of CF3CH=CH2 in 700 Torr of air in the absence of NOx gives CF3C(O)CH2Cl and CF3CHO in yields of 70+/-5% and 6.2+/-0.5%, respectively. Reaction with Cl atoms proceeds via addition to the >C=C< double bond (74+/-4% to the terminal and 26+/-4% to the central carbon atom) and leads to the formation of CF3CH(O)CH2Cl and CF3CHClCH2O radicals. Reaction with O2 and decomposition via C-C bond scission are competing loss mechanisms for CF3CH(O)CH2Cl radicals, kO2/kdiss=(3.8+/-1.8)x10(-18) cm3 molecule-1. The atmospheric fate of CF3CHClCH2O radicals is reaction with O2 to give CF3CHClCHO. The OH radical initiated oxidation of CxF2x+1CH=CH2 (x=1 and 4) in 700 Torr of air in the presence of NOx gives CxF2x+1CHO in a yield of 88+/-9%. Reaction with OH radicals proceeds via addition to the >C=C< double bond leading to the formation of CxF2x+1C(O)HCH2OH and CxF2x+1CHOHCH2O radicals. Decomposition via C-C bond scission is the sole fate of CxF2x+1CH(O)CH2OH and CxF2x+1CH(OH)CH2O radicals. As part of this work a rate constant of k(Cl+CF3C(O)CH2Cl)=(5.63+/-0.66)x10(-14) cm3 molecule-1 s-1 was determined. The results are discussed with respect to previous literature data and the possibility that the atmospheric oxidation of CxF2x+1CH=CH2 contributes to the observed burden of perfluorocarboxylic acids, CxF2x+1COOH, in remote locations.

Atmospheric Chemistry of a Model Biodiesel Fuel, CH3C(O)O(CH2)2OC(O)CH3: Kinetics, Mechanisms, and Products of Cl Atom and OH Radical Initiated Oxidation in the Presence and Absence of NOx

Relative rate techniques were used to study the kinetics of the reactions of Cl atoms and OH radicals with ethylene glycol diacetate, CH3C(O)O(CH2)2OC(O)CH3, in 700 Torr of N2/O2 diluent at 296 K. The rate constants measured were k(Cl + CH3C(O)O(CH2)2OC(O)CH3) = (5.7 +/- 1.1) x 10(-12) and k(OH + CH3C(O)O(CH2)2OC(O)CH3) = (2.36 +/- 0.34) x 10(-12) cm3 molecule-1 s-1. Product studies of the Cl atom initiated oxidation of ethylene glycol diacetate in the absence of NO in 700 Torr of O2/N2 diluent at 296 K show the primary products to be CH3C(O)OC(O)CH2OC(O)CH3, CH3C(O)OC(O)H, and CH3C(O)OH. Product studies of the Cl atom initiated oxidation of ethylene glycol diacetate in the presence of NO in 700 Torr of O2/N2 diluent at 296 K show the primary products to be CH3C(O)OC(O)H and CH3C(O)OH. The CH3C(O)OCH2O* radical is formed during the Cl atom initiated oxidation of ethylene glycol diacetate, and two loss mechanisms were identified: reaction with O2 to give CH3C(O)OC(O)H and alpha-ester rearrangement to give CH3C(O)OH and HC(O) radicals. The reaction of CH3C(O)OCH2O2* with NO gives chemically activated CH3C(O)OCH2O* radicals which are more likely to undergo decomposition via the alpha-ester rearrangement than CH3C(O)OCH2O* radicals produced in the peroxy radical self-reaction.

Kinetics, Products, and Stereochemistry of the Reaction of Chlorine Atoms with cis- and trans-2-Butene in 10−700 Torr of N2 or N2/O2 Diluent at 297 K

The reactions of Cl atoms with cis- and trans-2-butene have been studied using FTIR and GC analyses. The rate constant of the reaction was measured using the relative rate technique. Rate constants for the cis and trans isomers are indistinguishable over the pressure range 10-900 Torr of N2 or air and agree well with previous measurements at 760 Torr. Product yields for the reaction of cis-2-butene with Cl in N2 at 700 Torr are meso-2,3-dichlorobutane (47%), DL-2,3-dichlorobutane (18%), 3-chloro-1-butene (13%), cis-1-chloro-2-butene (13%), trans-1-chloro-2-butene (2%), and trans-2-butene (8%). The yields of these products depend on the total pressure. For trans-2-butene, the product yields are as follows: meso-2,3-dichlorobutane (48%), dl-2,3-dichlorobutane (17%), 3-chloro-1-butene (12%), cis-1-chloro-2-butene (2%), trans-1-chloro-2-butene (16%), and cis-2-butene (2%). The products are formed via addition, addition-elimination from a chemically activated adduct, and abstraction reactions. These reactions form (1) the stabilized 3-chloro-2-butyl radical, (2) the chemically activated 3-chloro-2-butyl radical, and (3) the methylallyl radical. These radicals subsequently react with Cl2 to form the products via a proposed chemical mechanism, which is discussed herein. This is the first detailed study of stereochemical effects on the products of a gas-phase Cl+olefin reaction. FTIR spectra (0.25 cm(-1) resolution) of meso- and DL-2,3-dichlorobutane are presented. The relative rate technique was used (at 900 Torr and 297 K) to measure: k(Cl + 3-chloro-1-butene) = (2.1 +/- 0.4) x 10(-10), k(Cl + 1-chloro-2-butene) = (2.2 +/- 0.4) x 10(-10), and k(Cl + 2,3-dichlorobutane) = (1.1 +/- 0.2) x 10(-11) cm3 molecule(-1) s(-1).

Investigation of the radical product channel of the CH3C(O)O2 + HO2 reaction in the gas phase

The reaction of CH(3)C(O)O(2) with HO(2) has been investigated at 296 K and 700 Torr using long path FTIR spectroscopy, during photolysis of Cl(2)/CH(3)CHO/CH(3)OH/air mixtures. The branching ratio for the reaction channel forming CH(3)C(O)O, OH and O(2) (reaction ) has been determined from experiments in which OH radicals were scavenged by addition of benzene to the system, with subsequent formation of phenol used as the primary diagnostic for OH radical formation. The dependence of the phenol yield on benzene concentration was found to be consistent with its formation from the OH-initiated oxidation of benzene, thereby confirming the presence of OH radicals in the system. The dependence of the phenol yield on the initial peroxy radical precursor reagent concentration ratio, [CH(3)OH](0)/[CH(3)CHO](0), is consistent with OH formation resulting mainly from the reaction of CH(3)C(O)O(2) with HO(2) in the early stages of the experiments, such that the limiting yield of phenol at high benzene concentrations is well-correlated with that of CH(3)C(O)OOH, a well-established product of the CH(3)C(O)O(2) + HO(2) reaction (via channel (3a)). However, a delayed source of phenol was also identified, which is attributed mainly to an analogous OH-forming channel of the reaction of HO(2) with HOCH(2)O(2) (reaction ), formed from the reaction of HO(2) with product HCHO. This was investigated in additional series of experiments in which Cl(2)/CH(3)OH/benzene/air and Cl(2)/HCHO/benzene/air mixtures were photolysed. The various reaction systems were fully characterised by simulations using a detailed chemical mechanism. This allowed the following branching ratios to be determined: CH(3)C(O)O(2) + HO(2)--> CH(3)C(O)OOH + O(2), k(3a)/k(3) = 0.38 +/- 0.13; --> CH(3)C(O)OH + O(3), k(3b)/k(3) = 0.12 +/- 0.04; --> CH(3)C(O)O + OH + O(2), k(3c)/k(3) = 0.43 +/- 0.10: HOCH(2)O(2) + HO(2)--> HCOOH + H(2)O + O(2), k(17b)/k(17) = 0.30 +/- 0.06; --> HOCH(2)O + OH + O(2), k(17c)/k(17) = 0.20 +/- 0.05. The results therefore provide strong evidence for significant participation of the radical-forming channels of these reactions, with the branching ratio for the title reaction being in good agreement with the value reported in one previous study. As part of this work, the kinetics of the reaction of Cl atoms with phenol (reaction (14)) have also been investigated. The rate coefficient was determined relative to the rate coefficient for the reaction of Cl with CH(3)OH, during the photolysis of mixtures of Cl(2), phenol and CH(3)OH, in either N(2) or air at 296 K and 760 Torr. A value of k(14) = (1.92 +/- 0.17) x 10(-10) cm(3) molecule(-1) s(-1) was determined from the experiments in N(2), in agreement with the literature. In air, the apparent rate coefficient was about a factor of two lower, which is interpreted in terms of regeneration of phenol from the product phenoxy radical, C(6)H(5)O, possibly via its reaction with HO(2).

Kinetics and mechanism of the gas phase reaction of chlorine atoms with i-propanol

FTIR smog chamber techniques and ab initio calculations have been used to investigate the kinetics and mechanism of the reaction of Cl atoms with i-propanol in 700 Torr of N(2) at 296 K. The reaction is observed to proceed with a rate constant of k(1) = (8.28 +/- 0.97) x 10(-11) cm(3) molecule(-1) s(-1) and gives CH(3)C(OH)CH(3) and CH(3)CH(OH)CH(2) radicals in yields of 85 +/- 7 and 15 +/- 7%, respectively. Calculations indicate that abstraction of the secondary H can proceed through a lower energy pathway than the primary. Rapid decomposition of the chlorination product CH(3)CCl(OH)CH(3) complicates its direct detection, likely due to heterogeneous chemistry. IR spectra for the chlorides CH(3)CCl(OH)CH(3) and CH(3)CH(OH)CH(2)Cl were inferred experimentally and assignments confirmed via comparison with ab initio computed spectra.

Atmospheric Chemistry of n-CxF2x+1CHO (x = 1, 2, 3, 4): Fate of n-CxF2x+1C(O) Radicals

Smog chamber/FTIR techniques were used to study the atmospheric fate of n-C(x)F(2)(x)(+1)C(O) (x = 1, 2, 3, 4) radicals in 700 Torr O(2)/N(2) diluent at 298 +/- 3 K. A competition is observed between reaction with O(2) to form n-C(x)()F(2)(x)()(+1)C(O)O(2) radicals and decomposition to form n-C(x)F(2)(x)(+1) radicals and CO. In 700 Torr O(2)/N(2) diluent at 298 +/- 3 K, the rate constant ratio, k(n-C(x)F(2)(x)(+1)C(O) + O(2) --> n-C(x)F(2)(x)(+1)C(O)O(2))/k(n-C(x)F(2)(x)(+1)C(O) --> n-C(x)F(2)(x)(+1) + CO) = (1.30 +/- 0.05) x 10(-17), (1.90 +/- 0.17) x 10(-19), (5.04 +/- 0.40) x 10(-20), and (2.67 +/- 0.42) x 10(-20) cm(3) molecule(-1) for x = 1, 2, 3, 4, respectively. In one atmosphere of air at 298 K, reaction with O(2) accounts for 99%, 50%, 21%, and 12% of the loss of n-C(x)F(2)(x)(+1)C(O) radicals for x = 1, 2, 3, 4, respectively. Results are discussed with respect to the atmospheric chemistry of n-C(x)F(2)(x)(+1)C(O) radicals and their possible role in contributing to the formation of perfluorocarboxylic acids in the environment.

Atmospheric Chemistry of Perfluorinated Aldehyde Hydrates (n-CxF2x+1CH(OH)2, x = 1, 3, 4): Hydration, Dehydration, and Kinetics and Mechanism of Cl Atom and OH Radical Initiated Oxidation

Smog chamber/Fourier transform infrared (FTIR) techniques were used to measure k(Cl+C(x)F(2x+1)CH(OH)(2)) (x = 1, 3, 4) = (5.84 +/- 0.92) x 10(-13) and k(OH+C(x)F(2x+1)CH(OH)(2)) = (1.22 +/- 0.26) x 10(-13) cm(3) molecule(-1) s(-1) in 700 Torr of N(2) or air at 296 +/- 2 K. The Cl initiated oxidation of CF(3)CH(OH)(2) in 700 Torr of air gave CF(3)COOH in a molar yield of 101 +/- 6%. IR spectra of C(x)F(2x+1)CH(OH)(2) (x = 1, 3, 4) were recorded and are presented. An upper limit of k(CF(3)CHO+H(2)O) < 2 x 10(-23) cm(3) molecule(-1) s(-1) was established for the gas-phase hydration of CF(3)CHO. Bubbling CF(3)CHO/air mixtures through liquid water led to >80% conversion of CF(3)CHO into the hydrate within the approximately 2 s taken for passage through the bubbler. These results suggest that OH radical initiated oxidation of C(x)F(2x+1)CH(OH)(2) hydrates could be a significant source of perfluorinated carboxylic acids in the environment.

Formation of C7F15COOH (PFOA) and other perfluorocarboxylic acids during the atmospheric oxidation of 8:2 fluorotelomer alcohol

Calculations using a three-dimensional global atmospheric chemistry model (IMPACT) indicate that n-C8F17CH2CH2OH (widely used in industrial and consumer products) degrades in the atmosphere to give perfluorooctanoic acid (PFOA) and other perfluorocarboxylic acids (PFCAs). PFOA is persistent, bioaccumulative, and potentially toxic. Molar yields of PFOA depend on location and season, are in the range of 1-10%, and are of the correct order of magnitude to explain the observed levels in Arctic fauna. Fluorotelomer alcohols such as n-C8F17CH2CH2OH appear to be a significant global source of persistent bioaccumulative perfluorocarboxylic acid pollution. This is the first modeling study of the atmospheric chemistry of a fluorotelomer alcohol.

Atmospheric chemistry of perfluoroalkanesulfonamides: kinetic and product studies of the OH radical and Cl atom initiated oxidation of N-ethyl perfluorobutanesulfonamide

Perfluorooctanesulfonamides [C8F17SO2N(R1)(R2)] are present in the atmosphere and may, via atmospheric transport and oxidation, contribute to perfluorocarboxylates (PFCA) and perfluorooctanesulfonate (PFOS) pollution in remote locations. Smog chamber experiments with the perfluorobutanesulfonyl analogue N-ethyl perfluorobutanesulfonamide [NEtFBSA; C4F9SO2N(H)CH2CH3] were performed to assess this possibility. By use of relative rate methods, rate constants for reactions of NEtFBSA with chlorine atoms (296 K) and OH radicals (301 K) were determined to be kCL) = (8.37 +/- 1.44) x 10(-12) and kOH = (3.74 +/- 0.77) x 10(-13) cm3 molecule(-1) s(-1), indicating OH reactions will be dominant in the troposphere. Simple modeling exercises suggestthat reaction with OH radicals will dominate removal of perfluoroalkanesulfonamides from the gas phase (wet and dry deposition will not be important) and that the atmospheric lifetime of NEtFBSA in the gas phase will be 20-50 days, thus allowing substantial long-range atmospheric transport. Liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis showed that the primary products of chlorine atom initiated oxidation were the ketone C4F9SO2N(H)COCH3; aldehyde 1, C4F9SO2N(H)CH2CHO; and a product identified as C4F9SO2N(C2H5O)- by high-resolution MS but whose structure remains tentative. Another reaction product, aldehyde 2, C4F9SO2N(H)CHO, was also observed and was presumed to be a secondary oxidation product of aldehyde 1. Perfluorobutanesulfonate was not detected above the level of the blank in any sample; however, three perfluoroalkanecarboxylates (C3F7CO2-, C2F5CO2-, and CF3CO2-) were detected in all samples. Taken together, results suggest a plausible route by which perfluorooctanesulfonamides may serve as atmospheric sources of PFCAs, including perfluorooctanoic acid.

Atmospheric Chemistry of CF3OCF2CF2H and CF3OC(CF3)2H: Reaction with Cl Atoms and OH Radicals, Degradation Mechanism, Global Warming Potentials, and Empirical Relationship between k(OH) and k(Cl) for Organic Compounds

Using FTIR smog chamber techniques, k(Cl + CF3OCF2CF2H) = (2.70 +/- 0.52) x 10(-16), k(OH + CF3OCF2CF2H) = (2.26 +/- 0.18) x 10(-15), k(Cl + CF3OC(CF3)2H) = (1.58 +/- 0.27) x 10(-18) and k(OH + CF3OC(CF3)2H) = (3.26 +/- 0.95) x 10(-16) cm3 molecule(-1) s(-1) were measured. The atmospheric lifetimes of CF3OCF2CF2H and CF3OC(CF3)2H are estimated to be 27 and 216 years, respectively. Chlorine atom initiated oxidation of CF3OCF2CF2H in 700 Torr of air in the presence of NO(x) gives CF3OC(O)F in a molar yield of 36 +/- 5% and COF2 in a molar yield of 174 +/- 9%, whereas oxidation of CF3OC(CF3)2H gives CF3OC(O)CF3 and COF2 in molar yields that are indistinguishable from 100%. Quantitative infrared spectra were recorded and used to estimate global warming potentials of 3690 and 8230 (100 year time horizon, relative to CO2) for CF3OCF2CF2H and CF3OC(CF3)2H, respectively. All experiments were performed in 700 Torr of N2/O2 diluent at 296 +/- 2 K. An empirical relationship can be used to estimate the preexponential factor, which can be combined with k(298 K) to give the temperature dependence of reactions of OH radicals with organic compounds proceeding via H-atom abstraction: log(A/n) = (0.239 +/- 0.027) log(k(OH)/n) - (8.69 +/- 0.372), k(OH) is the rate constant at 298 K and n is the number of H atoms. The rates of H-atom abstraction by OH radicals and Cl atoms at 298 K from organic compounds are related by the expression log(k(OH)) = (0.412 +/- 0.049) log(k(Cl)) - (8.16 +/- 0.72). The utility of these expressions and the atmospheric chemistry of the title hydrofluoroethers are discussed.

Formation of methyl nitrite and methyl nitrate during plasma treatment of diesel exhaust

FTIR spectroscopy was used to identify CH3ONO and CH3ONO2 as products of the nonthermal plasma treatment of simulated diesel exhaust. This is the first observation of CH3ONO formation in such systems. The yield of CH3ONO relativeto CH3ONO2 scaled linearly with the average [NO]/ [NO2] ratio in the system. A plot of [CH3ONO]/[CH3ONO2] versus [NO]/[NO2] gives a slope of 1.81 +/- 0.30. This result is indistinguishable from the literature value of the rate constant ratio k(CH3O + NO)/k(CH3O + NO2) = (2.6 x 10(-11))/ (1.5 x 10(-11)) = 1.73 +/- 0.37. The experimental observations suggest that reactions of CH3O radicals with NO and NO2 are the sources of CH3ONO and CH3ONO2 in such systems. The linear relationship between the yields of CH3ONO and CH3ONO2 provides a means of estimating the yield of these compounds during nonthermal plasma treatment of diesel exhaust.

Atmospheric lifetime of fluorotelomer alcohols

Relative rate techniques were used to study the kinetics of the reactions of Cl atoms and OH radicals with a series of fluorotelomer alcohols, F(CF2CF2)nCH2CH2OH (n = 2, 3, 4), in 700 Torr of N2 or air, diluent at 296 +/- 2K. The length of the F(CF2CF2)n- group had no discernible impact on the reactivity of the molecule. For n = 2, 3, or 4, k(Cl + F(CF2CF2)nCH2CH2OH) = (1.61 +/- 0.49) x 10(-11) and k(OH + F(CF2CF2)nCH2CH2OH) = (1.07 +/- 0.22) x 10(-12) cm3 molecule(-1) s(-1). Consideration of the likely rates of other possible atmospheric loss mechanisms leads to the conclusion that the atmospheric lifetime of F(CF2CF2)nCH2CH2OH (n > or = 2) is determined by reaction with OH radicals and is approximately 20 d.

Atmospheric chemistry of HFE-7500 [n-C3F7CF(OC2H5)CF(CF3)2]: reaction with OH radicals and Cl atoms and atmospheric fate of n-C3F7CF(OCHO*)CF(CF3)2 and n-C3F7CF(OCH2CH2O*)CF(CF3)2 radicals

Relative rate techniques were used to measure k(OH + HFE-7500) = (2.6+/-0.6) x 10(-14), k(Cl + HFE-7500) = (2.3+/-0.7) x 10(-12), k[Cl + n-C3F7CF(OC(O)H)CF(CF3)2] = (9.7+/-1.4) x 10(-15), and k[Cl + n-C3F7CF(OC(O)CH3)CF(CF3)2] < 6 x 10(-17) cm3 molecule(-1) s(-1) at 295 K [HFE-7500 = n-C3F7-CF(OC2H5)CF(CF3)2]. From the value of k(OH + HFE-7500) an estimate of 2.2 years for the atmospheric lifetime of HFE-7500 is obtained. Two competing loss mechanisms for n-C3F7-CF(OCHO.CH3)CF(CF3)2 radicals were identified in 700 Torr of N2/O2 diluent at 295 K; reaction with O2 and decomposition via C-C bond scission with kO2/k(decomp) = 0.013+/-0.006 Torr(-1). The Cl atom initiated oxidation of HFE-7500 in N2/O2 diluent gives n-C3F7CF(OC(O)CH3)CF(CF3)2 as the major product and n-C3F7CF(OC(O)H)CF(CF3)2 as a minor product. The atmospheric oxidation of HFE-7500 gives n-C3F7-CF(OC(O)CH3)CF(CF3)2 and n-C3F7CF(OC(O)H)CF(CF3)2 as oxidation products. The results are discussed with respect to the atmospheric chemistry and environmental impact of HFE-7500.