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1.
Rate constants have been measured for the gas-phase reactions of hydroxyl radical with two halons and three of their proposed substitutes and also with CHClBr-CF3 using the discharge-flow-EPR technique over the temperature range 298–460 K. The following Arrhenius expressions have been derived (units are 10–13 cm3 molecule–1 s–1): (9.3 –0.9 +1.0 ) exp{–(1326±33)/T} for CHF2Br; (7.2 –0.6 +0.7 ) exp{–(1111±32)/T} for CHFBrCF3; (8.5 –0.8 +0.9 ) exp{–(1113±35)/T} for CH2BrCF3; (12.8 –1.2 +1.5 ) exp{–(995±38)/T} for CHClBrCF3. The rate constants at 298 K have been estimated to be <2×10–17 cm3 molecule–1 s–1 for CF3Br and CF2Br—CF2Br. The atmospheric lifetimes due to hydroxyl attack have been estimated to be 5.5, 3.3, 2.8, and 1.2 years for CHF2Br, CHFBr—CF3, CH2Br—CF3 and CHClBr—CF3, respectively.  相似文献   

2.
The kinetics of the aqueous phase reactions of NO3 radicals with HCOOH/HCOO– and CH3COOH/CH3COO– have been investigated using a laser photolysis/long-path laser absorption technique. NO3 was produced via excimer laser photolysis of peroxodisulfate anions (S2O 8 2– ) at 351 nm followed by the reactions of sulfate radicals (SO 4 – ) with excess nitrate. The time-resolved detection of NO3 was achieved by long-path laser absorption at 632.8 nm. For the reactions of NO3 with formic acid (1) and formate (2) rate coefficients ofk 1=(3.3±1.0)×105 l mol–1 s–1 andk 2=(5.0±0.4)×107 l mol–1 s–1 were found atT=298 K andI=0.19 mol/l. The following Arrhenius expressions were derived:k 1(T)=(3.4±0.3)×1010 exp[–(3400±600)/T] l mol–1 s–1 andk 2(T)=(8.2±0.8)×1010 exp[–(2200±700)/T] l mol–1 s–1. The rate coefficients for the reactions of NO3 with acetic acid (3) and acetate (4) atT=298 K andI=0.19 mol/l were determined as:k 3=(1.3±0.3)×104 l mol–1 s–1 andk 4=(2.3±0.4)×106 l mol–1 s–1. The temperature dependences for these reactions are described by:k 3(T)=(4.9±0.5)×109 exp[–(3800±700)/T] l mol–1 s–1 andk 4(T)=(1.0±0.2)×1012 exp[–(3800±1200)/T] l mol–1 s–1. The differences in reactivity of the anions HCOO– and CH3COO– compared to their corresponding acids HCOOH and CH3COOH are explained by the higher reactivity of NO3 in charge transfer processes compared to H atom abstraction. From a comparison of NO3 reactions with various droplets constituents it is concluded that the reaction of NO3 with HCOO– may present a dominant loss reaction of NO3 in atmospheric droplets.  相似文献   

3.
Vapor phase concentrations of acetone, acetaldehyde and acetonitrile over their aqueous solutions were measured to determine Henry's law partition coefficients for these compounds in the temperature range 5–40 °C. The results are for acetone: ln(H 1/atm)=–(5286±100)T+(18.4±0.3); acetaldehyde: ln(H 1/atm)=–(5671±22)/T+(20.4±0.1); and acetonitrile: ln(H 1/atm)=–(4106±101)/T+(13.8±0.3). Artificial seawater of 3.5% salinity in place of deiionized water raisesH 1 by about 15%. A similar technique has been used to measure the equilibrium constants for the addition compounds of acetone and acetaldehyde with bisulfite in aqueous solution. The results are ln(K 1/M –1)=(4972±318)/T–(11.2±1.1) and ln(K 1/M –1)=(6240±427)/T–(8.1±1.3), respectively. The results are compared and partly combined with other data in the literature to provide an average representation.  相似文献   

4.
The absolute rate constants for the gas-phasereactions of the NO3 radical with a series ofaldehydes such as acetaldehyde, propanal, butanal,pentanal, hexanal and, heptanal were measured overthe temperature range 298–433 K, using a dischargeflow system and monitoring the NO3 radical byLaser Induced Fluorescence (LIF).The measured rate constants at 298 K for thereaction of NO3, in units of 10–14 cm3molecule–1 s–1, were as follows:acetaldehyde 0.32 ± 0.04, propanal 0.60 ± 0.06, butanal 1.46± 0.16, pentanal 1.75 ±0.06, hexanal 1.83 ± 0.36, and heptanal 2.37 ±0.42. The proposed Arrhenius expressions arek1 = (6.2 ± 7.5) × 10–11 exp[–(2826 ± 866)/T] (cm3 molecule–1s–1),k2 = (1.7 ± 1.0) × 10–11 exp[–(2250 ± 192)/T] (cm3 molecule–1s1), k3 =(7.6 ± 9.8) × 1011 exp[–(2466 ± 505)/T] (cm3 molecule–1s–1),k4 = (2.8 ± 1.4) × 10–11 exp[–(2189 ± 156)/T] (cm3 molecule–1s–1), k5 = (7.0 ± 1.8) ×10–11 exp [–(2382 ± 998)/T](cm3 molecule–1 s–1), andk6 = (7.8 ± 1.0) × 10–11 exp[–(2406 ± 481)/T](cm3 molecule–1 s–1).Tropospheric lifetimes for these aldehydes werecalculated at night and during the day for typicalNO3 and OH average concentrations and showed thatboth radicals provide an effective tropospheric sinkfor these compounds and that the night-time reactionwith the NO3 radical can be an important, if notdominant, loss process for these emitted organics andfor NO3 radicals.  相似文献   

5.
The rate parameters for the reaction of the OH radical with CH3Br have been measured using the discharge flow-electron paramagnetic resonance method. The result isk 1=(1.86±0.48)×10–12 exp[–(1230±150)/T] cm3 molecule–1 s–1. This value is compared to earlier data and is found to be in excellent agreement with the most recent results, which greatly increases the accuracy of the ozone depletion potential of CH3Br which can be derived from these kinetic data.  相似文献   

6.
The following temperature-dependent rate coefficients (k/cm3 molecule–1 s–1) of the reactions of hydroxyl radicals with aliphatic ethers have been determined over the temperature range 247–373 K by a competitive flow technique: diethyl ether,k OH=5.2×10–12 exp[(262±150)/T]; methyln-butyl ether,k OH=5.4×10–12 exp[(309±150)/T]; ethyln-butyl ether,k OH=7.3×10–12 exp[(335±150)/T]; di-n-butyl ether,k OH=5.5×10–12 exp[(502±150)/T] and di-n-pentyl ether,k OH=8.5×10–12 exp[(417±150)/T]. The data have been measured relative to the rate coefficientk(OH + 2,3-dimethylbutane)=6.2×10–12 cm3 molecule–1 s–1 independent of temperature.Previous discrepancies in the room-temperature rate coefficients for the OH reactions with ethyln-butyl ether and di-n-butyl ether, obtained in the flow and static experiments of Bennett and Kerr (J. Atmos. Chem. 8, 87–94, 1989;10, 29–38, 1990) compared with those of Wallingtonet al. (Int. J. Chem. Kinet. 20, 541–547, 1988;21, 993–1001, 1989) and of Nelsonet al. (Int. J. Chem. Kinet. 22, 1111–1126, 1990) have been resolved. The results are considered in relation to the available literature data and evaluated rate expressions are deduced where possible. The data are also discussed in terms of structure-activity relationships.  相似文献   

7.
The reaction of Cl with cyclohexanone (1) was investigated, for the first time, as a function of temperature (273–333 K) and at a low total pressure (1 Torr) with helium as a carrier gas using a discharge flow-mass spectrometry technique (DF-MS). The resulting Arrhenius expression is proposed, k 1= (7.7 ± 4.1) × 10–10 exp[–(540 ± 169)/T]. We also report a mechanistic study with the quantitative determination of the products of the reaction of Cl with cyclohexanone. The absolute rate constant derived from this study at 1 Torr of total pressure and room temperature is (1.3 ± 0.2) × 10–10 cm3 molecule–1 s–1. A yield of 0.94 ± 0.10 was found for the H-abstraction channel giving HCl. In relative studies, using a newly constructed relative rate system, the decay of cyclohexanone was followed by gas chromatography coupled with flame-ionisation detection. These relative measurements were performed at atmospheric pressure with synthetic air and room temperature. Rate constant measured using the relative method for reaction (1) is: (1.7 ± 0.3) × 10–10 cm3 molecule–1 s–1. Finally, results and atmospheric implications are discussed and compared with the reactivity with OH radicals.  相似文献   

8.
The effect of temperature on the solubility of PAN and on its hydrolysis rate in near-neutral and slightly acidic water were studied in a bubble column apparatus. The results obtained are a Henry's law coefficient H=10–9.04±0.6 exp[(6513±376)/T] M atm–1, and a first-order hydrolysis rate constant k=106.60±1.0 exp[(–6612±662)/T] s-1, which was independent of pH in the range 3.2pH6.7. The products formed are nitrite and nitrate in approximately equal proportions under near-neutral conditions. At a pH<4, nitrite is oxidized in a secondary reaction, and nitrate becomes the only product at low pH. Previously measured deposition velocities of PAN on stagnant water surfaces are shown to be hydrolysis rate limited.  相似文献   

9.
Oxidation reactions of the proposed CFC substitutes HCFC-123 (CF3CHCl2) and HCFC-141b (CFCl2CH3) have been studied in the laboratory using long-path Fourier transform infrared spectroscopy. The air oxidation of the HCFCs was initiated by the photolysis of Cl2 forming Cl atoms that abstract H atoms from the HCFC. CF3C(O)Cl was the only carbon containing compound observed in the infrared spectrum of the products of the HCFC-123/Cl2 irradiations and its yield was approximately one. The product data are consistent with formation of CF3C(O)Cl by Cl elimination of the intermediate halogenated alkoxy radical CF3CCl2O. The Cl-initiated oxidation of HCFC-141b led to the formation of CO and C(O)FCl. The product data are consistent with a 1 : 1 relationship between C(O)FCl formed and HCFC-141b reacted. Product data were compatible with both decomposition by cleavage of the C–C bond of the radical CFCl2CH2O leading to the prompt generation of C(O)FCl and reaction of the radical with O2 forming the two carbon halogenated aldehyde CFCl2CH(O), which in the presence of Cl was likely oxidized to C(O)FCl. An approximate method was developed in which the ratio was extracted from analysis of the time evolution of HCFC-141b, C(O)FCl, and CO. The data suggest that the contributions are comparable.  相似文献   

10.
A combined study of the OH gas phase reaction and uptake on aqueous surfacesof two carbonates, dimethyl and diethyl carbonate has been carried out todetermine the atmospheric lifetimes of these compounds. Rate coefficients havebeen measured for gas phase reactions of OH radicals with dimethyl and diethylcarbonate. The experiments were carried out using pulsed laser photolysis– laser induced fluorescence over the temperature range 263–372K and the kinetic data were used to derive the following Arrhenius expressions(in units of cm3 molecule–1 s–1):for dimethyl carbonate, k1 = (0.83±0.27)×10–12 exp [–(247± 98)/T] and fordiethyl carbonate, k2 = (0.46±0.15)×10–12 exp [(503± 203)/T]. At 298 K, therate coefficients obtained (in units of 10–12 cm3molecule–1 s–1) are: k1 =(0.35± 0.04) and k2 = (2.31± 0.29). The results arediscussed in terms of structure-activity relationships.The uptake coefficients of both carbonates on aqueous surfaces were measuredas a function of temperature and composition of the liquid phase, using thedroplet train technique coupled to a mass spectrometric detection. Dimethyland diethyl carbonate show very similar results. For both carbonates, themeasured uptake kinetics were found to be independent of the aqueous phasecomposition (pure water, NaOH solutions) but dependent on gas-liquid contacttime which characterises a surface saturation effect. The uptake coefficientvalues show a slight negative temperature dependence for both carbonates.These values vary from 1.4×10–2 to0.6×10–2 in the temperature range of 265–279 Kfor dimethyl carbonate, from 2.4×10–2 to0.9×10–2 in the temperature range of 270–279 Kfor diethyl carbonate. From the kinetic data, the following Henry's lawconstants were derived between 279 and 265 K: dimethyl carbonate,H1 = 20–106 M atm–1; and diethyl carbonate,H2 = 30–98 M atm–1. The reported data showthat the OH reaction is the major atmospheric loss process of these twocarbonates with lifetimes of 33 and 5 days, respectively, while the wetdeposition is a negligible process.  相似文献   

11.
Rate coefficients have been measured for the gas phasereactions of hydroxyl (OH) radicals and ozone with twounsaturated esters, allyl acetate(CH3C(O)OCH2CH=CH2) and isopropenylacetate (CH3C(O)OC(CH3)=CH2). The OHexperiments were carried out using the pulsed laserphotolysis – laser induced fluorescence technique overthe temperature range 243–372 K and the kinetic dataused to derive the following Arrhenius expressions (inunits of cm3 molecule-1 s-1): allylacetate, k 1 = (2.33 ± 0.27) ×10-12 exp[(732 ± 34)/T]; and isopropenyl acetate,k 2 = (4.52 ± 0.62) × 10-12exp[(809 ± 39)/T]. At 298 K, the rate coefficients obtained (inunits of 10-12 cm3 molecule-1 s-1)are: k 1 = (27.1 ± 3.0) and k 2= (69.6± 9.4). The relative rate technique has been usedto determine rate coefficients for the reaction ofozone with the acetates. Using methyl vinyl ketone asthe reference compound and a value of4.8 × 10-18 cm3 molecule-1s-1 asthe rate coefficient for its reaction with O3,the following rate coefficients were derived at 298 ± 4 K (in units of10-18 cm3molecule-1 s-1): allyl acetate, (2.4 ± 0.7) andisopropenyl acetate (0.7 ± 0.2). Theresults are discussed in terms of structure-activityrelationships and used to derive atmospheric lifetimesfor the acetates.  相似文献   

12.
The absorption cross-sections of HCFC-123 (CF3–CHCl2), HCFC-141b (CH3–CFCl2) and HCFC-142b (CH3–CF2Cl) are measured between 170 and 250 nm for temperatures ranging from 295 to 210 K with uncertainties between 2 and 4%. They are compared with other available determinations. Temperature effects are discussed and parametrical formulae are proposed to compute the absorption cross-section for wavelengths and temperatures useful in atmospheric modelling calculations. Photodissociation coefficients are presented and their temperature-dependence is discussed.  相似文献   

13.
Henry's law constants KH (mol kg–1 atm–1) for the reaction HOCl(g)=HOCl(aq) near room temperature, literature data for the associated enthalpy change, and solubilities of HOCl in aqueous H2SO4 (46 to 60 wt%) at temperatures relevant to the stratosphere (200 KT230 K) are shown to be thermodynamically consistent. Effective Henry's law constants [H*=mHOCl/pHOCl, in mol kg–1 atm–1] of HOCl in aqueous H2SO4 are given by: ln(H*)=6.4946–mH2SO4(–0.04107+54.56/T)–5862 (1/To–1/T) where T(K) is temperature and To=298.15K. The activity coefficient of HOCl in aqueous H2SO4 has a simple Setchenow-type dependence upon H2SO4 molality.  相似文献   

14.
Henry's law constantsK H (mol kg–1 atm–1) have been determined at 298.15 K for the following organic acids: formic acid (5.53±0.27×103); acetic acid (5.50±0.29×103); propionic acid (5.71±0.34×103);n-butyric acid (4.73±0.18×103); isobutyric acid (1.13±0.12×103); isovaleric acid (1.20±0.11×103) and neovaleric acid (0.353±0.04×103). They have also been determined fromT=278.15 K toT=308.15 K forn-valeric acid (ln(K H)=–14.3371+6582.96/T);n-caproic acid (ln(K H)=–13.9424+6303.73/T) and pyruvic acid (ln(K H)=–4.41706+5087.92/T). The influence of 9 salts on the solubility of pyruvic acid at 298.15 K has been measured. Pyruvic acid is soluble enough to partition strongly into aqueous atmospheric aerosols. Other acids require around 1 g of liquid water m–3 (typical of clouds) to partition significantly into the aqueous phase. The degree of partitioning is sensitive to temperature. Considering solubility and dissociation (to formate) alone, the ratio of formic acid to acetic acid in liquid water in the atmosphere (at equilibrium with the gas phase acids) is expected to increase with rising pH, but show little variation with temperature.  相似文献   

15.
Rate constants for the gas-phase reactions of OH radicals, NO3 radicals and O3 with the C7-carbonyl compounds 4-methylenehex-5-enal [CH2=CHC(=CH2)CH2CH2CHO], (3Z)- and (3E)-4-methylhexa-3,5-dienal [CH2=CHC(CH3)=CHCH2CHO] and 4-methylcyclohex-3-en-1-one, which are products of the atmospheric degradations of myrcene, Z- and E-ocimene and terpinolene, respectively, have been measured at 296 ± 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained (in cm3 molecule–1 s–1 units) were: for 4-methylenehex-5-enal, (1.55 ± 0.15) × 10–10, (4.75 ± 0.35) × 10–13 and (1.46 ± 0.12) × 10–17 for the OH radical, NO3 radical and O3 reactions, respectively; for (3Z)-4-methylhexa-3,5-dienal: (1.61 ± 0.35) × 10–10, (2.17 ± 0.30) × 10–12, and (4.13 ± 0.81) × 10–17 for the OH radical, NO3 radical and O3 reactions, respectively; for (3E)-4-methylhexa-3,5-dienal: (2.52 ± 0.65) × 10–10, (1.75 ± 0.27) × 10–12, and (5.36 ± 0.28) × 10–17 for the OH radical, NO3 radical and O3 reactions, respectively; and for 4-methylcyclohex-3-en-1-one: (1.10 ± 0.19) × 10–10, (1.81 ± 0.35) × 10–12, and (6.98 ± 0.40) × 10–17 for the OH radical, NO3 radical and O3 reactions, respectively. These carbonyl compounds are all reactive in the troposphere, with daytime reaction with the OH radical and nighttime reaction with the NO3 radical being predicted to dominate as loss processes and with estimated lifetimes of about an hour or less.  相似文献   

16.
Rate constants for the reaction of hydroxyl radicals with dibromomethanehave been measured by discharge flow-resonance fluorescence technique(DF-RF) over the temperature range 288–368 K. The derived Arrheniusequation is k1=(1.51 ± 0.37)× 10-12 exp(-(720 ±60)/T) cm3 molec.-1 s-1.The tropospheric lifetime of dibromomethane has been estimated to be 0.29years. An ozone depletion potential (ODP) value of 0.10 for dibromomethanehas been obtained.  相似文献   

17.
Absolute rate coefficient measurements have been carried out for the reactions of Cl atoms with propene and a series of 3-halopropenes, at room temperature (298 ± 2) K using a newly constructed laser photolysis-resonance fluorescence (PLP-RF) system. The rate coefficients obtained (in units of cm3 molecule–1 s–1) are: propene (1.40± 0.24) ×10–10, 3-fluoropropene (4.92 ± 0.42) ×10–11, 3-chloropropene (7.47 ± 1.50) × 10–11, 3-bromopropene (1.23± 0.14) ×10–10 and 3-iodopropene (1.29± 0.15) ×10–10. In order to test this new system, the reactions of Cl atoms with acetone and isoprene have also been studied and compared with data previously reported. The rate coefficients determined at room temperature for these last two reactions are (2.93 ± 0.20) ×10–12 cm3 molecule–1 s– 1 and (3.64± 0.20)×10–10 cm3 molecule–1 s–1, respectively. The measured values were independent of pressure over the range 20–200 Torr. The influence of the different halogen atoms substituents on the reactivity of these alkenes with Cl atoms as well as the atmospheric implications of these measurements are studied and discussed for the first time in this work and compared with the reactivity with NO3 and OH radicals.  相似文献   

18.
We present here experimental determinations of mass accommodation coefficients using a low pressure tube reactor in which monodispersed droplets, generated by a vibrating orifice, are brought into contact with known amounts of trace gases. The uptake of the gases and the accommodation coefficient are determined by chemical analysis of the aqueous phase.We report in this article measurements of exp=(6.0±0.8)×10–2 at 298 K and with a total pressure of 38 Torr for SO2, (5.0±1.0)×10–2 at 297 K and total pressure of 52 Torr for HNO3, (1.5±0.6)×10–3 at 298 K and total pressure of 50 Torr for NO2, (2.4±1.0)×10–2 at 290 K and total pressure of 70 Torr for NH3.These values are corrected for mass transport limitations in the gas phase leading to =(1.3±0.1)×10–1 (298 K) for SO2, (1.1±0.1)×10–1 (298 K) for HNO3, (9.7±0.9)×10–2 (290 K) for NH3, (1.5±0.8)×10–3 (298 K) for NO2 but this last value should not be considered as the true value of for NO2 because of possible chemical interferences.Results are discussed in terms of experimental conditions which determine the presence of limitations on the mass transport rates of gaseous species into an aqueous phase, which permits the correction of the experimental values.  相似文献   

19.
Turbulence statistics, including higher order moments, in the surface layer over plant canopies were compared with those observed over several different surfaces, using a nondimensional height (z – d)/z 0: The values of (z – d)/z 0extend over a very wide range from 10 over plant canopies to 107 over the ocean. Several properties such as intensities of turbulence and skewness factors show a remarkable height-dependency in the air layer below (z – d)/z 0 = 102, which is supposed to be much influenced by the underlying surface. In that layer, some peculiar phenomena, such as a downward energy transport and positive flux of shear stress, are frequently observed.  相似文献   

20.
There are large uncertainties in identifying and quantifying the natural and anthropogenic sources of chloromethanes – methyl chloride (CH3Cl), chloroform (CHCl3) and dichloromethane (CH2Cl2), which are responsible for about 15% of the total chlorine in the stratosphere. We report two years of in situ observations of these species from the AGAGE (Advanced Global Atmospheric Gas Experiment) program at Cape Grim, Tasmania (41° S, 145° E). The average background levels of CH3Cl, CHCl3 and CH2Cl2 during 1998–2000 were 551± 8, 6.3± 0.2 and 8.9± 0.2 ppt (dry air mole fractions expressed in parts per 1012) respectively, with a two-year average amplitude of the seasonal cycles in background air of 25, 1.1 and 1.5 ppt respectively. The CH3Cl and CHCl3 records at Cape Grim show clear episodes of elevated mixing ratios up to 1300 ppt and 55 ppt respectively, which are highly correlated, suggesting common source(s). Trajectory analyses show that the sources of CH3Cl and CHCl3 that are responsible for these elevated observations are located in coastal-terrestrial and/or coastal-seawater regions in Tasmania and the south-eastern Australian mainland. Elevated levels of CH2Cl2 (up to 70 ppt above background) are associated mainly with emissions from the Melbourne/Port Phillip region, a large urban/industrial complex (population 3.5 million) 300 km north of Cape Grim.Now at the Centre for Atmospheric ChemistryNow at School of Environmental Sciences  相似文献   

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