首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
The kinetics and mechanism of the reactionNO3+CH2=C(CH3)–CH=CH2productswere studied in two laboratories at 298 K in the pressure range 0.7–3 torr using the discharge-flow mass-spectrometric method. The rate constant obtained under pseudo-first-order conditions with excess of either NO3 or isoprene was: k 1=(7.8±0.6)×10–13 cm3 molecule–1 s–1. The product analysis indicated that the primary addition of NO3 occurred on both -bonds of the isprene molecule.  相似文献   

2.
The I-atom sensitised decomposition of ozone in air at 1 atm pressure and ambient temperature has been investigated. Iodine atoms were produced by photolysis of I2 using visible light or of CH3I using ultraviolet light. In both cases, the quantum yield for O3 decomposition was 1.25 (±0.11) per I atom. An important role is proposed for the self-reaction of IO radicals leading to higher oxides of iodine, IO+IO(+M)I2O2(+M)higher oxides, which predominated over the bimolecular reaction leading to regeneration of I atoms, IO+IO2I+O2, with k 2a/k 2b4. Simple computer modelling calculations indicate that reaction (2a) may be important in determining the fate of photolabile iodine species in the atmosphere. The consequences for the behaviour of radioiodine releases are also discussed.  相似文献   

3.
Kinetics and products of the gas-phase reactions of dimethylsulphide (DMS), dimethylsulphoxide (DMSO) and dimethylsulphone (DMSO2) with Br atoms and BrO radicals in air have beeninvestigated using on-line Fourier Transform Infrared Spectroscopy (FT-IR) as analytical technique at 740 ± 5 Torr total pressure and at 296 ± 3 K in a480 L reaction chamber. Using a relative rate method for determining the rate constants; the following values (expressed in cm3molecule–1 s–1) were found: kDMS+Br = (4.9 ±1.0) ×10–14, kDMSO + Br < 6 × 10–14,kDMSO 2 + Br 1 × 10–15,kDMSO + BrO = (1.0 ± 0.3) × 10–14 andkDMSO 2 + BrO 3 × 10–15 (allvalues are given with one on the experimental data). DMSO, SO2, COS, CH3SBr andCH3SO2Br were identified as the main sulphur containing products of the oxidation of DMS by Br atoms. From the reaction between DMSO and Br atoms, DMSO2and CH3SO2Br were the only sulphur containing products thatwere identified. DMSO, DMSO2 and SO2 were identified as themain sulphur containing products of the reaction between DMS and BrO.DMSO2 was found to be the only product of the reaction between DMSO and BrO. For the reactions of DMSO2 with Br and BrO no products were identified because the reactions were too slow.The implications of these results for atmospheric chemistry are discussed.  相似文献   

4.
Rate constants have been measured for the reactions of hydroxyl radicals with alkyl nitrates and with some oxygen-containing organic compounds by a competitive technique. Mixtures of synthetic air containing a few ppm of nitrous acid, ethylene and the organic substrate were photolysed in a Teflon bag smog chamber. Based on the value k HO+C2H4}=8.1×10-12 cm3 molecule-1 s-1 the following rate constants were obtained for the hydroxyl radical reactions at 750 Torr and at 303 K in units of 10-12 cm3 molecule-1: CH3ONO2, 0.37±0.09; C2H5ONO2, 0.48±0.20; n-C3H7ONO2, 0.70±0.22; C2H5OH, 3.6±0.4; CH3COCH3, 0.26±0.08; CH3CO2 i-C3H7, 3.0±0.8; CH3CO2 n-C3H7, 2.4±0.2. The results are discussed in relation to the available literature data and the implications of the results are considered in terms of the smog reactivity of these molecules.  相似文献   

5.
The activation of Br- and Cl- to atomic Br and Cl in sea-spray aerosol was investigated in smog-chamber experiments. In the presence of O3, hydrocarbons and NaCl aerosol alone no activation was observed. By adding Br- to the aerosol, the chain reaction: Br + O3 BrO, BrO + HO2 HOBr, HOBr HOBr(aq), HOBr(aq) + H+ + Br- Br2 (6), HOBr(aq) + H+ + Cl- BrCl (7) was verified. The step from reaction (6) to (7) is accompanied by a decrease of the Br-/Cl- ratio from 1/600 to less than 1/2000. In the absence of sulphate, the chain is initiated by the reaction of OH(aq) with Br-. The pH value decreases to less than 2 during the first minutes of the experiment and later on to almost 1 (in the absence of NOx or SO2). This is caused by the formation of oxalic acid from alkanes and toluene. In stopped flow experiments, the reduction of Br2 by oxalic acid was observed to occur through a two-step mechanism: HC2O4 - + Br2 Br- + BrC2O4H (k22, k-22), BrC2O4H Br- + H+ + 2 CO2 (23) with the following rate constants and ratios of rate constants, k ± 2: k22k-23 / k-22 = (2.9 ± 0.3) · 10-4 s-1, k-22 / k-23 = 7000 ± 3000 13000 M-1, k22 = 2 ±-1 4 M-1 s-1, and k-23 > 0.1 s-1, k-22 > 600 M-1 s-1. Oxalic acid may be responsible for the inhibition of the chain reaction observed at the end of the experiments.  相似文献   

6.
Rate coefficients have been measured for the reactions of hydroxyl radicals with a range of aliphatic ethers by a competitive technique. Mixtures of synthetic air containing a few ppm of nitrous acid, isobutene and an ether were photolyzed in a Teflon-bag smog chamber. From the rates of depletion of the ether and of the isobutene, and based on the value of the rate coefficient k(OH+i-C4H8)=5.26×10-11 cm3 molecule-1 s-1, the following rate coefficients were obtained for the hydroxyl radical reactions at 750 Torr and at 294±2K in units of 10-12 cm3 molecule-1 s-1: diethylether = 12.0±1.1, di-n-propylether = 15.3±1.6, di-n-butylether=17.1±0.9, ethyl n-butylether = 13.5±0.4, ethyl t-butyl-ether = 5.6±0.5, and di-isobutylether = 26.1±1.6. The quoted error limits correspond to 2 standard deviations but do not include any contribution from k(OH+i-C4H8) for which the error limits are estimated to be about ±10%. The results are discussed in relation to the available literature data and considered in terms of the structure-activity relation for hydroxyl radical reactions with organic molecules.  相似文献   

7.
The kinetics of the reaction of NO2 with O3 have been investigated at 296 K, using UV absorption spectroscopy to monitor decay of NO2 or O3 and infrared laser absorption spectroscopy to monitor formation of the reaction product N2O5. The results both for the rate coefficient at 296 K (k 1=3.5×10-17 cm3 molecule-1 s-1) and the reaction stoichiometry (NO2/O3=1.85±0.09) are in good agreement with previous studies, confirming that the two step mechanism involving formation of symmetrical NO3 as an intermediate is predominant.% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeOtaiaab+% eadaWgaaWcbaGaaeOmaaqabaGccqGHRaWkcaqGpbWaaSbaaSqaaiaa% bodaaeqaaOWaa4ajaSqaaaqabOGaayPKHaGaaeOtaiaab+eadaWgaa% WcbaGaae4maaqabaGccqGHRaWkcaqGpbWaaSbaaSqaaiaabkdaaeqa% aaaa!41D7!\[{\text{NO}}_{\text{2}} + {\text{O}}_{\text{3}} \xrightarrow{{}}{\text{NO}}_{\text{3}} + {\text{O}}_{\text{2}} \]% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaeOtaiaab+% eadaWgaaWcbaGaae4maaqabaGccqGHRaWkcaqGobGaae4tamaaBaaa% leaacaqGYaaabeaakiabgUcaRiaab2eadaGdKaWcbaaabeGccaGLsg% cacaqGobWaaSbaaSqaaiaabkdaaeqaaOGaae4tamaaBaaaleaacaqG% 1aaabeaakiabgUcaRiaab2eaaaa!4464!\[{\text{NO}}_{\text{3}} + {\text{NO}}_{\text{2}} + {\text{M}}\xrightarrow{{}}{\text{N}}_{\text{2}} {\text{O}}_{\text{5}} + {\text{M}}\]A possible minor role for the unsymmetrical ONOO species is suggested to account for the lower-than-expected stoichiometry factor. The importance of this reaction in the oxidation of atmospheric NO2 is discussed.  相似文献   

8.
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   

9.
Accurate values for the rate and temperature dependence of the reaction NO + O3 NO2 + O2 are important in the chemical modelling of photochemical processes in the atmosphere. Previous measurements have been made at low total pressures and/or with very large mixing ratios relative to those observed in the atmosphere. In this study the reaction rate has been measured using a novel approach under tropospheric conditions of temperature and pressure, and at tens of ppb (mixing ratios of 1 in 108) between 263 and 328 K. The resultant Arrhenius expression (k=Ae-Ea/RT) gives a larger activation energy (Ea/R=1670 ± 100) than the recommended literature value (Ea/R=1400 ± 200), and a larger pre-exponential factor (A=5.1 ± 1.6 × 10-12 cf. recommended A=2.0 × 10-12), but the second-order rate constant at 298 K (1.90 × 10-14 molecules cm-3 s-1 ± 10%) is similar to the recommended value. The results confirm a lack of pressure dependence of the reaction, but were made over too small a range in temperature to address the issue of curvature of the simple Arrhenius expression.  相似文献   

10.
The rate coefficients for the reaction between atomic chlorine and a number of naturally occurring species have been measured at ambient temperature and atmospheric pressure using the relative rate technique. The values obtained were (4.0 ± 0.8) × 10-10, (2.1 ± 0.5) × 10-10, (3.2 ± 0.5) × 10-10, and (4.9 ± 0.5) × 10-10 cm3 molecule-1 s-1, for reactions with isoprene, methyl vinyl ketone, methacrolein and 3-carene, respectively. The value obtained for isoprene compares favourably with previously reported values. No values have been reported to date for the rate constants of the other reactions.  相似文献   

11.
A simple kinetic mechanism of nitrate radicals uptake on dry sea-salt NaCl, NaBr surfaces is proposed. The mechanism includes adsorption/desorption equilibrium and unimolecular decomposition of the adsorbed complex: NO3(g) + NaX(s) (NO3-NaX)(s); (NO3-NaX)(s) NaNO3 + X(s) Two techniques were used: the matrix isolation ESR and mass spectrometry. The uptake coefficient () is found to be dependent on exposure time of salt to NO3 for raw coating. The initial (t0) is higher than the observable steady-state obs. At room temperature obs is independent of [NO3] at low [NO3] = 3 × 109 - 1011 cm-3, but it is inversely proportional to [NO3] at concentrations higher than 1012 cm-3. At temperatures above 100 °C, obs becomes independent of [NO3] in a wider range of [NO3]. An increased number of dislocations is supposed to exist in the case of raw coating. Due to a wide spread of the surface sites binding energy with the ionic lattice near dislocations, the part of surface complexes has lower binding energy and "burns" more rapidly. That burning determines the transition from (t0) down to obs.The kinetic parameters and elementary rate coefficients are obtained. The recommended for low atmospheric NO3 concentration are in the range of 0.002 ± 0.04 for NaCl and 0.1-0.3 for NaBr depending on a mechanism of the (t) relaxation.  相似文献   

12.
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   

13.
The results of an intercomparison campaign of eight different long path UV-visible DOAS instruments measuring NO2, O3 and SO2 concentrations in a moderately polluted urban site are presented. For effective optical path lengths of 230 and 780 m the overall spread of these measurements (±1) are 5×1010, 6×1010 and 1×1010 molec·cm-3 (2.0, 2.4, and 0.4 ppb) for these molecules respectively when all instruments used a common set of absorption cross sections. The remaining differences are not completely random and the systematic differences are attributed to the different retrieval methods used for each instrument.  相似文献   

14.
We have employed a pulsed laser photolysis-pulsed laser induced fluorescence technique to study the kinetics and mechanism of the reaction of OH with dimethylsulfoxide and its deuterated analogue. A rate coefficient of (1.0±0.3)×10-10 cm3 molecule-1 s-1 was obtained ar room temperature. The rate coefficient was independent of pressure over the range 25–700 Torr, showed no dependence on the nature of the buffer gas and showed no kinetic isotope effect. A limited study of the temperature dependence indicated that the reaction displays a negative activation energy. The gas phase ultraviolet absorption spectrum was obtained at room temperature and showed a strong absorption feature in the far ultraviolet. The absolute absorption cross-section at 205 nm, the absorption peak, is (1.0±0.3)×10-17 cm2, where the large uncertainty results from experimental difficulties associated with the low vapor pressure and stickiness of DMSO.  相似文献   

15.
The gas phase reactions of peroxyacetyl nitrate (PAN) with OH and Cl have been studied using the discharge-flow EPR method. The rate constants are found to be k 3=(7.5±1.4)×10-14 and k 4=(3.7±1.7)×10-13 cm3 molecule-1 s-1 at 298 K, respectively. These results confirm that the OH+PAN reaction will be the dominant sink of PAN in the middle and upper troposphere, whereas the reaction Cl+PAN will be negligible in contrast with previous estimations.  相似文献   

16.
The kinetics of the reaction of nitrous acid (HONO) with nitric acid (HNO3), nitrate radicals (NO3) and dinitrogen pentoxide (N2O5) have been studied using Fourier transform infrared spectroscopy. Experiments were performed at 700 torr total pressure using synthetic air or argon as diluents. From the observed decay of HONO in the presence of HNO3 a rate constant of k<7×10-19 cm3 molecule-1 s-1 was derived for the reaction of HONO with HNO3. From the observed decay of HONO in the presence of mixtures of N2O5 and NO2 we have also derived upper limits for the rate constants of the reactions of HONO with NO3 and N2O5 of 2×10-15 and 7×10-19 cm3 molecule-1 s-1, respectively. These results are discussed with respect to previous studies and to the atmospheric chemistry of HONO.  相似文献   

17.
Rate coefficients have been measured for the reactions of hydroxyl radicals with five aliphatic ethers over the temperature range 242–328 K. Competitive studies were carried out in an atmospheric flow reactor in which the hydroxyl radicals were generated by the photolysis of methyl nitrite in the presence of air containing nitric oxide. The reaction of OH with 2,3-dimethyl-butane was used as the reference reaction and the following Arrhenius parameters have been obtained for the reactions: OH+RORproducts:
RORE/kJ mol–1 1012 A/cm3 molecule–1 s–1
dethyl ether–2.8±0.43.5±0.6
di-n-propyl ether–1.2±0.611.5±2.7
methylt-butyl ether0.85±0.594.0±1.3
ethyln-butyl ether–1.3±0.58.7±1.7
ethylt-butyl ether–1.2±0.63.0±0.8
  相似文献   

18.
Using a filter radiometer, the meridional profile of the NO2 photolysis frequency, J(NO2), was measured between 50° N and 30° S during the cruise ANTVII/1 September/October 1988 of the research vessel Polarstern on the Atlantic Ocean. Simultaneously, global broadband irradiance and acrosol were monitored. Clean marine background air with low aerosol loads (b sp=(1–2)×10-5 m-1) was encountered at the latitudes 25° N–30° N and 18° S–27° S, respectively. Under these conditions and an almost cloudless sky J(NO2) reached 7.3×10-3 s-1 (2 sr) for a zenith angle of 30°. Between 30° N and 30° S, the latitudinal variation of the J(NO2) noontime maxima was less than ± 10%, while the mean value at noon was 7.8×10-3 s-1. For the set of all data between 50° N and 30° S, a nearly linear correlation of J(NO2) vs. global broadland irradiance was found. The slope of (8.24±0.03)×10-5 s-1/mW cm-2 agrees within 10% with observations in Jülich (51° N, 6.2° E).  相似文献   

19.
The design and performance of a smog chamber for the study of photochemical reactions under simulated environmental conditions is described. The chamber is thermostated for aerosol experiments, and it comprises a gas chromatographic sample enrichment system suitable for monitoring hydrocarbons at the ppbv level. By irradiating NO x /alkane-mixtures rate constants for the reaction of OH radicals with n-alkanes are determined from n-pentane to n-hexadecane to be (k±2)/10–12 cm3 s–1=4.29±0.16, 6.2±0.6, 7.52 (reference value), 8.8±0.3, 10.2±0.3, 11.7±0.4, 13.7±0.3, 15.1±0.5, 17.5±0.6, 19.3±0.7, 22.3±1.0, and 25.0±1.3, respectively at 312 K. Rate constants, (k±2)/10–17 cm3 s–1, for the reaction of ozone with trans-2-butene (21.2±1.0), cis-3-methylpentene-(2) (47.2±1.7), cyclopentene (62.4±3.5), cyclohexene (7.8±0.5), cycloheptene (28.3±1.5), -pinene (8.6±1.3), and -pinene (1.4±0.2) are determined in the dark at 297 K using cis-2-butene (13.0) as reference standard.  相似文献   

20.
Measurements of the stable carbon isotope ratio in atmospheric CO2 permit a distinction between variations resulting from biospheric and oceanic exchange. In situ extraction of CO2 from Cape Grim air (41°S) for isotopic analysis commenced in 1977; however difficulties with technique reliability were experienced until 1982. Since 1982, 2.6 years of relatively consistent values have accumulated.For a preliminary assessment of the latter data, estimates of the isotopic behaviour from the global transport and inter-reservoir exchange model of Pearman and Hyson (1985) have been employed. The assessment demonstrates the precision requirements of a carbon isotope monitoring program and the relevance of the isotope measurements as a constraint on parameterization of the model.Clear evidence of the changes due to fossil fuel combustion is seen in the year-to-year differences in 13C, with the mean and standard error of the overall trend being –0.025±0.005 yr-1. A significant seasonal variation in 13C is apparent, despite considerable inter-annual variability possibly associated with the 1982/83 ENSO phenomena. The average peak-to-peak amplitude is 0.055±0.014 with a maximum on day 85±15 (approx. 26 March).There is some evidence for a complex seasonal inter-relationship between concentration and isotope ratio, both in the Cape Grim data and in Mook et al. (1983) South Pole data, but with marked differences between the stations, and with both different from the model estimates.In particular, the Cape Grim results suggest that exchange with Southern Hemisphere biosphere is the main contributor to the seasonal variation in isotope ratio at this latitude.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号