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1.
Henry's law constants KH (mol kg-1 atm-1) have been measured between 278.15 K and 308.15 K for the following organic acids: CH2FCOOH (ln(KH[298.15 K]) = 11.3 ± 0.2), CH2ClCOOH (11.59 ± 0.14), CH2BrCOOH (11.94 ± 0.21), CHF2COOH (10.32 ± 0.10), CHCl2COOH (11.69 ± 0.11), CHBr2COOH (12.33 ± 0.29), CBr3COOH (12.61 ± 0.21), and CClF2COOH (10.11 ± 0.12). The variation of KH with temperature was determined for all acids except CH2FCOOH and CBr3COOH, with r H° for the dissolution reaction ranging from –85.2 ± 2.6 to –57.1 ± 2.5 kJ mol-1, meaning that their solubility is generally more sensitive to temperature than is the case for the simple carboxylic acids. The Henry's law constants show consistent trends with halogen substitution and, together with their high solubility compared to the parent (acetic) acid (ln(KH[298.15 K]) = 8.61), present a severe test of current predictive models based upon molecular structure. The solubility of haloacetic acids and strong dissociation at normal pH mean that they will partition almost entirely into cloud and fog in the atmosphere (0.05–1.0 g H2O m-3), but can reside in both phases for the liquid water contents typical of aerosols (10-5-10-4 g H2O m-3).  相似文献   

2.
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   

3.
Weekly bulk aerosol samples collected at Funafuti, Tuvalu (8°30S, 179°12E), American Samoa (14°15S, 170°35W), and Rarotonga (21°15S, 159°45W), from 1983 through most of 1987 have been analyzed for nitrate and other constituents. The mean nitrate concentration is about 0.11 g m–3 at each of these stations: 0.107±0.011 g m–3 at Funafuti; 0.116±0.008 at American Samoa; and 0.117±0.010 at Rarotonga. Previous measurements of mineral aerosol and trace metal concentrations at American Samoa are among the lowest ever recorded for the near-surface troposphere and indicate that this region is minimally affected by transport of soil material and pollutants from the continents. Consequently, the nitrate concentration of 0.11 g m–3 can be regarded as the natural level for the remote marine boundary layer of the tropical South Pacific Ocean. In contrast, over the tropical North Pacific which is significantly impacted by the transport of material from Asia and North America, the mean nitrate concentrations are about three times higher, 0.29 and 0.36 g m–3 at Midway and Oahu, respectively. The major sources of the nitrate over the tropical South Pacific are still very uncertain. A very significant correlation between the nitrate concentrations at American Samoa and the concentrations of 210Pb suggests that transport from continental sources might be important. This continental source could be lightning, which occurs most frequently over the tropical continents. A near-zero correlation with 7Be indicates that the stratosphere and upper troposphere are probably not the major sources. A significant biogenic source would be consistent with the higher mean nitrate concentrations, 0.16 to 0.17 g m–3, found over the equatorial Pacific at Fanning Island (3°55N, 159°20W) and Nauru (0°32S, 166°57E). The lack of correlation between nitrate and nss sulfate at American Samoa does not necessarily preclude an important role for marine biogenic sources.  相似文献   

4.
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   

5.
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   

6.
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   

7.
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   

8.
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   

9.
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   

10.
The Henry's law constants, K H, of dilute aqueous formic and acetic acids were determined experimentally as a function of concentration and temperature using a new counterflow packed-column technique. K H was found to be (8.9±1.3)×103 and (4.1±0.4)×103 M atm-1 at 25°C for HCOOH and CH3COOH, respectively. The reaction enthalpies, H, were found to be –51±2 kJ mol-1 and –52±1 kJ mol-1 for formic and acetic acid, respectively. These are in good agreement with calculated thermochemical values.Whereas the K H values are in reasonably good agreement with certain other experimentally determined values, K H (HCOOH) is two to three times higher than calculated thermochemical values while K H (CH3COOH) is lower than the two calculated values.The best experimental values appear to be (11±2)×103 M atm-1 and (7±3)×103 M atm-1 for HCOOH and CH3COOH, respectively.  相似文献   

11.
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   

12.
Daily measurements of atmospheric sulfur dioxide (SO2) concentrations were performed from March 1989 to January 1991 at Amsterdam Island (37°50 S–77°30 E), a remote site located in the southern Indian Ocean. Long-range transport of continental air masses was studied using Radon (222Rn) as continental tracer. Average monthly SO2 concentrations range from less than 0.2 to 3.9 nmol m-3 (annual average = 0.7 nmol m-3) and present a seasonal cycle with a minimum in winter and a maximum in summer, similar to that described for atmospheric DMS concentrations measured during the same period. Clear diel correlation between atmospheric DMS and SO2 concentrations is also observed during summer. A photochemical box model using measured atmospheric DMS concentrations as input data reproduces the seasonal variations in the measured atmospheric SO2 concentrations within ±30%. Comparing between computed and measured SO2 concentrations allowed us to estimate a yield of SO2 from DMS oxidation of about 70%.  相似文献   

13.
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   

14.
Measurements of Hg (total gas-phase, precipitation-phase andparticulate-phase), aerosol mass, particulate 210Pb and7Be and precipitation 210Pb were made at an atmosphericcollection station located in a near remote area of northcentral Wisconsin,U.S.A. (46°10N, 89°50W) during the summers of 1993, 1994and 1995. Total Hg and 210Pb were observed to correlate strongly(slope = 0.06 ± 0.03 ng mBq-1; r 2 =0.72) in rainwater. Mercury to 210Pb ratios in particulate matter(0.03 ± 0.02 ng mBq-1; r 2 = 0.06) wereconsistent with the ratio in rain. Enrichment of the Hg/mass ratio (approx.5–50×) relative to soil and primary pollutant aerosols indicatedthat gas-to-particle conversion had taken place during transport. Comparisonof these results with models for the incorporation of Hg into precipitationindicates that atmospheric particles deliver more Hg to precipitation than canbe explained by the presence of soot. A lack of correlation between totalgas-phase Hg (TGM) and a 7Be/210Pb function suggests novertical concentration gradient within the troposphere, and allows an estimateof TGM residence time of 1.5 ± 0.6 yr be made based on surface airsamples.  相似文献   

15.
The relative rate technique has been used to measure rate constants for the reaction of chlorine atoms with peroxyacetylnitrate (PAN), peroxypropionylnitrate (PPN), methylhydroperoxide, formic acid, acetone and butanone. Decay rates of these organic species were measured relative to one or more of the following reference compounds; ethene, ethane, chloroethane, chloromethane, and methane. Using rate constants of 9.29×10–11, 5.7×10–11, 8.04×10–12, 4.9×10–13, and 1.0×10–13 cm3 molecule–1 sec–1 for the reaction of Cl atoms with ethene, ethane, chloroethane, chloromethane, and methane respectively, the following rate constants were derived, in units of cm3 molecule–1 s–1: PAN, <7×10–15; PPN, (1.14±0.12)×10–12; HCOOH, (2.00±0.25)×10–13; CH3OOH, (5.70±0.23)×10–11; CH3COCH3, (2.37±0.12)×10–12; and CH3COC2H5, (4.13±0.57)×10–11. Quoted errors represent 2 and do not include possible systematic errors due to errors in the reference rate constants. Experiments were performed at 295±2 K and 700 torr total pressure of nitrogen or synthetic air. The results are discussed with respect to the previous literature data and to the modelling of nonmethane hydrocarbon oxidation in the atmosphere.In recent discussions with Dr. R. A. Cox of Harwell Laboratory, UKAEA, we learnt of a preliminary value for the rate constant of the reaction of Cl with acetone of (2.5±1.0)×10–12 cm3 molecule–1 sec–1 measured by R. A. Cox, M. E. Jenkin, and G. D. Hayman using molecular modulation techniques. This value is in good agreement with our results.  相似文献   

16.
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   

17.
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   

18.
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   

19.
Further laboratory studies of emission by O(1 S) and by O2 A 3 u + ,A3 u andc 1 u – in the oxygen afterglow lead to the conclusion that Barth's mechanism for the excitation of the auroral green line O 2 * +O(3P=O2+O(1S)–(1) is correct and that levelsv=6 and 7 of O2 A 3 u + are Barth precursors. The value ofk 1=7×10–11 cm3 s–1 deduced for these levels is shown to be in fair agreement with atmospheric measurements.  相似文献   

20.
Measurements of the concentrations of carbonyl sulfide (COS) in the marine atmosphere were made over a period of two years in the southern Indian Ocean (Amsterdam Island, 37°50 S–77°31 E; March 1987–February 1988 and April 1989–February 1990). The mean atmospheric COS concentration for the whole period was 475±48 pptv (n=544). Atmospheric COS concentrations show no significant seasonal variation with a summer to winter ratio of 1.05. Taking into account the observed variability of the atmospheric COS concentration (10%), a value of 1.4 yr is estimated as a lower limit for the atmospheric COS lifetime. A comparison of the COS data at Amsterdam Island with those obtained in the Southern Hemisphere in the past 12 yr does not reveal any significant trend in the tropospheric background COS mixing ratio.  相似文献   

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