Environ. Sci. Technol. 1983, 17, 479-484
(26) Renberg, L.; Lindstrom, K. J . Chromatogr.1981,214,327. (27) Muller, M. D. Chimia 1982, 36, 437. (28) Schneider, J. K.; Gloor, R.; Giger, W.; Schwarzenbach, R. P., to be submitted for publication in Water Res. (29) Gloor, R.; Leidner, H. Anal. Chem. 1979,51, 645. (30) Kappeler, E.; Wuhrmann, K. Water Res. 1978, 12, 327. (31) Schwarzenbach, R. P.; Giger, W.; Hoehn, E.; Schneider, J. K., EAWAG, CH-8600 Dubendorf, unpublished data. (32) Giger, W.; Schaffner, C. Stud. Environ. Sei. 1981,17,517. (33) Marinucci, A. C.; Bartha, R. Appl. Environ. Microbiol. 1979, 38, 811. (34) Ballschmitter, K.; Scholz, Ch. Chemosphere 1980,9,457. (35) Schellenberg, K. H.; Schwarzenbach, R. P., to be submitted for publication in Environ. Sci. Technol. (36) Gjessing, E. T. In “Physical and Chemical Characteristics of Aquatic Humus”; Ann Arbor Science: Ann Arbor, MI, 1976.
(37) Matthess, G.; Pekdeger, A. GWF, Gas- Wasserfach: WasserlAbwasser 1980, 121, 214. (38) Davis, J. In “Contaminants and Sediments”: Baker, R. A,, Ed.; Ann Arbor Science: Ann Arbor, MI 1980; p 279. (39) Hansch, C.; Leo, A. In “Substituent Constants for Correlation Analysis in Chemistry and Biology”; Elsevier: Amsterdam, 1979. (40) Tute, M. S. Adv. Drug. Res. 1971, 6 , 1. (41) Mackay, D.; Bobra, A,; Shin, W. Y.; Yalkowsky, S. H. Chemosphere 1980, 9, 701. (42) Kurihara, N.; Uchida, M.; Fujita, T.; Nakajima, M. Pestic. Biochem. Physiol. 1973, 2, 383.
Received for review November 19,1982. Accepted March 3,1983. This work was funded by the Swiss National Science Foundation (Nationales Forschungsprogramm Wasserhaushalt).
OH Radical Rate Constants and Photolysis Rates of a-Dicarbonyls Christopher N. Plum, Eugenlo Sanhueza,t Roger Atklnson, William P. L. Carter,” and James N. Pitts, Jr.
Statewide Air Pollution Research Center, University of California, Riverside, California 9252 1 Photolysis rates of glyoxal, methylglyoxal, and biacetyl and OH radical reaction rate constants for glyoxal and methylglyoxal have been determined at 298 f 2 K in an environmental chamber, by using the photolysis of CH30NO-air mixtures to generate OH radicals. The OH radical rate constants obtained were (1.15 f 0.04) X lo-’’ and (1.73 f 0.13) X lo-’’ cm3molecule-l s-’ for glyoxal and methylglyoxal, respectively. The photolysis rates of glyoxal, methylglyoxal, and biacetyl increased throughout this series, and average quantum yields for the wavelength region 1290 nm of 0.029 f 0.018,0.107 f 0.030, and 0.158 f 0.024 were derived for glyoxal, methylglyoxal, and biacetyl, respectively. In addition, upper limits to the rate constants for the reaction of O3 with glyoxal and methylglyoxal of 340 nm Cp, = 1 for X I340 nm
It can be seen from Table I1 that the observed photolysis rate ratios are significantly less than the calculated maximum values. However, it is also clear from Table I1 that the a-dicarbonyl photodissociation quantum yields at X > 340 nm must be nonnegligible, since the use of = 1 (A 5 340 nm) and CpA = 0 (A > 340 nm) leads to calculated photolysis rate ratios much lower than the observed values. Thus these data show that for glyoxal 295% and for methylglyoxal and biacetyl >99% of the presently observed a-dicarbonyl photodissociation occurs from the
Table 111. Atmospheric Lifetimes of Glyoxal, Methylglyoxal, and Biacetyl due t o Photolysis, Reaction with OH Radicals, and Reaction with 0, photo1 3
-dicarbonyl ha TOH, h b T O 3 , hC glyoxal 5 24 >9x1O4 2 16 >4 x 1 O 4 meth ylglyoxal 1 2900 2 4 x104d biacetyl a At a zenith angle of 0”. At an OH radical concentration of 1 x l o 6 ~ r n - ~ .At an 0, concentration of 1 X lo1* Estimated by analogy with glyoxal and ~ 1 1 7 ‘(40 ~ ppb). methylglyoxal. 01
340-470-nm absorption band and that relaxation processes such as fluorescence or relaxation to the ground state compete significantly with photodecomposition in this wavelength region. The “effective”quantum yields for the photodissociation of the a-dicarbonyls studied here, obtained by dividing the observed photolysis rate ratios by those calculated assuming dA= 1, are given in Table I1 and are 0.03 for glyoxal, 0.11 for methylglyoxal, and 0.16 for biacetyl. Since in general it is expected that will vary with wavelength, these “effective” quantum yields are valid only for the particular spectral distribution used in this study. However, since the spectral distribution of the filtered solar simulator used is similar to that of sunlight in the lower troposphere (15),then the photolysis rate ratios k3/kNO2 observed here can be used with the NO2photodissociation rate constants kNOzto estimate the atmospheric a-dicarbonyl photolysis rates k3. The estimated atmospheric photodecomposition lifetimes for glyoxal, methylglyoxal, and biacetyl are compared in Table I11 with the estimated lifetimes for removal of these species by reaction with OH radicals and with 03. It can be seen that, despite the relatively low “effective” photodissociation quantum yields, the photodissociation lifetimes are appreciably shorter than the lifetimes due to reaction with OH radicals or O3 (the latter reaction being essentially negligible). Photolysis of these a-dicarbonyls is thus clearly their major tropospheric loss process. The formation of peroxyacetyl nitrate (PAN) was observed during the irradiation of methylglyoxal-NO,-air and biacetyl-NO,-& mixtures, showing that in both cases, photodissociation yields, at least partially, CH3C0 radicals: CH3COCHO + hv -.+ CH3CO CHO CH3COCOCH3 + hv 2 CH3CO
+
-
followed by CH3CO + 0 2 CH3CO3 CH3C03 + NO2 + CH&(O)OON02 PAN However, the magnitude of these and other photodissociation pathways were not determined in this work. For glyoxal, the observation of formaldehyde shows that the process (CH0)2 + hv HCHO CO +
-+
+
occurs, with the formaldehyde yield corresponding to approximately 13% of the glyoxal photolyzing via this pathway. (Loss of formaldehyde by photolysis and reaction with OH radicals were minor under the irradiation conditions employed.) Hence the major photodissociation pathway of glyoxal is probably (CHO):! + hv 2CO + H2 as has been discussed recently (19). +
While obviously further work is needed concerning the photodissociation pathways and wavelength-dependent quantum yields for the region >290 nm, the present data concerning the photodissociation rates and OH radical rate constants are important and necessary inputs to chemical kinetic computer modeling studies of the aromatic hydrocarbons and of isoprene. In particular, this work indicates that the photolysis rate of methylglyoxal, a critical parameter in NO,-air photooxidation chemical computer models for toluene and other aromatics ( 4 , 6) is significantly lower than has been previously assumed (thus the present photolysis rate ratio of k3/kNo2 = 0.019 f 0.005 can be compared to the previously assumed ratios of -0.045 (6) and 0.15 ( 4 ) ) . Thus it is obvious that all present chemical computer models of the aromatic--NO,-air systems need to be reevaluated in the light of these present data. Acknowledgments We thank Sara M. Aschmann for carrying out the gas chromatographic analyses and William D. Long for assistance in conducting the chamber experiments. Supplementary Material Available Table A, listing the absorption cross sections for glyoxal, meill appear following these pages thylglyoxal and biacetyl(3 pages) w in the microfilm edition of this volume of the journal. Photocopies of the supplementary material from this paper or microfiche (105 X 148 mm, 24X reduction, negatives) may be obtained from Distribution Office, Books and Journals Division, American Chemical Society, 1155 16th St., NW., Washington, DC 20036. Full bibliographic citation (journal, title of article, author, page number) and prepayment, check or money order for $6.00 for photocopy ($8.00 foreign) or $6.00 for microfiche ($7.00 foreign), are required. Registry No. Og,10028-15-6;OH radical, 3352-57-6; glyoxal, 107-22-2; methylglyoxal, 78-98-8; biacetyl, 431-03-8.
Literature Cited (1) Nojima, K.; Fukaya, K.; Fukui, S.;Kanno, S. Chemosphere 1974,5, 247-252. (2) Darnall, K. R.; Atkinson, R.; Pitta, J. N., Jr. J. Phys. Chem. 1979,83, 1943-1946. ( 3 ) Takagi, H.; Washida, N.; Akimoto, H.; Nagasawa, K.; Usui, Y.; Okuda, M. J. Phys. Chem. 1980,84, 478-483. (4) Atkinson, R.; Carter, W. P. L.; Darnall, K. R.; Winer, A. M.; Pitta, J. N., Jr. Int. J. Chem. Kinet. 1980,12,779-836. ( 5 ) Besemer, A. C. Atmos. Enuiron. 1982, 16, 1599-1602. (6) Killus, J. P.; Whitten, G. 2. Atmos. Enuiron. 1982, 16, 1973-1988. (7) Zimmerman, P. R.; Chatfield, R. B.; Fishman, J.; Crutzen, P. J.; Hanst, P. L. Geophys. Res. Lett. 1978,5, 679-682. (8) Lloyd, A. C.; Atkinson, R.; Lurmann, F. W.; Nitta, B. Atmos. Enuiron., in press. (9) Pate, C. T.; Atkinson, R.; Pitts, J. N., Jr. J . Enuiron. Sci. Health 1976, A l l , 1-10. (10) Atkinson, R.; Aschmann, S. M.; Winer, A. M.; Pitts, J. N., Jr. Znt. J. Chem. Kinet. 1981,13, 1133-1142. (11) Kleindeinst, T. E.; Harris, G. W.; Pitts, J. N., Jr. Environ. Sci. Technol. 1982, 16, 844-846. (12) Kyle, K.; Orchard, S. W. J. Photochem. 1977, 7, 305-317. (13) Atkinson, R.; Aschmann, S. M.: Winer, A. M.: Pitts. J. N.. Jr. Int. J . Chem. Kinet. 1982, 14, 507-516. (14) Atkinson, R.; Aschmann, s. M.; Carter, w. p. L.; Winery A. M. Int. J. Chem. Kinet. 1982,14,919-926. (15) Winer, A. M.; Graham, R. A.; Doyle, G. J.; Bekowies, P. J.; McAfee, J. M.; Pitts, J. N., Jr. Adu. Enuiron. Sci. Technol. 1980, 10, 461-511. (16) Platt, U.; Perner, D.; Patz, H. W. J. Geophys. Res. 1979, 84,6329-6335. (17) Coveleskie, R. A.; Yardley, J. T. J . Am. Chem. SOC.1975, 97, 1667-1672. Environ. Sci. Technol., Vol. 17, No. 8, 1983
483
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(18) Atkinson, R.; Aschmann, S. M.; Carter, W. P. L. Znt. J . Chem. Kinet. 1983,15, 51-61. (19) Osamura, Y.; Schaefer, H. F., 111; Dupuis, M.; Lester, W. A., Jr. J . Chem. Phys. 1981, 75,5828-5836. (20) Atkinson, R.; Pitts, J. N., Jr. J . Chem. Phys. 1978, 68, 3581-3584. (21) Stief, L. J.; Nava, D. F.; Payne, W. A.; Michael, J. V. J . Chem. Phys. 1980, 73, 2254-2258. (22) Atkinson, R.; Lloyd, A. C. J . Phys. Chem. Ref. Data, in
press.
(23) Evaluation No. 5, NASA Panel for Data Evaluation, Jet Propulsion Laboratory, Pasadena, JPL Publication 82-57, July 1982. (24) Calvert, J. G.;Pitts, J. N., Jr. “Photochemistry”;Wiley: New York, 1966.
Received for review December 17,1982. Accepted March 7,1983. We gratefully acknowledge the financial support of the California Air Resources Board Contract A1 -030-32.
Mass Transfer of Volatile Organic Contaminants from Aqueous Solution to the Atmosphere during Surface Aeration Paul V. Roberts” Department of Civil Engineering, Stanford University, Stanford, California 94305
Paul G. Dandllker Balzari and Schudei, 3000 Bern, Switzerland
rn The transfer of six organic compounds and of oxygen from aqueous solution to the atmosphere was studied by using an agitated vessel contactor. The transfer rate constants were measured under conditions of controlled energy input in the range P/ V = 0.8 to 320 W/m3. The data were interpreted on the basis of the assumption of liquid-phase control. The transfer rate constants, KLa, were proportional to power input in the turbulent regime. Transfer rate constants for the organic compounds were approximately 60% as great as that of oxygen, independent of power input. The ratio of the individual phase-transfer coefficients was inferred to be kG/kL 25 in the turbulent regime. Under the conditions of these experiments, the customary criterion for neglecting the gas-phase resistance must be reassessed.
Introduction Contamination of water supplies by synthetic organic chemicals is a problem of increasing concern in water supply. Particularly, halogenated organic substances are recognized as a threat to public health that in some instances must be dealt with by removing the chemicals from water supplies through suitable treatment. Many of the halogenated compounds of health concern are known to partition from water to air, owing to their hydrophobic behavior in aqueous solution (1-3). Hence, transfer to the atmosphere by air-water contact represents a convenient and possibly cost-effective treatment method for removing volatile compounds (4-7). Numerous previous stydies have shQwn that the equilibrium is favorable for transfer of halogenated organics to the atmosphere (1-3) and that the transfer proceeds at an appreciable rate (2, 3, 5, 8-10). Moreover, it has been observed that volatile organic contaminants are transferred to the atmosphere from natural water bodies at substantial rates (11). In this paper a methodology is demonstrated that is useful for quantifying the transfer rates of volatile organic contaminants from an agitated tank to the atmosphere. The methodology consists of comparing the overall liquid-phase transfer rate constants (KLa)of the individual compounds with one another and with that of oxygen, under conditions of controlled energy input. Methods The aeration device (Figure 1)consisted of a cylindrical glass vessel open to the atmosphere. The stirrer speed was 484
Environ. Sci. Technol., Vol.
17, NO. 8, 1983
adjusted by means of a voltage regulator and monitored by means of an electronic counter. The impeller was a compound device comprised of a ring-guarded turbine with three upward-curved blades (75-mm diameter) positioned at the water surface and a flat-bladed paddle (90-mm diameter) positioned at the bottom of the vessel. This design manifested a practical compromise to achieve two objectives: intense disturbance of the air-water interface to promote mass transfer as is typical in water and wastewater treatment, and thorough mixing of the vessel contents to assure representative liquid samples. The power input to the stirrer was measured with an in-line torque meter (Bex-0-Meter, Model 38) that was installed on the shaft between the motor and the stirrer. The torque was read from a calibrated scale, with a stroboscopic light, while the instrument was rotating. The power input P (W) was calculated from the measured torque 7 (J) and the impeller speed N (s-l) by using the relation
P = 2mN
(1)
It was observed that the torque depended strongly on the rotational speed, with the result that the calculated power input P increased approximately in proportion to W.15(1.2 = 0.99), as shown in Figure 2. The experiments were conducted within a forced-draft exhausting fume hood. The continuous removal of air (0.4 m3/s) prevented accumulation of organic compounds in the air above the water surface. The air velocity in the vicinity of the aeration vessel was approximately 0.5 m/s. Water for the mass-transfer experiments was purified by passing tap water through a Milli-Q reagent grade water system. The product water had the following characteristics: TOC, 0.25 mg/L; turbidity, 0.1 TU; electrical conductance, 0.8 pS. The volume of water was 7.3 L in all experiments reported here. After the water had been equilibrated to a constant temperature of 20 f 1 “C, the oxygen was purged from the system by bubbling nitrogen through the vessel. Thereafter the reactor was spiked with a solution of the following six compounds: Freon-12, CC12F2;chloroform, CHC13; l,l,l-trichloroethane, CH3CC13;carbon tetrachloride, CC1,; trichloroethylene, CHC1=CC12; tetrachloroethylene, CC12=CC1,. Their properties are summarized in Table I. These six compounds were chosen because their Henry’s constants cover a range of nearly 3 orders of magnitude,
0013-936X/83/09 17-0484$01.50/0
0 1983 American Chemical Society
