Environ. Sci. Technol. 1992, 26, 1798-1807
Smith, E. C.; Metzler, D. E. J. Am. Chem. SOC.1963,85, 3285-3288. Fritz, B. J.; Kasai, S.; Matsui, K. Photochem. Photobiol. 1987, 45, 113-117. Fritz, B. J.; Matsui, K.; Kasai, S.; Yoshimura, A. Photochem. Photobiol. 1987, 45, 539-541. Holmstrom, B.; Oster, G. J. Am. Chem. Soc. 1961, 83, 1867-1871. Ishikawa, M.; Fukuzumi, S.; Tanii, K. Chem. Lett. 1989, 2189-2192. Fukuzumi, S.; Tanii, K.; Tanaka, T. J. Chem. Soc., Perkin Trans. 2 1989, 2103-2108. Tamao, K.; Hayashi, T.; Ito, Y. J. Chem. SOC.,Chem. Commun. 1988,795-797. Fukuzumi, S.; Tanii, K.; Tanaka, T. J . Chem. Soc., Chem. Commun. 1989,816-818. McCormick, D. B. J . Heterocycl. Chem. 1970, 7,447-450. Yagi, K.; Okuda, J.; Dmitroviskii, A. A.; Honda, R.; Matsubara, T. J. Vitaminol. 1961, 7, 276-280. Keller, P. J.; Van, Q. L.; Bacher, A.; Floss, H. G. Tetrahedron 1983,39,3471-3481. Moonen, C. T.; Vervoort, J.; Muller, F. Biochemistry 1984, 23,4859-4867.
(17) Fukuzumi, S.; Tanaka, T. In Photoinduced Electron Transfer,1st ed.; Fox, M. A,, Chanon, M., Eds.; Elsevier: New York, 1988; Vol. 3, Chapter 4, pp 636-687. (18) Goodgame, M.; Johns, K. W. Inorg. Chim. Acta 1979,34, 1-4. (19) Halwer, M. J. Am. Chem. SOC.1951, 73, 487@-4874. (20) Gould, E. S. Mechanism and Structure in Organic Chemistry; Holt, Rinehart, and Winston: New York, 1959; pp 220-227. (21) Zepp, R. G.; Cline, D. Environ. Sci. Technol. 1977, 11, 359-366. (22) Moore, W. M.; McDaniels, J. C.; Hen, J. A. Photochem. Photobiol. 1977, 25, 505-512. (23) Hayase, K.; Zepp, R. G. Environ. Sei. Technol. 1991,25, 1273-1279. Received for review October 23, 1991. Revised manuscript received April 7, 1992. Accepted May 21, 1992. We thank the Illinois Department of Energy and Natural Resources, Hazardous Waste Research and Information Center, for financial support and the Molecular Spectroscopy and Mass Spectrometry Laboratories, School of Chemical Sciences, University of Illinois, for use of equipment and assistance.
Gas-Phase Atmospheric Chemistry of Selected Thiocarbamates Erlc S. C. Kwok,? Roger Atklnson,*,$ and Janet Arey*s$
Statewide Air Pollution Research Center, University of California, Riverslde, California 9252 1 The kinetics and products of the gas-phase reactions of OH radicals, NO, radicals, and 0,with the thiocarbamates S-methyl N,N-dimethylthiocarbamate (MDTC), S-ethyl N,N-dipropylthiocarbamate(EPTC), and S-ethyl N-cyclohexyl-N-ethylthiocarbamate(cycloate) have been studied at 298 f 2 K and -735 Torr air. By use of relative rate techniques, all three thiocarbamates were observed to react with OH and NO, radicals, with the following respective reaction rate constants (in cm3 moland 7.3 X EPTC, ecule-l &): MDTC, 1.33 X 3.18 X and 9.2 X cycloate, 3.54 X and 3.29 X 10-14. No reactions with 0,were observed, and upper limits to the rate constants (cm3molecule-l s-l) were determined: MDTC, ~ -kSH, , and k+, for OH radical interaction witk N and S atoms in the amines and organosulfur compounds are available (15,16), the NC(0)S group in the thiocarbamates should be viewed as a single group, since it is expected that the C=O group will deactivate the N and S atoms toward OH radical addition. Using this formulism, the overall rate constant for EPTC [ (CH3CHzCH,)2NC(0)SCH,CH3] is given by koverdl = 3kprimF(CH2) + ~~S~$'(CH~)J'(CHZ) + 21zae$(CHz)F(NC(0)S) + k,e$'F(CH,)F(SC(O)N) + kNC(0)S
and similarly for MDTC and cycloate. Using rate Constants kprim,k,,, and kkt at 298 K of (in 10-'2 cm3molecule-l s-l) 0.144,0.838, and 1.83, respectively, and substituent factors at 298 K of F(CH3) = 1.00 and F(CH,) = F(CH) = 1.29 (15),then three equations relating
F(NC(O)S), F(SC(O)N), and lzNC(0)S are obtained. Unfortunately, the experimental data do not allow for an accurate differentiation of F(NC(0)S) and F(SC(0)N). However, on the basis of previous substituent factors of F(>N-) -10 and F(-S-) -9 (15,16),it may be expected that F(NC(0)S) F(SC(0)N). With this assumption and minimizing the s u m of the squares of the percentage errors, a unit-weighted nonlinear least-squares analysis of the MDTC, EPTC, and cycloate OH radical reaction rate constants yields values of
react with O2 rather than undergoing unimolecular decomposition:
-
cm3 molecule-l s-l
kNC(0)S= 1.18 X and
F(NC(0)S) = F(SC(0)N) = 4.2 Using these parameters, the measured and calculated OH radical reaction rate constants for MDTC, EPTC, and cycloate agree to within 15%. These parameters allow rate constants for the gas-phase reactions of the OH radical and, hence the atmospheric lifetimes, for other thiocarbamates for which no experimental data presently exist to be calculated with a reasonable degree of reliability. OH and NO3Radical Reaction Mechanisms. On the basis of the above discussion dealing with the calculation of OH radical reaction rate constants and consideration of the products observed and their yields, the OH radical reaction with MDTC can proceed by H atom abstraction from the various C-H bonds or OH radical addition to the N or S atom on the NC(0)S group. The majority (-85%) of the reaction is estimated to proceed by initial OH radical addition to the NC(0)S group, which must then be followed by an overall H atom abstraction:
II
This overall reaction process accounts for 86 f 14% of the overall OH radical reaction for MDTC, and no other products were observed. The initial reactions in the NO3 radical reaction with MDTC must be analogous to those for the OH radical reaction. Since peroxy radicals are not expected to be converted to alkoxy radicals by reaction with NO in N205-N03-N02-air mixtures (because of the rapid reaction of NO with NO3 radicals) the peroxy radical OOCH2(CH3)NC(0)SCH3must be efficiently converted to the alkoxy radical OCH2(CH3)NC(0)SCH3under our experimental conditions, presumably by self-reaction. The OH radical reaction with EPTC appears to proceed in large part by a similar mechanism, with the C3H7(CHO)NC(0)SC2H, product being formed by + H 2 0 + C H
3 ,1
.
0
I1
/NCSC2HS
C2HSCH
I
1
0
OH + ( C H ) NCSC2H5 II
3 1 2
,r
followed by
I CH H20 +
0 II
2,
/NCSCH3 CH3
to yield mainly the CH,(CH,)NC(O)SCH, radical (from pathway b and/or pathway c). In air in the presence of NO, the following reactions are then expected to occur. CH 0 2,N,CSCH3II
+ O2
CH3
*\
OOCH
/ CH3
+
C H
OOCH S>!CH,
3
OCH
1 I
NCSCH3 + NO
+
7
/ C2H5FH 0.
CH3
0
with this product accounting for -30-50% of the overall reaction products in both the OH and NO3 radical reactions with EPTC. The absence of C3H7(C2H,C(0))NC(O)SC2H5 (product B) as a product of the OH radical-initiated reaction of EPTC in the presence of NO, shows that the intermediate alkoxy radical
NO2 +
CH3
This OCH2(CH3)NC(0)SCH3alkoxy radical must then
4
NCSC2H5
undergoes unimolecular decomposition rather than reacting with O2 at atmospheric pressure of air and 298 K. However, product B is observed from the NO3 radical reaction with EPTC. As noted above, peroxy radicals are not expected to be converted to alkoxy radicals by reaction with NO in N205-N03-N02-air mixtures. However, the Environ. Sci. Technol., Vol. 26, No. 9, 1992
1805
A
144
loo)
80-
z
9
40
20
0
80
60 60
40
100
140
I20
I60 160
Table VI. Calculated Lifetimes of MDTC, EPTC, and Cycloate in the Troposphere with Respect to Photolysis and Gas-Phase Reaction with OH and NO3 Radicals and O3 thiocarbamate
OH"
MDTC EPTC cycloate
1.2 days 5.8 h 5.2 h
lifetime due to reaction with NOSb 03c photolysisd 6.3 days 5.0 days 1.4 days
>1.1 y >125 days >55 days
>8 h >8 h
24.5 h
"For a 12-h-average daytime OH radical concentration of 1.5 X lo6 molecule ~ r n (32). - ~ *For a 12-h-averagenighttime NO3 radical concentration of 5 x IOs molecule cm-3 (12). CFora 24-h-average O3 concentration of 7 X 10" molecule cm-3 (33). dFor a light intensity corresponding to a 12-h-average NOz photolysis rate of 5.2 X s d (23),with a black lamp spectral distribution (23).
MASS/CHARGE
Conclusions The three thiocarbamates studied all react with OH and NO, radicals in the gas phase, but not with 0,. The dominant atmospheric reaction is calculated to be by reaction with the OH radical, leading to lifetimes of EPTC and cycloate in the troposphere of a few hours. The experimentally determined OH radical reaction rate constants have been used to extend the empirical estimation technique of Atkinson (15)to allow the OH radical reaction rate constants, and hence atmospheric lifetimes, of other thiocarbamates to be calculated. The products observed provide insight into the reaction mechanisms and for the OH radical reactions are generally consistent with the reaction pathways as predicted by the estimation method.
16-
FREQUENCY (crn-l)
Acknowledgments
Flgure 9. (A) Mass spectrum and (B) I R spectrum of the product observed from the gas-phase reaction of cycloate with the OH radical In the presence of NO,.
formation of both products can be rationalized by the self-reaction of the peroxy radicals 2
w
C3H7,
/
NCSC2H5
-
C H
3 7\
2
ical), 3352-57-6; NO3 (radical), 12033-49-7; cycloate, 1134-23-2.
0 I1
/NCSC2H5
C2H5FH
+
O2
'2'5YH
C H
3 7\
2
0
I1
HC/NCSC2H5 11
0
C3H7, 2
fl
/NCSC2H5 C2H5FH
0
OH
(B)
although the anticipated coproduct to B was not observed. Similar reaction pathways can occur between nonidentical peroxy radicals (14). The only product tentatively identified from the OH radical reaction with cycloate [C,H5(CHO)NC(0)SC2H5] suggests that this product occurs after cleavage of the cyclohexyl ring, by pathways which are not fully understood at the present. 1806
Envlron. Scl. Technol., Vol. 26, No. 9, 1992
We gratefully thank IC1 Americas, Inc., for the generous synthesis of (CH,),NC(O)SCH,, CH,(CHO)NC(O)SCH,, and C3H7(CHO)NC(0)SC2H5 and for supplying samples of EPTC and cycloate. Registry No. MDTC, 3013-02-3; EPTC, 759-94-4; HO (rad-
Literature Cited Bidleman, T. F. Environ. Sci. Technol. 1988,22,361-367. Arey, J.; Zielinska, B.; Atkinson, R.; Winer, A. M. Atmos. Environ. 1987, 21, 1437-1444. Coutant, R. W.; Brown, L.; Chuang, J. C.; Riggin, R. M.; Lewis, R. G. Atmos. Environ. 1988,22, 403-409. Atkinson, R.; Arey, J.; Winer, A. M.; Zielinska, B.; Dinoff, T. M.; Harger, W. P.; McElroy, P. A. A survey of ambient concentrations of selectad polycyclic aromatic hydrocarbon (PAH) at various locations in California. Final Report to California Air Resources Board, Contract No. A5-185-32, Sacramento, CA, May 1988. Spencer, W. F.;Cliath, M. M. In Long Range Transport of Pesticides;Kurtz, D. A., Ed.; Lewis Publishers: Chelsea, MI, 1990; Chapter 1. Nash, R. G.; Hill, B. D. In Long Range Transport of Pesticides;Kurtz, D. A., Ed.; Lewis Publishers: Chelsea, MI, 1990; Chapter 2. Clendening, L. D.; Jury, W. A.; Ernst, F. F.In Long Range Transport of Pesticides; Kurtz, D. A., Ed.; Lewis Publishers: Chelsea, MI, 1990; Chapter 4. Woodrow, J. E.; McChesney, M. M.; Seiber, J. N. In Long Range Transport of Pesticides; Kurtz, D. A., Ed.; Lewis Publishers: Chelsea, MI, 1990; Chapter 5. Strachan, W. M. J.; Eisenreich, S. J. In Long Range Transport ofPesticides;Kurtz, D. A., Ed.; Lewis Publishers: Chelsea, MI, 1990; Chapter 19. Atkinson, R. Atmospheric transformations of automotive emissions. In Air Pollution, the Automobile, and Public Health; Watson, A. Y., Bates, R. R., Kennedy, D., Eds.; National Academy Press: Washington, DC, 1988; pp 99-132.
Environ. Sei. Technol. l W 2 , 26, 1807-1815
Atkinson, R. J. Phys. Chem. Ref. Data 1989, Monograph 1, 1-246. Atkinson, R. J. Phys. Chem. Ref. Data 1991,20,459-507. Atkinson, R.; Carter, W. P. L. Chem.Rev. 1984,84,437-470. Atkinson, R. Atmos. Environ. 1990,24A, 1-41. Atkinson, R. Znt. J. Chem. Kinet. 1987, 19, 799-828. Atkinson, R. Environ. Toxicol. Chem. 1988, 7, 435-442. Goodman, M. A.; Aschmann, S. M.; Atkinson, R.; Winer, A. M. Arch. Environ. Contam. Toxicol. 1988,17,281-288. Goodman, M. A.; Aschmann, S. M.; Atkinson, R.; Winer, A. M. Environ. Sci Technol. 1988, 22, 578-583. Winer, A. M.; Atkinson, R. In Long Range Transport of Pesticides; Kurtz, D. A., Ed.; Lewis Publishers: Chelsea, MI, 1990; Chapter 9. Atkinson, R. Sei. Total Environ. 1991, 104, 17-33. Worthing, C. R. The Pesticide Manual, 8th ed.; The British Crop Protection Council: Croyden, UK, 1987;pp 201,341. Atkinson, R.; Aschmann, S. M. Znt. J. Chem. Kinet. 1988, 20,513-539. Atkinson, R.; Aschmann, S. M.; Arey, J.; Zielinska, B.; Schuetzle, D. Atmos. Environ. 1989, 23, 2679-2690. Arey, J.; Atkinson, R.; Aschmann, S. M.; Schuetzle, D. Polycyclic Aromat. Compd. 1990, 1, 33-50.
Atkinson, R.; Plum, C. N.; Carter, W. P. L.; Winer, A. M.; Pitts, J. N., Jr. J. Phys. Chem. 1984, 88, 1210-1215. Atkinson, R.; Aschmann, S. M.; Pitts, J. N., Jr. J. Phys. Chem. 1988,92, 3454-3457. Japar, S. M.; Wu, C. H.; Niki, H. J.Phys. Chem. 1976,80, 2057-2062. Arey, J.; Atkinson, R.; Aschmann, S. M. J. Geophys. Res. 1990, 95, 18539-18546. Taylor, W. Do;Allston, T. D.; Moscato, M. J.; Fazekas, G. B.; Kozlowski, R.; Takacs, G. A. Znt. J . Chem. Kinet. 1980, 12, 231-240. Scanlon, J. T.; Willis, D. E. J. Chromatogr. Sei. 1985,23, 333-340. Atkinson, R.; Aschmann, S. M.; Carter, W. P. L.; Winer, A. M.; Pitts, J. N., Jr. J. Phys. Chem. 1982,86,4563-4569. Prinn, R.; Cunnold, D.; Rasmussen, R.; Simmonds, P.; Alyea, F.; Crawford, A.; Fraser, P.; Rosen, R. Science 1987, 238, 945-950. (33) Logan, J. A. J. Geophys. Res. 1985,90, 10463-10482.
Received for review April 13,1992. Accepted May 28,1992. This research was supported by ZCI Americas, Znc. through Project Y6-23009-CH (Project Officer Dr. C. K . Tseng).
Dry Deposition of Atmospheric Particles: Application of Current Models to Ambient Data Thomas M. Holsen" and Kenneth E. Noll
Pritzker Department of Environmental Engineering, Illinois Institute of Technology, Chicago, Illinois 60616 The dry deposition mass flux for atmospheric particles was calculated as a function of particle size (mass-flux size distribution). The mass-flux size distribution increased rapidly with particle size with the majority of the calculated flux due to particles larger than 1pm (>go%). The evaluation of dry deposition was based on (1)atmospheric mass-ize distributions between 0.01 and 100 pm diameter obtained from field measuremenh with a cascade impactor and a Noll rotary impactor (NRI) and data in the literature obtained with a wide-range aerosol classifier (WRAC) system, (2) field dry deposition sampling data using a surrogate swface, and (3) dry deposition calculations based on various models that estimate dry deposition velocity as a function of particle size. Results of model calculations using the atmospheric particle size distribution data were compared to measured flux data to show that realistic estimates can be made for the total dry deposition flux. Calculations using models that account for particle size distribution show that results are extremely sensitive to the mass of large particles and that large particles control dry deposition flux due to their high deposition velocities. Current dry deposition modeling techniques that use average particle concentrations and average deposition velocities underestimate the contribution of coarse particles to dry deposition and therefore underestimate dry deposition. Introduction Even though an accurate determination of the dry deposition of contaminslnts is critical in understanding their movement in the environment, there is still no generally acceptable technology for sampling and analyzing dry deposition flux (1-7). The quantification of dry deposition flux is difficult because of large spatial and temporal variations. The use of a surrogate surface to collect dry deposition is a technique that allows a comparison to be 0013-936X192/0926-1807$03.00/0
made of measured and modeled data because it can be used to directly assess deposited material. Surrogate surfaces can be used (1)over extended periods of time and at different locations to provide qualitative information on temporal and spatial variations in dry deposition of a species, (2) to estimate lower limits of aerosol dry deposition to rougher, natural surfaces if they are smooth horizontal collectors that do not appreciably disturb airflow, and (3) as research instruments for investigating the influence of surface geometry, atmospheric properties, and characteristics of the depositing species on dry deposition (3). Dry deposition modeling studies typically use micrometeorological techniques such as eddy correlation, eddy accumulation, and gradients; however, these techniques cannot be reliably applied to larger particles influenced by sedimentation (3). Recent work in our laboratory and by others has shown that pollutants associated with these larger particles can be responsible for an appreciable fraction of the total dry deposition flux. For example Davidson and Friedlander (8) found that in Los Angeles the total mass dry deposition of P b is dominated by sedimentation of the small fraction of large airborne Pbcontaining particles. PCBs in dry deposition near urban areas of Lakes Huron and Michigan have also been found to be associated with large particles (9, 10). Davidson et al. (3) demonstrated that dry deposition of supermicron sulfur-containing particles may be responsible for an appreciable fraction of the total sulfur dry deposition in spite of the relatively large fraction of submicron sulfate in the atmosphere. Studies over the western Mediterranean and North Sea have shown that large mineral aerosol particles dominate the dry deposition flux (11, 12). These large atmospheric particles make up one of the three size modes of atmospheric particles, each of which is usually considered to be log-normally distributed. The
0 1992 American Chemical Society
Environ. Sci. Technoi., Vol. 26, No. 9, 1992
1807
