Environ. Sci. Technol. 1988, 22, 952-956
Kitto, A.-M. N.; Harrison, R. M., unpublished data. Harrison, R. M.; Pio, C. A. Tellus 1983, 35B. Rapsomanikis, S.; Weber, J. H. Environ. Sci. Technol. 1985, 19, 352-356. Miller, S. C.; Miller, S. N. Statistics for Analytical Chemistry; Horwood: Chichester, U.K., 1984.
(18) Yamamoto, N.; Nakazuka, E.; Shirai, T. Nippon Kagaku Kaishi 1981,8, 1226-1230. Received for review August 25,1986. Accepted February 2, 1988. Supported by the U.K. Natural Environment Research Council.
Borohydride, Micellar, and Exciplex-Enhanced Dechlorination of Chlorobiphenyls Gary A. Epling,” Emily M. Florio, Andre J. Bourque, Xhi-Hong Qlan, and James D. Stuart Department of Chemistry, University of Connecticut, Storrs, Connecticut 06268
The photodechlorination of polychlorinated biphenyls (PCB’s) has been studied in the presence of sodium borohydride, detergents, and exciplex-forming additives. In a family of 13 representative PCB’s these variations generally led to a dramatically increased rate of photodegradation. Further, the products of photoreaction in the presence of sodium borohydride are more cleanly the simple dechlorinated aromatics, with fewer side reactions than observed with ordinary photolysis.
Introduction Since their introduction decades ago polychlorinated biphenyls (PCB’s) have been widely used throughout the world. However, the property of exceptional stability that made them useful has also created a serious environmental problem. Because of these environmental concerns, the development of methods for destruction and disposal of PCBs has been an area of intense study (1). As with other haloaromatic compounds (2),one method of detoxification that has been given attention is photodestruction (3,4). Irradiation of aromatic halides causes a light-induced cleavage of the halogen ( 5 ) . However, the utility of photolysis for destruction of PCB’s is limited by two major disadvantages. First, the “quantum efficiency” (the statistical number of molecules which react per photon of light absorbed) is extremely low for many congeners (6-11). The quantum yield is usually particularly low in those compounds lacking an ortho chlorine but bearing meta or para substituents and also many of the highly chlorinated biphenyls. Unfortunately, these may be the more toxic compounds (12). Further, side reactions commonly lead to formation of other undesired materials, including hydroxy chlorobiphenyls and even the more toxic chlorinated dibenzofurans (13). Hence, modification of the “normal” photoreaction paths of PCB’s in a manner that overcomes these deficiencies could potentially be of practical value. In a preliminary communication we reported (14) that the quantum yield of photoreaction of a group of four chlorobiphenyls was greatly increased when sodium borohydride was present during photolysis. We have expanded our study to include a wide variety of chlorobiphenyls (including some highly chlorinated congeners) and now report that the enhanced photoreactivity previously communicated appears to be general for a wide range of substitution patterns and heavily chlorinated compounds. The enhancement in reaction rate is most pronounced with those compounds that ordinarily are the most photostable. Another gratifying observation is that the photoreactions are cleaner in the presence of borohydride, leading to photoreduction without side reactions of photosubstitution involving solvent. 952
Environ. Sci. Technol., Vol. 22, No. 8, 1988
We further have examined the effect of detergent solutions and exciplex-forming additives on photoreaction. These variations also lead to enhancement of the rate of photodechlorination. The enhancement in micelles appears particularly promising as a modification that successfully tolerates the presence of water.
Experimental Section Materials. Chlorobiphenyls were obtained from Aldrich Chemical Co. (Milwaukee, WI), Foxboro/Analabs (North Haven, CT), and Ultra Scientific (Hope, RI) or synthesized by established methods (15). Commercial samples were generally of satisfactory purity as received; exceptions were vacuum distilled or recrystallized prior to use. Acrylonitrile (Aldrich) was freshly distilled prior to use. Sodium borohydride was obtained from Fisher Scientific. Other materials (scavengers and quenchers) were obtained from Aldrich and used as received. Irradiations. Solutions of ca. 0.003-0.02 M (depending on solubility and photoreactivity) of the halide, usually in 9:l acetonitrile/water, were prepared using Baker Photrex acetonitrile and deionized water that was further purified by using a cartridge purification system (Barnstead Dual-cartridge system, equipped with ion exchange and organic removal cartridges). Irradiations used an Osram HNS W/U OFR mercury lamp, an Applied Photophysics Model RS-50 semi-micro photochemical reactor, or a Rayonet RPR-100 chamber reactor, equipped with RPR2537 lamps. The spectral output of all these low-pressure mercury lamps was principally at 254 nm, which is close to the K band A,, for chlorobiphenyls (16). Benzophenone/benzpinacol actinometry was used to establish the light output of the lamps. Irradiations in the presence of sodium borohydride typically contained from 0.2 to 0.4 M sodium borohydride. In most of the experiments the solutions were purged with nitrogen for 10 min, and then blanketed with nitrogen during the photolysis to exclude oxygen. However, oxygen was found to have little effect on the rate of photoreaction; similar results were obtained when the solutions were stoppered with a Teflon stopper and irradiated with an initial oxygen concentration that was in equilibrium with air. Quantification. The extent of photolysis was quantified by HPLC or GC. HPLC analysis utilized an IBM Instruments ternary gradient HPLC equipped with an octadecyl-bonded silica column, 4.5 X 250 mm, packed with 5 ym size particles. Typically, 7:3 acetonitrile/water was used as the eluent, though higher percentages of acetonitrile were used with some of the more highly chlorinated compounds. Gas chromatography used a Perkin-Elmer Sigma 4 chromatograph equipped with a thermal con-
0013-936X/88/0922-0952$01.50/0
@ 1988 American Chemical Society
~
~~
Table I. Sodium Borohydride Enhanced Dechlorination of Chlorobiphenyls 0,with
borohydride
compound
2a
3e
4 0
50
60
70
Figure 1. Separation of a mixture of 11 PCB’s by capillary column gas chromatography. Initial column temperature of 50 OC for 3 min, followed by a temperature program at 3 OC min-‘ to 250 O C .
ductivity detector and an OV-1 column or a HewlettPackard 5980A chromatograph equipped with a crosslinked methyl silicone gum capillary column, 12 m X 0.2 mm. This chromatograph was connected to a Model 5970B mass selective detector, allowing GC/MS analysis of photolysates. In each case, the average of duplicate or triplicate injections was used in the quantitation of the percent reaction. Temperature programming allowed excellent separation of the many isomers and congeners involved in this work, as exemplified by Figure 1which shows the separation of a mixture of 2-chlorobiphenyl (l),4chlorobiphenyl (2), 2,4-dichlorobiphenyl (3), 2,4,6-trichlorobiphenyl (4), 2,2’,4,6-tetrachlorobiphenyl (5), 2,2’,3’,4,5-pentachlorobiphenyl (6), 2,2’,3,4,5,6-hexachlorobiphenyl(7),2,2‘,3,4,4‘,5’,6-heptachlorobiphenyl(8), 2,2’,3,3‘,5,5’,6,6’-octachlorobiphenyl (9), 2,2’,3,3’,4,4’,5,6,6’-nonachlorobiphenyl ( l o ) , and 2,2’,3,3’,4,4’,5,5’,6,6’-decachlorobiphenyl (11) to demonstrate the chromatographic separation. Products. Products were determined by isolation (column chromatography) followed by NMR analysis of the isolated materials, or by GC/MS analysis, comparing the retention time and mass spectra with those of authentic materials. The excellent mass balance found upon isolation of products from borohydride-enhanced photolysis established that highly polar or polymeric products were not formed. This was not observed in “normal”photolyses, where significant material losses were evident upon chromatography. Typically, a “large-scale” photolysis of 4,4‘-dichlorobiphenyl used 223 mg of 4,4‘-dichlorobiphenyl, 2.0 g of sodium borohydride, and 75 mL of 9:l acetonitri1e:water. Irradiation for 120 min using the Osram lamp, with continual stirring by a stream of nitrogen gas, led to near-total reaction as determined by HPLC (1.7% of the 4,4’-dichlorobiphenyl remained). The excess borohydride was quenched by the cautious addition of 5 % phosphoric acid. The solution was diluted with 500 mL of water and extracted 4 times with hexane. The organic solution was dried (anhydrous sodium sulfate) and concentrated to a volume of ca. 10 mL and then chromatographed by flash chromatography using 50 g of silica gel (Merck 9385,230-400 mesh), eluting with EM Omnisolv pentane, to give 162 mg (86%) of 4-chlorobiphenyl and 12.3 mg (8%) of biphenyl, confirmed by 270 MHz proton NMR.
Results and Discussion Enhancement of Photodechlorination by Sodium Borohydride. The photodechlorination of many of the isomers of the PCB’s has been examined. There is a considerable range in the photoreactivity. 2-Chlorobiphenyl was reported (6) to react with a quantum efficiency of 0.39. However, 4,4’-dichlorobiphenyl (0.0006),
2-chlorobiphenyl 0.11 3-chlorobiphenyl 0.082 4-chlorobiphenyl 0.037 3,5-dichlorobiphenyl 0.23 4,4’-dichlorobiphenyl 0.050 0.072 2,4,4/-trichlorobiphenyl 0.39 2,5,3’-trichlorobiphenyl 0.23 2,4,2’,4/-tetrachlorobiphenyl 2,5,2/,5/-tetetrachlorobiphenyl 0.14 0.099 3,5,3/,5’-tetrachlorobiphenyl 2,3,4,5,6-pentachlorobiphenyl 0.27 2,3,4,5,6,3/-hexachlorobiphenyl 0.54 2,4,6,2’,4/,6’-hexachlorobiphenyl0.76 100
0,without enhanceboroment hydride ratio
0.11 0.005 1 0.0090 0.00095 0.0010 0.014 0.045 0.10 0.025 0.00058 0.053 0.031 0.048
1.0 16 41 240 50 5.1 8.7 2.3 5.8 170 5.1
17 16
.m
0
75
Y
-
i
.’
clig+-cl CI
P V 4 Y
z
50
-i
CI
CI CI
I-
z W
V 0: W
n
5
10
15
20
T I M E (rnin)
Figure 2. Photochemical reaction of 2,2’,4,4’,6,6’-hexachlorobiphenyl in the presence of (4) and absence ( 0 )of sodium borohydride.
2,2’,5,5’-totrachlorobiphenyl(0.0053), and 3,3’,5,5’-tetrachlorobiphenyl(O.0003)are representative congeners that react much more slowly (6). Because the quantum efficiency of photoreduction of aryl halides is solvent-dependent (17), it was essential to perform parallel irradiations of the PCB’s (both in the presence and absence of sodium borohydride) to ensure that changes in quantum efficiency of photodestruction were due solely to the presence of borohydride. A family of compounds was examined in this manner-the results are summarized in Table I. Virtually without exception the presence of borohydride significantly increased the rate of photodestruction of the PCB’s. Further, the destruction continued smoothly to total destruction of the compound, unlike ordinary photolysis where light-absorbing products tended to cause diminution of the rate of reaction at high conversions (Figure 2). Thus, we find the photodestruction of both highly chlorinated PCB’s and less photoreactive congeners considerably accelerated by the presence of sodium borohydride and that photoreaction can be carried to essentially total destruction of the PCB’s. These results differ from those of Tsujimoto (18),who mistakenly concluded that their quantum yields for photodechlorination in the presence of sodium borohydride were “quite low in comparison with literature values”, a quantitative error that seems due to failure to perform parallel irradiations in the presence and absence of the hydride. Products of Borohydride-Enhanced Photodechlorination. Ordinarily, photoreaction of PCB’s (like Environ. Sci. Technol., Vol. 22, No. 8, 1988 953
Table 11. Sodium Borohydride Enhanced Dechlorination of Chlorobiphenyls in Micellar Solutions
compound
detergent
AOTb (0.06 M)‘ AOT (0.06 M)‘ Brij 58 (0.13 M)d 4,4’-dichlorobiphenyl Brij 58 (0.13 M)d 2,4,2’,4’-tetrachlorobiphenyl AOT (0.06 M)c 2,5,2’,5’-tetrachlorobiphenyl AOT (0.06 M)‘ 2,3,4,5,6,3’-hexachloroAOT (0.06 M)‘ biphenyl 2,4,6,2’,4’,6’-hexachloro- AOT (0.06 M)c biphenyl
2-chlorobiphenyl 4-chlorobiphenyl
Figure 3. Product distribution at low conversion in 2,4,4’-trichlorobiphenyl photolysis in the presence of sodium borohydride.
*r
enhancement ratio”
0.28 0.030 0.097 0.10 0.30 0.125 0.51
2.5 33 108 100 3.0 5.0 17
0.94
20
Relative to photoreaction in 9:l acetonitri1e:water (without hydride). bAOT is sodium dioctyl sulfosuccinate. cIn 9:l acetonitri1e:water. In water. Table 111. Enhanced Dechlorination of Chlorobiphenyls by Exciplex-Forming Additives
:
compound
‘ dl
1
11
I
L
5
,
,
10 , Time
.-
(m n
20 L - 4 5 .
‘I
4 I
Flgure 4. Product distribution at low conversion in 2,4,4’-trichlorobiphenyl photolysis in the absence of sodium borohydride.
other chloro aromatic compounds) gives rise to a variety of products, such as the reduced aromatic compound, hydroxybiphenyls, higher oligomers, and chlorinated dibenzofurans. In the presence of sodium borohydride it was obvious that the photoreaction pathways were altered because the photolysates did not become yellow as when borohydride was absent. Product analysis confirmed the photoreaction to be “cleaner”, with photoreduction to the dechlorinated aromatic being the predominant path.
+...
+ CI,
wc,NaBH,
Figures 3 and 4 contrast the photoproducts from 2,4,4‘trichlorobiphenyl in the presence and absence of sodium borohydride by showing the gas chromatographic separation of the corresponding photolysates. Enhanced Photodechlorination in Micellar Solutions. The low solubility of PCB’s in polar solvents (19, 20) caused an undesirable limitation on the quantity of the highly chlorinated PCB’s that would be irradiated in a given experiment. Their higher solubility in aqueous solutions containing detergents suggested irradiation of detergent-containing solutions as a means of overcoming this difficulty. We found that such solutions also exhibited accelerated photodechlorination in the presence of sodium borohydride (Table 11). In many cases the acceleration was even greater than in acetonitrilelwater solutions containing borohydride. The micelles may lead to an even greater enhancement in one of several ways. First, a “solvent effect” may be exhibited due to PCB being sequestered in a more hydrocarbon-like environment. Alternatively, a PCB concentration effect may be operable, 954
Environ. Sci. Technol., Vol. 22, No. 8, 1988
additive
DCNBb (0.05 M) BuzS (0.05 M) EtsN (0.025 M) EtSN (0.05 M) RSH‘ (0.05 M) DCNBb (0.05 M) 4,4’-dichlorobiphenyl Et3N (0.05 M) 2,4,4’-trichlorobiphenyl Et3N (0.05 M) DCNBb (0.05 M) 2,5,3’-trichlorobiphenyl Et3N (0.05 M) 2,4,2’,4’-tetrachlorobiphenyl Et3N (0.05 M) 2,5,2’,5’-tetrachlorobiphenyl DCNBb (0.05 M) EtSN (0.05 M) EtBN (0.05 M) 2,3,4,5,6-pentachlorobiphenyl DCNBb (0.05 M) 2-chlorobiphenyl 3-chlorobiphenyl 4-chlorobiphenyl
enhancement ratioD 0.21 0.0078 0.11
0.23 0.0047 0.079 0.16 0.073 0.098 0.087 0.25 0.17 0.073 0.10 0.26
1.9 1.5 12
26 0.52 8.8 160 5.2 7.0 1.9 2.5 6.8 2.9 1.9 4.9
a Relative to photoreaction in 9:l acetonitri1e:water (without hydride). 1,3-Dicyanobenzene plus NaBH4. n-Dodecanethiol.
due to the more concentrated “local environment” of the micelle interior (perhaps leading to a more favorable propagation of a radical chain component of the reaction). Finally, the micelle structure may enhance the photodechlorination by the enhancement of photoionization (21). Enhanced Photodechlorination via Exciplex Formation. Attention has been recently directed to enhancing the rate of photodehalogenation of halo aromatics by irradiation in the presence of amines such as triethylamine (22-26). With some compounds an excellent enhancement in rate has been observed. Nevertheless, some problems of concern are that the rate of photodehalogenation of some compounds is even retarded by the presence of amines (27). Further, the rate of photoreaction is strongly dependent on amine concentration, sometimes reaching an optimum rate at about 0.05 M amine and then declining at higher amine concentrations (24). Finally, in one report the photoreactionof methanolic solutions of halo aromatics was not accelerated by the presence of amines (28). We have examined the enhancement of photoreaction of some of the PCB’s at an amine concentration expected to be near the optimum (0.05 M) for comparison with the borohydride enhancement. These results are shown in Table 111. Also shown in Table I11 is the study of 4-chlorobiphenyl in the presence of n-dodecanethiol and 3-chlorobiphenyl in the presence of n-butyl sulfide. A preliminary communication (29) reported electron-transfer photodechlorination from ethyl sulfide. However, we found a
Table IV. Effect of Acrylonitrile on Borohydride-Enhanced Dechlorination of Chlorobiphenyls compound
[acrylonitrile], M
0,
3-chlorobiphenyl
none 0.0050 0.050 0.10 none 0.0037 0.052
0.082 0.087 0.089
4-chlorobiphenyl
0.086
0.013 0.016 0.023
slight retardation in rate for dodecanethiol, and a small enhancement from butyl sulfide, and so did not extensively examine sulfur compounds. Finally, Table I11 shows the results of photoreactions performed in the presence of both 1,3-dicyanobenzene and sodium borohydride. These experiments probed the possibility of achieving a charge transfer from the halo aromatic to the 1,3-dicyanobenzene, producing an exciplex with a positive charge on the ArX. This species would be readily attacked by a hydride, initiating a reaction probably leading to dechlorination. The experiments involving triethylamine generally led to good enhancements in reaction rate. In some cases the enhancement was as good as observed with sodium borohydride, though with several compounds the enhancement was not as dramatic. With 1,3-dicyanobenzene and borohydride the results were also “mixed”;in some cases (e.g., 4-chlorobiphenyl) the enhancement was slight-in other cases (2-chlorobiphenyl and 2,4,4’-trichlorobiphenyl)the enhancement was greater than with borohydride alone. Mechanism of Enhancement. The excellent enhancements in photoreactivity in the presence of borohydride prompted consideration of the mechanism of this enhancement. With bromobenzene (30) and polybromobiphenyls (31) a borohydride-enhanced photodebromination proceeds with quantum yields exceeding unity, implicating a chain mechanism for the photodebromination. Further, the quantum yield of reaction is lessened by irradiation in the presence of both borohydride and acrylonitrile, which apparently scavenges free radicals responsible for propagation of a chain mechanism. However, with the PCB’s we never observed quantum yields higher than unity. Also, the presence of acrylonitrile failed to slow the rate of borohydride-enhanced photodechlorination (Table IV). Oxygen had little effect on the rate of the borohydride-enhanced photodechlorination, nor did common free-radical scavengers such as hydroquinone and BHT. Consequently, it appears that there may be more than one way for borohydride to enhance the rate of photodehalogenation-one way involves radical chain propagation (31), and others which do not. Nonchain mechanisms may involve electron transfer from borohydride to the excited aryl halide or a direct attack by borohydride on the excited aryl halide (32). Tsujimoto’s
OR
[Ar@“]’
& transfer
[
A,@“]’
-
A,@*
+
Cle
deuterium labeling experiments (18) involving sodium borodeuteride, which probed the mechanism of dechlorination in the presence of hydrides, led to mixed resultsincorporation of more than one type of hydrogen in the product. This result was explained as caused by the scrambling of the deuterium labels during the experiment.
We have repeated such labeling experiments under conditions where no such scrambling occurred and confirmed the qualitative observation that more than one type of hydrogen is incorporated in the product. This result is consistent both with a mixed mechanism or a predominantly electron-transfer pathway. Further studies t o clarify the mechanism(s) of enhancement are in progress. Conclusions. The borohydride-enhanced photodechlorination was observed to lead to consistently faster destruction of PCB’s. The presence of water is no hindrance to the enhanced photodestruction, and the photoreaction leads more cleanly to the reduced aromatic than ordinary photoreaction. The borohydride enhancement has some advantages over amine-enhanced photodechlorination-primarily in being a consistent accelerant with every compound. The enhancement is the most pronounced with the least reactive compounds, which is environmentally significant in that these compounds are probably the ones of the greatest toxicity. Thus, it would appear that this method of photodestruction of the compounds such as the PCB’s merits further study. Registry No. Brij 58, 9004-95-9; DCNB, 626-17-5; Bu2S, 544-40-1; EtBN, 121-44-8; sodium borohydride, 16940-66-2; 2chlorobiphenyl, 2051-60-7; 3-chlorobiphenyl, 2051-61-8; 4chlorobiphenyl, 2051-62-9; 3,5-dichlorobiphenyl, 34883-41-5; 4,4’-dichlorobiphenyl, 2050-68-2; 2,4,4’-trichlorobiphenyl, 701237-5; 2,5,3’-trichlorobiphenyl,38444-81-4; 2,4,2’,4’-tetrachlorobiphenyl, 2437-79-8; 2,5,2’,5’-tetrachlorobiphenyl,35693-99-3; 3,5,3’,5’-tetrachlorobiphenyl, 33284-52-5; 2,3,4,5,6-pentachlorobiphenyl, 13259-05-7;2,3,4,5,6,3’-hexachlorobiphenyl, 41411-62-5; 2,4,6,2’,4‘,6’-hexachlorobiphenyl, 33979-03-2; sodium dioctyl sulfosuccinate, 577-11-7; n-dodecanethiol, 1322-36-7;acrylonitrile, 107-13-1; 4,4’-dichloro-2-hydroxybiphenyl, 62120-49-4.
Literature Cited Ackerman, D. G.; Scinton, L. L.; Bakshi, P. S.; Delumyea, R. G.; Johnson, R. J.; Richard, G.; Takata, A. M.; Sworzyn, E. M. Destruction and Disposal of PCBs by Thermal and Non-Thermal Methods; Noyes Data Corp.: Park Ridge, NJ, 1983. Helsel, R.; Alperin, E.; Geisler, T.; Groen, A,; Fox, R.; Stoddart, T.; Williams, H. Natl. Meet.-Am. Chem. SOC. Diu. Environ. Chem. 1986, 26, 244. Bunce, N. J. Chemosphere 1982, 11, 701. Draper, W. M.; Stephens, R. D.; Ruzo, L. 0. In Solving Hazardous Waste Problems; Exner, J. H., Ed.; ACS Symposium Series 338; American Chemical Society: Washington, DC, 1987; pp 350-366. Davidson, R. S.; Goodin, J. W.; Kemp, G. Adv. Phys. Org. Chem. 1984,20, 191. Bunce, N. J.; Kumar, Y.; Ravanal, L.; Safe, S. J. Chem. SOC., Perkin Trans. 2 1978, 880. Ruzo, L. 0.;Zabik, M. J.; Schuetz, R. D. J. Am. Chem. SOC. 1974, 96, 3809. Dulin, D.; Drossman, H.; Mill, T. Enuiron. Sci. Technol. 1986, 20, 72. Ruzo, L. 0.;Safe, S.; Zabik, M. J. J. Agric. Food Chem. 1975, 23, 594. Nishiwaki, T.; Shinoda, T.; Anda, K.; Hida, M. Bull. Chem. SOC.J p n . 1982,55, 3565. Nishiwaki, T.; Shinoda, T.; Anda, K.; Hida, M. Bull. Chem. SOC. J p n . 1982,55, 3569. Safe, S. CRC Crit. Rev. Toxicol. 1984, 13, 319. Crosby, D. G.; Moilanen, K. W. Bull. Enuiron. Contam. Toxicol. 1973, 10, 372. Epling, G. A,; Florio, E. Tetrahedron Lett. 1986,27, 675. Hutzinger, 0.; Safe, S.; Zitko, V. The Chemistry of PCB’s; R. E. Krieger: Malabar, FL, 1983; pp 41-70. Hutzinger, 0.;Safe, S.; Zitko, V. The Chemistry of PCB’s; R. E, Krieger: Malabar, FL, 1983; pp 189-193. Grimshaw, J.; de Silva, A. P. Chem. SOC. Rev. 1981,10,181. Tsujimoto, K.; Tasaka, S.; Ohashi, M. J. Chem. SOC.,Chem. Commun. 1975, 758. Environ. Sci. Technol., Vol. 22, No. 8, 1988
955
Environ. Sci. Techno/. 1988,22,956-962
Dickhut, R. M.; Andren, A. W.; Armstrong, D. E. Environ. Sci. Technol. 1986, 20, 807. Hutzinger, 0.;Safe, S.; Zitko, V. The Chemistry of PCB’s; R. E. Krieger: Malabar, FL, 1983; p 16. Braun, A. M.; Gilson, M.-A.; Krieg, M.; Maurette, M.-T.; Murasecco, P.; Oliveros, E. Organic Phototransformations in Nonhomogeneous Media; Fox, M. A,, Ed.; ACS Symposium Series 278; American Chemical Society: Washington, DC, 1985; pp 79-97. Meuser, J. M.; Weimer, W. C. Amine-Enhanced Photodegradation of Polychlorinated Biphenyls;Report CS-2513, Electric Power Research Institute: Palo Alto, CA, 1982. Christensen,D. C.; Weimer, W. C. Proc. Ind. Waste Conf. 1979, 160. Bunce, N. J. J. Org. Chem. 1982,47, 1948. Ohashi, M.; Tsujimoto, K.; Seki, K. J . Chem. SOC.,Chem. Commun. 1973,384.
(26) Ohashi, M.; Tsujimoto, K. Chem. Lett. 1983, 423. (27) Bunce, N. J.; Ravanal, L. J. Am. Chem. SOC.1977,99,4150. (28) Davidson, R. S.; Goodin, J. W. Tetrahedron Lett. 1981,22, 163. (29) Davidson, R. S.; Goodin, J. W.; Pratt, J. E. Tetrahedron Lett. 1982, 23, 2225. (30) Barltrop, J. A.; Bradbury, D. J. Am. Chem. SOC.1973, 95,
5085. (31) Epling, G. A.; McVicar, W.; Kumar, A. Chemosphere 1987, 16, 1013. (32) Klinger, R. J.; Mochida, K.; Kochi, J. K. J. Am. Chem. SOC. 1979, 101, 6626.
Received for review April 20,1987. Accepted January 28,1988. This study was financially supported by the National Institutes of Health (ES03527) and the University of Connecticut Institute for Hazardous Materials and Wastes.
Detailed Hydrocarbon and Aldehyde Mobile Source Emissions from Roadway Studies Roy B. Zweldlnger,” John E. Slgsby, Jr., Sllvestre B. Tejada, Fred D. Stump, David L. Dropkln, and William D. Ray Mobile Source Emissions Research Branch, Environmental Sciences Research Laboratory, US. Environmental Protection Agency, Research Triangle Park, North Carolina 2771 1
John W. Duncan Northrop Services, Inc., Research Triangle Park, North Carolina 27709
A field study was conducted along U.S.Highway 70 near Raleigh, NC, to evaluate methods for estimating emission factors and, in particular, for determining volatile organic carbon (VOC) species (i.e., individual hydrocarbons and aldehydes) emitted from traffic. Integrated samples were collected 1m from the roadway between 7:30 and 830 a.m. at four different roadside locations representing various combinations of traffic conditions (cruise, acceleration, deceleration, and idle). The light-duty traffic component (>go%) was classified by model year between 1975 and 1983. On a percent of total non-methane basis, the distribution of VOC’s varied little between sampling sites. The roadside VOC distribution was compared to dynamometer/dilution tube test results on in-use vehicles, which were weighted to reflect the same model year distribution observed on the roadway. Some of the differences seen were attributed to fuel effects, while others may reflect an insufficient data base. Mass emission rates calculated from release of a tracer gas by a pace car varied unpredictably and were higher than those calculated by the Mobile3 model or observed with the in-use vehicle dynamometer data. Introduction
Since the role of individual hydrocarbons (HC’s) in oxidant formation varies greatly, detailed speciation data can aid substantially in predicting ambient air quality. However, most data related to mobile source emissions are limited to measurements of total hydrocarbon (THC), CO, and oxides of nitrogen (NO,) derived from laboratory dynamometer/dilution tube studies in which vehicles are operated in a fixed, prescribed manner. For example, a current method for estimating mobile source emission factors (THC, CO, and NO, only) employs the Mobile3 model (1) and its associated data base (2),which is based on testing vehicles using the federal test procedure (FTP) (3). By comparison, only a minimal amount of data exists 956
Environ. Sci. Technol., Vol. 22, No. 8, 1988
for detailed HC speciation from mobile sources. Even less data exist for aldehydes and other carbonyls. Emission inventories of carbonyl compounds are of particular interest because these compounds play an important role in both the formation and perpetuation of atmospheric “smog”. The establishment of a detailed speciation data base is costly and time consuming when conducted on a vehicleby-vehicle basis in the laboratory. Furthermore, most laboratory testing is conducted on relatively new vehicles in proper operating condition, a situation which may not reflect the “real world”. An alternative is to conduct roadside sampling, which provides an opportunity to obtain integrated samples of vehicle types and ages under a variety of operating conditions. While a number of such roadside studies have been conducted in the past, they have frequently been limited to tunnels ( 4 ) or roadway situations where accurate emission rates could not be calculated (5). By employing tracer gas techniques (6),it is possible to determine dilution factors for samples collected in the field and to calculate mass emission rates. In 1983 we conducted a series of preliminary field studies to define and evaluate alternative procedures for collecting HC and aldehyde speciation data from mobile sources via roadway sampling. We sought (1)to determine if differences in emissions could be observed for sites influenced by cruise, acceleration, and deceleration traffic modes and (2) to compare the observed emissions with those measured in dynamometer/dilution tube experiments. In addition, we were curious to determine, under the conditions employed, what sort of mass emission rates could be obtained from the release of a tracer gas. Experimental Section
The field experiments reported here were conducted along a section of U.S. Highway 70 near Raleigh, NC, during May 1983.
0013-936X/88/0922-0956$01.50/0
0 1988 American
Chemical Society
