(24) Larson, R. A., Blankenship, D. W., Hunt, L. L., in “Sources,
(12) Takahashi, M., Seibert, D. L., Thomas, W. H., Deep Sea Res., 24,775 (1977). (13) Andelman,J. B., Suess, M. J.,in “Organic Compounds in Aquatic Environments”, S. J. Faust and J. V. Hunter, Eds., pp 439-68, Marcel Dekker, New York, N.Y., 1971. (14) Corner. E.D.S.. Harris. R. P.. Kilvineton.’ C. C.. O’Hara. S.C.M.. j . Mar. ~ i o iASS&. . UK,’M, iii (19765. (15) Harris, R. F., Berdugo, V., Corner, E.D.S., Kilvington, C. C., O’Hara. S.C.M.. in “Fate and Effects of Petroleum Hvdrocarbons in Marine Organisms and Ecosystems”, D. A. Wdlfe, Ed., pp 286-304, Pergamon Press, New York, N.Y., 1977. (16) Lee, R. F., in “Proceedings of the 1975 Conferenceon Prevention and Control of Oil Pollution”, pp 549-53, American Petroleum Institute, Washington, D.C., 1975. (17) Dunn, B. P., Stich, H. F., Bull. Enuiron. Contarn. Toxicol., 15, 398 (1976). (18) DiSalvo, L. H., Guard, H. E., in “Proceedings of the 1975 Conference on Prevention and Control of Oil Pollution”, pp 169-73, American Petroleum Institute, Washington, D.C., 1975. (19) Harrison, W., Winnik, M. A., Kwong, P.Z.Y., Mackay, D., E n uiron. Sci. Technol., 9, 231 (1975). (20) McAuliffe, C. D., in “Fate and Effects of Petroleum Hydrocarbons in Marine Organisms and Ecosystems”, D. A. Wolfe, Ed., pp 19-35, Pergamon Press, New York, N.Y., 1977. (21) Ocean Affairs Board, National Research Council, “Petroleum
Effects and Sinks of Hydrocarbons in the Aquatic Environment”, pp 298-308, American Institute of Biological Sciences,Washington, D.C., 1976. (25) Nagata, S., Kondo, G., in “Proceedings 1977 Oil Spill Conference”, pp 617-25, American Petroleum Institute, Washington, D.C., 1977. (26) Bassin, N. J., Ichiye, T., J . Sediment. Petrol., 47,671 (1977). (27) Lee, R. F., in “Proceedings of the 1977 Oil Spill Conference”,pp 611-16, American Petroleum Institute, Washington, D.C., 1977. (28) Meyers, P. A,, Quinn, J. G., Nature, 244,23 (1973). (29) Gordon, D. C., Keizer, P. D., Hardstaff, W. R., Aldous, D. G., Enuiron. Sci. Technol., 10,580 (1976). (30) Cox, B. A,, Anderson, J. W., Parker, J. C., in “Proceedings of the 1975 Conference on Prevention and Control of Oil Pollution”, pp 607-612, American Petroleum Institute, Washington, D.C. (31) Soto, C., Hellebust, J. A., Hutchinson, T. C., Can. J. Bot., 53,118 ( 1975). (32) Herbes, S. E., Water Res., 11,493 (1977). (33) Lee, R. F., in “Sources, Effects and Sinks of Hydrocarbons in the Aquatic Environment”, pp 333-44, American Institute of Biological Sciences, Washington, D.C., 1976. (34) Blumer, M., Sass, J., Science, 176,1120 (1972).
~
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in the Marine Environment”, National Academy of Sciences, Washington, D.C., 1975. (22) Atlas, R. M., Bartha, R., Enuiron. Pollut., 4,291 (1973). (23) Walker, J. D., Colwell,R. R., Petrakis, L., Can. J . Microbiol., 22,
Received for review October 31, 1977. Accepted January 25, 1978. Work supported by National Science FoundationlIDOE Grants GX-39249 and OCE76-84108.
423 (1975).
Rapid Weathering Processes of Fuel Oil in Natural Waters: Analyses and Interpretations Fritz Zurcher” and Markus Thuer’ institute for Water Resources and Water Pollution Control, Swiss Federal Institute of Technology, CH-8600 Dubendorf, Switzerland
w The fate-determining steps of weathering petroleum in the aquatic environment were studied in model experiments. Capillary column gas chromatography and infrared absorption measurements showed different weathering processes for No. 2 fuel oil, depending on the turbulence and the level of suspended solids (kaolinite) in water during experiments. Partial dissolution, adsorption, dispersion, and agglomeration of No. 2 fuel oil initially occurred and resulted in the fractionation of the original oil mixture. Alkylated benzenes and naphthalenes were enriched in the water phase (up to 5 m g b ) , certain aliphatic hydrocarbons above mol wt 250 were adsorbed onto kaolinite (200 mg/kg), and oil droplets were agglomerated with suspended minerals (20 g/kg) after increased turbulence. The same fractionation pattern was observed for a ground water oil spill, although the oil was already biochemically altered. One would like to be able to characterize the processes that influence the fate of oil in the aquatic environment. A number of authors ( I ) have described various physical and biological processes that contribute t o the distribution and degradation of petroleum products in the aquatic environment. Difficulties have arisen in determining the relative magnitude of the various processes. Reliable information on the distribution of oil components in aquatic environments is important because the more water soluble aromatic hydrocarbons, even in minute concentrations, may have toxic effects on aquatic organisms (2). 1 Present address, CIBA-GEIGY AG, Environmental-Technology Dept., CH-4000Basel, Switzerland.
838
Environmental Science & Technology
This work presents a n analysis of the initial short-term processes affecting the distribution of fuel oil in surface water containing a suspended clay mineral. Processes studied include dissolution, suspension, agglomeration, and adsorption. Evaporation was not studied, since surface oil spills generally contribute less t o oil pollution than continuous inputs from diffuse sources ( 3 ) . Model experiments were done with No. 2 fuel oil and water containing suspended particulates. Then a comparison was made of these model experiments and an actual case involving polluted ground water. Experimental
Model Experiments. A 250-mL erlenmeyer flask was filled with distilled water containing sodium chloride (10-3 M) and sodium bicarbonate t o stabilize the p H at 7.5. T o withdraw samples, a U-tube was placed in the flask, with one end near t h e bottom and t h e other end outside. Ten milliliters of No. 2 fuel oil were carefully placed on top of the water body with a pipet, avoiding single oil droplets. The flasks were then stirred with a magnetic stirrer at a constant speed (3 cycles/s). Different flow conditions were achieved by changing the length of the magnetic stirrer: 2 cm for low intensity and 3 cm for high intensity (oil/water interface disrupted). Ten grams per liter of kaolinite (0.2-2 pm) with a relatively high specific surface (10 m2/g) were used as the particulate material. Experiments were performed for a period of 24 h a t 20 “C as follows: I: oil/water without suspended solids, low stirring intensity; 11: oil/water with suspended solids, low stirring intensity; 111: oil/water with suspended solids, high stirring intensity; IV: gasoline/water without suspended solids, low stirring intensity.
0013-936X/78/0912-0838$01 .OO/O
@ 1978 American Chemical Society
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Figure 1. No. 2 fuel oil fractions from model experiments Gas chromatogram and partial IR spectra (C-H stretch region) of: (A) original composition; (E)water-soiubie fraction: (C) adsorbed fraction; (D) agglomerate fraction. For identification of GC peaks, refer to Table I. Column: SE 52 coated glass capillary (20 m X 0.30 mm i.d.). Conditions: 1.5 pL, splitless, carrier gas pressure H2, 5.9psig, 3 'Clmin, 25-250 OC
Samples of 50 mL were withdrawn through the U-tube and ultracentrifuged (30 000-g centrifugal force) for 30 min to separate settlable, dissolved, and floating oil fractions. The carefully separated sediment was allowed to dry at room temperature and was then completely powdered by mixing with the same amount of dry sodium sulfate. This powder was transferred to a small chromatographic column (6 mm id., 80 mm height), and eluted with a minimal volume (2.5 mL) of carbon tetrachloride for the quantification of hydrocarbons by IR spectrometry. Recovery was between 80 and 90% when compared to soxhlet extraction. For gas chromatographic analyses, the sediments were eluted from the columns with pentane. The water phase was extracted in a separatory funnel with carbon tetrachloride for IR analyses or with pentane for GC analyses. The floating oil fraction was prepared by diluting with carbon tetrachloride for IR analyses or with pentane for GC analyses. Samples from a ground water contaminated by an oil spill were taken in the following manner: Before the excavator reached the ground water table (4m below surface), a soil-sand sample was collected directly into an aluminum box. About 20 cm deeper the water sample was taken with an all glass bottle. At the same level a sample of the oil film was collected. For control, another water sample was taken from a digging
50 m downstream, with respect to the ground water flow. No oil film could be observed. The workup of these samples was the same as for the model experiment except that the water/oil phases were separated by settling instead of centrifuging.
Analytical I n f r a r e d Measurements (IR). The hydrocarbon content of the samples was determined by IR according to the API method ( 4 ) .The sum of the absorptions from wavenumbers 2850,2925,2870, and 2960 cm-I was compared with the corresponding sum from No. 2 fuel oil used as a calibration standard. The detection limit was 0.5 mg fuel oil type hydrocarbons per liter of water sample and 20 mg/kg dry sediment. In addition to the IR, a Total Organic Carbon Analyzer was used to quantify the soluble fraction from No. 2 fuel oil. For determination of alkylated benzenes the TOC values were corrected by a factor of 1.1for their carbon content. G a s Chromatography (GC). Gas chromatography was performed on a Carlo Erba gas chromatograph, equipped with glass capillary columns ( 5 ) ,which had been purchased from H & G Jaeggi, CH-9043 Trogen, Switzerland (50 m OV-101 and 56 m Ucon HB) or provided by K. Grob (20 m SE-52). The Grob splitless injection technique was used (6). The column Volume 12, Number 7, July 1978 839
temperature was programmed a t 3"/min from 30 to 250 "C (180" for Ucon HB). Peak identifications were based on retention times and coinjection with standards. Reagents. Reagents used were: practical grade pentane and redistilled hexane; carbon tetrachloride, nanograde (Mallinckrodt, Inc., St. Louis, Mo.); anhydrous sodium sulfate, dried, AR grade; and kaolinite (M. Muller-Vonmoos, Institute for Petrography, ETH-Zurich).
Results Model Experiments. The results of the model experiments are shown in Figure 1. On the left, the separation of the hydrocarbon mixture by capillary GC is shown. The key components that were followed in this study are listed in Table I. The right side gives the corresponding IR spectra in the C-H stretch region for the unseparated mixtures. The absorptions are indicative of CHs, CH2, and aromatic CH bands. The original mixture of No. 2 fuel oil, which has a broad boiling range of 170-350 "C, is shown in chromatogram A. The mixture is dominated by rz-paraffins, isoparaffins, and naphthalenes. This pattern was also found for the oil phase separated in model experiments I and I1 (low intensity stirring with and without suspended solids). As expected the IR spectrum for No. 2 fuel oil has only weak aromatic CH absorption since the aromatic content of No. 2 fuel oil is less than 10% and the C-H stretch in aromatic compounds is normally weak. In contrast, the water phase of model experiments 1-111 gave patterns dominated by alkylated benzenes (peaks 1-7) and naphthalenes (peaks 8-10). The aromatic character was demonstrated by the IR spectrum. Absorption between 3100 and 3000 cm-l can be attributed to hydrogen attached to aromatic rings, and the shoulder a t 2930 cm-l (on CH2 band) to methyl groups bound to aromatic rings (7). It appears that the amount and distribution of dissolved aromatic hydrocarbons in water ranging from benzene to about C2-naphthalenes depend on their concentration in the original mixture (distillate fraction). Figure 2 compares the water soluble aromatics originating in gasoline and No. 2 fuel oil. For this comparison we used a GC column (Ucon HB) suitable for separation of alkylated benzenes. Since the gasoline has a high aromatic content (-30%), the GC chromatograms of gasoline (Figure 2a) and of that portion of the gasoline dissolved in water (Figure 2b) are similar (see Peaks 1-6). In contrast to water soluble parts of No. 2 fuel oil, benzene and toluene dominated in water soluble fractions of gasoline, whereas C4-benzenes and naphthalenes were found only in minute concentrations. Qualitatively, the water soluble components of these two petroleum products are similar. T o quantitate the partial dissolution of No. 2 fuel oil in distilled water, the saturation level
Table 1. List of Hydrocarbons Indicated in Chromatograms Peak no.
Benzene Toluene Ethylbenzene mlpxylene *Xylene C3-benzenes C4-benzenes Naphthalene Methylnaphthalenes C2-naphthalenes +Alkanes Cll-CZ7 Farnesane Pristane Phvtane 840
Environmental Science & Technology
1 2
3 4 5 6 7
a
9 10 11-27 Fa Pr Ph
reached after 1h a t 20 "C during experiment I was determined by TOC: 5 mg/L (f0.5). The saturation concentration of gasoline determined by TOC and also found by gas chromatography was: 200 mg/L distilled water, 20 "C, after 1 h (experiment IV). In experiment 11, we were able to measure the maximum adsorption capacity of kaolinite because of the large oil reservoir that allowed each substance to have a maximum partial pressure in water during the experiment. The saturation level for aliphatic hydrocarbons in water fell below the detection limit (10 g g L ) (chromatogram B, Figure 1).The distribution and characterization of hydrocarbons on the solid surface are shown in chromatogram C (Figure 1)and the corresponding IR spectrum. In contrast to A, a drift to higher boiling hydrocarbons can be observed and is demonstrated by the increase of n-alkane traces (No. 22-27). This agrees with the Traube rule (8) that homologous series of organic substances adsorb more rapidly from water with increasing molecular weight. The IR measurement (C) shows further that straight-chain structures dominate the adsorbed hydrocarbon mixture because of the higher CHz/CH3 ratio compared to the IR spectrum A. The clay mineral contained about 200 mg hydrocarbons per kg dry material after 10 h exposure in experiment 11. This hydrocarbon loading did not change even after 100 h exposure time. In experiment I11 the water/oil interface was disrupted by the high stirring intensity (turbulence). Oil droplets were dispersed and came into contact with the suspended kaolinite. The resulting oil/particle agglomerates were still settlable. Chromatogram D (Figure 1)of the agglomerated oil, separated by centrifugation, is similar to that of the original No. 2 fuel oil mixture. Loss of highly volatile hydrocarbons a t the beginning of the chromatogram is mainly due to evaporation during sample preparation (see experimental). The IR spectrum D does not differ from that of the original fuel oil A. Quantitative IR measurements showed an oil load on kaolinite of 20 g fuel oil per kg dry material after 20 h exposure time in experiment 111. This value is a hundred times higher than the amount of hydrocarbons adsorbed out of solution. Case Study. The analyses of the oil spill-contaminated ground water showed a fractionation pattern (Figure 3) similar to model experiment 11. Because of the unknown history of the spill, we were not able to identify a distinct type of petroleum distillate that had been lost from tanks. We would assume a mixture of No. 2 fuel oil and gasoline type fractions. Their boiling ranges overlap and give indications for the type of oil only a t the lower and upper end of the distribution. The more volatile components, dominated by isoparaffins and probably naphthenes (Figure 3a: gas chromatogram and IR spectrum), could have originated from gasoline-type distillates. The isoprenoids pristane (Pr) and phytane (Ph) are common constitutents in fuel oil. The absence of the corresponding n-alkanes (peaks 17 and 18)indicate a possible biological degradation of parts of the hydrocarbons (9). The soluble aromatics (peaks 1-9) detected in the ground water (Figure 3b) are the same as those demonstrated by model experiment 11. Biological degradation seems to be less probable for dissolved aromatics than for n-alkanes. The alkylated benzenes and naphthalenes are mobile in the ground water and therefore show a large spreading tendency. Analyses of the ground water in other nearby locations again showed these aromatic hydrocarbons, whereas no oil phase could be detected. The adsorption of aliphatic hydrocarbons on soil in the zone with residual ground water saturation is shown in chromatogram 3c. High boiling hydrocarbons such as farnesane, pristane, phytane, and series of n-alkanes above CZOhave been found, These results agree with those of model experiment I1 where oil was allowed to stay in contact with slowly moving
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1 Figure 2. Low molecular aromatic hydrocarbons dissolved in water from petroleum products Gas chromatographic analyses of (a) gasoline; (b) water, saturated with gasoline, hexane extract; (c) water, saturated with No. 2 fuel oil, hexane extract. For identification of GC peaks, refer to Table I. Column: Ucon HB coated glass capillary (56 m X 0.32 mm i.d.). Conditions: 1.5 pL, splitless, carrier gas pressure H2, 8.8 psig, 3 OC/min, 25-180
OC
water containing mineral particulates. As approximated by the model, we found about 80 mg hydrocarbons per kg dry soil. The high pristaneln-heptadecane ratio indicates substantial biological degradation (9).
Discussion The analyses of model experiments and the ground water pollution case have shown that mineral-oil products (No. 2 fuel oil) do physically fractionate after contact with water. The liquid phase and the solid phase control the distribution of oil in the water column by dissolution, suspension, adsorption, and agglomeration. These processes start from the beginning of oil-water contact and are easily detectable within the first hours. Under model conditions the saturation level for No. 2 fuel oil in water was reached after 15 min of contact. The amount of hydrocarbons adsorbed on kaolinite reached a constant value within the first 10 h. Suspended oil in water
existed only during the intensive stirring period and acted as a transition state for agglomerates. Within the first 5 h the amount of oil (droplets) on settlable kaolinite particles in experiment I11 exceeded threefold the values of adsorptive loading. We therefore conclude that the fate of oil in the water column is strongly directed by fast dissolution, adsorption, dispersion, and agglomeration. These primary weathering processes are followed by sedimentation, biochemical alteration, etc. The water-soluble aromatic hydrocarbons are ideal tracers for the study of pollution because of their mobility and relatively slow biological degradation (10).Therefore, it appears that one- and two-ring aromatic hydrocarbons are found in water samples due to dissolution of soluble petroleum fractions. Our observations are in good agreement with results from Boylan and Tripp (11);they found principally the same water-soluble fractions from two different crude oils (Kuwait Volume 12, Number 7, July 1978 841
3200
MOO 2800cm-’ 100%
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Flgure 3. Gas chromatogramsof hexane extracts from a ground water (a) Oil film found at ground water level, 4 m below ground (1 g/L in hexane); (b)ground water, hexane extract; (c) soil, hexane extract. For identification of GC peaks, refer to Table I. Partial IR spectrum of oil film, see (a). Column: OV 101 coated glass capillary (50 m X 0.34 mm i.d.). Conditions: 1.5 pL. splitless, carrier gas pressure H2, 7.3 psig, 3 OC/min
and Louisiana). Jeltes and Tonkelaar (12) have measured saturation levels of seven different oil products in water by gas chromatography. They found predominantly aromatic hydrocarbons in water extracts from No. 2 “diesoline” fuel oil (8 mg/L) and “super” gasoline (173 mg/L), which supports our observations. Brown and Huffman (13)have also found oneand two-ring aromatic hydrocarbons in subsurface seawaters of tanker routes, but in contrast to the observations of Boylan and Tripp (11) and our model experiments I and XI, they concluded that their source could not be shipped petroleum with its one- to four-ring aromatic content. Harrison et al. (14) have determined evaporation rates for isopropylbenzene (cumene) and nonane by measuring the decreasing content of these substances in spilled crude oil. They attributed the faster loss rates of cumene to a higher solubility of nonane in the oil phase. Since evaporation from an oil slick is in competition with dissolution, our results would suggest that the rapid loss of cumene, compared to nonane, is mainly due to dissolution. Kaolinite clay was used as a suspended solid for model experiments I1 and 111. Meyers and Quinn (15) have compared the association of No. 2 fuel oil with different minerals in saline solutions at 25 O C and found that minerals derived from natural sediments behaved as the laboratory clay experiment 842
Environmental Science & Technology
predicted. Their value for kaolinite fuel oil associates (162 mg/kg dry kaolinite) is in good agreement with our value. Corresponding to this and the ground water pollution case study, a similar hydrocarbon distribution was also found in sediments from regions with known mineral oil discharge (16, 17). Sutton and Calder (18) found a solubility decrease of rz-paraffins in unfiltered seawater compared to distilled water. Since the seawater had been spiked with alkanes and afterward filtered through a 0.45-wm membrane before analyses, we suggest that their observation was due to adsorption of hydrocarbons on natural suspended solids rather than to salting effects. Such adsorptions would also explain the increasing discrepancy between measured and predicted salting out parameters (18)with increased chain length of rz-paraffins. From model experiment 111and the discussion of Thiier and Stumm (19), we would predict that oil layers from spills are rapidly removed from flowing water (river, rough sea) by dispersion followed by agglomeration with particulates. These processes would promote the distribution of oil products in the water column by subsequent dissolution, adsorption, suspension, and sedimentation. Since weathering processes do change the original oil mixture, we would not support the interpretation of oil pollution
cases by simple comparison of waterborne oil with common oil products as suggested by Dell’Acqua et al. (20).Exclusively in the case of dispersion and agglomeration, we found almost the original paraffinic and naphthenic oil hydrocarbons in “water samples” as in oil.
Conclusions The fractionation of the original hydrocarbon mixture in water into residual oil, dissolved, and solid surface-bound fractions has been demonstrated in the model experiments as well as in the ground water spill study. From our observations we can conclude that dissolution, adsorption, and agglomeration play an important role as initial processes in weathering of oil in natural aquatic systems. These processes seem to be rapid and instrumental in the elimination of an oil phase because the fractionation pattern of oil components is not changed by biological activity in the examined ground water area. Dissolution of one- and two-ring aromatic hydrocarbons in water always occurs independent of the type of oil (fuel oil, gasoline, crude oil) and reaches a saturation level depending largely on the one- and two-ring aromatic content. These experiments permit distinction between two types of oil/solid associations. The adsorption of higher boiling hydrocarbons (mol wt > 250) is dependent on the character of the solid surface. In a water containing 20 mg/L suspended kaolinite, 4 pg hydrocarbons/liter could be adsorbed. From analysis of sediments (3, 16, 17), it would seem that the adsorbable amount of hydrocarbons in natural systems would be even higher. The agglomeration depends on the formation of dispersed oil droplets through water turbulence and interfacial tension of the oil, and plays a substantial role in oil sedimentation (19). T h e amount of oil agglomerates in a water containing 20-mg/L suspended kaolinite could reach 0.4 mg/L. These experiments have shown that the understanding of the fate of oil in natural aquatic systems will depend largely on the use of proper sample preparation and on the subsequent analytical interpretation. For identification of petroleum products in case of water pollution, we no longer analyze water samples without prior separation of particulates. Finally the differentiation between dissolved, adsorbed, and colloidally dispersed oil is of great ecological importance, as suggested by Blumer et al. (21): The water-soluble fraction is
responsible for acute toxicity, but the interruption of biological communication (chemotaxis) could possibly be caused by fractions adsorbed on particulates and accumulated in the sediments.
Acknowledgment The authors acknowledge the support and interest given by W. Stumm and W. Giger and thank M. Kavanaugh and S. Wakeham for reading and reviewing the manuscript. Literature (1) Petroleum in the Marine Environment, Ocean Affairs Board, National Academy of Sciences, Washington, D.C., 1975. (2) Jacobson, St. M., Boylan, D B., Nature, 241,213-15 (1973). (3) Thuer, M., PHD dissertation 5628, ETH-Zurich, Switzerland, 1975. (4) American Petroleum Institute, “Manual on Disposal of Refinery Wastes”, Vol IV, Method 733-58,1958. (5) Grob, K., Grob, G., Chrornatographia, 5,3-12 (1972). (6) Grob, K., Grob, K., Jr., J . Chrornatogr., 94,53-64 (1974). (7) Hediger, H. J., “Infrarotspektroskopie”, Akad. Verlagsgesellschaft, Frankfurt am Main, Germany, 1970. (8) Adamson, A. W., “Physical Chemistry of Surfaces”, Wiley-Interscience, New York, N.Y., 1967. (9) Blumer, M., Sass, J., Science, 176,1120-2 (1972). (10) Kappeler, T., PhD dissertation 5688, ETH-Zurich, Switzerland, 1976. (11) Boylan, D. B., Tripp, B. W., Nature, 230,5,44-7 (1971). (12) Jeltes, R., Tonkelaar, W.A.M., Water Res., 6,271-8 (1972). (13) Brown, R. A., Huffman, H. L., Jr., Science, 191,847-9 (1976). (14) Harrison, W., Winnik, M. A., Kwong, P.T.Y., Mackay, D., Enuiron. Sci. Technol., 9, 231-4 (1975). (15) Meyers, P. A., Quinn, J. G., Nature, 244,23-4 (1973). (16) Giger, W., Reinhard, M., Schaffner, C., Stumm, W., Enuiron. Sci. Technol., 8,454-5 (1974). (17) Wakeham, S. G., Carpenter, R., Lirnnol. Oceanogr., 21,711-23 (1976). (18) Sutton, Ch., Calder, J. A., Enuiron. Sci. Technol., 8, 654-7 (1974). (19) Thuer, M., Stumm, W., “Sedimentation of Dispersed Oil in Surface Waters”, in “Progress Water Technology”, Vol 9, pp 183-94, Pergamon, 1977. (20) Dell’Acqua, R., Egan, J. A., Bush, B., Enuiron. Sci. Technol., 9, 38-41 (1975). (21) Blumer, M., Hunt, J. M., Atema, J., “Interaction Between Marine Organisms and Oil Pollution”, EPA Ecological Res. ser. R 3-73-042, 1973. Receiued for review January 3,1977. Accepted January 30, 1978.
CORRESPONDENCE
SIR: Calvert ( I ) has shown that [ O 3 ] [ N O ] / [ N 0 from 2 ] atmospheric measurements were generally higher than his estimates of k J k 3 in his analysis of LARPP operation 33 data. k l and k3 are rate constants of the reactions that are primarily responsible for the establishment of a photostationary state ozone concentration in photochemical smog.
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Calvert suggested this disagreement was the result of inhomogeneity of the air with respect to those species. Seinfeld ( 2 ) expanded this concept by defining a fictitious mixing fraction, 7,which is defined a t any point and may be characterized by a probability density function. Assuming that 7 was 0013-936X/78/0912-0843$01.00/0
normally distributed, he then showed the effects of changing both the standard deviation of 7 and polluted parcel concentration on the photostationary state relationship. The approach taken by Seinfeld illustrates quite well the effects of inhomogeneity, but its usefulness for characterizing the atmosphere is somewhat limited since there is no single set of concentrations that represents background air (parcel l), and no single set that represents recently polluted air (parcel 2). This letter is intended to set forth an alternate means of parameterizing the inhomogeneous character of ambient air and to show some of the properties of this parameterization. When measurements are taken on board a helicopter, they are spatial composites, not pollutant concentrations at a single point. They are weighted averages over some finite distance. The average rates of reactions of order greater than one are not necessarily equal to the rates calculated from measured (averaged) concentrations. The main reason for the apparent deviations from photostationary state is believed to be that
@ 1978 American Chemical Society
Volume 12, Number 7, July 1978
843
