Total soluble and insoluble sulfur concentrations in urban snow

Environ. Sci. Technol. 1983, 17, 542-546

Fredenslund, A.; Jones, R. L.; Prausnitz, J. M. AIChE J. 1975, 21, 6, 1086. Gmehling, J.; Rasmussen, P.; Fredenslund, A. Ind. Eng. Chem. Prod. Res. Deu. 1982,21, 118. Abrams, D. S.; Prausnitz, P. M. AIChE J . 1975,21, 116. Reid, R. C.; Prausnitz, P. M.; Sherwood, T. K. “The Properties of Gases and Liquids”, 3rd ed.; McGraw-Hill: New York, 1977; 354. Note added in proof. Before final proofreading of the article, the following text was found to contain detailed example calculations of activity coefficients using UNIFAC: Lyman, W. J.; Reehl, W. F.; Rosenblatt, D. H. “Handbook of Chemical Property Estimation Methods“, McGraw-Hill: New York, 1982, p 11-5. Mackay, D. Environ. Sei. Technol. 1977, 11, 1219. Banerjee, S.; Yalkowsky, S. H.; Valvani, S. C. Environ. Sci. Technol. 1980,14, 1227.

(14) Chiou, C. T.; Freed, V. H. Enuiron. Sei. Technol. 1977,11, 1220. (15) Mackay, D.; Chiu, C. Y.; Sutherland, R. P. Environ. Sei. Technol. 1979, 13, 333. (16) Kavanaugh, M. C.; Trussell, R. R. J . Am. Water Works Assoc. 1980, 72, 684. (17) Yalkowsky, S. H. Ind. Eng. Chem. Fundam. 1979,18,108. (18) Sorenson, J. M.; et al. Fluid Phase Equilibria 1979,297 (as reported in ref 19). (19) Magnussen, T.; Rasmusen, R.; Fredenslund, A. Ind. Eng. Chem. Process Res. Dev. 1981, 20, 331. (20) Perry, R. H.; Chilton, C. H. “Chemical Engineer’s Handbook”, 5th ed.; McGraw-Hill,New York, 1973;p 3-49.

Received for review July 7, 1982. Revised manuscript received January 14, 1983. Accepted April 11, 1983.

Total Soluble and Insoluble Sulfur Concentrations in Urban Snow Sheldon Landsberger* Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, Canada M5S 1A4

Robert E. Jervls Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, Canada M5S 1A4

George Kajrys and Serglo Monaro Laboratoire de Physique Nucieaire, UniversitB de Montreal, Montrgal, Quebec, Canada H3C 3J7

Roger Lecomte DBpartement de Medecine Nucleaire et Radiobiologie, Centre Hospitalier Universitaire, Sherbrooke, Quebec, Canada J 1H 5N4

Total soluble and insoluble sulfur concentrations in urban snow collected around the island of Montreal were measured by using proton-induced X-ray emission (PIXE) techniques. Cobalt was chosen as the internal standard for the soluble fractions while aluminum, whose concentration was determined by instrumental neutron activation analysis (INAA), was used for the particulate matter. Feasibility experiments using induced coupled plasma (ICP) spectrometry were also employed to determine soluble sulfur concentrations in snow collected from several inner-city Toronto sites and from Sault St. Marie, Ontario. The use of a 0.40-pm Nuclepore filter revealed that between 85% and 90% of the sulfur was water soluble. The average total concentration was about 1500 pg of S/L of snow. Total annual bulk deposition was estimated to be 1300 mg/(m2 year) for the souble portion and 200 mg/(m2 year) for the particulate matter. Enrichment factor values strongly suggested that sulfur arises predominantly from anthropogenic sources. Element pair correlations with manganese and the possible role of manganese as a catalytic oxidant of sulfur are discussed. Introduction One of the most prevalent air pollutants intensely studied over the past few decades is sulfur. Sulfur’s contribution to the formation of acid precipitation and subsequent environmental, ecological, and health damage is now well documented ( I ) . Recently, several studies have been carried out to investigate the speciation of sulfur compounds. These include analysis of sulfur(1V)aerosols (2), sulfur constituents in lake sediments (3), and the *To whom correspondence should be addressed at Nuclear Reactor, McMaster University, Hamilton, Ontario, Canada L8S 4K1. 542

Environ. Sci. Technol., Vol. 17,No. 9, 1983

speciation of sulfur dioxide, sulfuric acid, and sulfates (4-6). However, work on the detection of total sulfur concentrations in environmental samples has been pursued less vigorously. For instance, total sulfur concentrations in polluted soils and vegetation were recently investigated by combustion methods (7) while PIXE (proton-induced X-ray emission) has been successfully used for the determination of sulfur in aerosols (€49).In the last couple of years our group has successfully used nuclear analytical methods PIXE and INAA (instrumental neutron activation analysis) along with graphite-furnace atomic absorption spectrometry to determine trace pollutants in wet atmospheric deposition (10-13). While INAA was found to be unsuitable for sulfur determination at concentration levels found in rain or snow, our own preliminary studies have shown that PIXE techniques offer excellent sensitivities when used in conjunction with freeze-drying methods (10). Other than our own work only two groups have used PIXE to measure sulfur concentrations in wet atmospheric deposition: one in Pittsburgh (14) and one in Tallahassee (15). At present it appears that ICP has not been exploited for any sulfur determinations in either rain or snow. In this paper we report the determination of total (soluble and insoluble) sulfur concentrations in urban snow collected around the perimeter of the island of Montreal. Analysis of the soluble portion was done at 30 sample sites while the particulate matter was determined for 8 equidistant sample sites chosen among the 30. Some sulfur analysis was also done for snow samples collected in Toronto and Sault St. Marie, Ontario, by using ICP spectrometry. Since snowflakes fall more slowly than raindrops of equal mass and sweep out a larger volume, thus having a greater exposure to airborne Pollutants, they should be a good indicator of the presence of sulfur and other CO-

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contaminants (16). Average total sulfur concentrations in snow, estimation of annual bulk deposition, percentage of sulfur in soluble form, and enrichment factors will be discussed. Furthermore, the role of manganese, determined simultaneously with aluminum by using INAA, as a possible catalyst to accelerate the oxidation of sulfur dioxide is discussed in terms of elemental pair correlations with sulfur.

Experimental Section The complete snow sampling procedure, filtration and freeze-drying methods, PIXE experimental setup, methods and on-line elemental analysis are already fully described (10-13, 17-19). In this study we have collected snow samples from the ground at the end of a season at 34 equidistant locations (4-5 km)around the perimeter of the island of Montreal (45O N, 73O W). Snow samples were gathered over a single 24-h period in a 95 cm X 11 cm precleaned plastic cylinder that was inserted into the snow and then removed. Approximately 10 L from each sampling site was placed into a polyethylene bag and kept in cold storage until the day of analysis. This minimizes any adsorption and inhibits bacterial growth. To obtain a maximum amount of undisturbed snow in a single season, the last week of Feb 1979 was chosen as the collection time. Choosing such a period ensured that no serious meltdown occurred, as this problem is usually not encountered until March. Furthermore, sampling sites were chosen well away from the roadsides to minimize contamination from road salt and vehicles. Approximately 150 g of frozen snow was removed from the polyethylene bag, melted, and filtered through a preweighed 0.40-pm Nuclepore filter that was prerinsed three times with distilled and deionized water. Samples were acidified to 1% by using high purity nitric acid (Ultrex HNOJ to prevent absorpton of trace elements onto the walls of the flask. After filtration, the Nuclepore filters were weighed and dried by air overnight for subsequent PIXE analysis. The flasks containing about 100 g of the soluble portion were prefrozen in a mixture of dry ice and acetone and then quickly placed in a freeze-drier for about 30-36 h. At the end of the freeze-drying time 1 mL of high purity Ultrex "OB was added to give a concentration factor of about 100. The use of an internal standard combined with a relative yield curve is the simplest and most direct calibration method for PIXE analysis. The curve was obtained by bombarding targets prepared with elemental standard atomic absorption solutions (1000 ppm) from Harleco Co. When these commercial solutions were unavailable, they were prepared by using pure salts of the elements of interest. Reference to such curves removes the uncertainties due to X-ray production and absorption, integrated charge, and detection efficiency. Hence, when an internal standard with a relative X-ray yield curve is used, only the position of the detector, energy of the proton beam, and target backing must be kept constant. For the soluble portion of snow, cobalt was adopted as the internal standard because it was not present at detectable concentrations in any of the samples and its position in the spectra did not interfere with any neighboring X-ray peaks. A typical X-ray spectrum is shown in Figure 1. The spectrum from the snow particulate sample is shown in Figure 2. The introduction of an internal standard in a particulate sample is somewhat difficult and often impossible. Trace-element concentrations in such matrices can be determined either by normalizing to the

IOOml FREEZE-DRIED SNOW (SITE 13) CONCENTRATION FACTOR = 100 PROTON ENERGY 1.6 MeV T I ME = 3600 SECONDS BACKING=NUCLEPORE FILTER(O.Zum)

IO6

Co( INTERNAL STANDARD

I

300PPM

I

1

100

200

I

I

I

I

600

700

I

300 400 500 CHANNEL NUMBER

Flgure 1. Characteristic X-ray spectrum from a preconcentrated snow sample bombarded wlth 1.6-MeV protons. SNOW PARTICULATE (SITE 13) PROTON ENERGY = I.6MeV T I M E = 1800 SECONDS BACKING. NUCLEPORE FILTER

I

I

1

g io5 z

2 io4 0

a io3 a W

102

rf I O 1 "0 IO9

100

200

300

400

500

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Figure 2. Characteristlc X-ray spectrum from a snow particulate matter sample bombarded with 1.&MeV protons.

charge collected by a Faraday cup at the end of the beam line or by evaporating on the sample an element of known concentration (20). In this present study we have chosen a more simple and accurate method. After PIXE bombardment the Nuclepore filters, containing the particulate matter, were activated for 10 min with thermal neutrons (1 X 10l2neutrons cmq2s-l) from the Slowpoke-2 research reactor at the University of Toronto. y-Ray spectra were collected for each sample 15-20 min after removal from the reactor by using a 24% efficient Ge(Li) detector having a resolution of 1.9 keV at 1332 keV. Aluminum and manganese concentrations were then determined by using a semiabsolute method previously published (21). The aluminum concentration values were subsequently used as internal standards for the PIXE analysis of the particulate samples. While PIXE yielded reliable results for most of the elements in the snow-soluble portions (13), maximum reliability in the aluminum concentration values was not always achieved for levels below 150 ng/g (which was almost always the case) since the aluminum X-ray peak lies on the high Bremsstrahlung background, which makes its analysis difficult. Neutron activation analysis was then also employed to determine aluminum as well as manganese concentrations in the snow-soluble portions. Experimental conditions were kept the same as for the particulate samples except that y-ray spectra were collected 90 s after removal of the samples from the reactor. No preconcentration procedure was necessary. These determinations were done before the use of freeze-drying methods for PIXE and required only 1mL of solution. A typical INAA spectrum is shown in Figure 3. The need for a precise and accurate determination of A1 and Mn Environ. Scl. Technol., Vol. 17,

No. 9, 1983 543

Table I. Sulfur, Manganese, and Aluminum Concentrations in Montreal SnoaP Soluble Portion

estimation of total anniiald

element

mean, ng/g

range, ng/g

776-2836 10-166 21-636

Sb

MnC AIc

median, ng/g

1133 30 145

detection water 90error limit, ng/g soluble

1100 *10 12 *5 80 *5 Insoluble Portion

20 3 18

av EF

87

7000

70

27 =1

18

range, ug/g

element

mean, ug/g

ug/g

detection water 9.error limit, cg/g soluble +lo 120 13 30 t5 3 t5 160 82

3540-11 550 6460 5880 Mne 164-1434 360 205 24 700 21600-37450 24 800 AIC These calculations are based upon eight sample sites. Analyzed by PIXE. averace nrecioitation (snow and rain) of 100 em'. Sb

IO

~

" I_

' i ~ w

"

pew

~

'I_

YI

I

mw

I

I gem

I

l

rm

'

I sim

OUnaHIlw

npln 9. Typical qmclnnn of unconcenbated snowaolubb pwaon using INM:RUX = 1.0 X io'* neutrOns c d s-': t , = 10 mkl; t, = 90 s; 1. = 10 min.

concentrations used for enrichment factora and elemental pair correlations is discussed in the following section. For the sulfur determinations in snow collected in Toronto and Sault St.Marie an ARL 34ooo induced coupled plasma spectrometer with a background corrector waa used. The sulfur line used was 180.73 nm.

Results and Discussion Analytical Results. The analytical results for the soluble and insoluhle fractions of sulfur, manganese, and aluminum including concentration ranges, as well as the mean and median, detection limits, percentage of water solubility (or insolubility), enrichment factors (EF), and estimation of total annual depositions for the island of Montreal are shown in Table I. Detection Limits. The calculation of the detection limits for PIXE and INAA were baaed upon 3 times the square root of the background under the peak while the detection limits for the ICP spectrometer were calculated aa 3 times the standard deviation of the signal in a blank. Typical limitsfor soluble sulfur waa 20 ng/g for both PIXE and ICP and 120 pg/g for particulate sulfur. Solubility. From the point of view of toxicity a knowledge of water soluble/ine.oluble fractions ia important 5 U En-.

Scl. Technol.. Vd. 17, No. 9, 1983

1300 32 170 estimation of total annuaP

%

median,

deposition, mg m-' year.'

deposition,

av EF

mg m-' year-'

62 200 1.5 4 =1 640 Analyzed by INAA. Based on yearly

for many m n s , induding adding information on source, transformations, fate, and reactivity of the elements. P h p i d characteristicsof elements such &9 solubility along with other chemical characteristics (e.g., speciation) can be the ultimate indictor of their potential toxicological effect. The use of 0.40-rm Nuclepore filter in these experiments enabled us to distinguish the soluble and insoluble fractions. This procedure is often overlooked in wet atmospheric deposition studies. Both sulfur and manganese exhibited high solubilities, 87% and 70% respectively, in melted snow water. ol,the other hand, aluminum, being mainly soil derived, had a low solubility, 18%. as one would expect. Concentrations and Enrichment Factors. Total sulfur, manganese, and aluminum concentrations for the soluble (30 sample sites) and insoluble portions (8 sites among the 30) are given in Table I. With the exception of one sample site represented by the upper limit of the range of concentrations, the distribution of sulfur and manganese did not vary significantly. This may suggest the complex nature that long-range transport of pollutants and emissions from local sources may mask each others detectable contributions. The relatively high sulfur concentrations determined for site 13 close to petroleum refineries agrees well with the results of a recent study on sulfur dioxide pollution in Montreal (23). In order to distinguish naturally occurring elements in aerosola from those mainly due to human activities, Gordon et al. (24) proposed the use of an enrichment factor (EF). Such an EF has been successfully used by many researchers and is defined as follows: EF (X/C)aimmpb/(X/O&a -t where Xis the Concentration of the element of interest and C is the concentration of a normalizing element. An EF value greater than 1 suggests that the element arises predominantly from anthropogenic sources. However, values of 10 or greater are considered to be more significant since the concentration of the chosen normalizing element may vary from place to place. Ideally, the normalizing elements should have a high crustal abundance, and their crustal composition should be well-known. Aluminum fulfills these requirements and is the usual choice as a normaling element. Furthermore, Al concentrations can be very accurately and precisely meaaured by INAA. As can be seen from Table I sulfur in the soluble portion has a very high EF average value (EF .= 7000) and a

moderate EF value of 62 in the particulate fraction. Sulfur enrichment values in filtered rainwater in Tallahassee (15) (EF N 4900) and filtered snow in Toronto (EF N 700) and Sault St. Marie (EF N 1600), at the eastern tip of Lake Superior, are comparable to EF values determined in Montreal, although the average results are significantly higher for Montreal. These findings suggest a problem associated with sulfur deposition in eastern North America. No published data on total sulfur concentrations in insoluble fractions of precipitation have appeared, and hence no comparisons can be made. Enrichment factor values for manganese (EF N 27) in the filtered snow in Montreal are relatively lower than for sulfur. This value compares relatively well with EF values for filtered precipitation in Tallahassee (15) (EF N 6), Northern Minnesota (25) (EF N 6), Hiyoshi, Japan (26) (EF N 2), Gent, Belgium (27) (EF N 451, across Canada sampling sites (28) (EF N 75), Toronto (present work) (EF N 12), and Sault St. Marie (present work) (EF N 12). The particulate portion showed a negligible enrichment factor of 1.5, suggesting that virtually all the insoluble Mn was soil or crustal derived. Again this value compared well to the very low EF values of insoluble Mn in the above places. In all cases the above comparative E F values were evaluated by us from the published data. When aluminum concentrations were not available to be used as normalizing elements, iron was chosen instead. It is interesting to note that the calculated EF values show a consistency for cities many thousands of kilometers away from each other. Sulfur and Manganese Elemental Pair Correlations. It has been suggested that some metals may serve as catalysts to accelerate oxidation of SO2 in clouds (29-33). In particular two groups (29, 30) have studied the elemental pair correlation of Mn2+and SO-: concentrations in rainwater. Penkett et al. (29)have shown that for Mn2+ concentrations in Belgium, less than 1.1 pM, the correlation coefficient with S042-was low ( r = 0.31) and increased to r = 0.67 when the Mn2+ concentrations increased. The value of 1.1 pM was considered a "cutoff" point for catalytic oxidation of sulfur dioxide by Mn2+. On the other hand Lindberg (30) has shown that the cutoff value for Mn2+ was 0.07 pM. Below this value the correlation coefficient was determined to be r = 0.39 (PI 0.05), while increased above this cutoff value the correlation with substantially to r = 0.92 ( P I0.01). To check the above hypothesis, elemental pair correlation coefficients were also evaluated for the soluble manganese and sulfur concentrations in Montreal snow. To achieve reliable results, 30 sample sites were considered. All the manganese concentrations measured in this study were below 1.1 pM but greater than 0.07 pM with the single exception of one site (site 13 previously discussed). Sulfur concentrations varied between 10 and 110 pM. Their computed correlation coefficient was r = 0.42 (P I0.025). This result is much closer to the correlation coefficient of r = 0.37 determined by Penkett et al. (29), giving supporting evidence that Mn2+concentrations below 1.1 pM are not significantly correlated with SO-: ions. This study suggests that the Mn2+ concentrations measured by Lindberg may have come from other strong anthropogenic sources such as the Indiana ferrous industries less than 1000 km away. Further it would be wrong to assume that all the sulfur and manganese in the soluble portions in precipitation are in the ionic forms of Mn2+and S042-, although it is often believed that these species predominate in solution. It has also been pointed out by Linberg (30) that the relationship between these two ions in rainwater samples may be a result of postdepositional oxidation of

SO2 and sulfites catalyzed by Mn2+. As well it has been shown that the oxidation of SO2and SO3- has occurred in deposited rainwater following the collection of samples (311. Clearly a knowledge of total sulfur and manganese concentrations in wet atmospheric deposition is extremely valuable. Further investigations into the relationships between these two elements would help not only in identifying pollution sources but also in understanding the catalytic behavior of manganese in the oxidation of sulfur dioxide in the atmosphere. Conclusion

This work has demonstrated that PIXE is a reliable nondestructive method for the determination of soluble and insoluble sulfur concentrations in wet atmospheric deposition. It is also evident that sulfur determinations on soluble precipitation can be undertaken by the use of ICP spectrometry. Neutron activation analysis has shown its usefulness in determining aluminum, which can be used as internal standard for PIXE analysis for the particulate matter. Furthermore, the accurate and precise determination of aluminum by INAA proved to be very pragmatic in evaluating enrichment factors in both the soluble and insoluble fractions. Enrichment factor results suggests that sulfur in both soluble and insoluble fractions and manganese in the soluble portion predominantly arose from anthropogenic sources. Comparisons of intercity EF values for manganese and sulfur showed a consistency in values. Elemental pair correlations between sulfur and manganese in the soluble fractions gave qualitative support to the hypothesis that Mn2+concentrations below 1.1 pM can be considered to be a cutoff value for Mn2+catalytic oxidation of sulfur dioxide. Registry No. Sulfur, 7704-34-9. Literature Cited (1) Shriner, D. S., Richmond, C. R., Lindberg, S. F., Eds. In "Atmospheric Sulphur Deposition"; Ann Arbor Science: Ann Arbor, MI, 1981. (2) Fortune, C. R.; Dellinger, B. Enuiron. Sci. Technol. 1982, 16, 62-6. (3) Mitchell, M. J.; Landers, D. H.; Brodowski, D. F. Water, Soil Air Pollut. 1981, 16, 351-59. (4) Cheney, J. L.; Homolya, J. B. Enuiron. Sci. Technol. 1979, 13, 584-8. (5) Homoloya, J. B.; Fortune, C. R. Atmos. Enuiron. 1978,12, 2511-4. ( 6 ) Stevens, R. K.; Dzubay, T. G.; Russwurm, G.; Rickel, D., presented at the International Symposium on Sulfur in the Atmosphere, Dubrovnik, Yugoslavia, Sept 1977. (7) Killman, K.; Wainwright, M. Enuiron. Pollut. Ser. B. 1981, 3, 81-5. (8) Winchester, J. Nucl. Instrum. Methods 1977,142, 85-90. (9) Winchester, J. Nucl. Instrum. Methods 1981,181,367-381. (10) Landsberger, S.; Jervis, R. E.; Lecomte, R.; Paradis, P.; Monaro, S. Enuiron. Pollut. Ser. B. 1982, 3, 215-23. (11) Jervis, R. E.; Landsberger, S.; Lecomte, R.; Paradis, P.; Monaro, S. Nucl. Instrum. Methods 1982,193, 323-9, (12) Landsberger, S.; Jervis, R. E.; Aufreiter, S.; Van Loon, J. C. Chemosphere 1982, 3, 237-247. (13) Jervis, R. E.; Landsberger, S.; Aufreiter, S.; Van Loon, J. C.; Lecomte, R.; Monaro, S. Int. J . Environ. Anal. Chem., in press. (14) Chan, K. C.; Cohen, B. L.; Frohliger, J. 0.; Shabason, L. Tellus 1976, 28, 24-30. (15) Tanaka, S.; Darzi, M.; Winchester, J. W. Enuiron. Sci. Technol. 1981, 15, 354-7. (16) Schemenauer, R. S.; Berry, M. 0.; Maxwell, J. B. In "Handbook of Snow; Principles, Processes, Management and Use"; Gray, D. M., Male, D. H., Eds. Permagon Press: Environ. Sci. Technol., Vol. 17, No. 9, 1983

545

Environ. Sci. Technol. 1983, 17, 546-548

Toronto, Canada, 1981; Chapter 4, p 147. (17) Barrette, M.; Lamoureux, G.; Lebel, E.; Lecomte, R.; Paradis, P.; Monaro, S. Nucl. Instrum. Methods 1976,134, 189-96. (18) Lecomte, R.; Paradis, P.; Monaro, S.; Barrette, M.; Lamoureux, G.; Menard, H. A. Nucl. Instrum. Methods. 1978, 150, 289-97. (19) Lecomte, R.; Paradis, P.; Landsberger, S.; Desaulniers, G.; Monaro, S. X-Ray Spectrom. 1981,10, 113-16. (20) Houdayer, A. J.; Beaudoin, P.; Lessard, L. Nucl. Instrum. Methods 1982,202,487-91. (21) Bergioux, C.; Kennedy, G.; Zikovsky, L. J. Radioanal. Chem. 1979, 50, 229-34. (22) Day, J. P.; Fergusson, J. E.; Chee, T. M. Bull. Environ. Contam. Toxicol. 1979, 23, 497-502. (23) Cleroux, R.; Roy, R.; Fortin, N. Water,Air Soil Pollut. 1980, 13,143-56. (24) Gordon, G. E.; Zoller, W. H.; Gladney, E. S. In "Trace Substancesin EnvironmentalHealth"; Hemphill, D. D., Ed.; University of Missouri: Columbia, MO, 1973; Vol. VII, pp 167-75. (25) Thorton, J. D.; Eisenreich, S. J.; Munger, J. W.; Gorham, E. In "Atmospheric Pollutants"; Eisenreich, S. J. Ed.; Ann Arbor Science: Ann Arbor, MI, 1981; Chapter 14.

(26) Hashimoto, Y.; Osada, Y.; Tanaka, S.; Chiba, R.; Yokota, H.Nucl. Instrum. Methods 1981,181, 227-30. (27) Schuyster, P.; Maenhaut, W.; Dams, R. Anal. Chim. Acta 1978,100,75-85. (28) Hamilton, E. P.; Chatt, A. J . Radioanal. Chem. 1982, 71, 29-45. (29) Penkett, S. A.; Jones, B. M. R.; Eggleton, A. E. J. Atmos. Environ. 1979, 13, 139-47. (30) Lindberg, S. E. Atmos. Environ. 1981, 15, 1749-53. (31) Barrie, L. A.; Georgii, H. W. Atmos. Environ. 1976, 10, 743-49. (32) Barrie, L. A.; Beilke, S.; Georgii, H. W. In "Precipitation Scavenging"; Semonin, R. G., Beadle, R. W., Eds.; EDRA Symp. Ser. No. 41, CONF-741003, National Technical Information Service, 1977, Springfield, VA. (33) MAP3S, "The MAP3S Precipitation Network: First Periodic Summary Report"; Pacific Northwest Laboratory, Richland, WA, PNL-2402, 1977.

Received for review November 22, 1982. Revised manuscript received March 2,183. Accepted March 29,1983. This work has been supported by the Natural Sciences and Engineering Research Council of Canada.

Reaction Rates of Polynuclear Aromatic Hydrocarbons with Ozone in Water Vjera Butkovlb, Leo Klaslnc, Matko Orhanovlb, * and Jasmlna Turk Rudjer BogkoviB Institute, Zagreb, Croatia, Yugoslavia

Hans Gusten"

Kernforschungszentrum Karlsruhe GmbH, Institut fur Radiochemie, 7500 Karlsruhe, Federal Republic of Germany The rate constants for the reaction of pyrene, phenanthrene, and benzo[a]pyrene with ozone in water were determined by means of stopped-flow spectrometry. The second-order rate constants amount to about 4 X lo4, 1.5 X lo4, and 0.6 X lo4 dm3.mol-1.s-1, respectively, over the pH range 1-7. The corresponding half-lives in presence of M ozone at pH 7 are less than a second, i.e., they are 10000 times shorter than the values for pyrene and benzo[a]pyrene that are dissipated widely in the literature. Implications of these results are discussed with respect to the removal of polynuclear aromatic hydrocarbons from drinking water as well as to their atmospheric residence times. Introduction Polynuclear aromatic hydrocarbons (PAH) are ubiquitous in our environment. Many PAH's are known to be carcinogenic to animals and probably to man. Thus, in recent years, a concern has been growing about their release, amount, stability, and fate in the environment ( I , 2). For an ecotoxicological assessment of the PAH's the knowledge of their residence times in the atmosphere and water has become important. Since ozone is commonly used in Europe for the purification of urban drinking water, the half-lives of the PAH's in the reaction with ozone are of importance for an economic ozonation treatment (3, 4 ) . I t is surprising that kinetic data concerning this reaction in water have not been determined as yet. In the related study by Il'nitskii et al. (5) on the ozonation of five PAH's including pyrene and benzo[a]pyrene, it was reported that these compounds at 0.67 X g/mL in acetone and acetoneln-octane solutions completely disappeared from the solution after 2.5 min of 546

Environ. Sci. Technol., Vol. 17, No. 9,1983

contact with bubbling ozonefoxygen mixtures at 18-21 "C. After only 1 min of contact time the residual amount of the different PAH's was reported to range between 39% and 0%. These data, observed under ill-defined experimental conditions and obtained for a nonaqueous solution with unrealistically high concentrations of both PAH and ozone, were then uncritically taken by Radding et al. (6) to apply for water as the solvent and used to calculate rate constants and half-lives of PAH's at environmentally M in water and 2 relevant ozone concentrations, i.e., X low9M in air. These half-lives for the different PAH's of up to 1 h in water and of several hundred hours in air indicate that such a slow reaction with ozone hardly seems to be an important process for the degradation of the PAHs in our environment (6). Since the authors (6) made an error in the dimension for the rate constant k by using L-mol-l-s-linstead of L.mol-l.min-l, the calculated half-lives in air would actually result in the order of 10OOO h. These calculated half-lives of the PAH's are now dissipated widely in the secondary literature (I,2, 7-9). On the other hand, Hoign6 and Bader reported that the reaction of ozone with organic compounds in water can be very fast (IO). This situation prompted us to start an investigation of reaction rates of PAH's with ozone in water. Experimental Section Kinetic Measurements. Preliminary experiments showed that the disappearance of PAHs with ozone in water is several thousand times faster than the literature data above indicated (5, 7,8). Thus, contrary to the method of Hoign6 and Bader (IO),which determines the reaction rate constant from the consumption of ozone by the solute, we determined the rate constants by monitoring the change of concentration of a PAH in an excess of

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0 1983 American Chemical Society