that salinities up to 4.0% do not interfere, suggesting that there should be no particular problems in the analysis of seawater. Some types of biological samples may also be analyzed by this procedure. Trace analysis of waters in the Lake Tahoe basin (Figure 3) demonstrate, as expected, very low levels of metals. Most metals are present primarily in the particulate form. The lake itself is an extremely oligotrophic system, and as such, it contains very low nutrient levels. If those levels are increased by amounts which would be insignificant in most other systems, there can be quite marked effects upon the biotic community in the lake. The scarcity of dissolved iron renders this element an especially important limiting nutrient. Maintenance of the present water clarity a t Lake Tahoe is threatened by the large influxes of iron which result from erosion of devegetated soils in the watershed. It is common to see a great deal of variability in nutrient levels in Lake Tahoe and its tributaries, as exemplified by the high level of iron found in the Truckee River. This is often due to changes in periphyton growth in the streams. The periphyton strips nutrients from the water while it is growing but releases them rapidly during large death and deconiposition periods that occur during the winter. Conclusions
Energy-dispersive X-ray fluorescence has much to offer in the field of trace metal monitoring of ecological systems. Coupled with dithiocarbamate precipitation for conversion of water samples to XRF targets, it is capable of rapid, multielement analysis at relatively low cost. It is also a convenient technique for performing separate analyses on dissolved and particulate fractions. For studies requiring analyses of only one or two metals, atomic absorption spectrophotometry or colorimetric methods may be more appropriate. Studies of alkali and alkaline-earth metals, and elements lighter than titanium may also require other techniques. Where the transition metals are of interest, how-
ever, use of X-ray fluorescence for ecological studies of natural water systems has obvious merits. Acknowledgments
The authors wish to thank Charles Goldman for his support of this research and review of the manuscript. Personal consultation with Charles Nash and scanning electron micrographs provided bv Hans Paerl were also appreciated. Literature Cited (1) Goldman, C. R., Mem. 1st. Ital. Idrobiol., 18, Suppl., 121-35 (1965). (2) Murad, E., Anal. Chim. Acta, 67,37-53 (1973). (3) Leoni, L., Saitta, M., X-Ray Spectrom., 3,74-7 (1974). (4) West, N. G., Hendry, G. L., Bailey, N. T., X - R a y Spectrom., 3, 78-87 (1974). (5) Morris, A. W., Anal. Chim. Acta, 42,397-406 (1968). (6) Armitage, B., Zeitlin, H., ibid., 53,47-53 (1971). (7) Murata, M., Noguchi, M., ibid., 71,295-302 (1974). (8) Reymont, T. M., Dubois, R. J., ibid., 56, 1-6 (1971). (9) Luke, C. L., ibid., 41, 237-50 (1968). (IO) Rhodes, J. R., Amer. Lab., 5,57-73 (1973). (11) Giauque, R. D., Goulding, F. S., Jaklevic, J. M., Pehl, R. H., A n d . Chem., 45,671-81 (1973). (12) Watanabe, H., Berman, S., Russell, D. S., Talanta, 19, 136375 (1972). (13) Malissa, H., Schoffmann, E., Microchim. Acta, 1955, 187-202 (1955). (14) Hulanicki, A., Talanta, 14,1371-92 (1967). (15) Usatenko, Y. I., Barkalov, V. S., Tulyupa, F. M., Zh. Anal. Khim., 25, 1458-61 (1970, Russ.). [Transl. J . Anal. Chem. U.S.S.R.,25,1257-9 (19701.1 (16) Brooks, R. R., Presley, B. J., Kaplan, I. R., Talanta, 14,80916 (1967). (17) Chau, Y. K., J . Chromat. S a . , 11,579 (1973). (18) Kunkel. R.. Manahan, S. E., Anal. Chem., 45,1465-8 (1973). (19) Armstrong, F. A. J., Williams, P. M., Strickland, J. D. H., Nature, 2,481-2 (1966). (20) Perry, S. K., Brady, F. P., Nucl. Znst. Meth., 108, 389-96 (1973).
Received for review October 1, 1973. Accepted June 23, 1975. Work supported by the RANN Division of the National Service Foundation.
Atmospheric Fates of Halogenated Compounds Daniel Lillian,' Hanwant Bir Singh,* Alan Appleby, Leon Lobban, Robert Arnts, Ralph Gumpert, Robert Hague, John Toomey, John Kazazis, Mark Antell, David Hansen, and Barry Scott Cook College, Busch Campus, Rutgers University, New Brunswick. N.J. 08903
Based on the U.S. Tariff Commission report and the many uses of halocarbons, evidence exists that halocarbons as a group of pollutants are emitLed to the atmosphere in significant quantities. Halocarbons are used extensively, especially in developed countries, as refrigerants, aerosol propellants, solvents, cutting fluids, synthetic feedstocks, and in the production of textiles and plastics. Production figures indicate a healthy growth rate of the halocarbons industry in excess of 6% per annum. Their total production in the U S . between January and July 1973 (7 months) exceeded 10 billion pounds ( I ) , suggesting a yearly worldwide production greater than 30 billion lb. Atmospheric emission rates for CC13F alone have increased from an average of 0.14 billion lb per year between 1961 and 1965 to 0.51 billion lb per year between 1971 and 1972, with the U S . ' P r e s e n t a d d r e s s , U.S. Army Industrial Hygiene Agency, Edgewood Arsenal, Md. * Present address, Stanford Research Institute, Menlo Park, Calif. 1042
Environmental Science & Technology
and Canada accounting for 44% of the world emissions (2). Similarly, the yearly worldwide injections of CC12F2 and C2Cl4 into the troposphere in 1974 are estimated to be nearly 1 billion lb each. Because of the significant emissions of these and other halocarbons, their potential environmental impact, including the destruction of the protective stratospheric ozone layer, and their usefulness as chemical and physical tracers for understanding complex atmospheric and environmental factors, we have undertaken an extensive ongoing study to characterize the atmospheric behavior of this relatively unstudied group of air contaminants. Reported here are aerometric halocarbon and SFs data obtained during several programmed field studies initiated since March 1973 at various locations in the U S . which should be representative of a wide gamut of emission patterns and meteorological conditions. The compounds included in the present study are CCl3F, CC12F2, CH3CC13, CC12CC12,CCL, CHCICClp, CH31, SF6, CH2CHC1, CHC13,
Concentrations of eleven halogenated compounds were measured under various geographical and meteorological conditions at selected locations in the US. Compounds such as CC13F, CC12F2, CH3CC13, and CC14 were ubiquitous, and' generally present in sub-ppb concentrations. C2C14 could be measured a t least 50% of the time a t all locations a t concentrations exceeding 60 ppt, and its nonubiquitous nature is attributed to its tropospheric reactivity. C2HC13, another nonubiquitous reactive halocarbon, was measurable primarily near urban areas. Other nonubiquitous halogenated compounds such as SF6, CH3I, CHzCHC1, CHC13, and CC12F-CClF2 were measurable only in areas where a reasonable source could be invoked. Their absence was attributed either to high tropospheric reactivity (CH31,
CH2CHCl) or low source strength (SF6, CHCl3, CC12FCClF2). Vinyl chloride was measured only in Delaware City, Del., where concentrations were up to 1.5 ppm. Laboratory studies simulating tropospheric conditions established the tropospheric stability of CC13F, CC12F2, CH3CC13, cc14, and CC12F-CClF2. Simulated stratospheric sunlight irradiations of tropospherically stable compounds (CClsF, cc14, and CC12F-CClF2) confirmed their stratospheric reactivity. The adventitious labeling of urban air masses was used to demonstrate urban ozone transport to rural areas. It is proposed that the controversy over the origins of nonurban ozone may be resolved by simultaneously monitoring halocarbons.
and CC12F-CClF2. Of these, several were subjected to simulated tropospheric stability studies. Compounds tropospherically stable were tested for possible stratospheric reactivity. Correlations between ozone and halocarbon concentrations monitored at a nonurban location were used for the first time to demonstrate the feasibility and utility of tracing large-scale air masses for elucidation of photochemical smog phenomena.
sunlight and attributed the observed loss of less than 2% per day for the above compounds to permeation through the walls of the film bags. Hester et al. (6) provided support for the short-term tropospheric stabilities of CC12F2 and CCl3F based on smog simulation studies. Wilson (12) reported the photoreactivity of trichloroethylene and its possible involvement in the photochemical smog phenomenon. Molina and Rowland (13) and Cicerone et al. (14) have recently suggested the possible destruction of the stratospheric ozone layer by chlorine-atom-propagated chain reactions initiated by the photolysis of CCl3F and CC12F2. Experimental smog chamber data supporting the assumed long-term tropospheric stability of these compounds, however, is insufficient. No data at all exist on the tropospheric stability of many other chlorinated compounds present in the troposphere a t comparable concentrations to CC13F and CC12F2.
Literature Review The dearth of information on analytical procedures, ambient concentrations, and the atmospheric chemistry of halocarbons is not surprising in light of the only recent interest in this group of air contaminants. Lovelock ( 3 ) reported CCl3F and SF6 values in southwest Ireland of lo-" and 2.9 X (v/v), respectively, as representative of northern hemispheric background concentrations. Air passing over the continent from an easterly direction exhibited corresponding concentrations approximately an order of magnitude higher for both. Atmospheric concentrations ranging from 0.05-0.17 ppb CC13F in Bowerchalke, England, were also reported by Lovelock ( 4 ) for the period October 1970-71. No significant seasonal variation of CC13F was observed. Lovelock et al. (5) also reported mean aerial concentrations of 0.049 CClsF, 0.001 CH31, and 0.071 cc14 ppb ( v h ) over the North and South Atlantic Ocean. Hester et al. (6) reported CC13F and CC12F2 levels at various indoor and outdoor locations in the Los Angeles Basin. Ambient CC12F2 and CC13F levels were in the range of 0.1-1.25 and 0.05-147 ppb, respectively. Simmonds et al. (7) in a three-day study reported levels of CClSF, CC14, CH3CC1:3, and CpCl4 in the Los Angeles Basin. The reported concentration (ppb) ranges were 0.11-2.2 for CClsF, 0.1-1.63 for CC14, 0.01-2.3 for CH3CC13, and 0.01-4.2 for C2C14. Lillian and Singh (8) reported typical urban levels of CC13F, CH31, CH3CC13, CC14, CHClCC12, and CzCl4 in the New Brunswick, N.J., area and more recently (9) ambient concentrations of CClsF, CC12F2, CH31, CClzF-CClF2, CHC13, CH3CC13, CC14, CHClCC12, and C2Cl4 on a typically polluted day in Bayonne, N.J. Detailed analytical and confirmatory procedures were given along with estimates of potential errors associated with the use of an EC detector as a gas coulometer. Analytical methods for SF6, CBrF3, CHClF2, CH2CHC1, and COC12 in air were also presented, and in a later paper ( 1 0 ) pulse flow coulometry was developed and used successfully to obviate the normal errors caused by column sorption in conventional gas phase coulometric analysis. Saltzman et al. ( 1 1 ) irradiated mixtures of reactive atmospheric pollutants, CBrF3, SF6, and C4Fa with simulated
Experimental A Winnebago motor home equipped with the required aerometric monitoring instruments was used for on-site field studies initiated after May 1974. A gas chromatograph (GC) with a 15 mCi 63Ni EC detector and a flame ionization detector was used for halocarbon analysis. The GC analytical procedures have already been discussed in detail (9). The other instruments used in this study included an Aerochem NO-NO, - 0 3 analyzer, a REM ozone analyzer, and an MRI integrating nephelometer. Prior to May 1974, grab samples from various locations were analyzed in the New Brunswick, N.J., laboratory. One hundred ml all-glass syringes each fitted with a three-way Luer-Lok valve and a septum proved most convenient for this program and exhibited less than 10% halocarbon loss over a 48-hr period. All-glass syringes were used for GC injections. An all-glass manifold was used for ambient sampling of nitric oxides and ozone. Permeation tubes were used for GC calibrations of CC13F, cc14, CzCl4, CHClCCl2, CHJ, CHPCHCl, and CC12F-CClF2. Calibrations of other compounds were performed by standard multiple dilution procedures. In the case of CC12F2, our values could be as much as 30% low, accounted for by the CC12F2 peak eluted immediately after the water peak, and in days with high humidity, there was a reduction in the detector sensitivity due to moisture. 'The overall error for all the other compounds is considered to be less than about f 1 5 % (standard deviation). Tropospheric simulation studies were conducted using plastic film bags. These studies were also conducted with a 72-1. Pyrex glass flask when long irradiation times were required. A mix of 40-W sun, black light, and black-lightVolume 9, Number 12, November 1975
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'1
LOCATION. WHITE FACE MOUNTAINS i ELEV. WOO F T I N 1. STATE 9/17/ 1974
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Figure 2.
Halocarbons as tracers of urban ozone transport to nonurban areas
Flgure 1.
blue lamps (kl = 0.39/min) was used for simulated solar irradiations of bags. The geometry of the irradiation facility along with the blending procedures and experimental techniques employed have been discussed ( 1 5 ) . The 72-1. reactor was irradiated in an air-conditioned chamber equipped with 24 black lights (kl = 0.3/min). A 1-1. Hanovia photochemical reactor equipped with a 450-W high-pressure mercury vapor lamp (>2200 A) was used to study the UV photochemical degradation of selected halocarbons in air.
HALOCARBON I I N I I R l + S O P p h m N O ~ + M Y . R H + h V IN A 72 LITER WREX GLAS5 REACTOR
Results The maximum, minimum, and average concentrations of selected halocarbons and SF6 at several locations in the United States are presented in Table I. The averages are of determinations where detectable levels were measured. Table I1 gives typical ambient concentrations of these compounds at several urban and nonurban locations and over
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Flgure 3. Stability of CCl3F and CC12F2in NO2-air mixtures when subjected to tropospheric irradiations
Table I. Maximum and Minimum Halocarbon Levels a t Various Locations in United States Concentrations, ppb Monitoring period and location 6/18-6/19/74 Seagirt, N.J. (National Guard Base) 6/27-6/28/74 New York, N.Y. (45th & Lexington) 7/2-7/5/74 Sandy Hook, N.J. (Fort Hancock) 718-711 0174 Delaware City, Del. (Road 448 & Route 72 intersection) 7/11-7/12/74 Baltimore, Md. (1701 Poncabird Pass, Ford Holabird area) 7/16-7/26/74 Wilrnington, Ohio (Clinton County Air Force Base] 9/16-9/19/74 White Face Mountains (New York State) 3/73-12/73 Bayonne, N.J.
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Levels CCI,F
Max Min Mean Max Min Mean Max Min Mean Max Min Mean
0.55 0.12 0.25 3.8 0.50 1.44 0.75 0.10 0.28 0.21 0.095 0.13
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0.38 0.25 0.32 3.8 0.5 1.5 3.2 0.4 1.2 1.3 0.4 0.68
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Volume 9, Number 12, November 1975
1045
CC12F2, CH3CC13, and CC14, since June 1973, at the times and locations indicated in Table I are 0.046, 0.06, 0.03, and 0.05, respectively. I t is interesting that the values for CC13F and C C 4 are comparable to the reported background concentrations for the two, of 0.05 and 0.06 ppb, respectively (5, 16). The minimum CClzFz concentration of 0.06 is an order of magnitude less than the concentration used by Su and Goldberg (17) to calculate a 30-year residence time for CC12F2. Their background CClzFz concentration of 0.7 ppb is inconsistent with cummulative world production data. The integrated worldwide CC12F2 production would give an average background concentration of less than 0.1 ppb. During extended periods of inversion, the ambient concentrations of the ubiquitous halocarbons may attain values as high as 100-500 times their minimum concentrations. For example, the maximum concentrations observed for CC13F, CC12F2, CH3CC13, and CC14 during a three-day inversion in Bayonne, N.J., were 8.8, 47.0, 14.4, and 18.0 ppb, respectively (Table I). The maximum, minimum, and average data of Table I for all the halogenated compounds are indicative of a complex variable emission pattern and a strong dependency on meteorological factors and should be representative of the lower and upper limits one can expect at typical urban and nonurban locations. However, the Bayonne, N.J., data show that, a t times, meteorological conditions are probably more significant than local emission patterns. At this location not only were many of the maximum but also minimum halocarbon readings obtained. The frequency of minimum halocarbon data in Bayonne was understandably low when compared to rural area data, for example the White Face Mountains. Representative levels of halocarbons that one can expect in urban and rural areas are given in Table 11. Also included in Table I1 are data indicating a dramatic increase in halocarbon concentration as one enters an inversion layer from aloft. The apparent ubiquitous nature of CC13F, CC12F2, CH3CC13, and CC14, the probability of their near exclusive anthropogenic origin, their significant emissions, their low solubility in water, and theoretical chemical and biological inertness all suggested, early in our experiments, that these compounds would continue to accumulate in the troposphere and upon photolysis in the stratosphere play a significant role in stratospheric chemistry. However, there were insufficient data on CC13F and CClzF2 and no data on cc14 and CH3CC13 that rigorously precluded their reactions with typical reactive tropospheric species such as OH., O., RO., etc. The tropospheric stability of these four compounds in unequivocally demonstrated in Figures 3 and 4. In these experiments kl for NO2 photolysis was 0.39/min. Accordingly, in terms of total energy input, our laboratory irradiation times are equivalent to much longer tropospheric irradiation times. Similar experiments were conducted in which characteristic reactive hydrocarbons were also present. Again, with the exception of the small initial decay attributable to surface adsorption, these halocarbons were stable. Since NO2 was replenished periodically (up to 50 pphm NO2 every 24 hr) during the course of the irradiation, reactive tropospheric intermediates were continuously available for reaction with the halocarbons. While atmospheric CC13F, CC12F2, and CH3CC13 are clearly anthropogenic, the occurrence of CC14 in the atmosphere cannot be accounted for from direct production emission data (5, 18). No valid explanation for the CC14 budget is available to date. Promising research in this laboratory supports the possibility of considerable atmospheric CC14 formation by the photodecomposition of chloroalkenes in the troposphere (18). “Nonubiquitous” Halocarbons. Of the nonubiquitous 1046
Environmental Science & Technology
HALOCARBON DECAY IN A 1 LITER U.V 1>22OOAI REACTOR HALOCAR0ON t AIR + U V.
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Figure 6. Decay of tropospherically stable halocarbons when subjected to stratospheric ultraviolet irradiation
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