The mercuric chloride balance during the described events, shown in the right-hand column of Table IV indicates that a total of 4375 gg of mercuric ion was lost to the container. Additional studies, summarized in Figure 1, demonstrate that nearly all of the mercuric chloride that has been lost to the container can be recovered with the aid of NaCl and/or HCI. Chloride ions in aqueous and in acid solution appear to prevent binding of HgZT to the container. We also examined the sorption of mercuric chloride by glass containers. In typical experiments, the Hg2+ concentration of a 12-ppb mercuric chloride solution in a 10-liter glass carboy dropped to 10 ppb after 24 hr. This corresponds to a 17% loss or 0.008 gg HgZ+/cmz. Similarly, a 30-ppb mercuric chloride solution in a 1-liter volumetric flask lost about 35% of its Hgz+ after 9 days, corresponding to 0.02 +g Hg2+/cmz. Additional experiments have shown that it is relatively safe to store mercuric chloride in the ppm range, since the total loss falls within the experimental error of the analyses. Precleaning the glassware with 5% to 10% " 0 3 , followed by rinsing of the container with a 0.1N HC1 solution
containing IN NaC1, effectively removes any adsorbed mercury from the surface. Similarly, addition of NaCl and/or HC1 to dilute mercuric ion solutions prevents loss of mercury to container. Sorption of mercuric ion on glass has been considered as a source of error in analyses since the eighteen hundreds. However, we have not seen any quantitative studies which show distribution of mercuric ion between plastic or glass containers and the solvent, except for a recent report (Carr and Wilkaiss, 1973) which appeared after this work was completed. Our results show that it is possible to desorb nearly all of the mercuric salt from the container with the aid of chloride ion and hydrochloric acid and that wool effectively competes with the container for mercuric ions. This observation is not only of theoretical interest but of obvious practical importance.
Literature Cited Carr, R. A,, Wilkaiss, D. E., Enuiron. Sci. Technol., 7,62 (1973). Friedman, M., Waiss, Jr.. A . C., ibid.,6,457 (1972). Masri, M. S., Friedman, M., ibid.,6,745 (1972).
Received for reuieu February 20, 1973. Accepted July 16, 1973.
Ultraviolet Photography of Sulfur Dioxide Plumes Gary M. Klauber Department of Electrical Engineering, The Johns Hopkins University, Baltimore, M d . 21218
A method to image normally invisible SO2 plumes on photographic film, using the sun's ultraviolet light in the absorption band of SO2 near 300 nm, is described. Design of a primitive SOz plume camera is described, and a sample uv SO2 plume photograph is presented. A knowledge of the geometry and ultimate rise of smoke plumes is necessary to predict the ground level concentrations of sulfur dioxide downwind of tall, stationary sources. This has typically been done (Hoult et al., 1969) by shutting off the electrostatic precipitators to release visible particulates and photographing this soot plume. This note describes a novel technique for photographing SO2 plumes using the ultraviolet light of the sun and exploiting the uv absorption properties of S O z .
Theory SO2 gas absorbs light in the 232-315-nm wavelength range, with a typical Beer-Lambert law absorption coefficient of 0.013 cm-I torr-I a t 304 nm (Warneck et al., 1964). Daytime sunlight typically arrives at the earth's surface only at wavelengths above 295 nm, increasing in intensity with increasing wavelength (Coblentz and Stair, 1936; Knestrick and Curcio, 1970). In principle, if a camera body were fitted with a lens which passes uv light and an interference filter which admits only those wavelengths absorbed by SO2, photographs of SO2 plumes are possible. The absorption bands of C02, CO, 0 2 , H20, KzO, "3, and N O fall outside of the SO2 band of interest (Thompson et al., 1963). Absorption of NO2 is typically a factor of three lower than that of SO2 near 300 nm (Hall and Blacet, 1952). Nitrogen oxides are less than 10% NO2 near the stacks, and the stack exit NO, concentration is typically one third of the SO2 concentration (Cuffe and Gers-
tle, 1967). Therefore, NO2 interference is two orders of magnitude below SO:! signals near the stack. In the region of ultimate plume rise in urban atmospheres, NO2 interference may be as much as 107'0, due to rapid oxidation of NO to NO2 in the plume.
Apparatus
A fused quartz simple lens, with focal length 9.5 cm in the ultraviolet, was mounted on a single lens reflex camera body at a lens-to-film distance equal to the focal length. A 10-nm bandwidth interference filter centered a t 298 nm was mounted immediately behind the lens. The entrance aperture was fl6. T o estimate exposure and to adjust the focus, a series of trial exposures was made. Kodak High Contrast Copy Film 5069, processed according to manufacturer's directions, was used. The apparatus was then used to photograph power plant plumes perpendicular to their axes. Resul t s A series of pictures was taken of the H. A. Wagner power plant, southeast of Baltimore, Md., on Monday, April 16, 1973, from 11:05to 11:lO A.M. EST. The bearing of the stacks from the camera was 285" a t a range of 1.1 km. Surface winds 10 min earlier a t Friendship Airport, 11 km to the east, were 220" a t 4 m sec-I. Skys were partly cloudy, with a 40% cirrus cover. Figure 1 shows an ordinary visible light photograph of the scene, taken through a standard 50-mm camera lens, where no smoke is visible above the stacks. Figure 2 is an ultraviolet photograph, exposed for 2 sec, taken about 2 min after Figure 1. Note that one of the stacks, number 1 (left), is not in operation. Superposition of absorption by plumes from units 3 and 4 is apparent. The Volume 7. Number 10, October 1973
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Figure 1. Ordinaryvisibie-light photograph of Wagner power plant Stacks. Baltimore. Md.. April 16. 1973.11:05 A M ESl
Figure 2. Ultravi olet photograph of v\ilagner,power plant stacks. Baltimore, Md., April 16, 1973, 11~07A M EST
plume from stack 4 bends over sooner than that from stack 3, presumably due t o a difference in stack exit conditions. Fuzziness near the edge of the picture is caused hy aherration in the lens. White spots on the photo are caused by scratches in the interference filter, and other flaws were generated in photographic processing.
Conclusions Ultraviolet photography of SOz plumes has great potential in characterizing plume geometry. Attempts t o quantify SO2 flux from photographs by densitometry will he complicated hy the nonlinearity of the photographic process and by variation in films and processing from hatch t o hatch. A calibrated absorption cell of SO2 interposed in the optical path to calibrate the system may eliminate some of these problems. In oxidizing urban atmospheres, however, rapid conversion of NO to NO2 in the plume may cause up to about 10% interference from NO2 absorption. 954
Environmental Science 8 Technology
Acknowledgments
I wish to thank G. Fastie and Peter E, for their support and encouragement throughout the
of this ~i~~~~~~~~cited Coblentz, W. W., Stair, R., J. Res. Not1 Bur. Standards, 17, 1 (1936).
Cuffe, S. T., Gerstle, R. W., "Emissions From Coal-Fired Power Plants: A Comprehensive Summary," U.S. Department of Health, Education, and Welfare, Public Health Service Pub. 999-AP-35, Durham, N.C., 1967. Hall, T. C., Blacet, F. E., J. Chem. Phys., 20,1745(1952). Hoult, D.P.,Far, J. A., Fourney, L. J., J. Air Pollut. Contr. Ass., 19,585 (1969).
Knestrick, G. L., Curcio, J. A.,Appl. Opt., 9,1574 (1970). Thompson, B. A., Harteck, P.,Reeves, R. R.,J. Geaphys. Res., 68,6431(1963). Warneck, P., Manna, F. F., Sullivan, J. 0..J. Chem. Phys., 40, 1132 (1964). Receiuedforreuiew June 27, 1973. Accepted July 18, 1973
