the absorption column and measuring cell due to the reactivity of HF with the system components. Thus these response data are only qualitative in nature. A possible explanation of the negative response with H F could be the suppression of the ionization of H?S04by the large amount of HF added. Conclusions The SOz readings obtained with the Thomas Autometer are substantially accurate even when significant levels of NO and NOz also are present. This specificity for SOe in the presence of nitrogen oxides is due to the nature of the absorbing reagent and absorption system used. Other gases such as HCI, Cln, and NH3, although not considered to be universal pollutants, would cause significant errors in the SO. readings obtained with the Autometer and other conductance-type instruments. The versatility of the flow mixing system used to prepare the parts-per-million gas mixtures of this study has been demonstrated. The system is simple and easy to use, and should be valuable whenever reactions involving parts-permillion gas mixtures are to be studied. Thomas and Amtower (1966) in a recent paper described a gas-mixing technique and interference study very similar to the one described above. Their results o n the effects of NOe o n SOLconductance values were in general agreement with those reported here. A similar absorbing reagent but a different absorption device were employed, however. These authors reported difficulty in dispensing nitrogen oxides from syringes. Similar difficulties also were encountered in the pres-
ent work with nitrogen oxides. Nevertheless it was possible to obtain several hours’ operating time before the needle became clogged. This time was sufficient to perform the tests reported. Literature Cited Hochheiser, S., Procedure A-1, Selected Methods for the Measurement of Air Pollutants, U S . Public Health Service, Pub. 999-AP-11 (1965). Hochheiser, S., Santner, J., Ludmann, W. F., J . Air Pollution Control Assoc. 16, 266 (1966). Jutze. G. A.. Tabor. E. C.. J . Air Pollution Control Assoc. 13, 278 (1963). Kuczynski, E. R., J . Airpollution Control Assoc. 13,435 (1963). Leeds & Northrup Co., Philadelphia, Pa., Direction Book No. 77-10-0-10, Issue 3 (1964). Moore. C . E. Cole. A. F. W..’ Katz., M.., J . Air Pollution Conirol Assoc. 7, 1 (1957). Olivo, R., Minerca Med., 1958, 1015-16; C A 52, 10466a (195 8). Saltzman, B. E., Am. Znd. H y g . Assoc. Quart. 16, 2 (1955). Sanderson, H. P., Penner, P. E., Katz, M., A n d . Chenz. 36, 2296 (1964). Terraglio, F. P., Manganelli, R . M., Anal. Clieni. 34,675 (1962). Thomas, M. D., Amtower, R . E., J . Air Pollution Control Assoc. 16, 618 (1966). Thomas, M . D., Ivie, J. O., Fitt, T. C., Ind. Eng. Chem., Anal. Ed. 18,383 (1946). West, P. W., Gaeke, G. C., Anal. Cheni. 28, 1916 (1956). West, P. W., Ordoveza, F., Anal. Chein. 34, 1324 (1962). Yocom, J. E., Richardson, R . L., Saslaw, I. M., Chapman, S., Proceedings of Air Pollution Control Association, Buffalo, N. Y . , 1956. Receioed for reciew Nocetnber 7, 1966. Accepted December 21, 1966.
COMMUNICATIONS
Remote Sensing and Characterization of Stack Gases by Infrared Spectroscopy An Approach Using Multiple-Scan Interferometry
vv
-e have explored the feasibility of monitoring smokestack effluents by measuring the infrared emission spectra of the stack gases from a ground location remote from the stack. The results of the experiments indicate that such measurements can be carried out and offer a new approach to studies in air pollution. The sensing instrument used was a Block Model 200 infrared interference spectrometer. The principles and methods of infrared interference spectroscopy have been described in detail (Low and Low and Coleman, 1966). The small optical system of the instrument was mounted on an 8-inch reflecting telescope, which served to limit the field of view of the instrument to a portion of the plume of a smokestack of a Rutgers power plant burning No. 6 bunker fuel. The interferometer-telescope combination was located approximately 600 feet from the plume. The interference spectrometer covers the range 2500 to 250 cm.-1 in a scan of 1-second duration, with a resolution of approximately 18 c n r l Successive scans can be added coherently and stored in a built-in computer core memory. The memory can function in a “subtract” as well as in an “add” mode, so that it is possible t o correct spectra by sub-
tracting “background.” Some typical spectra recorded on the same evening are shown in Figures 1 and 2 . The ordinates are displaced to avoid overlapping. Spectrum A of Figure 1 shows the relative emission of the sky near the smokestack, obtained at 6 P.M. The sky was slightly hazy but cloudless. The well-known “10- to 14-micron window” of the sky is prominent in spectrum A. The telescope was then pointed at the wispy, tenuous plume. and spectrum B was recorded. A series of bands due to the infrared emission of the stack gases is seen to be superimposed on the sky “background.” When the background (spectrum A ) was subtracted electronically from the total emission spectrum B: emission spectrum C resulted. Figure 2 shows the results of a similar series of measurements. The spectra were recorded at 11 P.M., when the sky had become heavily overcast. The plume was barely visible, but appeared to be somewhat larger than that at 6 P.M. As shown in spectrum A of Figure 2 of the relative emission of the night sky, the atmospheric “window” had been decreased by the cloud cover, so that spectrum B of the total relative emis$ion of the plume was only slightly modified when the correction for backgroimd was made t o result in spectrum C. Volume 1, Number 1, January 1967 73
A
1
co,
I I 1
A
& I
I
I
I
1500
I
,
,
I
Id00 '
,
'50Ocd
Figure 1. Infrared emission spectra of stack effluent
Figure 2. Infrared emission spectra of stack effluent
Spectra recorded at 6 P.M., each resulting from 50 scam A . Skv near ulume B. P l h e plis sky C . Plume only (sky "background"-Le.. spectrum A-subtracted from spectrum B )
Spectra recorded at 11 PAJ.. each resulting from 100 scans A. Sky near plume B. Plume plus sky C. Plume ' m l y (sk) "background"-i.e.. spectrum A-subtracted from spectrum B )
Spectrum C shows a prominent, broad emission band in the 500- to 800-cm.-' region due to the emission of hot CO:. The band is split into two components by the narrower absorption band of cold atmospheric C o n .The assignment of the emission band marked f is uncertain at present; it is probably due to incompletely burned fuel. The noise level of the spectrum can be seen from the portion of the spectrum at wavenumbers higher than 1400 cm.-* Numerous minor bands of slightly or even appreciably greater intensity than noise are due to H20.Also shown and marked are the infrared emission bands of SO2pollutant resulting from the combustion of the fuel. The data obtained so far are qualitative in nature, and work is required to study the effects of atmospheric conditions, plume-to-instrument distance, and the like. However, the results of the above and similar exploratory experiments suggest the feasibility of the technique. Infrared spectra can be recorded from a position remote from the source of pollution, and the discharge of pollutants not observable by direct visual inspection can be detected. Significantly, this can be
done at night, when surveillance by other methods becomes difficult if not impossible. The method could thus become useful to monitor known sources, to inspect suspected sources, and to uncover previously unknown sources of pollution. The results thus point to a potentially valuable avenue of approach to various monitoring and detection problems in air pollution.
74 Environmental Science and Technology
Literature Cited
Low, M. J. D., J . Cliern. Ediic. 43, 637 (1966). Low, M. J. D., Coleman, I., Spectrochim. Acfn22, 369 (1966).
M.J. D. Low School of Chemistry Rutgers, The State University New Brunswick, N. J. F. K. Clancy Block Engineering, Inc. Cambridge, Mass. Receiced for reciew Nocernber 29, 1966. Accepted December 19, 1966. Work supported b). a grant from the Dicision of Air Pollution, Bureau of Stnte Serrices Public Health Seruice.
