(11) Novgorodov, M. Z., Sobolev, N. N., “The Properties of Low
(15) Herron, J. T., Huie, R. E., J . Phys. Chem. Ref. Data, 2, 467
Temperature Molecular Plasma”, Vol. I, pp 215-66, Proc. 11th International Conference on Phenomena in Ionized Gases, L. Pekarek and L. Laska, eds., Prague, 1973. (12) Johnston, H. S., “Gas Phase Reaction Kinetics of Neutral Oxygen Species”, NSRDS-NBS 20, Nat. Bur. Stds., Washington, 1968. (13) Niki, H., Daby, E. E., Weinstock, B., Am. Chem. Soc., Advan. in Chem. Ser. N o . 113, p. 62 (1972). (14) Weaver, J., Shortridge, R., Meagher, J., “The Photoxidation of CD3 N2CD3”, CAES No. 363-74, Dept. of Chemistry and Center for Air Environment Studies, Penn. State Univ. (1974).
(1973). (16) Heicklen, J., p 23, Am. Chem. Soc., Aduan. Chem. Ser. No. 76 (II), 1968. (17) Bell, A. T., Kwong, K., AIChE J . , 18,990 (1972). (18) Schultz, G. J., Dowell, J . T., Phys. Reu., 128, 174 (1962). (19) Kaufman, F., Prog. Reaction Chem., 1, 1 (1961). Received for revieu M a y 8, 1975. Accepted January 19, 1976. Work supported from N S F Grant GK-37469, N A S A Grant NCAZOR773-501, and support 0fD.L.F. by a N A S A I A S E E Summer Faculty Fellowship.
NOTES
Evaluation of Continuous Mercury Monitor on Combustion Sources R. Statnick”, R. Grote, and R. Steiber U.S. Environmental Protection Agency, Industrial Environmental Research Laboratory, Research Triangle Park, N.C.2771 1
A continuous mercury monitor was evaluated a t two fossil fuel-fired boilers. Within the accuracies of the measurements, the continuous analyzer and either the wet chemical mercury sampling procedure or mercury material balance calculations were in agreement. T h e system can be operational in 5% h from a cold start. T h e time includes installation (20 min), 4 h t o preheat catalytic converter (combusts organics which might be present), and 1 h to calibrate the system. The system once operational requires minimum attention.
T h e measurement of toxic materials emitted from energy transformation processes is a necessary part of any environmental assessment of those processes. T h e emission rates of the trace constituents of coal and/or oil is dependent upon the source of the fuel and the degree of fuel preparation. Studies by the Illinois Geological Survey ( I ) have shown the variability of the mercury content within run-of-mine coal and the variability of the coal mercury content between different mines. Since the mercury emission rates vary as a function of the mercury content of the coal, the continuous or semicontinuous analysis of the toxic stream components is of great importance. A study (2) has recently been made to evaluate various commercially available total mercury vapor monitors. T h e instruments in question were evaluated a t a chlor-alkali plant,
11 1,
u
1
1
PROBE HEAT I CONTROLLER,
a zinc smelter, and a mercury processing plant. Since the results obtained were encouraging, a study was initiated to evaluate one of the mercury monitors on a coal-fired utility boiler and on an oil-fired experimental burner.
Experimental The instrument selected for field evaluation was the Geome,t Model 103 Mecury Monitor. The monitor is designed t o measure elemental mercury in the vapor phase. A flow diagram of the monitoring system developed for use on the combustion sources is shown in Figure 1. The Geomet Model 103 Mercury Monitor samples flue gas a t a nominal rate of 4.8 l./min. T h e mercury vapor is collected by amalgamation on two silver grids. At the end of the preselected sampling period, these grids are sequentially heated to desorb the collected mercury. T h e vapor is then analyzed using the UV absorption line a t 253.6 nm. The total sampling time can be varied from 0-30 min. T h e first site a t which the mercury monitor was evaluated was a coal-fired utility boiler which generates 138 MW of electric power. After calibration, using procedures recommended by the manufacturer, flue gas monitoring was initiated. T h e flue gas conditions are given in Table I. Manual samples for mercury vapor were acquired simultaneously with the instrumental data using a technique developed earlier in our laboratory ( 3 ) .The sampling period for t h e manual procedure was about 20 min. T h e Geomet was
1
OEKORON HEAT CONTROLLER ~
l
Figure 1. Geornet test apparatus
Volume 10, Number 6 , June 1976
595
Table 1. Flue Gas Conditions Temperature, OC Velocity, cm/s Composition co*,VOI % 0 2 , VOI % H20, VOI Yo Son, ppm
162
3400 15.1 4.1 6.0 1200- 1300
Table II. Comparison of Instrumental and Manual Mercury Vapor Sampling Techniques Test
Manual procedure, ~ g / m ~
a
Geomet, ~ g / r n ~ ~
4.0
3
8.6 5.3 6.2
Av
6.7 f 1.7
5.7 f 1.6
1 2
6.0 7.2
The values are averages of at least three instrument readouts
operated on a 5-min sampling period. A minimum of three instrument readings were obtained for each manual sample acquired. T h e results of both the manual and instrumental tests are given in Table 11. A second test was performed on an oil-fired experimental burner a t t h e EPA’s Industrial Environmental Research Laboratory a t Research Triangle Park, N.C. T h e concentration of mercury vapor detected by the monitor was compared to the total level of mercury in the fuel as fired. T h e material balance calculations for mercury, based on detected mercury levels in the flue gas, indicated t h a t 0.112 ppm (w/w) of mercury was present in the fuel oil. T h e analysis of the fuel oil using standard procedures indicated t h a t the fuel oil contained less than 0.2 ppm of mercury.
T o bring the sampling system and the analysis system online from a cold start requires about 5% h. Twenty minutes are required t o install the device, 4 h are required t o preheat the catalytic converter, and 1 h is required to calibrate the system. (This is a three-point calibration curve.) T h e system is very stable and requires minimum attention when it is in continuous operation. (Recalibrate once a week with routine system monitoring twice a day.) During 80 h of operation on the two-fossil fuel combustion sources, no apparent problems with the sampling system or the instrument occurred. Conclusion
T h e studies performed with t h e Geomet analyzer indicate that mercury concentration data can be obtained on a semicontinuous basis from utility boilers. T h e analyses can be performed without dilution of the flue gas and with minimal interference from other flue gas constitutents. A study ( 4 ) by T R W Systems Group has shown t h a t 90+% of the mercury contained in fossil fuels is emitted as the elemental vapor upon combustion. Instruments such as the Geomet analyzer can be highly useful in the evaluation of mercury emissions from high-temperature energy transformation processes. L i t e r a t u r e Cited (1) Shimp, N., et al., “Occurrence and Distribution of Potentially
Volatile Trace Elements in Coal”, P B 238-0911AS; McGee, E. M., et a]., “Potential Pollutants in Fossil Fuels”, P B 225039/AS. ( 2 ) Katzman, L., Lisk, R., Ehrenfeld, J., “Evaluation of Instrumentation for Monitoring Total Mercury Emissions from Stationary Sources”, EPA-65012-74-039. ( 3 ) Statnick, R. M., Oestreich, D. K., Steiber, R.. “Sampling and Analysis of Mercury Vapor in Industrial Streams Containing SO?”, presented at the ACS National Meeting (August 1973). (4) “Procedures for Process Measurements: Trace Inorganic Materials”, TRW Systems, Inc., EPA Contract No. 68-02-1393. Receiced for revieu July 29, 1975. Accepted January 26, 1976. Mention of commercial products is for identification only and does not constitute endorsement by the Encironrnental Protection Agencji of the U . S . Gocernment.
Average Tropospheric Concentration of Carbon Tetrachloride Based on Industrial Production, Usage, and Emissions A. P. Altshuller Environmental Sciences Research Laboratory. U S . Environmental Protection Agency, Research Triangle Park, N.C. 2771 1
Carbon tetrachloride along with fluorocarbon-11 and fluorocarbon-12 has been identified as a long-lived chlorinated species capable of surviving reaction and removal processes. Carbon tetrachloride has a very long lifetime in the troposphere based on the only significant known reaction process-the extremely slow rate of reaction with O H radicals ( I ) permitting diffusion of this molecule well into t h e stratosphere. Possible losses into t h e oceans or by removal by precipitation processes are uncertain a t present. Gas chromatographic measurements by Lovelock e t al. ( 2 ) and Wilkness et al. (3) for 1971-72 averaged 73 ppt. However, carbon tetrachloride concentrations measured over t h e Atlantic in October 1973 averaged 138 p p t and concentrations of carbon tetrachloride measured near the U.K. in a flight on J u n e 6, 1974, into the stratosphere ranged from about 120 p p t near the surface down to 95 to 100 p p t a t the 596
Environmental Science & Technology
tropopause ( 4 ) . Hanst and co-workers ( 5 ) using an infrared FTS technique have analyzed samples a t East Coast U.S. sites in 1975 and obtained minimum carbon tetrachloride concentrations in the 70-80-ppt range as low as reported earlier by Lovelock (2) and Wilkness e t al. (3).Grimsrud and Rasmussen (6) have reported carbon tetrachloride concentrations of 120 4 15 ppt. It has not been clear from these results whether these concentrations of carbon tetrachloride could be accounted for by anthropogenic emissions or whether significant natural sources of carbon tetrachloride may exist. An independent computation of average tropospheric concentration of carbon tetrachloride can be made assuming that anthropogenic sources of carbon tetrachloride are the sole source of tropospheric carbon tetrachloride. This computation requires a reasonably accurate estimate of
