Environ. Sei. Technol. 1982, 16, 763-770
only an order of magnitude of the fall velocity is known. (2) The density stratification and currents at possible discharge sites in Santa Monica Basin are such that the discharged sludge would rise to a distance on the order of 50 m above the bottom due to buoyancy. (3) Two mechanisms participate in the downward migration and sedimentation of the particulates, (i) falling and (ii) downward diffusion. The second mechanism is significant for particulates with small fall velocities (e.g., cm/s). (4) Approximate estimation of horizontal diffusion using current meter data measured along the slope in the Santa Monica Basin indicates that the phenomenon is anisotropic with diffusion along the bottom contour substantially more energetic than in the perpendicular direction. (5) Based on available data, an approximate determination was made of the initial bottom fallout pattern for several choices of discharge site. Results indicate that for fall velocity of lo+’ cm/s the areal extent of the zone where the sedimentation rate is equal to the background oxidation rate is on the order of 120 km.This area has an oblong shape with the long axis oriented effectively along the contour. (6) The general conclusion that can be reached is that a few percent of the particulate would settle within a kilometer of the discharge. The bulk would be quite dispersed over an oblong shaped region oriented along the bottom contour. Acknowledgments
I thank N. H. Brooks, J. J. Morgan, and G. A. Jackson
for stimulating discussions and T. Fall and M. Gray for assistance in preparation of the manuscript. Literature Cited Jackson, George A.; Koh, Robert C. Y.; Brooks, Norman H.; Morgan, James J. EQL Report No. 14, Environmental Quality Laboratory, California Institute of Technology, Pasadena, CA, 1979. Jackson, George A. Environ. Sci. Technol., preceding paper in this issue. Wright, S. J. Report No. KH-R-36,W. M. Keck Laboratory of Hydraulics and Water Resources, California Institute of Technology, Pasadena, CA, 1977. Fischer, Hugo B.; List, E. John; Koh, Robert C. Y.; Imberger, Jiirg; Brooks, Norman H. “Mixing in Inland and Coastal Waters“; Academic Press: New York, 1979. Faisst, W. K. EQL Report No. 13, Environmental Quality Laboratory, California Institute of Technology, Pasadena, CA, 1976. Myers, E. P. Ph.D. Thesis, California Institute of Technology, Pasadena, CA, 1974. Brooks, N. H., “Settling Analyses of Sewage Effluents”; memorandum to Hyperion engineers, July 5, 1956. Morel, F. M. M.; Westall, J. C.; O’Melia, C. R.; Morgan, J. J. Environ. Sci. Technol. 1975, 9, 756-761.
Received for review October 9,1981. Revised manuscript received July 13,1982. Accepted July 19,1982. Acknowledgment is made to the Sanitation Districts of Los Angeles and Orange Counties, the City of Los Angeles, and the Ford and Rockefeller Foundations for financial support.
Characterization of Fluorocarbon-Film Bags as Smog Chambers Nelson A. Kelly Environmental Science Department, General Motors Research Laboratories, Warren, Michigan 48090 and/or spiked with nitrogen oxides (NO,) or hydrocarbons Experiments were conducted to characterize fluorinated (HC) to assess the effects of different control strategies ethylene-propylene copolymer (FEP Teflon) plastic bags and future emission scenarios. Also, trends in the maxias reactors for the photolysis of hydrocarbon/nitrogen mum ozone produced in the bags were compared with the oxides mixtures (smog chambers). The results of several EPA Empirical Kinetics Modeling Approach (EKMA) (9). tests show that such bags are suitable for the sunlight Many researchers are hesitant, however, to apply smog irradiation of urban air without extensive conditioning but chamber results to the atmosphere because there is disunsuitable for rural air even after conditioning. At typical agreement in the scientific community regarding the effects urban levels of hydrocarbons and nitrogen oxides, ozone of spectral distribution, walls, and contamination on the production was reproducible in both differently condiresults (10-14). This is due to the wide variety of irrationed and sized bags. Also, the dark ozone half-life in the diation sources, wall materials, and chamber cleanup or bags was comparable to that in other larger smog chamconditioning procedures employed in different smog bers, and the surface reaction between ozone and Teflon chambers. For experiments conducted outdoors in FEP produced negligible amounts of gas-phase products. Teflon (registered trademark of E. I. Du Pont de Nemours However, large amounts of carbon monoxide‘were released and Co, Wilmington, DE) bags, which are transparent to by new Teflon film and caused large ozone production at low NO, levels in the bags. Even conditioned bags, with the full solar spectrum, spectral distribution effects, which negligible CO release, exhibited some excess reactivity and cause major differences in indoor chambers, should not be were therefore unsuitable for simulating rural photoa problem. However, the effects of wall conditioning and chemistry. contamination are potentially very important for Teflon chambers. For example, Lonneman et al. (15) reported that some bags made of new FEP Teflon film released Introduction large amounts of volatile residues from the film manu- ’ Recently, smog chambers made of inert, transparent, facturing process. Others have reported that used Teflon fluorocarbon film have been widely used to investigate bags exhibited far greater reactivity than new bags (16); photochemical reactions in both synthetic and ambient air they attributed this to excess OH radicals produced by the samples (1-8). For example, we conducted captive-air release of products left over from previous experiments irradiations of ambient Houston air to evaluate the ca(17). In addition, the general permeability of many plastic pacity of morning samples of air to generate ozone ($9). films, including Teflon, to a wide variety of compounds Samples of the morning air were diluted with zero air such as HC and NO, has been documented by groups who ___
0013-936X/82/0916-0763$01.25/0
0 1982 American Chemical Society
Environ. Sci. Technol., Vol. 16, No. 11, 1982 763
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edges. When bags survived past the first day, they were pumped out in the evening and filled with zero air overnight. The following morning they were again pumped out and reused. The purpose of this procedure was to minimize contaminants desorbing from the walls. While ozone was the only variable routinely measured during the irradiation experiments, NO, and HC measurements were occasionally made in the bags. Hydrocarbons were measured with a Perkin-Elmer Model 900 gas chromatograph (GC), which used two columns with independent sampling systems, detectors, and electrometers for each column (7). The two columns separated hydrocarbons into light hydrocarbons (C,-C,) and heavy hydrocarbons (C5-Cl2). The nitrogen oxides were measured with a Teco Model 14B analyzer using a 450 "C molybdenum converter with an efficiency for NOz >95% as determined by gas-phase titration. Differences less than 5 ppb NO, could be measured in dry air, although humidity, which caused a positive interference, reduced the detection limit for ambient air analysis. A Beckman 6800 GC was used to measure CO by catalytically converting the CO to methane, which was then measured by a flame ionization detector. The detection limit was 0.2 ppm CO. The Beckman analyzer was also used to measure total hydrocarbons. Also, for some experiments, nonmethane hydrocarbons (NMHC) and CO were measured with a Bryon 401 GC. The Byron analyzer measures NMHC by separating them from methane chromatographically, converting them to COz using a cupric oxide catalyst heated to 700 "C, and then catalytically converting COz to methane to give a ppm carbon (ppmC) response for every carbon atom initially present in an organic compound. Methane, CO, and COPwere also measured as separate peaks by the analyzer during each NMHC analysis. Finally, to determine the ozone half-life in the dark, bags were filled with ozone generated from zero air by a MacMillan MEC-1000 generator, and the ozone was sampled for 10 min of each hour for approximately a 10-h period.
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Figure 1. Ultraviolet-visible transmission spectra of new and used Teflon film.
hoped to use such bags for storing mixtures (18-20). This report summarizes the progress we have made and the problems we have observed in our attempts to optimize the bag irradiation procedure as applied to studying the photochemistry of ozone production. Included are (1) chamber characterizations including studies of contamination due to the nature of Teflon film, (2) measurements of the dark ozone half-life in bags as well as the consequences of the ozone/Teflon reaction, and (3) studies of the reproducibility and validity of bag irradiations. Experimental Section
The reactors tested in this study were made from 0.05mm (0.002 in.) FEP Teflon, type A (hereafter referred to as Teflon). Two square sheets of film, 137 cm on an edge were heat-sealed together around the edges. When inflated, a bag was pillow-shaped and had a volume of approximately 450 L, giving a surface-to-volumeratio of 0.083 cm-l. Two bulkhead fittings were located in the middle of the bag. One was a 3.75-mm fitting and was used to sample the contents of the reactor; the other was a 6.35mm fiitting and was used to fill or pump out the bag. Both fittings were also made of Teflon. Bags made of thin Teflon film are fragile but have excellent light transmission. For example, samples of the 0.05-mm film held over an Eppley ultraviolet radiometer transmitted >95% of the solar radiation. Spectra of both new and used bags in Figure 1 show the excellent transmission of the full solar spectrum (wavelengths >300 nm). There was only a small reduction in the transmission of used film, which was probably caused by wrinkling of the film when the bags were inflated and deflated. Attempts to make the bags sturdier by using 0.13-mm (0.005 in.) film for the bottom panel that contained the two fittings, as well as making the whole bag from 0.13-mm film, did little to improve the durability. Furthermore, the results of Lonneman et al. (15) suggest that 0.13-mm film is more contaminated by organic compounds than 0.05-mm film, although this may just be a function of the specific rolls of film involved. Therefore, we have settled on bags made of 0.05-mm Teflon as preferable for photochemical reactors. Irradiation experiments were conducted outdoors with the bags suspended on nylon nets. Bags were filled through the 0.635-mm fitting either with ambient air in 10 min by using a metal bellows pump or with cylinder air in -5 min. When desired, additions of HC or NO, were made during filling, by using syringes and a septum in the filling line. For NO additions, this typically resulted in N 10% conversion to NOz by thermal oxidation. After a bag was filled with either ambient air or a synthetic mixture, the ozone produced in the bag was measured for 10 min of each hour during the experiment with a Monitor Labs 8110 chemiluminescent ozone analyzer. This instrument was calibrated about every 3 days against a Dasibi 1003-AH ultraviolet photometer. Occasionally, on windy days, new bags would begin leaking after being used only 1day and therefore had to be discarded. Failure usually occurred at the heat-sealed
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Envlron. Scl. Technol., Vol. 18, No. 11, 1982
Results and Discussion
Smog chamber characterization. We sought to determine the "background reactivity" of the bags (the amount of ozone formed in new or used bags in the absence of added reactants or when only HC or only NO, were added) as well as the amount formed from a reactive mixture. Therefore, four types of irradiation experiments were performed: (1)experiments with zero air only; (2) experiments with zero air plus hydrocarbons; (3) experiments with zero air plus NO,; (4) experiments with zero air plus hydrocarbons plus NO,. The results of these tests are shown in Table I and are referred to as series 1-4, respectively. Several different experiments comprise series 1. First, several new bags filled with zero air and irradiated for a day produced less than 5 ppb ozone. Second, a bag that had been used the day before to irradiate ambient Houston air was flushed out, filled with zero air overnight, refilled with zero air the next morning and irradiated; only 14 ppb ozone was produced. We have observed up to 35 ppb O3produced by the irradiation of clean air in used bags that were not allowed to degas overnight before subsequent use, so further reference to used bags indicates they have undergone overnight cleaning. Third, other used bags that had previously been used to irradiate ethylene/ NO, mixtures produced 5-10 ppb ozone when they were filled with zero air and irradiated for a day. Also, in series 2, both new and used bags containing zero air plus butane, ethylene, or propylene produced negligible ozone. Thus, both new and used bags produced low amounts of ozone when zero air or zero air plus hydrocarbons were irradiated. In contrast, some large outdoor chambers, which are harder
Table I. Ozone Production by Irradiated Bags Filled with Zero Air or Zero Air and Additions
additions
bag con- O,(max), dition ppb
none
new
Series 1 C, hydrocarbons. Also, several new bags filled in the morning with zero air and irradiated showed increases in NMHC of
