Gas Phase Titration of Atmospheric h n e J. J. Bdrlii U. s. lkpofc“ r ---A, Ohio 45226
Fmmtnn_ and Welfare, National Air Pollution Control Administration, 4676 Columbia Parkway,
mixture. The Mast instrument has the unfortunate character- istic of l m q e d m y . Although methods have been developed to eliminate many
of these problems, these improved methods have their own .. doqmmsk. The Bravo and Lodge (1W) method calls for the use of a very corrosive acid and thus can be applied routinely only by skilled technicians. The Hauser and Bradley (1%6) method appears to be nonspecific (Cohen, Purcell, et nl., 1%7; Hausg and Bradley, 1%7)- The NO, equivalent method (salamanand Gilbert, 1959) is diiiicult. The nitric oxide must be carefully controlled, since the 2NO C 0 2 2NU &on will give large blanks. At low ozone concentrations, the ozone level may not be discernible from the high background. The rnethod is also nonspecific since PAN and PPN both give positive interferences (Cohen, Purcell, et a/.,
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xidantsszach as omme and pemxyacetyl nitmte (PAN) are reported as products of photochemical reactiors More recent reportshave shown that other oxidants such as akyl hydroperoxides (Ahshuller, Coben, et ol.,
1%6)andhYdroganpemxkks(Rnrell and cohen, 1%7)are alsoformedinphotocbc - 1 QpelIsdiom. Tbe hasic technique used for oxidant determination has been thep&asilmiodide - .‘-method.TheMastozone ~ b a k o b e P n u s e d since ~ , the instrument is ~illmpmkeand P-tabkThe&j€of the potassium iodide h o d is its imppkdility to 6eld work. The color developed by iodine h i often hsts only a few minutes. Also, the voMility of tbe sobecomes a problem with the IrKII
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The investigation reported here was initiated to determine whether the Mast instrument could be made specific for ozone. Figure 1 shows the apparatus used in these studies. The entire apparatus is slightly larger than the Mast instrument. F a d application is not affected by this system. The sample is introduced via ball socket S. If the timer, T, is not activating the solenoid, S,the sample is introduced into mixing chamber, C, and directly into the Mast, M. This position of the timer is shown by the reading of 18.5 p.p.h.m shown in Figure 2. As the timer activates the sol-
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VObc2,Nda9,-1968
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enoid, trans-2-butene is introduced into the mixing chamber through a venturi. The ozone concentration reading drops to 1.75 p.p.h.m. as shown in Figure 2. Since the timer is set to activate and deactivate the solenoid for a 15-minute cycle, a square wave results. The data shown in Figure 2 indicate that about 95% of the ozone has reacted. Calculations based on the equations for a stirred flow reactor, a flow rate of 5 cc. per minute of lo3p.p.m. of trans-2butene through the venturi, a flow rate of 140 cc. per minute for the Mast with a residence time of 0.28 minute, and a rate constant for the trans-2-butene-ozone reaction of 2.0 x 105 liters per mole second result in a 9 8 x reaction for the ozone. This value agrees well with the observed value. The slight discrepancy may arise from the lack of stoichiometry between the two reactants (Bufalini and Altshuller, 1965; Wei and Cvetanovic, 1963). The reaction can be driven to greater completion by increasing the olefin concentration in lecture bottle L. This modification necessitates the use of very narrow or capillary tubing between the solenoid and the venturi, since small amounts of diffusion will seriously affect the ozone readings when the solenoid is in the "off' position. A more complete reaction can also be obtained by raising the flow of trans-2butene, but the sample pulled by the pump of the Mast will be diluted by a proportionately larger value. The specified flow rate of 5 cc. per minute is only 3.6% of the total flow. The most convenient manner of driving the reaction to completion is to raise the residence time in the reaction chamber. The square wave shown in Figure 2 becomes somewhat sinusoidal, but a judicious choice of cycling time eliminates this problem. The pressure regulator, R, is necessary since the solenoid does not hold very high pressure. The regulator also enables careful control of the flow when used with needle valve, V . To determine whether peroxyacetyl nitrate (PAN) would react with tram-?-butene in the mixing chamber, PAN was prepared by irradiating 20.2 p.p.m. of tram-2-butene with 9.2 p.p.m. of nitrogen dioxide. After irradiation for 1 hour at a k,+ of 0.24 min.-l for NOS, the total oxidant measured on the Mast recorder was 1.14 p.p.m. When the olefin was introduced, the oxidant reading dropped to 0.55 p.p.m., an indication that 0.59 p.p.m. of oxidant had reacted with the olefin. This same sample was then introduced into an ultraviolet photometer (Cohen, Purcell, et al., 1967). The photometer indicated 0.56 p.p.m. of ozone, a value in excellent agreement with that measured by the difference method on the Mast. The remaining 0.55 p.p.m. that does not react with the olefin is probably PAN and NO?. The remaining NO2 was
measured by the modified Griess-Ilosvay reagent (Saltzman, 1954) and was 0.42 p.p.m. The PAN was measured with a Beckman IR-4 that uses a 10-meter cell, and the concentration was 4.24 p.p.m. Assuming an 8% response of the Mast to NOS (previously determined) and the remaining oxidant as PAN, the Mast response to PAN is 12%. Hydrogen peroxide, n-butyl hydroperoxide, and peracetic acid were all tested for possible reaction with trans-2-butene in the gas phase. A concentration of 2.7 p.p.m. of H 0 4 showed no reaction with the butene and gave a slow Mast response of 0.2 p.p.m. The n-butyl hydroperoxide (2.4 p.p.m.) gave only a slight response to the Mast (0.025 p.p.m.) and showed no reaction with the olefin. Peracetic acid gave a very good response to the Mast. The instrument showed 0.47 p.p.m., while the concentration as measured by the KI colorimetric method was 0.46 p.p.m. The trans-2-butene reacted with the peracid to the extent of 2.1 %. These tests show that ozone can be selectively removed from a gas stream containing other oxidants, the ozone concentrations can be measured by differences, and other oxidants are unaffected by the presence of a reactive olefin. Although the Mast oxidant analyzer was chosen as a typical oxidant analyzer for these measurements, other analyzers such as the Technicon AutoAnalyzer or the Beckman ozone monitor can also be employed. If the latter are employed, care must be taken in keeping the residence time of the gases in the reaction chamber to a reasonable time so reaction is near completion. Literature Cited Altshuller, A. P., Cohen, I. R., Purcell, T. C., Can. J. Chem 44,2973 (1966). Bravo, H. A., Lodge, J. P., Anal. Chem. 36,671 (1964). Bufalini, J. J., Altshuller, A. P., Can. J. Chem. 43, 2243 (1965). SCI. Cohen, I. R., Purcell, T. C., Altshuller, A. P., ENVIRON. TECHNOL. 1,247 (1967). Hauser, T. R., Bradley, D. W., Anal. Chem. 38, 1529 (1966). Hauser, T. R.,Bradley, D. W., Anal. Chem. 39, 1154 (1967). Purcell, T. C., Cohen, I. R.,ENVIRON.SCI.T E C H N ~1, L .845 (1967). Saltzman, B. E., Anal. Chem. 26, 1949 (1954). Saltzman, B. E., Gilbert, N., Am. Ind. Hyg. Assoc. J. 20, 379 (1959). Wei, Y. K., Cvetanovic, R.J., Can. J. Chem. 41, 913 (1963). Receiced ,for reciew May 13, 1968. Accepted July 1.5, 1968. Mention of commercial products does nor constitute endorsement bj* the (1. s. Public Health Sercice.
