ing, but by the 20-30th washings, all pozzolanic tendencies disappeared. Rainfall on open stockpiles of fly ash would bring about H2O:ash ratios considerably less than five. At such ratios, runoff and leaching water would contain high salt concentrations, of which over 50% of the cations in most cases could be sodium (Table I, ashes no. 2, 3, and 4), and pozzolanic activity would be high. Thus, any application of ash to surfaces should be accompanied by concomitant mixing to prevent lump or crust formation on soils susceptible to crusting. A possible use of lignite fly ash is as a soil amendment; either acid or sodic soils might be improved. As a soil amendment for the amelioration of sodic (alkali) soils, fly ash a t 5 T/acre-furrow slice will give a Hz0:ash ratio of 100, and a t 20 T/acre-furrow slice, will give a H2O:ash ratio of 25, at a soil water gravimetric content of 50%. If we initially release high concentrations of salts, flocculation and permeability of sodic soils should be increased, and subsequent releases, made largely of Ca, could replace Na on the soil colloid exchange sites as the leaching process takes place. For example, a sodium adsorption ratio of 0.87 was observed in the equillibrium water-ash solution a t the 5th washing of ash no. 3 with a water:ash ratio of 1OO:l. Such a sodium adsorption ratio would not impart sodium ions to clay systems, but rather remove sodium and add calcium. Independent soil column investigations in this laboratory have indicated such takes place; field studies are in progress ( 4 ) . Phosphorus reduction in lake waters and generating plant cooling waters is another possible use. Tenney and Echelberger ( 5 ) , in a study of fly ash utilization in the
treatment of polluted waters, stated that the degree of phosphate removal achieved by a fly ash dosage is determined by the water-extractable lime and gypsum obtained from the fly ash. Typical lignite fly ashes from the Northern Great Plains have been found to have water-soluble constituents of about 8.55% while a typical bituminous fly ash will have about 2.51%. However, it appears from Ksp values of ferric and aluminum phosphates that the soluble iron (ca 20 ppm) derivable from the ashes would have a considerable potential for reducing phosphates in solutions. Kardos ( I ) has proposed that aluminum from gibbsite may reduce soluble phosphate in soilwater systems by 99.98%. The ferric oxides in these fly ashes can supply a t least as much soluble iron to combine with phosphates.
Literature Cited (1) Kardos, L. T., “Soil Fixation of Plant Nutrients,” in “Chemistry of the Soil.” Amer. Chem. SOC.Monograph 160, 1967. ( 2 ) Sondreal, E. A,, Kube, W. R., Elder, 3. L., in “Analysis of the Northern Great Plains Province Lignites and Their Ash; A Study of Variability,” U.S.Bur. Mines R e p . Inuest. 7158 (1968). ( 3 ) Doran, J. W., Martens, D. C., “Molybdenum Availability as Influenced bv AoDlication of Flv Ash to Soil.” J Enciron. Qual 1, 186-9 (1952). (4) Shannon, D. G., Fine, L. O., in h o c 28th Ann Meet Sod Conserr SOC Amer , “Soil Core Studies of Profile Modification for Amelioration of Salt-Affected Soils,” pp 85-8, 1973. ( 5 ) Tenney, M. W., Echelberger, W.F., Jr.,,, “Fly Ash Utilization in the Treatment of Polluted Waters, U.S. Bur. Mines Inform. Cir. 8488, Ash Utilization, Proc. 2nd Ash Utilization Symp., U.S. Dept. of Interior, 1970.
Receiced for recieu October 23, 1973. Accepted May 28, 1974
Inhibition of Photochemical Smog Reactions by Free Radical Scavengers Chester W. Spicer,* David F. Miller, and Arthur Levy Battelle, Columbus Laboratories, 505 King A v e . , Columbus, Ohio 43201
w Several free-radical scavengers which appear to have potential as photochemical smog inhibitors have been studied in a series of smog chamber experiments. The inhibition of smog manifestations by the proposed compounds was investigated for pure hydrocarbons and also for synthetic auto exhaust. Particular emphasis in this investigation was placed on uncovering possible detrimental side effects resulting from the use of the inhibitors. In this regard, several of the compounds investigated, while demonstrating an inhibitory effect with respect to NO photooxidation and ozone formation, also yield remarkably large increases in light-scattering aerosol production. These findings have great significance in terms of the possible future use of smog inhibitors in the atmosphere. The formation of photochemical smog, initiated by the rapid conversion of NO to NO2, has long been thought to involve a chain mechanism for NO photooxidation. In such smog systems the chain carrier, which is both reactant and product in the KO conversion process, has been postulated to be the hydroxyl radical (I, 2). Such a mechanism involving butane and nitric oxide follows:
1028
Environmental Science & Technology
+ NO C4HgO’ + 02 HO2’ + NO C,Hg02*
+
-
--t
C,H,O*
C,H,CHO NO2
+
+ NO2
(3)
+ HO2*
(4 )
HO.
(5)
A possible means of slowing the conversion of NO to NOz, thereby inhibiting smog formation, has recently been suggested by Heicklen (3) and Gitchell et al. ( 4 ) . It involves removal of the chain carrying HO radicals in such a way that the chain is not regenerated. Radical scavengers such as phenol, benzaldehyde, aniline ( 4 ) , and naphthalene ( 5 ) , were suggested because of their easily abstractable hydrogen atoms and because they have no hydrogen atom associated with the a-carbon atom, thus inhibiting chain regeneration. Stephens et al. (6) investigated the effect of several possible smog inhibitors on aerosol formation in mixtures of 2 ppm pentene-2/1 ppm N02/0.5 ppm SO2. Phenol and 4n-hexylresorcinol slightly depressed aerosol formation, although another phenol, 2,6-ditertiary butyl 4-methylphenol, and pyrolidine enhanced aerosol formation. Still another phenol, 2,6-ditertiary butyl 4-methoxyphenol, along with pyrogallol and morpholine, had no effect on aerosol formation. Aniline and N,N-dimethylaniline increased aerosol formation at both the 0.5- and 5 p p m levels. N Methylaniline depressed aerosol formation when it was
present a t 0.5 ppm but increased aerosol formation at the 5-ppm level. These seemingly conflicting findings may be explained by the methodology employed. Aerosol formation was monitored by 21 forward-scattering smoke photometer in a stirred dynamic reactor having a residence time of 34 min. Stirring has been shown to adversely affect aerosol formation (7, 8), with the magnitude of the effect depending on the particular hydrocarbon system under study. Also, the short residence time coupled with the method of monitoring aerosols may lead to results which are difficult to interpret. For example, in certain chemical systems where nucleation follows an induction period, small aerosols might not have grown to light-scattering size because of the short residence time, but in other chemical systems such growth may have occurred earlier so that a larger fraction of the total aerosol surface was in the light-scattering size range. Dimitriades and Wesson (9, 10) studied the reactivity of several aldehydes present in automobile exhaust and observed that addition of 0.5 ppm of benzaldehyde to an irradiated propklene/NO, system reduced the rate of NO2 formation by almost a factor of 2 and lowered maximum oxidant by about one third. Benzaldehyde addition also decreased PAN and CHzO levels but increased PBzN formation. The addition of benzaldehyde thus inhibited many of the classical smog manifestations; however, the increase in the severe lachrymator PBzN is a very negative side effect. Aerosol formation was not monitored. A study by Kuni,z et al. (11) has also shown the inhibition effect of benzaldehyde. In a recent smog chamber experiment carried out in Battelle-Columbus’ 610-ft3 chamber, a trace quantity of phenol was found to yield a severalfold increase in aerosol production in a synthetic auto exhaust experiment. Because such a detrimental side effect as increased aerosol production would obviate the use of the proposed smog inhibitors in urban atmospheres, we initiated a program to more thoroughly investigate the effect of some proposed smog inhibitors under conditions more representative of polluted atmospheres than earlier inhibition studies, giving particular attention to adverse side effects. Experimental The Battelle 610-ft3 smog chamber has been described previously ( 1 2 ) . Light intensity measurements by NO2 photolysis (13) and 0-nitrobenzaldehyde photolysis (14) agree quite well when compared as described by Gordon
( 1 5 ) .The value for K d is 0.45 min-1. Total hydrocarbon is determined by flame ionization, CO by NDIR, SO2 by flame photometry, 0 3 by chemiluminescence, NO and NO2 by automated Saltzman and by chemiluminescence, PAN by electron capture gas chromatography, and light scattering and visibility by broadband (420-570 nm) integrating nephelometry. The synthetic automobile exhaust was made up of 50% by weight of a high aromatic automobile fuel (simulating fuel-derived exhaust constituents) and 50% by weight of a C1-C4 hydrocarbon mixture (which simulates combustion-derived exhaust components). The composition of this “light-end” mix by volume is ethane 4.0%, ethylene 44.170, acetylene 28.W0, propylene 16.070, 1-butene 6.270, and trans-2-butene 1.7%. Aniline was obtained from Baker; isooctane and benzaldehyde from Eastman; and naphthalene from Matheson, Coleman, and Bell. These compounds were used without further purification. Results and Discussion The results of our experimental program are shown in Table I. The first comparison is between Runs 1 and 8 which are essentially duplicate experiments, run to ensure that the chamber had not become contaminated with the low-volatility additives used in the experiments. Such contamination would be expected to greatly increase light scattering in subsequent runs. The similarity in Ab-scat values for these two runs indicates that contamination was minimal. A comparison of other reactivity parameters demonstrates rather good reproducibility, certainly within the variation generally exhibited in smog chamber experimentation (16). Run 2 is similar to Runs 1 and 8, with the addition of 0.4 ppm aniline to test its efficiency and side effects as a smog inhibitor. As reported by Gitchell et al. ( 4 ) , the maximum NO2 level was decreased and the time to achieve this maximum was considerably lengthened. In addition, the maximum ozone level was almost halved and the PAN maximum was cut substantially. All of these beneficial effects, however, are more than offset by the phenomenal increase in light-scattering aerosol, as measured by Ab-scat. The detrimental effect on visibility of such greatly increased light scattering is demonstrated by the drop in visibility from about 17 miles to less than 0.3 mile. In Run 3 we attempted to determine whether the increased light scattering was hydrocarbon-composition related; for example, is the increased light-scattering phe-
Table I. Smog Inhibition Experiments. Run: Additive, pprn (v/v): Hydrocarbon, pprn C:
1
2 Aniline, 0.4
3 Aniline, 0.8
Syn. exhaust, 16
Syn. exhaust, 16
Isooctane, 16
4 Ani I i ne, 0.8
5 Benzaldehyde, 0.4 Syn. exhaust, 16
6 Naphthalene, 0.4 Syn. exhaust, 16
7 Naphthalene, 0.4
8
Syn. exhaust, 16
0.83 0.80 0.76 0.80 0.80 0.83 NO, p p m 0.76 0.76 0.19 0.20 0.20 0.20 0.20 0.20 NOZ, p p m 0.21 0.20 0.10 0.10 0.00 0.00 0.10 0.12 0.11 SO,, ppm 0.10 NO?, max, p p m 0.72 0.44 N o max 0.62 No max 0.72 No max 0.71 NOi t-max, m i n t 55 90 55 60 53 O3max, ppni 0.80 0.42 0.07 0.64 0.00 0.70 0.00 0.89 OJ t-max, min. 140 150 240 135 165 140 P A N rnax, ppm 0.64 0.43 0.56 Ab-Scat., 1 0 - 4 m - 1 ~ 1.35 102 53.8 67.8 25.0 3.10 7.50 2.35 Final visibilily, miles, approx. (78) 17.0
