I
F. V. MORRISS, CALVIN BOLZE, and JOHN T. GOODWIN, Jr. Midwest Research Institute, Kansas City, Mo.
Smog Chamber Studies of Unleaded vs. Leaded Fuels Neither tetraethyllead nor halogen-containing scavengers of lead have any detectable effect on the smog-forming potential of automobile exhaust
TETRAETHYLLEAD is caused by a combination of several factors. Large amounts of pollutants are
(TEL), introduced in 1923 as an antiknock agent in gasolines, is now used in over 99% of the motor fuels sold in the United States. Throughout the years, extensive research has been conducted on the roIe played by T E L and its combustion products within the engine. In practice, T E L is added to gasolines as part of a n antiknock fluid mix, which includes scavengers-ethylene dichloride and/or ethylene dibromide-the function of which is to convert nonvolatile lead oxide to the more volatile halides, minimizing lead deposits in the engine. The major exhaust products from T E L and these scavengers are particulate solids from 0.01 micron to several millimeters in diameter, composed mainly of lead chlorobromidr, PbCl. Br, and 01 and p forms of the binary complex of this halide with ammonium chloride, “.&I, 2PbCI Br and 2NHdCl. PbCl. Br (4). Other halogen-containing products are also undoubtedly formed, because a slight excess of the scavenger is normally used. Because automobile exhaust gas has been implicated as a major source of smog-producing chemicals (7), it was decided to investigate the possible effect of T E L and halogen scavengers used in antiknock fluids on smog manifestations, despite their very low concentrations (a maximum of 3.0 ml. of T E L per gallon) in gasolines. The smog problem in Los Angeles
emitted to the air daily from industry, incinerators, and automobile exhaust. As low wind velocities and frequent lowaltitude temperature inversions limit the amount of air available to dilute and remove these pollutants, they remain over the city for a considerable time. Sunlight initiates chemical reactions, producing oxidant and other substances responsible for the major symptoms of smog-eye irritation, plant damage, and reduced visibility. These symptoms also may be produced by irradiating certain hydrocarbons in the presence of nitric oxide or nitrogen dioxide. The great interest in the chemistry of these systems has led to considerable knowledge of the nature of major reactions (7-g), but the specific reactions and products responsible for the physiological symptoms of smog remain unknown. Therefore thorough evaluation of the possible contribution of fuel additives must involve direct measurement of the important symptoms in addition to chemical analysis. Lead and its scavengers could influence smog measurements in several ways. First, the surfaces of these small particles might catalyze gaseous reactions, and thus alter the chemical composition of polluted air. A second influence could be a synergistic effect on the chemicals that cause eye irrifation.
No such effect has been found, but the possibility cannot be overlooked. The lead-containing particulate matter from exhaust gas could act as a carrier for the eye-irritating gases. If the large surface area of these minute particles adsorbed irritants, irritants might be released in contact with the eye in larger amounts than otherwise possible. There is no experimental evidence of any such relationship between particulate matter and eye irritants. Assay of the symptoms of smog with and without lead compounds should indicate whether any of these mechanisms are important. Apparatus and Techniques The experimental apparatus and techniques used have been described in detail (2, 5, 6). The apparatus consisted essentially of two large glass reaction chambers built from a greenhouse, and equipped with air-sampling systems, to measure the concentrations of various chemicals. Each chamber had a volume of about 2200 cubic feet, and was large enough to permit the entrance of personnel for measurement of eye irritation without drastically affecting the system being studied. The test fuels were burned in a 1952 Ford station wagon equipped with a n automatic transmission. h’ew piston rings, valves, and spark plugs were inVOL. 50, NO. 4
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Table I. Measurement Oxidant
co
Oxides of nitrogen Aldehydes
Test Fuels
Base fuel. Rest coast premium-gasoline base stock Fuel Composition, M1. TEL./Gal.
B
Table 111.
Afternoon
Morning
674
18 30 42 18 27 36 45
9 0
9 0
0---27
Experiment Design 1900
R.P.M. R.P.M. 25 Sec. 40 Sec. 25 Sec. 40 Sec. Test Seauence 2 12
Y
B
R
B
1
Y
R
B
Y
5 4
INDUSTRIAL AND ENGINEERING CHEMISTRY
11 10 2
3 6 8
54 63 54-63 54-63
72 81 90 99
54
66
36-45
Exhaust Charge
Time
6
The base gasoline was obtained from a major petroleum refiner supplying the Los Angeles area, and was typical of fuels currently being utilized, both in hydrocarbon composition and volatility. The fuel-additive compositions investigated are shown in Table 11, with the code used for their identification. A
1500
Chamber North South Fuels B R R Y
9 18 27 36 45 18-27 36-45 18-27
Experimental Design
Without TEL antiknock compound +3.0 a s Motor Mix antiknock compound (0.5 theory ethylene dibromide and 1.0 theory ethylene dichloride) $3.0 a s Motor Plus antiknock compound (0.6 theory ethylene dibromide and 1.0 theory ethylene dichloride)
Y
0
20, into each chamber a t 9-minute intervals. They remained in the chamber for 2 minutes, and then indicated their reactions on a formal questionnaire (2, 5, 6 ) . The two nearly identical chambers permitted direct comparisons between the fuels. eliminating the need for a correction for variations in sunlight level. Four runs were made per day, two in each chamber. Prior to each experiment. the reaction chambers were thoroughly swept with air filtered through activated carbon. After the engine had been warmed up for 15 minutes, the fuel system was switched to the test fuel and the fuel lines were thoroughly purged to ensure no carryover of the warm-up fuel. The desired engine speed was set as indicated by the tachometer, and a timed charge of total exhaust was released into one of the reaction chambers. The fuel line then was switched to the second fuel, the lines were again purged, and a similar charge was released into the second reaction chamber. The analyses were started immediately after charging (Table I).
stalled in the engine, and the carburetor was adjusted for optimum operation. The total exhaust was introduced into the chambers for a timed interval through a connection to the tail pipe. An auxiliary fuel system was designed to allow quick change from one fuel to another. These lines were thoroughly purged between runs to prevent carryover of one fuel into the other. Table I lists chemical, physical, and physiological measurements, with the schedule of sampling. The more important chemical measurements were for oxides of nitrogen and hydrocarbon. as these oxides undergo smog-forming reactions. Of special interest were methods of oxidant measurement and evaluation of eye irritation, which measure important symptoms of the Los Angeles type smog. KO attempt was made to assess visibility or plant damage. Eye irritation was measured by sending one or two persons, from a panel of
Table II.
Observations, Minutes after Charging
Rubber cracking KI, impingers Phenolphthalin, impingers Fe(CNS)x, impingers KI, recorder Panel of 20 persons Infrared, freeze-out MSA meter Saltzman’s reagent, recorder NaHS03 and iodometry, impingers
Eye irritation and odor Hydrocarbons
Code R
Schedule for Sampling and Testing
Method
12 7 9
18
--45 36 36
54 54
63
78 72 81 90 99 99
______s--
63 54 45-------72
72
90
”theory,” as used here. defines the stoichiometric amount of halogen-ethylene dibromide or ethylene dichloride-required to convert all of the lead in the tetraethyllead to the normal lead halide. Both antiknock formulations are used in motor gasolines sold in the Los Angeles area; the Motor Plus fluid mix contains the highest total scavenger concentration used commercially. To avoid possible bias on the part of the investigators; or panel members, the test fuels were blended in the Detroit Research Laboratories of Ethyl Corp. and shipped to the Midwest Research Institute. The code was not revealed to the individuals concerned until after the experiments had been completed, the data analyzed, and the conclusions reported. To secure data having the highest degree of statistical significance, a type of balanced, incomplete-block design was used to investigate the three fuels (Table 111). As smog formation is dependent on incident light and possibly relative humidity and temperature, which vary from day to day, the most efficient estimates of differences between the test fuels could be obtained only by simultaneously comparing two fuels, one in each chamber. These comparisons were made with several combinations of experimental conditions. This was particularly important because the effects of amount of exhausi and relative concentrations of oxides of nitrogen and unburned hydrocarbons were not known. The ratio of concentration of nitrogen dioxide to hydrocarbons is highly important in such systems ( 3 ) . Therefore, two different engine speeds. 1500 and 1900 r.p.m., were used to provide a range of these ratios. The use of two different charge times resulted in two levels of exhaust concentration. The experiment involved 48 individual runs. Table 111 shows that the design is balanced in all respects, including chamber and time of day. Balancing of chamber effects was desirable because the two chambers were slightly different in volume and surface area; other chamber effects might include a difference in loss rates due to leakage, and the possibility that sampling lines were somewhat different. Results of morn-
FUEL SMOG CHAMBER STUDIES ing and afternoon runs were expected to differ because of the nature of the incident light. Light intensity increases in the morning, and decreases in the afternoon. The effects of such possible differences are automatically canceled in a direct comparison of the effects of fuels on smog symptoms. The exhaust levels and the motor speeds were chosen in ranges known to produce eye irritation and oxidant. Concentration of pollutants was kept in thc range of values observed in actual urban pollution.
Treatment of Data The analytical values were analyzed directly in most cases. However, the hydrocarbon values, nitrogen oxide values, and oxidant determinations by ferrous thiocyanate and phenolphthalin were converted to logarithms before analysis. This transformation compensates for the increase in variances as larger values are obtained. The leakage effect should be constant under these conditions.
\.\
401 35
34
0 -5 - ' O b /
.
-I%-
20 ' 40
I
Figure 1,
E
60 ' 80 ' MINUTES
too ' tho
'
I&'
Typical oxidant and nitrogen oxide curves
I
I
0 25 SEC. 40 SEC.
Results and Conclusions As expected, typical smog symptoms were found throughout the experiments (Figures 1 to 5 ) . Reported levels of eye irritation ranged from zero to severe, and large amounts of oxidant were formed. Analytical values were all in the range normally experienced during actual smog formation. The oxidant values averaged about 40 p.p.h.m. after 20 minutes, as measured by phenolphthalin oxidation (the range found in Los Angeles during smog attacks). This was a little over twice the value secured by the ferrous thiocyanate technique. The oxidant recorder gave values in this range during the latter portions of the experiments. However, the recorded values were below zero in the early part of each experiment, and considerable time elapsed before the oxidant level became appreciable (Figure l), the average oxidant value was very low. The potassium iodide reagent in this instrument is recycled through a column of activated charcoal, to remove iodine produced. The adsorption is not quantitative, and the amount of iodine remaining is determined largely by the previous history of the charcoal. As the amount of iodine remaining in solution determines the position of the zero point, below zero readings must be caused by reaction with some pollutant. The oxidant reading can climb to a high value only when this pollutant disappears from the air or the oxidant concentration becomes greater
I
4l 3
-----
I n
EYE ALD. HYD. RUB. IRR. CRK.
" Figure 2.
All factors increased directionally as charging time increased
I
E
0. P
z 0
0 1500 RPM 1900 RPM
50 252
Xm
4
40 ;;
89
30-x
31
Z
0
2
20 "+
53 1035'
IRR.
.
0 RUB. N OXIDANT, CRK. OX. PHENO.
Figure 3. Increased engine speed decreased hydrocarbon concentration and increased nitrogen oxide concentration VOL.
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UR-BASE FUEL BY-WITH MOTOR MIX B-WITH MOTOR PLUS
---------
0
a3
HYD.
N OXIDES
lo
E
c c
60 E
OXIDANT PHENO
Figure 4. Adding antiknock compounds has little effect on hydrocarbon concentration, oxides of nitrogen, and oxidant level
than the concentration of the pollutant. Nitric oxide is the major oxide of nitrogen in exhaust gases. As in Los Angeles smog formation, it was rapidly converted to nitrogen dioxide during each experiment, and the total measurable oxides of nitrogen decreased throughout the experiment (Figure 1). The average levels of eye irritation were low. The panel members were not screened before the experiment. and some members were probably not very sensitive to eye irritation. The panel members entered the chambers in groups of one or two a t intervals as the experiment progressed. Low levels of eye irritation would be expected during the early part of each experiment, as nonirradiated exhaust is not irritating in these concentrations. The amount of data available for analysis from the 48 individual runs was staggering. In considering how best to present the results it was decided to show first that the technique detects effects of changes in operating variables on smog symptoms. To establish this, the effect of charge time on various measurements was determined (Figure 2). The amount of tptal exhaust charged to the chamber
has a pronounced effect. The dotted horizontal lines for each group of bars represent the 9570 confidence region of experimental values. O n the basis of accepted methods of statistical analysis of the data. if the value for the 40-second charge falls outside these limits there are less than 5 chances out of- 100 that there is no real difference between the effects of the 25- and 40-second charges. Such observed differences are considered statistically significant. All average values increased as charging time was increased, and, except for aldehydes and rubber cracking, increases were statistically significant (Figure 2). The differences between the effects of the two engine speeds, 1500 and 1900 r.p.m.. are shown in Figure 3. As expected, increasing the engine speed altered the exhaust-gas composition decreasing the hydrocarbon concentration and increasing the nitrogen oxide concentration. Therefore, the ratio of hydrocarbons to nitrogen oxide was different under the two types of test conditions. Rubber cracking was significantly reduced a t the higher speed, while some of the other smog indices were changed only slightly. In all cases, the
20 .-r‘
5 HY- WITH MOTOR MIX I B - W I T H MOTOR
E
16 o\
12 Y
85 w;
a w 4 m
I
m
n
EYE IRR.
ALD.
RUB. CRK.
u
3
a
Figure 5. Adding antiknock compounds has little effect on eye irritation, aldehydes, or rubber cracking
676
INDUSTRIAL AND ENGINEERING CHEMISTRY
results are averages for all three fuels under investigation. Although the two chambers are almost identical in size and in surface volume ratio, the slight differences significantly affect several analytical determinations made during the run. The effects of fuel composition on hydrocarbon concentration. oxides of nitrogen, and oxidant level are shown in Figure 4. Again. the 95% confidence limits established for comparing either of the leaded fuels to the unleaded fuel are shown as dotted horizontal lines for each group of bars. The differences are small in all cases, and not statistically significant. The data on eye irritation. aldehyde concentration, and rubber cracking are shown in Figure 5. Here again, measured values for all three fuels differ very little, and none of the differences are significant. Although data on carbon monoxide content and oxidant obtained by potassium iodide or ferrous thiocyanate impingers are not included, they have been analyzed in a similar manner; no significant difference between fuels was found. I t is concluded that addition of tetraethyllead to gasoline does not contribute materially to the Los Angeles smog problem.
Acknowledgment The authors acknowledge the efforts of many colleagues in this research, particularly Fred Baiocchi, Charles F. Berg, Jr., and Chaylon Honts, who carried out many of the chemical analyses.
literature Cited (1) Faith, W. L., Hitchcock, L. B., Neiburger, M., Renzetti, N.A., Rogers, L. H., Second Technical Progress Report, Air Pollution Foundation, Los Angeles, Calif., November 1955. 12’1 Goodwin. J. T.. Jr.. Bolze. Calvin. Morriss, F. V,, I&D. ENG. CHEM: 49,1249 (1957). (3) Haagen-Smit, A. J., Fox, M. M., Air Rebair 4, 105, hTo.3 (Novembcr 1954).(4) Hirschler, D. A.. Gilbert, L. F., Lamb, F. W., h‘iebylski. L. M., IND.CNG. CHEM.49, 1131 (1957). (5) Morriss, F. V., Bolze, Calvin, “Reactions of Auto Exhaust in Sunlight,” Air Pollution Foundation, Los Angeles, Calif., Rept. 19, March 1957. (6) Morriss, F. V., Bolze, Calvin, King, Frank, “Symposium on Air Pollution, 130th Meeting, ACS, Atlantic City, N. J., September 1956. (’7) Stanford Research Institute, “Smog Problem in Los Angeles County,” January 1954. (8) Stephens, E. R., Hanst, P. L., Doerr, R. C., Scott, W. T., IND.ENG. CHEW48, 1498 (1956). (9) Stephens, E. R., Scott, W. E., Hanst, P. L., Doerr, R . C., J . Air Pollutzon Control. Assoc. 6, 159 (1956).
RECEIVED for review May 24, 195’7 ACCEPTEDSeptember 27, 1957
