I
D. A. HIRSCHLER, L.
F.
GILBERT,
F. W. LAMB,
and L. M. NlEBYLSKl
Research Laboratories, Ethyl Corp., Detroit, Mich.
Particulate Lead Compounds in Automobile Exhaust Gas Why do urban atmospheres retain so little lead from the vast quantities of leaded gasoline burned daily? A detailed answer is given here
CURRENT
interest in automobile exhaust gas as an atmospheric pollutant has led to many studies of its minor constituents such as incompletely burned hydrocarbons, carbon monoxide, and the oxides of nitrogen. However, no recent work has been reported on particulate lead compounds also present to a small degree because virtually all automotive gasolines contain tetraethyllead (TEL) in concentrations u p to 3.0 ml. per gallon (0.113 weight yo lead). TEL, used in this manner since 1923, has helped to provide economically in fuels the improved antiknock quality required to keep pace with more efficient engines having higher compression ratios. Commercial antiknock fluids also contain ethylene dibromide and ethylene dichloride, known as scavengers, which are used to prevent accumulation of lead oxide in engine combustion chambers. Their function is to convert lead oxide to lead halides which have greater volatility a t engine temperatures and can be expelled. Therefore, elimination of lead from engines could be accompanied by the discharge of particulate oxides and halides of lead. w h e n TEL was first- used, public health authorities were apprehensive about hazards which its exhaust products might create. Therefore, physiological effects caused by exposure to the products of combustion of leaded fuels (5-9, 72) were extensively investigated both here and abroad. These studies showed no need for concern a t normally used concentrations of TEL, even under the most adverse conditions such as in tunnels, confined garages, and heavy traffic. The ventilation required to prevent excessive concentrations of exhaust gas and carbon monoxide provided ample dilution. These conclusions have been entirely borne out by experience in ensuing years. NQ trouble from lead poisoning has developed, and analyses of air in many
cities have shown lead concentrations, as judged by current hygienic criteria, to be insignificant. These analyses have suggested also that much of, the lead burned in gasoline is not exhausted in forms which can remain suspended in the atmosphere. Therefore, the manner in which lead compounds are exhausted from modern cars and laboratory engines was studied to determine amount, composition, and particle size. Reported investigations of suspended solids in urban atmospheres have shown that particles larger than 3 microns in diameter were present rarely and that most were less than 2 microns (2). Because of this, exhausted lead compounds for this study were separated physically into two size ranges-fine particles 5 microns in diameter or smaller, and coarse particles larger than 5 microns. The fines were further classified microscopically into ranges separated from each other by 1 micron. I n preliminary studies, exhausted particulate material was collected from single-cylinder engines with a minimum length of exhaust pipe. Following this, dynamometer tests were made under constant speed and load conditions with a passenger car engine equipped with its complete exhaust system. Finally, to simulate passenger car service under city driving conditions, chassis dynamometer tests were made under a city-type driving test cycle with two cars of different makes. I n these last tests, effects of operating conditions and of three fuel variables were studiedTEL concentration, sulfur concentration, and phosphorus-containing additives. Equipment and Methods
Exhaust Particle Collector. Preliminary studies showed that particulate lead compounds could be recovered satisfactorily from engine exhaust gas by means of an electrostatic precipitator, and that
lead burned by a single-cylinder engine could be accounted for by combining lead recovered from the exhaust gas with that remaining in engine deposits. However, good results were obtained only when the entire exhaust gas stream, rather than a sample, was passed through the precipitator. The samples were subject to error from particle size segregation caused by gas velocity differences in the sampled and main streams, nonhomogeneity of particulate matter in the exhaust stream, and fusion of lead compounds on the sampling probe. Consequently, in the reported work, the entire engine exhaustgas flow was mixed with filtered air for cooling and then passed through a modified Westinghouse PO-12 Precipitron for extracting particulate matter. Because of dilution, exhaust gas constituted only about 6 to 12 weight % of the gas which passed through the precipitator. Blank runs showed that the added cooling air introduced a negligible amount of additional lead. To recover lead compounds from the precipitator in a form useful for particle size studies, all parts of the precipitator and ducting in contact with exhaust gas were dipped or brushed with a poly(vinyl acetate) plastic coating. This coating could be later dissolved to release the collected particles as a suspension in the coating solvent. The precipitator was modified to contain a removable stainless steel lining in order to permit easy application and removal of this coating. Collection efficiency of the precipitator was measured by determining the lead content of the effluent gas. Samples were passed thiough a second, smaller precipitator or through a Millipore filter (Millipore Filter Corp., Watertown 72, Mass.) ; quantities of lead thus recovered showed that the primary precipitator collected from 90 to 95y0 of the lead present in the exhaust gas. Lead passing through the primary precipitator, VOL. 49, NO. 7
JULY 1957
1 131
Primary electrostatic DreciDitator for entire exhaust gas and secondary precipitators for sampling effluent gas from the primary precipitator
estimated on the basis of collection efficiencies as determined for each group of tests, was added as unclassified lead to the particle samples actually collected. Sample Handling. Collected particulate matter was recovered by washing the collecting units and ducting in a solution of trichloroethylene containing 5y0toluene. This solution dissolved the plastic coating and released the lead particles which had negligible solubility. Oil droplets and much of the carbonaceous material collected by the precipitator were dissolved by the trichloroethylene and not recovered. Therefore, this method is applicable only to the study of inorganic particulate matter. After the parts had been washed in the trichloroethylene solution, they were then treated with a solution of 10% nitric acid, which also u'as used to wash the containers, filters, and glassware used in processing the particle samples. Lead dissolved in this acid solution was added as unclassified lead to the total collected during the run. Particles were concentrated by settling and filtering the supernatant trichloroethylene solution through a fritted glass filter. The filtrate contained a small amount of lead that passed the filter, and this also was added as unclassified lead to the total. The concentrated particulate matter was transferred into a n equal volume solution of toluene and ethyl alcohol and separated into fractions of fine (5-micron diameter or smaller) and coarse particles (greater
1 132
than 5-micron diameter) by progressive centrifuging as guided by microscopic examinations. I n some runs, a 5- to 10-micron fraction also was separated in a similar manner, but it contained only a small portion of the exhausted lead. Hence, 5 microns appears to be a naturally occurring point for good separation, with most of the exhausted
particulate matter occurring in size ranges smaller than 5 microns or larger than 10. Count and Weight Distribution. Samples from the separated fraction of fine particles ere swpended in the toluene-ethyl alcohol solution and photomicrographed at 630 X magnificarion. Enough photographs were made to
Shadowed electron micrograph of exhaust particles of an in situ sample from Car M during city-type driving
INDUSTRIAL AND ENGINEERING CHEMISTRY
L E A D IN E X H A U S T G A S
.
count a t least 1000 fine particles in each test run to determine size distribution within the fines. T h e particles were irregular in shape with no dimension far exceeding any other. They were measured in a consistent direction in relation to the photomicrograph and it was assumed that average volume of the particles was pfoportional to the cubes of these dimensions. T o determine the magnitude of error caused by suboptical particles smaller than 0.2 micron and arrive a t a duitable correction for such particles which could be applied to the optical microscope counts, electron microscope studies were made of several samples collected in typical runs. Electron micrographs showed large numbers of suboptical particles, some as small as 0.01 micron, and also established a ratio between the number of particles smaller than 0.2 micron and those in the 0.2to 0.3-micron range. This ratio, 150 suboptical particles for each particle in the 0.2- to 0.3-micron range, was used as the basis for extrapolating optical microscopic count distribution measurements. Figure 1 is a typical plot of particle diameter against the logarithm of the number of particles larger than a given diameter, as counted by the optical microscope. The actual curve has been extended below the 0.2-micron size by using the previously mentioned ratio of suboptical particles to visible particles. From such curves constructed for each test group, the corrected particle count distribution percentages could be obtained. These curves also were used to determine particle weight distribution with the assumption of constant particle density. Average cubed diameter for each 1-micron size interval was determined by a method of approximations for small sections of the curve; from the cubed diameter and number of particles in the size interval, the percentage weight distribution was calculated. The correction has a pronounced effect on particle count distribution because of the large numbers of suboptical particles (Table I based on Figure 1). However, because of the small volume and weight of these particles, effect of the correction on weight distribution is small. Analyses. All separated samples of fine and coarse particles were analyzed chemically for lead, and also in many instances, for iron, sulfur, phosphorus, and halogens. Individual lead compounds were identified by x-ray diffraction analyses performed on both separated particulate samples and other samples not subjected to the size separation process. These latter samples, collected directly on glass slides mounted within
the precipitator, were analyzed in situ. These analyses, counts, and separation processes established the total weight of lead exhausted as both fine and coarse particles, weight distribution in the fines, and identification of exhausted lead compounds. Engines and Vehicles. The initial engine tests were made under constantspeed, road-load conditions a t 25, 45, and 60 miles per hour. For this work, a six-cylinder, 1950 model engine of Make D was operated on an engine dynamometer. The engine was equipped with the standard passenger car exhaust system cooled by fans to simulate road conditions. Prior to test work, this engine and exhaust system had been operated under road-load conditions for 410 hours (about 12,500 miles of road service) to produce normal deposits in the engine and exhaust system. When engine operating conditions were changed during the test program, efforts were made to produce exhaust system deposits typical of the condition under study by operating the engine under the new conditions for a t least 16 hours prior to the collection of exhausted particulate matter. Furthermore, each collection period was preceded by a n engine warmup period of 0.5 hour, to avoid erratic initial discharge of corrosion-released deposits which might occur
Table I. Size Range, Microns 0-1 1-2 2-3 3-4 4-5
30m ,-
I I
Figure 1. Extrapolated correction of typical microscope count for presence of suboptical particles
Effect of Extrapolation for Suboptical Particles on Typical Count and Weight Distribution Data Particle Count Actual Extrapolated 724 211 48 12 5
23,724 211 48 12 5
Table II.
Count Distribution, % Actual Extrapolated 72.4 21.1 4.8 1.2 0.5
Weight Distribution, % Actual Extrapolated
98.83 0.9 0.2 0.05 0.02
6.5 26.6 30.4 22.8 13.7
Road-Load Speed, M.P.H.
Engine speed, r.p.m. Engine load, b.h.p. Fuel-air ratio Coolant outlet temp.,
6.7 26.6 30.3 22.8 13.6
Conditions for Constant-Speed Dynamometer Tests 25
45
__ 60
1280 4.8 0.075 160
2300 15.4 0.064 160
3070 30.7 0.061 160
720 320 230
1090 625 450
1220 760 595
Exhaust gas quantity Lb. per hour Standard cu. ft./mix~.~
95 21.2
233 51.8
412 91.5
Precipitator gas mixture Lb. per hour Inlet temp., O F. Standard cu. ft./min." Wt. Yoexhaust gas
3640 96 810 2.6
3660 130 814 6.4
3550 162 790 11.6
4.5
2.0
1.2
O
F.
Exhaust gas temp., O F. At exhaust pipe entrance At tail pipe exit Tail pipe outside skin temp.,
Normal duration of run, hours 4
I
I I I 2 3 4 PARTICLE DIAMETER, MICRONS
O
F.
Corrected to 70' F. and 29.92 inches of mercury.
VOL. 49, NO. 7
JULY 11957
1 133
Table 111.
Operating Conditions Accel. to 25 m.p.h. Cruise a t 25 m.p.h. Decel. to idle Idle Accel. to 40 m.p.h. Cruise a t 40 m.p.h. Decel. to idle Idle Total
Chassis Dynamometer Test Conditions for Car B
Manifold Vacuum, In. Hg
City-Type Driving Test Cycle Engine ' , Speed, Time, R.P.M. Seconds Idle
4.6 (min.) 17.5 22.6 (max.) 18.5 2.5 (min.) 16.2 23.8 (max.) 18.5
17.2 47.2 18.6 500 17.8 1800 (max.) 17.6 1790 47.1 19.3 500 17.1 201.9
... ... ... 8.8 .. ...
1270 (max.) 1250
~
...
8.5 17.3
% ' of Total Cycle Accel. 8.5
...
...
...
8.7
... ... . a .
17.2
Cruise
Decel.
... 23.4 ... ... ... 23.3 ... ...
.". ... 9.2 ... ... . . &
9.6 ... 18.8
46.7
Full-Throttle Acceleration Test Cycle Operation Part-throttle accel. to 20 m.p.h. 20 m.p.h. road load Full-throttle accel. to 60 m.p.h. Closed-throttle decel. to 20 m.p.h. Decel. to idle
Duration, Sec (Only at start) 120.0 17.0-18.8 10.5-12.2 13.0
Cycle (Only at end)
Exhaust Gas Temp. Range Road-load speed, m.p.h. Gas at exhaust manifold exit, Gas at tail pipe exit, O F.
Table IV.
Operating Conditions Accel. to 25 m.p.h. Cruise a t 2 5 m.p.h. Decel. to idle Idle Accel. to 40 m.p.h. Cruiseat40m.p.h. Decel. to idle Idle Total
0 (idle) 480 200
F.
25 570 240
40 710 350
Chassis Dynamometer Test Conditions for Car M
City-Type Driving Test Cycle Manif old Engine Time, Vacuum, Speed, In. Hg R.P.M. Seconds Idle 11.5 (min.) 1200 (max.) 17.2 19.8 975 47.3 23.5 (max.) 17,5 19.0 500 19.0 9.4 6.0 (min.) 2050 (max.) 17.3 ,. 19.0 1450 47.2 25.5 (max.) 20.0 19.0 500 16.4 8.1 201.9 17.5
... ...
... . ... ...
% of Total Cycle Accel. 8.5
... ... ... 8.6 ... ... ...
Decel.
...
... 8.7 ... ... ... 9.9 ...
... ...
46.8
18.6
(Only at start)
1
Cycle
I
Exhaust Gas Temperature Range Road-load speed, n1.p.h. 0 (idle) Gas at exhaust manifold exit, F. Left 390 Right 430 Gas at tail pipe exit, O F. Left 135 Right 190
... 23.4 ... ... ...
23.4
17.1
Full-Throttle Acceleration Test Cycle Part-throttle accel. to 20 m.p.h. 15.0 20 m.p.h., road load 120.0 12.5-13.5 Full-throttle accel. to 60 m.p.h. Closed-throttle decel. to 20 m.p.h. 10.5-11.0 Decel. to idle 12.0
Cruise
(Only at end) 25
40
type of operating schedule consisted of several full-throttle accelerations from 20 to 60 miles per hour. The third type of schedule was a constant-speed cruising condition at 60 miles per hour at road load, for 1 hour (Tables I11 and IV). As in engine dynamometer tests, the cars were warmed up for 0.5 hour on the test cycle. before each exhaust collection period. The two test cars had V-8 engines and automatic transmissions, but in other respects represented widely different types. Car B, a popular, lower priced 1954 model, was equipped with a single exhaust system and muffler; Car M, a higher priced 1953 model, was equipped with a dual exhaust system which had one muffler and one resonator in each exhaust system. One commercial base gasoline was used for all test work. It contained 0.025 weight of sulfur and 3.0 ml. of T E L per gallon as Motor Mix Fluid except during tests in which additional TEL, sulfur, or phosphorus was introduced as a test variable. The Motor Mix Fluid contains 1.O theory ethylene dichloride and 0.5 theory ethylene dibromide, a theory representing the amount of halogen theoretically required to convert the total lead to the respective lead dihalide. A commercial MS grade lubricant was used in the two cars, and a straight mineral oil was used during the dynamometer tests on Engine
D. Before exhaust studies were begun, both cars had been driven in uncontrolled suburban road service comprised of both city and country driving. However, during the test programs which followed, the cars were driven only under the standardized test cycle on the chassis dynamometer for a n extended series of tests. Then they were returned to suburban road service and finally they were driven again only on the chassis dynamometer test cycle during a second series of exhaust studies. lests using higher concentrations of T E L or added sulfur or phosphorus, were preceded and followed by tests on the standard base-line fuel for comparison. r 7
460 520
545 650
145 190
160 250
Amount of l e a d Exhausted in Particulate Form
when the engine was started after an extended shutdown period. Collection periods ranged from 1 hour a t 60 miles per hour to 4.5 hours a t 25 miles per hour to provide a n exhausted lead sample of convenient size (Table 11). Following the dynamometer test series, another test program was carried out in two automobiles of different makes operated on a chassis dynamometer under three types of operating schedules. Most of the tests were run under a cycled operating schedule of varied speeds and
1 134
power outputs to simulate city drivingan average speed of 22 with a maximum of 40 miles per hour, periodic partthrottle accelerations, decelerations, and idling periods. This operating schedule was based on typical Los Angeles city driving reported to consist of 18Yc idling, 18% acceleration, 18% deceleration, and 46% road-load cruising ( 7 3 ) . Automatic, timed controls provided uniform repetition of the test cycle. Each test was of 5 hours' duration and covered about 110 miles. The second
INDUSTRIAL AND ENGINEERING CHEMISTRY
Amounts of lead exhausted under three constant-speed, road-load test conditions by Engine D operated on fuels of two different T E L concentrations, are presented in Figure 2. Considerably less lead was exhausted than was burned. Higher speeds tended to increase both total lead emission and that proportion exhausted as particles larger than 5 microns in diameter. The amount of lead exhausted was proportional to TEL concentration in the fuel, but concentration had no marked
or consistent effect on distribution of exhausted lead between fine and coarse particulate forms. Vehicle Tests. Figure 3 shows the amounts of lead exhausted during an extended mileage period of city-type driving by Car B, which had a conventional single exhaust system. Unclassified lead was combined with fine particulate lead to represent the maximum possible quantity of lead in fine form. Amount of lead exhausted depends not only on the type of operation which prevails a t the time of measurement, but also on the type of operation j n which the car has been used during-several thousand miles prior to the measurement. If fuel variables are not considered, the smallest quantity of lead was exhausted in the tests immediately following the two periods during which the car was in uncontrolled suburban service on the road. At these times, 20 to 24% of the input lead was exhausted, and 10 to l6Y0 of that burned was exhausted in the fine-plus-unclassified portion. With continued operation under the mild city driving schedule, the amount of exhausted lead increased markedly and reached a maximum after about 4000 miles, a t which time 50 to 60% of the lead burned was exhausted, and 30 to 50% of the lead burned was exhausted in the fine-plus-unclassified form. The deposit condition of the exhaust system is a major factor in influencing lead emission. Under each type of operation, an engine and exhaust system approach equilibrium as to lead retained and exhausted. Comparatively severe engine service, such as higher speed surburban driving to which the
yv
10
LEAD IN E X H A U S T G A S
UNCLASSIFIED LEAD
COARSE PARTICLES, '.':':' >5 MICRONS flNE PARTICLES, O T 0 5 MICRONS
TELCONC, ML/GAL 3 4 ROAD LOAD SPEED, MPH 25
3
4
3
45
4
60
Figure 2. Effect of engine speed and fuel TEL concentration on exhausted lead for dynamometer tests with Engine D Figures in parentheses are number of replicate tests averaged
and attain greater thickness and higher surface temperatures, these factors would promote deposit vaporization and flaking and cause progressively greater lead discharge and a reduced rate of deposit accumulation. This reasoning is further supported by other results obtained for Car B (Figure 4) when it was subjected to a brief period of severe driving during the latter part of the second test series, after the car had been operated for about 8000 miles under the mild city driving schedule on the chassis dynamometer. This severe driving consisted of a series of three full-throttle accelerations from
car was subjected prior to exhaust studies made on the chassis dynamometer, favors higher lead discharge and lower retention. This was shown by the earlier constant-speed test work in which greater quantities of lead were exhausted at higher speeds. More severe service should then produce comparatively light deposits in the exhaust system, which in turn would promote greater deposition and less lead discharge during subsequent service under mild driving conditions such as those used in the chassis dynamometer tests. Then, as additional deposits accumulate with continued mild operation
I
500
8
-TOTAL
I
LEAD EXHAUSTED
--
f 4 100:
a :
ap 50-
3 - 1
a 4'5 w
10:
-
5-
I-
Figure 3. Particulate lead compounds exhausted by Car B during an extended mileage period of chassis dynamometer testing
6
640
645
650 RUN NO.
655
660
-3
Figure 4. Effect of various driving conditions on amount of lead exhausted b y Car B VOL. 49.1 NO. 7
JULY 1957
1 1 35
ACCELERATIONS 8 HIGH SPEEOD R I V I N G * M UBURBAN ROAD SERVICE--+=’
-SUBURBAN ROAD SERVICE*+CITY-TYPE
C . TOTAL LEAD EXHAUSTED
MLTELA~4ML
FUEL: BASELINE ( 3 0.025 WT. % S )
4MLTEL
PARTICLES (0-5pJ 8 UNCLASSIFIED E A 0
D.-T) FINE
4 ML
si
40-
20-
FINE PARTICLES (0-5p.I EL UNCLASSIFIED LEAO-
0-
40
-
-------? ---_ ------J”i VI i -I--
TOTAL LEAD-
20-COARSE PARTICLES
(>5p)-
0 5245
7952
16741
I
262 ! , 19399
Figure 5. Particulate lead compounds exhausted by Car M during an extended mileage period of chassis dynamometer testing
20 to 60 miles per hour, a series of nine similar accelerations, and four successives tests, each composed of 1 hour of operation a t GO miles per hour road load. Prior to this period of severe service, the car exhausted 50 to 60Yo of the lead burned. However, the first series of three accelerations discharged 12 times as much lead as was burned, and the second series of nine accelerations discharged nearly nine times the lead input. Then during the next 4 hours a t GO miles per hour road load, lead emission fell progressively from 464 to 109% of input. Thus, by discharging previously deposited lead, the exhaust system was becoming cleaner and approaching a new equilibrium characteristic of G O miles per hour road-load op-
Table V.
eration. Following this 244-mile interval of severe service, the car exhausted less lead when it was again operated on the mild city driving schedule, I n fact, lead emission dropped to about 35y0 of input, which is comparable to the amount exhausted when the car was first tested after the periods of suburban driving on the road. For Car M, the larger car with the dual exhaust system, effects of mileage accumulation and of driving history were generally similar to those of Car B, but amount of lead exhausted was smaller (Figure 5). During city-type driving, immediately after periods of uncontrolled suburban driving, Car M exhausted a total of 20 to 25y0 of the input lead, and lead in the fine-plusunclassified form constituted from 16 to
Per Cent of Input Lead Exhausted in Particulate Form Total Lead
Type of Service
Car B
City driving after extended Suburban service City-type service Full-throttle acceleration to 60 m.p.h. Constant speed, m,p.h., road load
20-24 50-60 1233-873
60 45 25
... 464-109 ... . e .
Car RiL 20-25 30-40 1990 249-67
... ...
Lead Compounds 5 Microns or Smaller, pIus Unclassified Lead City driving after extended Suburban service 10-16 16-20 City-type service 30-50 20-30 779-561 1148 Full-throttle acceleration to 60 m.p.h. Constant speed, m.p.h., road load 60
45 25
1 136
395-81 . a . e . .
INDUSTRfAL AND ENGINEERING CHEMISTRY
188-57
... e..
Dynamometer Engine D . I
.. .. 54 9 .
28 14
...... 33 20 13
RUN NO.
Figure 6. Effect of various driving conditions on amount of lead exhausted
by Car M 20% of that burned. Lead discharge increased with mileage, and after about 4500 miles of city-type driving, 30 to 40% of the lead burned was exhausted as particulate matter and 20 to 30y0 of that burned was exhausted in fineplus-unclassified forms. The lower values obtained with Car M as compared with Car B indicate that more lead was deposited in the larger exhaust system; consequently, less lead was left to be exhausted. Exhaust system deposit data given subsequently, confirm this. The effects of more severe operation on the amount of lead exhausted from Car M are shown in Figure 6 . ‘The driving schedule of full-throttle accelerations and GO miles per hour cruising speed was the same as that used in Car B, but one sample was lost from the second series of nine accelerations. Therefore, data for Car M show only the results from the first series of three accelerations and from the four successive hours a t GO miles per hour. The first series of three full-throttle accelerations to GO miles per hour after a period of city-type driving, discharged 20 times the amount of lead burned. During 4 hours of driving a t 60 miles per hour road load, which followed the acceleration tests, the car discharged amounts of lead decreasing from 249 to G7% of the lead burned. Unlike Car B, Car M did not discharge less lead in city-type service after this brief period of severe service; probably because of its larger exhaust system, Car M would require more extensive high-speed operation to produce a noticeable cleanup of the exhaust system. Table V summarizes the data which
-
LEAD IN E X H A U S T G A S have been presented in respect to the quantities of exhausted lead. Lead Retention by Test Cars. Since the two cars exhausted considerably less lead than was burned in city driving service and considerably more than was burned under accelerating or high-speed driving conditions, the total amount exhausted over their entire service periods can be determined by subtracting the lead retained from the total amount consumed. Analyses of the car components which may retain lead compounds gave the results presented in Table VI. Both the lubricating oil and the exhaust system retained important quantities of lead. The dual exhaust system of Car M retained 14.6y0 of the lead burned, while the single exhaust system of Car B retained only 7.4y0. By difference between lead burned and lead retained, Car B exhausted 78.8% of the lead burned over its 27,000 miles of service, while Car M exhausted 72.5% in 19,500 miles. These values compare directionally with equilibrium leaddischarge values reached by the two respective cars after several thousand miles of city-type driving. Effects of Fuel Variables. As shown by Figures 3 and 5, a number of fuel variables were introduced during the test series made on the two cars. I n different test periods of about 700 to 2000 miles’ duration, which were bracketed by similar test periods on the base-line fuel, small changes were introduced into the same base gasoline. These changes included increasing T E L concentration from 3 to 4 ml. per gallon, sulfur from 0.025 to 0.105 weight % by adding disulfide oil, and adding two commercial phosphorus-containing fuel additives a t concentrations of 0.4 theory of phosphorus, the level of maximum commercial usage (A theory of phosphorus is the theoretical quantity required to convert all the lead to orthophosphate). The increasing amount of lead exhausted with increasing mileage makes it impossible to measure directly the effects of these fuel variables. Instead, a n y cbange in exhausted lead caused by a fuel variable must be observed as a deviation from the expected change caused by mileage accumulation, and the result is indicative only of substantial changes. No major effects due to fuel variables were present; data expressed as a percentage of the lead burned show regular and progressive changes in exhausted lead with mileage (Figures 3 and 5). The direct relationship between T E L concentration and the amount of lead exhausted, indicated by these results, was further substantiated by other results obtained with Car M. This car was operated on the road during two
25 MPH 0
IO
c
a
-
45 M P H
PARTICLE
SIZE RANGE,
MICRONS
Figure 7. Amount and size range of exhausted particulate lead compounds as affected by speed and TEL concentration Constant speed, road-laad dynamometer tests using Engine D
periods of uncontrolled suburban driving, each of which was followed by a period of chassis dynamometer testing and exhaust observations (Figure 5 ) . During the first period of road service and the testing period which followed, the car was operated o n fuel containing 3.0 ml. of TEL per gallon, but during the second corresponding periods, the fuel contained 4.0 ml. of T E L per gallon. Nearly identical percentages of the lead burned were exhausted in these two sets of experiments; thud the amount of particulate lead in the exhaust gas was proportional to the T E L concentration in the fuel.
Table VI.
Particle Size Distribution of Exhausted l e a d Compounds
Constant Speed Tests. The quantities of lead exhausted as fine and coarse particles in the dynamometer tests in Engine D have been shown in Figure 2 and Table V. Figure 7, which extends these results to include weight distribution of lead in the size ranges below 5 microns, shows that the major portion of lead in the fine fraction occurred in the 1- to 4-micron size range. Although increased speed produced greater lead emission in all size ranges, the coarse material was increased to a greater ex-
Lead Retained by Automobile Exhaust Systems and Lubricating Oil
Test mileage Total lead consumption, g.
Car B
Car M
26,996 5,300
19,345 4,154
Lead Recovered Cylinder heads and combustion chambers Manifolds and exhaust pipes Mufflers Tail pipes Oil sludge Oil 5lters Oil changes
Grams
% ’ of Input
76 64 247
1.4 1.2 4.7 0.1 1.1 9.7 3.0
5 59 515 160 1126
Grams
7,of Input
117 100 379 11 100
2.8 2.4 9.1
0.3
... 2.4
None used
-
436 -
10.5
21.2
1143
27.5
VOC. 49, NO. 7
JULY 19157
1137
I
FUEL USED DURING TEST GROUP
0BASELINE (3 Mlr TEL,
0.025% SI
u 4 ML TEL 0.105% S
W
PHOSPHORUS ADDITIVE A PHOSPHORUS ADDITIVE B
0-I
2-3
1-2
3-4
4-5
>5
UNCLASSIFIED
PARTICLE SIZE RANGE, MICRONS
Figure 8. using Car
Size distribution of exhausted lead compounds from 10 groups of tests run under city-type driving conditions
B
tent than the fines and constituted 7 , 29, and 39% of the total exhausted lead at 25, 45, and 60 miles per hour, respectively. Increased speed from 25 to 45 miles per hour had little effect on the amount of lead in any of the size ranges except above 5 microns; but further increase to 60 miles per hour produced appreciable increases in the amount of lead compounds both smaller than 2 microns and larger than 5. Variations in the amounts of unclassified lead impair comparisons between the fuels of two different TEL concentrations, but the only distinct difference in the size-distribution patterns obtained with the two fuels appears to be the greater amount of coarse material at 60 miles per hour which was produced by the fuel of higher TEL content. The general increase in coarse material with speed, and in material smaller than 2 microns a t 60 miles per hour implies that at least two mechanisms of particle formation are present. One is the breaking off of larger particles from material deposited in the exhaust system; this process is increased by higher exhaust gas velocities. The other process appears to be vaporization and subsequent condensation of lead compounds as very small particles. This becomes most pronounced at the highest temperature conditions. The net effect of operating condition variations on particle size can well be the result of these two effects. Vehicle Tests. Thus far, data have been expressed largely in terms of the amount of lead burned. However, since the amount of lead exhausted by the two test vehicles operated on the city driving test cycle progressively increased with mileage accumulation, particle size distribution can be expressed best as a percentage of lead exhausted rather than
1 138
of lead burned. Figures 8 and 9 show results for the the two cars under city driving conditions in this manner. The bars in each size classification represent the average values from each group of 7 to 15 individual tests on a given fuel, and are in the consecutive order in which the test groups were run. Figure 8, the data from Car B, indicates that no progressive change in particle size distribution occurred with increased mileage. Instead, the greater amount of lead exhausted after increased mileage accumulation was caused by increased amounts of particles in all size ranges. This indicates that particle size distribution is insensitive to deposit condition in the exhaust system within normal limits encountered in passenger car service. This is further indicated by the absence of marked shifts in size distribution between the
third and fourth bar in each size group, during which interval the 2500-mile period of suburban driving took place, and between the ninth and last bar of each size group, which were separated by the period of accelerations and high speed driving. I n two test groups using higher-sulfur fuel and Phosphorus Additive A, even though both variables may introduce changes in size distribution, the effects are small. Slightly larger proportions of exhausted lead occurred in the 3to 5-micron size range, with corresponding reductions in the range greater than 5 microns. The third fuel variable, TEL concentration, introduced no change in particle size distribution; this substantiates the constant-speed test results. Car M (Figure 91, also showed no size distribution shifts that can be defi-
FUEL USED DURING TEST GROUP: BASELINE (3 M b TEL, 0.025% S ) W
4 MLTEL
Iv) -
$1
9
8
201
IL
3
IO
0-1
1-2
2-3
3-4
4-5
>5
UNCLASSIFIED
PARTICLE SIZE RANGE, MICRONS
Figure 9. Size distribution of exhausted lead compounds from five groups of tests run under city-type driving conditions using Car hZ
INDUSTRIAL AND ENGINEERING CHEMISTRY
L E A D IN E X H A U S T G A S nitely related to mileage accumulation or changes in T E L concentration, although there is an indication that particle size distribution may move somewhat toward the coarse side with increased mileage. However, more severe . ;driving H service-7000 miles of suburban between the third and fourth bar in each size group and full-throttle accelerations and higher-speed driving which occurred between the fourth and last bar in each group-caused no consistent changes in the size distribution patterns found in subsequent city driving. In Figure 10 the test groups on highersulfur fuel and on both phosphorus additives have been omitted from the average for Car B. This figure provides additional evidence that more severe operating conditions which exhaust greater quantities of lead also tend to exhaust more lead as coarse particles. Of the lead exhausted from Cars B and M, 32 and 22% respectively was in coarse form during city driving conditions, but 36 and 42% was in coarse form during full-throttle accelerations. Under city-type driving conditions, Car B (single exhaust system) exhausted more lead in coarse form than did Car M (dual exhaust system). However, during accelerations, this relationship was reversed. I n city driving, Car B exhausted a larger percentage of the lead burned than did Car M ; therefore, it appears that Car B expelled more of its exhaust system deposits under city driving conditions and had less deposited lead left to be discharged in coarse form during accelerations. Thus, the larger dual exhaust system tends to reduce lead emission during city driving but under more severe driving conditions, exhausts more lead, and more of it in coarser particulate form. Both cars showed similar particle size distribution patterns under the citytype driving schedule and a t 60 miles per hour road load. However, Engine D showed considerable difference between the 60 miles per hour condition and the lower speeds. A possible explanation for this is that Engine D was smaller, and had a rated horsepower of 92 as compared to 130 and 210 for Ckrs B and M respectively. Therefore, operation a t 60 miles per hour would represent a larger fraction of the available power from Engine D, and would be a more severe, higher temperature type of operation which would tend to accentuate the differences. The higher exhaust system temperatures obtained with Engine D (Tables 11, 111, and IV), are in agreement with this thinking. From the data in this section it can be concluded that from 50 to 75% of the lead exhausted under city driving conditions is in the form of 5-micron and smaller particles, with the remainder
0UNCLASSIFIED
LEAD
El COARSE PARTICLES ( X p ) FIN E PARTICLES (0-5p)
a 0
8, P
D W
55
M
z2
25 MPH
%a
4
I .....................I
m
5 @ 8
60 MPH
CITY-TYPE DRIVING
m
a 60 MPH ROAD LOAD
9
ACCEL'S. TO 60 MPH
CITY-TYPE DRIVING I
9
60 MPH ROAD LOAD ACCEL'S TO 6OMPH
0
20
40
60
80
100
WEIGHT % OF TOTAL LEAD EXHAUSTED
Figure 10. Average particle size distribution 'of lead compounds exhausted by three engines under several operating conditions
as coarser material. The ratio of fine to coarse particulate material decreases somewhat under high-speed or high-load conditions which also increase the amount of lead exhausted. The largest numbers of particles exhausted are extremely fine and are smaller than 1 micron, but by weight they comprise less than 5y0 of the total exhausted lead. O n a weight basis, particle distribution appears to have two peaksone in the 1- to 4-micron range, and a second peak in an undetermined size range larger than 5 microns. With respect to fuel additives, TEL concentration appears to have no effect on particle size distribution, but increased sulfur or phosphorus concentration in gasoline may tend to produce slightly more particulate matter in the 3- to 5-micron size range and slightly less in the larger sizes. Composition of Exhausted Particulate l e a d Compounds
Elemental Analyses. Elemental chemical analyses of particulate matter separated into fine and coarse fractions gave the results in the following table. The fine particles generally contained higher percentages of lead than the coarse material, but the coarse contained greater amounts of iron, probably from exhaust system corrosion, and more
Element Lead Chlorine
Bromine Iron Sulfur Carbon
Range of Composition, % Fine particles Coarse particles 58-74 5.6-16.8 8.1-18.0 0-1.3 0-1.9 3.5-8.7
34-60 4.5-10.5 9.2-23 6 1.2-11.2 0.2-2.3 4.6-12.1
sulfur. Although no attempt was made in this work to study the carbonaceous and organic matter in exhausted material, the analyses showed that carbon was present in both the fine and coarse samples. The material as originally exhausted was probably higher in carbon content than shown by these values, because only carbonaceous matter which was not dissolved and removed by the trichloroethylene solvent used in the size separation process is represented. Because of this and the low density of carbonaceous material as compared to that of lead compounds, the above analyses indicate that carbonaceous material could account for a substantial amount of the exhausted material on a volume basis, but that lead compounds represent host of the weight. Identification of Lead Compounds by X-Ray Diffraction. In each test run, two or more samples of the exhausted material were collected on glass VOL. 49, NO. 7
JULY 1957
1 1 39
FUEL: BASELINE
t
+
BASELINEf 0 4 T PAS PHOSPHORUS ADDITIVE B
BASELINE 0.4 T P AS ADDITIVE A
I
2.0
I-
1.0 0.5
-
21,040 VEHICLE TEST MILEAGE
Figure 1 1. Phosphorus content of exhausted lead compounds in successive test runs after phosphorus was introduced into the gasoline. City-type driving tests using Car B
slides mounted within the precipitator. These samples, consisting of particulate matter smaller than 15 microns, were subjected to x-ray diffraction analysis in situ without size classification or other prior treatment. Table VI1 which presents the results of these analyses averaged by test groups in the two cars, shows that except when phosphorus was present in the fuel, only two general types of lead compounds were present-one, the normal lead halide, PbCI.Br; and the other, binary complex compounds of this halide and ammonium chloride. Distribution of lead between these two general forms was distinctly influenced by vehicle type and operating conditions. Under the city-type driving cycle or at 60 miles per hour road load, Car B (single exhaust system) exhausted about two thirds of the lead as PbCl Br, while Car M exhausted about two thirds of the lead as lead-ammonium halide complexes. However, both cars exhausted predominantly PbCl . Br during fullthrottle accelerations. These effects imply that lower temperature conditions, as found in the dual exhaust system of Car M or in relatively lighter load operation, favor emission of lead in the lead-ammonium halide type of compounds. This is consistent with the Table VII.
known thermal instability of these compounds a t high temperatures. Except for phosphorus, the fuel additive variables studied had no material effect on particle composition. ]so significant differences were associated with increased concentrations of either T E L or sulfur. However, either phosphorus additive caused about one fifth of the lead to be exhausted as 3Pb3(P04)2. PbC1.Br and possibly increased to a slight extent the concentration of the lead-ammonium halide complexes, with corresponding reductions in PbCl Br. Figure 11 shows the changes in phosphorus content of both fine and coarse material over the mileage interval during which phosphorus-containing fuel was used in Car B. When phosphorus was initially introduced, its content in the fine exhausted material quickly reached a high and stabilized level, and when its use was terminated, the phosphorus content of fine material diminished rapidly. Coarse material, on the other hand, was slower in reflecting the use of phosphorus, but the effects persisted for a t least 700 miles after phosphorus was no longer present in the fuel. This behavior supports the premise that fine particles are mainly materials exhausted directly from the combustion chamber, while the coarser particles
Average Composition of Exhausted Particulate Lead Compounds
(X-ray diffraction analyses made in situ on material deposited on glass slides mounted within precipitator) Wt. yo of Compounda or-NHdC1. B-NHACl. 2NHaC1. 3Pba(POl)z. PbC1.Br 2PbCi.Br 2PbCl.Br PbCl Br PbC1.Br Car E 68 24 6 2 City-type cycle, fuel $- TEL only 70 30 City-type cycle, added sulfur* 35 18 17 10 20 City-type cycle, added phosphorusC 60 20 20 . e Constant speed, 60 m.p.h., road load 85 10 5 *. Bull-throttle accelerations Car M . e
I .
....
.. e .
+
33 40 5 22 City-type cycle, fuel TEL only 30 30 35 5 Constant speed, 60 m.p.h., road load Full-throttle accelerations 90 10 a PbS04 and PbO PbCl Br H20 also occurred occasionally in concentrations of 5 % or less. Sulfur content increased from 0.025 t o 0.105 weight % ' by added disulfide oil. 0 0.4 theory phosphorus added as Phosphorus Additive A or B. 9 s
1 140
INDUSTRIAL AND ENGINEERING CHEMISTRY
*.
e .
..
e.
comprise more of the deposited material which is subsequently removed from the exhaust system by flaking and vaporization processes. Except for these differences caused by phosphorus, no major composition differences were found between the fine and coarse separated fractions by x-ray diffraction. One exception was extremely large particles, 0.5 mm. and larger, which were high in iron oxides and contained lead principally as the sulfate and PbO.PbSO1. This probably accounts for the slightly higher percentages of iron and sulfur found in the separated coarse fraction by elemental analyses. Comparisons between the fine and coarse processed fractions are indirect, however, because x-ray analyses of the processed samples differed from those of the corresponding unprocessed glass slides and showed that liquids employed in the size separation process introduced unanticipated changes in composition. Therefore, comparisons between the two size fractions are valid only if similar composition changes occurred in both fractions. The processed samples were found to contain mostly PbCl .Br and PbO PbCl Br H20, with smaller amounts of the lead-ammonium halide complexes than in the unprocessed material. O n contact with ethyl alcohol during processing, the lead-ammonium halide compounds can be decomposed to the primary salts, PbCl . Br and ammonium chloride, and the latter removed by solution in ethyl alcohol. Also, PbO.PbC1 Br HzO can be produced by hydration of PbCl Br. Therefore, it is believed that ethyl alcohol and trace amounts of dissolved water in the processing solutions may have been responsible for the composition changes. Some change in particle size might be expected to occur in processing concurrently with composition changes. However, no size change of sufficient magnitude to affect the size distribution data could be found. Microscopic observations and size counts made for untreated exhaust particles before and after wetting with the various process liquids showed no size distribution change. This finding also was corroborated by a study of the particle size distribution data from duplicate test runs in which widely different amounts of the hydrate compound (PbO PbCl. B r . H z O ) were found in the processed material. Since these comparisons also showed no appreciable difference in size distribution between high hydrate samples and low hydrate samples, it i s probable that size-separation processing of the exhausted material did not appreciably alter the original size distribution of the particles, even though substantial changes in particle composition occurred. Lead-ammonium halide complexes
L E A D IN E X H A U S T G A S found in the exhausted solids generally are not found in deposits from combustion chambers or exhaust systems, although they have been observed under specialized test conditions. Similarly, they have been reported by Street (77), as a constituent of combustion products extracted from a combustion chamber by means of a sampling valve during vario&sportions of the engine cycle. Because of the unusual nature of these compounds, experiments were conducted to determine if their presence in exhaust gas was normal or whether their formation might have resulted from the strong electrical field of the precipitator or from the passage of exhausted gases, even at high dilution, over other lead salts originally deposited on the precipitator plates. The former possibility was eliminated when lead-ammonium halide complexes were found in material filtered from air, sampled 2 feet behind an operating car. Moreover, because of the dilution a t this point, it is also improbable that extensive gas-solid reactions occurred on the filter. Similarly, lead-ammonium halide salts also were found in other experiments in which exhaust gas from a laboratory engine was impinged on a moving strip of Scotch tape which was quickly covered with another tape to prevent further exposure of the collected solids to gases. Because of these results it is probable that the lead-ammonium halide complexes were actually exhausted and not the result of any extraneous effect. Composition of Exhaust System Deposits. Composition studies of exhausted particulate matter were supplemented by x-ray diffraction analyses of the material deposited in the exhaust systems of the two test cars. The major deposit constituents were PbCl. Br and P b O . PbCl. Br. HzO (Table VIII). Because of the high amounts of PbO. PbCl. Br . H20 and relatively low amounts of lead-ammonium halide complexes, these findings suggest that deposited material removed and exhausted in particulate form may undergo gassolid reactions and composition conversion during passage through the exhaust system. Traces of halogen acid present in the exhaust gas would be expected to convert P b O . PbCl. Br .HzO into PbCl, Br, while ammonia, which also may be present in trace quantities, might produce further conversion of PbCl. Br into lead-ammonium halide forms. Ammonia concentrations as low as 20 p.p.m. would be theoretically sufficient to produce the observed quantities of leadammonium halide complexes. Such a mechanism could account for the major proportions of PbCl. Br and lead-ammonium halide complexes found in the exhausted material.
Table VIII.
Deposit Location
Composition of Exhaust System Deposits (As determined by x-ray diffraction analysis) PbO. orNH4C1. PbCl. Br PbCl .Br .Hz0 PbSO, PPbC1. Br Car B
Combustion chamber Exhaust manifolds Exhaust pipe Muiller Tail pipe
70 85 75 90
Combustion chamber Exhaust manifold Left Right Exhaust pipe Left Right Large mufaer Left Right Pipe between muaers Left Right Small mufiler Left Right Tail pipe Left Right
90
5
15 5 10 5
10
15 5
b
b
b
Car M 10
..
..* . .... I
15
75 45
95 80
5 5
....
....
65 55
..
20
..
15
30
60 90
..
10
..
25
10
40 60
15 20
....
20
40
Significance of Results in Relation to Atmospheric Pollution The emission of particulate matter by automobiles obviously bears on the problem of atmospheric pollution, as do other automobile emissions such as carbon monoxide, oxides of sulfur and nitrogen, and incompletely burned fuel. Importance of these various emissions is currently under study by many laboratories. The value of the reported work lies in establishing a general pattern of lead emission expected from a car during the idling, accelerating, cruising, and decelerating conditions typical of city service. I n city driving, a car probably exhausts little lead while the exhaust system is clean, but over a period of about 5000 miles its emission of lead tends to increase gradually to the point where 30 to 6OY0 of that burned is exhausted, of which 50 to 75y0 is in particles smaller than 5 microns and 4% smaller than 1 micron. Occasionally when the car is subjected to higher-speed highway driving or to high-speed full-throttle accelerations, it may exhaust considerably more lead than is burned, with a larger proportion in large particles which settle more rapidly. This emission cleans the exhaust system so that it again retains a high proportion of the lead burned. This pattern of behavior probably can be modified to some extent by design
15
...
... ... b
...
.
55
25
1 oa
..
.. ....
75 45
Other
.... ... ... ... 15"
10 a .
...
..
.. ..
1 5c 5d
... 4 5c
...
of the exhaust system. Current trends toward multiple mufflers and larger exhaust systems, which run cooler and have lower gas velocities, probably will reduce lead emission in city-type driving at the expense of somewhat increased lead emission under more severe highway-type driving. Similar effects can be expected from lower engine speeds relative to car speed, and larger engines which operate at relatively lighter load factors in city service. The foregoing mechanism may explain why surveys of the lead content of urban atmospheres have shown q u c h lower concentrations of lead than might be expected on the basis of T E L consumption if all of the lead burned became an air-borne dust. One of the most thoroughly studied urban atmospheres is that of the Los Angeles area where a n estimated 4,680,000 gallons of gasoline were consumed daily in 1954 (4). Published estimates of the daily dispersion air volumes in this area are 4.2 X 1013cubic feet in clear weather (2000-foot inversion layer) and 6.46 X 10la cubic feet during periods of severe smog caused by an atmospheric inversion layer at 500 feet ( 7 ) . If an average T E L concentration of 2.2 ml. per gallon is assumed (70),then uniform dispersion of this entire amount of lead in these air volumes would produce lead concentrations of 9.2 and 59.5 y per cubic meter, respectively. VOL. 49, NO. 7
JULY 1957
1141
These values may be compared with those from a published study of the suspended matter in Los Angeles air, as measured in 1954 during a 4-month period in which atmospheric inversions frequently hindered the dissipation of suspended matter ( 3 ) . This study showed concentrations of lead from all sources including automobiles (Table
IX) .
Lead occurs in measurable concentrations in areas remote from urban and industrial centers because of a variety of factors, including air-borne particles of dust from the soil. Combustion of coal, wood, and waste of vegetable origin contributes lead to the atmosphere. Therefore, the increment provided by combustion of tetraethyllead is indeterminate. Evidently, contributions from all sources are subject to dilution in accordance with the vagaries of wind, weather, and the earth’s topography, and therefore any attempt to interpret results of the analysis of atmospheric samples is difficult. The highest individual value in this study, 3 6.4 y per cubic meter (Table IX), together with other but lower values in the high range, were obtained during periods when the base of the inversion layer remained at 500 feet and lower. Similarly, lead concentrations for 30 metropolitan areas in 1954 were reported to range between 0.1 and 26.6 y per cubic meter, with an average of 2.15 in 588 observations. These observed data are appreciably lower than the preceding calculated lead concentrations. However, since only 10 to 509;bof the lead burned in city driving is exhausted in fine particulate form, as indicated by this study, surprisingly close agreement between calculated and observed lead concentrations can be obtained if the calculations include this factor. The public health aspects of lead compounds suspended in air are beyond the scope of this work, as these involve many factors in addition to lead concentration, and sources of lead other than the automobile. The present results, however, tend to substantiate the low lead concentrations which have been reported for urban atmospheres and also provide new infcrmation which will be useful in future hygienic studies of exhausted particulate material. Summary Studies to determine the amount. Table IX.
Month August September October November
1 142
composition, and particle size distribution of the lead compounds present in engine exhaust gases have been made with laboratory engines and with two conventional cars operated on fuels containing tetraethyllead. The exhausted carbon and organic particulate matter were not investigated. Approximately 20 to 3070 of lead burned in the fuel was retained in passenger car exhaust system deposits and lubricating oil, which left 70 to 80% of the lead to be exhausted over 20,000- to 30,000-mile periods of city and country driving. Lead emission was increased by speed. Under city-type driving conditions, which included idling, acceleration, deceleration, and cruise conditions, lead recovered from the exhaust gas normally ranged from 20% of the lead burned when the exhaust system was comparatively clean, to as high as boy0 when the exhaust system was heavily deposited after extensive lightduty service. However, under sustained high-speed driving conditions or during high-speed full-throttle accelerations, the amount of lead exhausted was initially several times greater than that burned, but diminished in quantity as the exhaust system became cleaner with continued severe service. Exhausted particles ranged from 0.01 micron to several millimeters in diameter, Particles smaller than 1 micron were by far the most numerous, but accounted for less than 5 weight TOof the exhausted lead. Heavy particles, 5 microns and larger, which might be expected to settle rapidly, represented about 27% of the exhausted lead under city-type driving but increased to about 39y0 under accelerating conditions. Lead was exhausted principally as mixtures of PbCl.Br, alpha and beta forms of NH,Cl. 2PbC1. Br, and 2SH4C1.PbCl Br. When phosphorus was present in the fuel, about 20% of the exhausted lead was 3Pba(P04)2. PbCl. Br. The amount of lead exhausted was proportional to the concentration of T E L in gasoline, but particle size distribution and composition were independent of this variable. Neither changes in fuel sulfur concentration nor the presence of phosphorus-containing gasoline additives introduced definite changes in the amount and size of the exhausted lead compounds, and only phosphorus altered their composition. The quantity of lead exhausted in
Concentration of Lead in 10s A n g e l e s Atmosphere (3) Lead Concn , y/Cu. M. NO. G f AV. Range
Observations
Downtown
Suburban
45 60 60 58
4.1 6.2
2.2 4.4 5.0 4.65
7.5 8.3
INDUSTRIAL AND ENGINEERING CHEMISTRY
Downtown 1.7-7.6 1.4-14.7 3.1-13.8 3.2-16.4
Suburban 1.1-4.1 0.8-12.8 1.9-10.4 1.2-11.4
particle sizes which might remain suspended in the atmosphere appears to be reduced by conditions which produce low gas velocities and low temperatures in exhaust systems. These include design factors such as larger engines and multiple exhaust systems as well as operating factors. That lower-speed driving as encountered in congested areas tends to minimize lead emission, probably explains why the reported analyses of urban air show lead concentrations which are low in relation to the amount of lead burned. Acknowledgment
The authors are indebted to many coworkers in the Ethyl Corp. Research Laboratories who made this report possible by their contributions. Among these persons. R. G. Lyben, Karl Beaver, and Loren Knowles developed experimental techniques, and E. B. Kifkin and H. E. Hesselberg assisted in planning the work and interpreting the results. Literature Cited (1) Air Pollution Control District, County of Los Angeles, “Second Tech. and Admin. Rept. on Air Pollution Control in Los Angeles County,” 195051. (2) Cholak, Jacob, “Nature of Atmospheric Pollution in a Number of Industrial Communities” ; Proc. 2nd National Air Pollution Symposium, Pasadena, Calif., 1952. (3) Cholak, J., Schafer. L. J., Yaeger, D. W.,Kehoe, R. -4., “Nature of Suspended Matter, An -4erometric Survey of the Los Angeles Basin, Aug.-l\;ov., 1954;” Air Pollution Foundation Rept. 9, 1955. (4) Goedhard, Neil, “Basic Statistics of the Los Angeles Area.” Air Pollution Foundation Rept. 6, 1955. ( 5 ) Kehoe, R. A,, Thamann, Frederick, Cholak, Jacob, J . Znd. I-lyg. 16, No. 2, 100-28 (1934). (6) Ibzd., 18, No. 1, 42-68 (1936). (7) Leake, J. P., U. S. Public Health Bull. 163, 1926. (8) Ministry of Health (Great Britain), His Majesty’s Stationery Office, “Final Report of the Departmental Committee on Ethyl Petrol,” London, England, 1930. ( 9 ) Sayers, R. R., Fieldner, A. C., Yant, W. P., Thomas, B. G. H., “Experimental Studies on the Effect of Ethyl Gasoline and Its Combustion Products,” U. S. Bureau of Mines, 1929. (10) Sittig, Marshall, Warren, Wayne, Petroleum Rejner 34, KO. 9, 230-80 (1 955). (11) Street, J . C., S.A.E. Quart. Trans. 61, 442-52 (1953). (1 2) Valentin, Harold, “Plomb TetraEthyle et Hygiene Industrielle,” Librairie E. Le Francois, Paris, 1936. (13) Viets, F. H., Fischer, G. I.. Fudurich. 4.P., “Hydrocarbon Pollution from Automobile Exhaust Gases, Report of Test 668 and Associated Work.” Air Pollution Control District, Los Angeles County, Sept. 12, 1952.
RECEIVED for review August 6, 1956 ACCEPTED January 4, 1957 130th Meeting, Petroleum Division, ACS, Atlantic City, N. J., September 195G.
