mass balance was obtained in terms of lead emitted from the vehicle and lead sized (or sampled) with the tunnel system.
SUMMARY Sampling techniques have been developed which enable the characterization of the particulate lead contained in vehicle exhaust. The tunnel sampling system used in conjunction with a car operated on a programmed chassis dynamometer offers a unique opportunity to examine the characteristics of lead particles under realistic operating conditions. Proportional samples of the exhaust particulate matter can be obtained and satisfactory operation of the system can be confirmed by a direct mass balance. Although only impactor sizing units have been used, the system is compatible with other sizing instruments. Physical properties and chemical composition of representative samples can be determined using the electron microscope, electron microprobe, X-ray diffraction, X-ray fluorescence, and other chemical analytical techniques. A total particulate lead filter has been developed which can be attached directly to the exhaust tail pipe of a vehicle. This filter provides a convenient means to investigate vehicle lead emissions under various types of vehicle operation. The filter is also a tool to check the adequacy of the mass balance obtained with the tunnel sampling system. Both the tunnel sampling system and the total filter have been shown to give reproducible measurements of the emitted lead. However, the particle size and amount of lead emitted vary widely with mode of vehicle operation, vehicle driving history, and probably other as yet undefined parameters, Extensive additional investigations will be required before the influence of all the important factors controlling lead emissions in the vehicle population can be defined. Such investigations are under way. Acknowledgment The author is indebted to J. B. Dunson, of Du Pont Engineering Department, for his advice and assistance in the general field of particulates.
Literature Cited Andersen, A. A., “A Sampler for Respiratory Health Hazard Assessment,” A m . Ind. Hygiene Assoc. J . 27, March, 1966. Brink, J. A., Jr., “Cascade Impactor for Adiabatic Measurements,” Znd. Eng. Chem. 50, 645 (1958). Broering, L. C., Jr., Werner, W. J., Rose, A. H., Jr., “Automotive Mass Emission Analysis by a Variable Dilution Technique,” presented at the Air Pollution Control Association Annual Meeting, Cleveland, Ohio, June, 1967. Davies, C. N., “The Rate of Deposition of Aerosol Particles from Turbulent Flow Through Ducts,” Ann. OCCUP. Hyg. 8, 239-45 (1965). Federal Register, “Control of Air Pollution from New Motor Vehicles and New Motor Vehicle Engines,” Vol. 33, No. 2, Part 11, Department of Health, Education, and Welfare, January, 1968. Flesch, J. P., Norris, C . H., and Nugent, A. E., Jr., “A Method for Calibrating Particulate Air Samplers with Monodisperse Aerosols: Application to the Andersen Cascade Impactor,” American Industrial Hygiene Conference, Pittsburgh, Pa., May, 1966. Goetz, A., Stevenson, H. J. R., Preiming, O., “The Design and Performance of the Aerosol Spectrometer,” Air Pollution Control Assoc. 10, 378-83 (1960). Hirschler, D. A., Gilbert, L. F., “Nature of Lead in Automobile Exhaust Gas,” Archives of Environmental Health, Symposium on Lead, February, 1964. Hirschler, D. A., Gilbert, L. F., Lamb, F. W., Niebylski, L. M., “Particulate Lead Compounds in Automobile Exhaust Gas,” Ind. Eng. Chem. 49, 1131-42 (1957). May, K. R., “Calibration of a Modified Andersen Bacterial Aerosol Sampler,” Appl. Microbiol. 12, 37 ( 1964). Mueller, P. K., Helwig, H. L., Alcocer, A. E., Gong, W. K., Jones, E. E., “Concentration of Fine Particles and Lead in Car Exhaust,” Symposium on Air Pollution Measurement Methods, Special Technical Publication No. 352, American Society for Testing and Materials, 1964. Postma, A. K., Schwendiman, L. C., “Studies in Micrometrics-Particle Deposition in Conduits as a Source of Error in Aerosol Sampling,” Report No. HW-65308, Hanford Atomic Products Operation, Hanford Atomic Products Operation, Richmond, Wash., May 12, 1960. Ranz, W. E., Wong, J. B., A M A Arch. Ind. Hyg. and Occup. Med. 5 , 464 (1952). Received f o r review June 20, 1969. Accepted October 7, 1969. Symposium on Air Conservation and Lead, Division of Water, Air, and Waste Chemistry, 157th National Meeting, ACS, Minneapolis, Minn., April 1963,
Discussion Characterization of Particulate Lead in Vehicle ExhaustExperimental Techniques P. K. Mueller Ph.D., Chief Air and Industrial Hygiene Laboratory, California State Department of Public Health, 2151 Berkeley Way, Berkeley, Calif. 94704
D
r. Habibi’s work stands as the first substantial advance in the technology of sampling particles emitted by the exhaust duct of cars in seven years. In view of the increasing urgency to set limits on lead emissions from cars ( I , 2 ) it is regrettable that past efforts on particulate matter emitted by vehicular exhausts have been so small. Seven years ago, in 1962, my group, at the California State Department of Public Health, set about to apply size-segregated collection methods to the sampling of exhaust aerosol 248 Environmental Science & Technolog?
from cars operated at cruise conditions under road load on an all-weather chassis dynamometer. The results of our work were presented to the scientific community ( I ) and published in great detail (2). In general terms, the results of our work then and subsequent unpublished work since demonstrated that cars burning 3 ml. of TEL or TML motor mix per gallon of fuel were emitting under cruise conditions about 5 to 60 pg. Pb per liter of exhaust depending on speed in the range of 25 to
65 m.p.h. And, that a large proportion (more than 40% by weight) of the particles we sampled were smaller than 0.3 p in equivalent diameter. Even though our sampling train was not as elaborate and our test cars were built in different model years, the sizes of particles observed both by Habibi and us under cruise conditions are not substantially different (Habibi’s Table IV). We considered the same factors in the design of our sampling procedures. However, there is a tendency in Habibi’s paper toward a greater MMED than was found in our work. Furthermore, the average concentration of lead-bearing particles (which are small enough to be well dispersed in the atmosphere) found in the exhaust of a popular US.made car operated under cyclic conditions was found by Habibi to be about 35 pg. Pb/liter. We estimated using our data and that published on total exhaust particles by McKee and McMahon (3) that the State of California 11-mode driving cycle would produce lead-bearing emissions with particle sizes likely to be suspended in the atmosphere at concentrations of about 25 pg. Pb/liter. Thus, the refinements in experimental techniques accomplished by Habibi have added little so far by way of providing numerical guides relating lead emissions from cars to atmospheric lead contamination. There is no question, however, that Habibi’s work has now given us the needed means to obtain such numerical guides. The result of Habibi’s work is also supplying the means to test processes designed to reduce the lead emissions and to characterize the nonlead fraction of the particles. The capability is now available to relate not only the quantity of lead additive to total emissions, but also to the particle size distribution and composition as a function of particle size. Habibi has already shown that the size range is tremendous, on the order of 106. It would be very interesting to find out what work has so far been done by the Du Pont group on the chemical composition of these particles. What fraction is lead? What fraction is water soluble? What is the molecular composition of the lead com-
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pounds? What is the composition of the other material? We found about 40z by weight of all particles was lead. The very large particles seem to be primarily produced during operating modes other than cruise. They are most likely created by attrition of deposits within the engine’s exhaust train. The validity of the numerical guides that should be developed by use of Habibi’s system depends much on how the information is treated. The size distribution given in his Figures 12-16 all include the very large particles which settle out within a short distance from the car. Previous speakers have shown they deposit on the surfaces of nearby plants, in addition to settling out on pavements, etc. About 5 0 z of these large particles are easily washed off from these surfaces. Through waste water systems, soluble and finely dispersed portions will be distributed in receiving bodies of water to be eventually deposited either in the Earth’s crust or to enter Diu biological processes into the food chain. The larger insoluble particles will be deposited in dumps mixed with other solid wastes. From a long-range ecological viewpoint, these large particles are of no lesser concern than the finer particles which will be dispersed for a period in the atmosphere. Finally, these are also deposited on the Earth’s surface. These finer particles are of immediate concern because they add substantially to the body burden of lead among urban residents by way of inhalation. This fact has been clearly demonstrated by H. V. Thomas of my laboratory group, together with coworkers of California and Los Angeles Health Departments. It is illustrated in Figure 1 ( 4 ) . Blood lead levels were substantially higher in the sample population living near the freeway. Among men in the population living near the freeway, the blood lead mean was 22.7 pg./lOO gm. whole blood. The mean value for men living near the coastal area was 16 pg./lOO gm. blood (P < 0.006). The corresponding values among women were 16.7 and 9.9 pg./lOO gm. blood (P < 0.0006). The near freeway group included a sample population
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Table I. Size Distribution and Concentration of Lead Containing Particles in Several Areas of the U.S. Average daytime No. of concentration Size Frequency Data (p) sample range 25 M MFn 75 ?z . .-. .-,” Sample area periods I.1g.lm.3 Average Range Average Range Average Range Los Angeles Freeway 2 8 . 2 to 18.3 0.06 0.06-0.07 0.12 0.11-0.14 0.26 0.23-0.30 Los Angeles Downtown 8 2.9 to 9.0 0.16(7) 0.10-0.22 0.26 0.19-0.29 0.49(7) 0.39-0.60 Los Angeles Vernon 5 1 . 9 to 4 . 6 0.17(4) 0.12-0.22 0.24 0.18-0.32 0.40 0.28-0.47 Los Angeles Pasadena 7 0 . 9 to 4 . 3 0.18 0.05-0.25 0.24 0.08-0.32 0.48(6) 0.13-0.67 San Francisco 3 2 . 8 to 6 . 1 0.11 0.06-0.13 0.25 0.15-0.31 0.45(2) 0.44-0.46 Cincinnati 7 1 . 0 to 11.7 0.15(3) 0.09-0.24 0.23 0.16-0.28 0.44 0.30-0.68 Chicago 12 0 . 5 to 7 . 8 0.19(7) 0.10-0.29 0.30 0.16-0.64 0.40(10) 0.28-0.63 Philadelphia 7 0 . 3 to 3 . 4 0.14(3) 0.09-0.25 0.24 0.19-0.31 0.41 0.28-0,56 Cherokee 1 0 . 1 to 0 . 3 0.25 0.31 0.71 ... 0.27 0.34 Mojave 1 0 . 1 to 0 . 4
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Number in parens indicates number of samples available for a specific value, when different from total number of samples.
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living within 250 feet of the freeway. This population showed no significant difference of blood lead concentration from that living in central Los Angeles County but more than 250 feet from a freeway. These observations are consistent with the notion that the small lead particles from cars are dispersed generally in the central metropolitan area and that the blood lead differences are due to the higher atmospheric lead concentrations in central Los Angeles, as compared to the coastal area. From the urban atmospheric pollution viewpoint then, it would be unwise to include in lead-bearing particle distributions the size groups which will settle out quickly, The major air pollution load would come from particles about 10 p or smaller. Several studies have demonstrated this situation. Table I is a summary of data obtained by E. R. Robinson, er af. (5, 6) in several places of the U.S. For all sampling sites, the MMED were in the range of 0.12 to 0.31 p. As part of a size segregated aerosol collection study my group conducted in Berkeley in 1965-66, two size groups were analyzed for lead content by emission spectroscopy (7). To obtain this data, a two-stage and a single-stage sampler were used side by side. Samples were taken each weekday, 8 A.M. to 12 P.M. and 12 P.M. to 4 P.M. The single-stage sampler which collected total suspended particles consisted of an open-face filter holder equipped with a 2.54-cm. diameter tared glass fiber filter. In the two-stage sampler a 2.54-cm. diameter tared glass filter was preceded by a 1.3-cm. diameter stainless steel cyclone collector. At a sampling rate of 18 liters/min. the cyclone collects particles from the air stream which closely approximate those particles that are deposited in the upper respiratory airways (ciliated airways). The particles which penetrate the cyclone approximate those which would be carried into the nonciliated airways are termed “respirable” by the U.S. Atomic Energy Commission (11, 12). Weekly mean total and “respirable” lead-bearing particulate concentrations are compared in Figures 2 and 3. The total lead concentrations were about 1.1 to 1.4 times the respirable lead concentration. In contrast, the total particle concentration was about 1.7 to 2.9 times the “respirable” particle concentration. This observation shows that the “respirable” particles contained a greater fraction of lead compounds than the larger particles in ambient Berkeley air. 250
Environmental Science & Technology
Source: SRI (Refs. 5 and
The size distributions of atmospheric lead-bearing particles so far obtained may, however, be suffering from a small bias toward the smaller sizes, because the attainment of isokinetic conditions is virtually impossible when wind velocities are constantly changing. The problem of quantitative sampling of aerosols containing particles of equivalent diameters greater than 10 p has apparently now been solved by No11 (8). It would be interesting to determine the extent the very large lead-containing particles remain suspended aerodynamically. Such particles may serve as convenient models for studying chemical changes of lead-bearing particles in the atmosphere. Thus the total size distributions presented by Habibi are interesting. They are useful in evaluation of control processes, but, as presented, they are not usable for making a connection between emissions and environmental concentrations. The data would be considerably more useful when tabular data giving quantities on each stage or size range are also given. The charts he has presented omit data about the particle size distribution of a major size fraction in the exhaust. In Figures 12-16, 20 to 40% of the total weight was classified as >9.5 p , which includes the fallout, This information could have been made available by simply stating what portion over 9.5 p category was contributed by the fallout and wall losses. Without such information it is impossible for others to make an accurate estimate of the particles that remained suspended
Table 11. Mass Median Diameter EstimatedQfor Dispersible Particles Compared with Those Given for Total Emissions Mass Median Diameter Excluding particles Andersen data >9.5 I.1 Habibi (total emissions) (dispersible) Figure no. I.C I.1 0.55 12 0.8 0.63 1 .o 13 0.70 14 2.8 0.68 15 4.2 0.53 16 0.6 a Mass median diameter estimated by geometric mean of truncated cumulative size distribution.
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Figure 3. Particulate lead in two size groups, weekly means of morning samples
at the end of the tunnel and which would represent particles that would be dispersed in the atmosphere. The nearest estimate one can make of the mean particle size that could be dispersed is by eliminating the >9.5 1.1 category entirely and calculating the new mass median equivalent diameter (geometric mean) on the artificially truncated size distribution. The results of such a calculation are given in Table 11. Thus the estimated MMED of the dispersible particles now all fall in the range of 0.1 to 1.0 1.1, which is in line with what has been observed for lead-bearing atmospheric aerosol. The above discussion of the data demonstrates the convenience of expressing particle size distributions in terms of parameters derived from an assumption of log normality. However, the car exhaust aerosol is generated by both mechanical and chemical processes. The plotting of data on log probability paper can easily lead to complacency about the assumption. It therefore becomes important to examine the true nature of the size distributions by means of histograms (9). The size distributions presented by Habibi demonstrate that the two impactors and the respective calibration procedures yielded results which coincided to some degree but not consistently. The deviation from log normality indicates the theoretical approach to calibration may be creating artifacts. In future work it would be advisable to calibrate in situ with the aerosol to be sampled. Consideration might also be given to using more modern impactors with fewer, but moving stages, such as the one developed by Lundgren (IO). Such devices yield information on changes in size distribution with time and can potentially lead to a speed-up in the research program.
will provide numerical guides for the control of particulate lead emissions.
Summary and Conclusions
With his paper Dr. Habibi has placed a new marker in the advancing technology of particle sampling from vehicle exhausts. He has developed and evaluated a sampling tunnel which permits a complete evaluation of particulate emissions. The manner in which this capability is to be used depends on the goals to be achieved. His presentation of data is relevant to the study of particle generation processes. Modified procedures are needed to evaluate the impact of particulate emissions on the quality of various aspects of the environment, and some approaches have been suggested. It is hoped the new capability will now lead rapidly to information which
Acknowledgment Assistance provided by Mrs. Suzanne Twiss and Mr. Miles Imada with some crucial aspects of the manuscript is very much appreciated. References (1) “Lead in the Environment and its Effects on Humans,” State of California, Department of Public Health, March 1967. (2) “The Automobile and Air Pollution: A Program for Progress,” U.S. Dept. of Commerce, October 1967. (3) McKee, H. C., McMahon, W. A., Jr., “Automobile Exhaust Particulates-Source and Variation,” J . Air Pollution Control Assn. 10, 457-64 (1960). (4) Thomas, H. V., Milmore, B. K., Heidbreder, G. A., Kogan, B. A., “Blood Lead of Persons Living Near Freeways,” Arch. Enairon. Health 15,695-702 (Dec. 1967). (5) Robinson, E., Ludwig, F., DeVris, J. E., Hopkins, T. E., “Variations of Atmospheric Lead Concentrations and Type with Particle Size,” Final Report, SRI Project No. PA4211, Nov. 1, 1963. (6) Robinson, E., Ludwig, F. L., “Size Distributions of Atmospheric Lead Aerosols,” Final Report, SRI Project No. PA-4788 (a continuation of PA-4211), April 30, 1964. (7) Mueller, P. K., Imada, M., “Size Distribution of Atmospheric Particles in California by Mass”; Mueller, P. K., Imada, M., Alcocer, A. E., “Size Distributions of LeadBearing Aerosols,” AIHL Repts. No. 58 and 59, respectively; State of California, Department of Public: Health, September 1968. (8) Noll, K. E., “Theoretical Considerations, Design, and Evaluation of a New Inertial Impactor,” Proceedings, 10th Conference on Methods in Air Pollution and Industrial Hygiene Studies, San Francisco, Calif., February 1969. (9) Irani, R. R., Callis, C. F., “Particle Size: Measurement, Interpretation, and Application,” New York, John Wiley & Sons, Inc. (1963). (10) Lundgren, D. A., “Determination of Aerosol Composition as a Function of Particle Size and Time,” Proceedings, 10th Conference on Methods in Air Pollution and Industrial Hygiene Studies, San Francisco, Calif., February 1969. (1 1) Lippmann, M. and Harris, W. B., Size-Selective Samples for Estimating Respirable Dust Concentration,” Health Physics 8, 155-63 (1962). (12) Partridge, J. E. and Ettinger, H. J. “Calibration of a Spinning-Disc Aerosol Generator and Two-Stage Air Samplers.” Report LA-4066, UC-41, Health and Safety, TID-4500. February 1969. Los Alamos Scientific Laboratory, Univ. of Calif., Los Alamos, New Mexico. Volume 4, Number 3, March 1970 251
