I
MOYER D. THOMAS Stanford Research Institute, Menlo Park, Calif.
Air Pollution Review 1954-1955 T H t initial ACS revie\\- of current air pollution literature was published by McCabe (59) in 1954. This second review c,overs 1954 and 1955 with a few references to earlier and later Tvork. Interest in air pollution appears to be increasing. I n this two-year period, many symposia have been held, the individual papers of which generally represent new research not previously discussed or published. T h e 1954 and 1955 ACS Air Pollution Symposia were devoted to analytical, biological, and engineering aspects of air pollution, and also to the chemical reactions of pollutants in the atmosphere. The First International Congress on Air Pollution in March 1953 (57), sponsored by the American Society of hfechanical Engineers, considered many phases of the subject, such as the Beaver report and management> administrative, engineering. meteorological, biological. and health problems. Eight papers were devoted to sulfur recovery in Great Britain and the United States, and five to air pollution in Europe. The Third National Air PollutionSymposium in April 1955 (87) had 29 papers covering a wide range of subjects, including many different analytical methods for aerosols and gases and their application to the measurement of air pollution in Los Angeles and other cities, the effects of air pollution on plants; health considerations, and legal problems. Other special symposia (60, 79) have been held, and a number of papers from them arc reprinted in the Journal of the L4irPollution Control Association. Slonographs of interest in this field which appeared in this period include: 1. ,‘Smog Problem in Los ;\ngeles County-A Report by Stanford Research Institute on the Nature and Causes of Smog,” in January 1954 (80) 3. Aerometric Survey of Los Xngeles Basin, August to November 1954 (68) 3. hleteroloqy and Atomic Energy. edited by U. S. LVeather Bureau in July 1953 ( W ) , a treatise on diffusion theory with applications to chimney effluents and r,xplosion debris clouds together with nornographs for making calculations of the diffusion 4. Bureau of hfines Bulletin 537 (23), a bibliography of 3902 references and a n author index 5. Particle Size Determination by Cadle (14) 6. Encyclopedia of Instrumentation for Air Pollution ( 8 9 ) , edited by U. S. Public Health Service
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7. Solar Radiation Absorption Rates and Photochemical Primary Processes in Urban Air, by Leighton and Perkins (52). The Handbook of Air Pollution, edited by Stanford Research Institute, will be published by SfcGraiv-Hill, New York, in about August 1956. Analytical Methods and Results There has been active development in the biennium of new analytical methods and instruments for both gases and aerosols. Papers have appeared for oxidants, the oxides of nitrogen, hydrocarbons, reduced sulfur compounds, and radioactive gases. .L\erosol papers were concerned with soiling and visibility studies; instruments for measuring concentration and size distribution of the particles in situ, by photography and light scattering; and a new method for exploring the range from about 0.5 micron in diameter to molecular dimensions. Oxidants. The importance of oxidants as pollutants in Los Angeles has been well established, and the analytical methods (53, 6.9, 72) based on the oxidation of potassium iodide or phenolphthalin have been used extensively. These reagents are reactive to ozone. They are also partially reactive to nitrogen oxides and the organic peroxides buL to different extents. Todd (SG) has proposed another reagent, ferrous thiocyanate, which can be readily determined colorimetrically as it changes to the ferric salt. This reagent is less than 10% reactive with ozone. Its reactivity with nitrogen dioxide and organic peroxides is nearly quantitative. If the claims of the author are substantiated by adequatr testing of the atmosphere, this method should be a useful adjunct to the others. I n combination Lvith an analyzer for nitric oxide and nitrogen peroxide, it should be possible to determine in detail the approximate composition of the principal oxidants by making simultaneous measurements tvith the thiocyanate and potassium iodide or phenolphthalin methods. Determination of ozone by ultraviolet absorption Tvould increase the value of these analyses. Oxides of Nitrogen. Determination of oxides of nitrogen is difficult because of the complexity of the system and absorption problems. A partial solution was suggested by Saltzman ( 7 4 : who showed that a nitrite reagent consisting of 0.5% sulfanilic acid and 20 p.p.m. of 1 - naphthylethylenediamine dihydrochloride in 14y0 acetic acid Iiould absorb nitrogen dioxide quantitatively from a n
INDUSTRIAL AND ENGINEERING CHEMISTRY
air stream containing less than 1 p.p.ni. of nitrogen dioxide. It was only necc‘ssary to use a fritted.glass bubbler of medium porosity to induce adequati frothing. The intense and stable coloI of the dye permitted the determination of the gas in the parts per hundred million range with a rather small ratio 01 gas to liquid volume. The !-ield of nitrous acid was not 5076,as \\-auld be expected from a simple dismutation of nitrogen dioxide. but about 72%. Although the reactions are obscure, they appear to be reproducible. Stanford Research Institute developrd a nitrogen dioxide recorder which has been used extensively by the .4ir Pollution Foundation in Los Angeles and reported by Rogers (771, Richards (70), and Romanovsky and others (72). T h r gas is absorbed in Saltzman‘s reagent in a long coil of 3-mm. inside diameter glass tubing or in a packed column. The color is measured continuously as the solution flows through a 15-cm. cell. Nitrous and nitric oxides do not interfcre, but by a controlled ozonization of a duplicate air sample, nitric oxide can be oxidized to dioxide and determined by difference in a second absorber system. Carbon Compounds. The determination of carbon-hydrogen bonds in the infrared spectrometer is usually done on samples collected in freeze-out traps. Littman and Denton (5$) describe a modification of the nondispersive infrared analyzer originally designed by Shell Development Co. The modified instrument has a strong source of infrared light; a thin polyethylene chopper; t\vo filter cells containing carbon dioxide and carbon monoxide ; two gas analyze1 cells, 10 feet long and 1 inch in diamrtrr, vacuum-aluminized on the inside ; a pair of microphone detector cells containing argon with 57, propane, each having two compartments separated by a sensitive diaphragm to detect unequal pulsation intensity of the chopped radiation due to unequal absorption in the sample and reference tubes; and a signal amplifier and a recorder. The range of the analyzer, highly specific for C-H bonds, is 0.1 to 10 p.p.rn. The air sample is divided into ~ W O streams, one of which passes directly to one analyzer cell, the other being ignited in a furnace a t 800” C. in the presence of a noble metal catalyst before entering the other cell. The tjro streams are identical in ivater content. For 15 minutes of each hour, both cells receive i%-
nited air to establish a zero reference. A considerable variation in the hydrocarbon concentration is evident throughout the day and short-time fluctuations are large but there is no obvious similarity to the diurnal oxidant pattern. Austin (5) described the partial development of a continuous analyzer for olefins. Gas phase reaction with bromine occurs a t 350’ C. in a tube packed with granulated borosilicate glass. Bromine is generated electrolytically a t a constant known rate, and reacted with the air stream in the furnace. The excess bromine is detected in a concentration cell and recorded. The principle of operation is essentially the same as in the Titrilog. Empirical calibration is necessary. The automatic features were not all worked out, but operation was satisfactory under manual control. Critical work needs to be done on the specificity of the high temperature bromination. Carbon monoxide is determined in a Mine Smelter Appliance Co. nondispersive infrared analyzer modified to increase its sensitivity (72). This instrument is somewhat similar to the hydrocarbon analyzer. I t employs two gloivers, a chopper, a filter cell containing carbon dioxide and a methane, a pair of 29-inch gas analyzer cells-one filled tvith nitrogen and the other with a stream of the dried air sample, and a microphone detector cell containing argon and carbon monoxide. The detector circuit varies the current to the gloivers to maintain a balanced condition in the detector. T h e variable glower current is recorded. Full-scale response of the instrument as modified is 25 p.p.m. a t 40 pounds,’square inch or 100 p.p.m. a t atmospheric pressure.
Plants. Each toxic gas can cause characteristic lesions on plants. The nature and extent of the injury depends on the exposure under definite environmental conditions. Biological tests for smog have been devised by Middleton (67)? which are qualitative and even semiquantitative methods of analysis. Bobrov (72) and Noble (63) describe in detail smog injury on many plants. Characteristic smog injury on each plant shows variations with variable smog composition and concentration. Ozone injury differs from smog injury. These biological responses are capable of revealing differences in smog, not indicated by other methods. Characteristic injury to 10 varieties of common weeds by 7 toxic gases is displayed in a n album prepared by Benedict and Breen ( 9 ) . Reduced Sulfur Compounds. Landsberg and Escher (47) published a critical study of the well-known Titrilog, indicating its performance, applications, limitations, and interferences. The article is helpful in clarifying the potentialities of this versatile instrument. Kew spot methods (64, 75) are also available for hydrogen sulfide. Odors. Following a n A S T M Sym-
posium (60) on odors, a number of papers have appeared on this subject. Turk (87) discussed combustion, absorption on activated carbon, and the use of counteracting and masking compounds as means of combatting the problem. Furnace combustion and catalytic combustion are ideal methods where applicable, and there is a limited use for carbon adsorption if the concentration of the malodor is not too high or too low. The methods of odor counteraction or masking appear to constitute a well-developed art. Pantaleoni (66) gives a list of 17 malodorous substances and 20 counteractants as illustrative of thousands of such compounds. Nothing is said as to specific compounds or concentrations for counteracting specific malodors. Evidently this is a field of trade secrets. Mateson (55) reviewed the numerous devices and techniques for determining odor concentration and described a new multistimulus olfactometer in which the faults of older equipment are corrected. The instrument is being used for basic threshold and product development work. ASThl (4)has adopted a tentative standard for collecting and measuring odorous substances in the atmosphere, using activated carbon.
The Sky Scanner. Beard and IVilhelmson ( 6 ) have constructed a n instrument to record the gamma radiation emitted by the radioactive noble gases in the effluent from a factory chimney. It consists of a large sodium iodide crystal mounted in heavy shielding. and rotated to scan a definite arc of the sky. The scintillating pulses are multiplied in a photomultiplier tube. amplified. then fed into a count-rate meter circuit and recorded. The instrument is calibrated with reference to a balloon containing a known amount of radioactive gas. I t is estimated that the crystal must see about 6000 curies of 0.5-m.e.v. gamma-emitting gases a t a distance of 1 mile in order to detect them. The instrument is used to study dispersion from a stack or to monitor a n area which was impossible earlier without elaborate sampling. Aerosols. The continuous papfr filtration method has been used in several studies of dust loading of the atmosphere. Gruber and Alpaugh ( 2 9 ) found in Cincinnati that Hemeon samplers operating a t considerable distances apart gave parallel and often nearly identical records. Hemeon (36) made similar observations in Pittsburgh. He obtained parallel records in areas 4 miles apart, and records in Pittsburgh and Columbus, Ohio, were very similar over a 3-\veek period. Gruber and Alpaugh (29) and also Katz (47) observed a striking negative correlation betizeen the spot density and wind speed. Since the aerosols dealt with were of small size, they would follow the ambient u h d . Their concentration would be rer‘uced by increased ventilation. Clayton and Giever (20) found no cor-
relation between the visibility in Detroit, measured by the transmissometer and the readings of the Hemeon sampler. They made no allowance for relative humidity, which is said to affect the visibility. According to Hall (32), visibility a t 60% humidity is about double and a t 457, about triple that a t 1OOcc. When Hall adjusted the visibility to a constant relative humidity, a satisfactory inverse relationship was found between visibility and absorbance of the deposit on the filter paper. A number of new instruments have been described for determining the mass concentration and size distribution in the aerosol. Lee and LaMer (57) developed a camera for obtaining dark field images of the particles. A flash tube giving flashes of 10-4-second duration supplied the light which was scattered in a forward direction by the aerosol particles. T h e images, slightly out of focus, were photographed, enlarged, and examined individually with a multiplier photometer by which the particle size in the range from 0.25 to 0.9 microns in diameter could be obtained. Cadle and Wiggins (75) photographed the individual particles directly as they drifted into the field of a microscope and ivere illuminated by a po\verful flash focused in front of the objective. ‘This camera proved most useful between 2 and 100 microns. Surface details of the particles could be distinguished. The Sinclair photometer (77, 7s) has been developed into a commercial instrument. A tiny volume of the aerosol stream, surrounded by clean air, is illuminated as it flolvs past a spot Ivhere a strong light is focused. The aerosol particles scatter the light in a forward direction. The scattered light is collected by lenses and received by a photomultiplier tube. The tube current is amplified and recorded. Calibration is done \.rith kno\vn aerosols and Freon. In addition, the unknown aerosol is filtered through a “niolecular” filter and weighed a t intervals, thus giving a relationship between average recorder reading and mass concentration. Each aerosol requires individual calibration. Instrument range is from 10 -’! to 100 . micrograms per liter. Further development of a n aerosol counter was described by Gucker and Rose (30), and of a counter-photometer by O’Konski and Doyle (65). The “aerosoloscope” \vas described by Fisher, and others (26). The first employs forward scattered light; the other t\.ro, right-angle scattering. These instruments have general characteristics somewhat similar to the Sinclair photometer except that the aerosol concentration, the flow rate, and the illuminated cell volume are adjusted so that not more than a single particle is in the field during the time required to count and record itabout one millisecond. VOL. 48, NO. 9
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T h e magnitude of the output current from the photomultiplier tube for a single particle is a function of the particle diameter. 4 means is thus afforded for obtaining the size distribution of the aerosol. The individual pulses are amplified in t\vo stages, then divided into t\vo channels. T h e first is an integral puls- height s:lector set at low bias voltage to count all pulses on a scaler. T h e second is a single channel selector to determine the number of pulses in a given voltage range. By changing this voltage range, the various sized particles are sorted. They may either be counted in a single scaler or multiple channels may be provided so that a number of size ranges may be counted simultaneously. I n the aerosoloscope 12 scalers are used. T h e O'Konski and Doyle instrument also records the direct current component from the preamplifier. I t is therefore a photometer as \cell as a counter. T h e Gucker and the O'Konski instruments are concerned primarily with particles from about 0.3 to 1.0 micron in diameter. Larger particles u p to 5 microns can also be measured, but with less precision. T h e aerosoloscope is designed for a size range from 1 to 64 microns. T h e limit of sensitivity of the O'Konski and Doyle instrument is 3 X 10-5 micrograms per liter of 0.3-micron particles. Aerosol particles smaller than 0.3 to 0.6 micron in diameter down to molecular dimensions have been studied by means of the nucleus counter (97)' which depends on increasing their size in a cloud chamber until they become visible. Investigation of the diffusion battery method is described by Thomas (85').Particles in this size range passing through a small tube or narrow channel are displaced toward rhe wall by Brownian movement. It is assumed that Lvhen they strike the Xvall they Lei11 adhere. If the fraction, F. of the ingoing particles which emerge from the channel is measured, the average particle size can be calculated. Since Brownian movement increases v i t h decreasing particle size, deposition in a given channel also increases and the valve of F decreases. A hydrodynamic solution for F owing to Nolan, involving the diffusion coefficient of the aerosol, the channel dimensions, and the flow rates, is discussed. I t is applied satisfactorily to ammonia and sulfur trioxide when passed through 3.5-cm. glass tubes with absorbents for the gases covering the inner icalls, also to aerosols u p to 0.6-micron diameter when passed through a battery of rectangular channels 12.7 X 47.3 X 0.01 cm., machined in carbon plates. Particles larger than 0.6 micron appear to be smaller than their actual size, but there is no apparent lower limit to the particle size that can be measured by this method. An ideal range would be 0.004 to 0.04 micron in diameter. Engineering. Significant develop-
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ment of new methods and new equipment for removing pollutants a t the source has been reported. Holvever. no attempt is made here to revielv in detail the voluminous literature. Reference is made to only a fee\\.unique processes. Silverman and coieorkers (70% 76) filtered open-hearth gases a t 600' to 1200" F., through a slag wool filter Ichich: when loaded, could he deposited into water to separate the dust from the fibers, Xvhich xvere re-used. The filter may be a traveling screen covered rcith a moving 1-inch thick pad of slag M.OOI so that the process is continuous. Efficiencies of 90YG on 0.6- to 0.8-micron fume \sere reported. The Hersey reverse-jet bag filter (37) has given some excellent performance in the atomic energy industry. I n handling uranium ores, Harris and Mason (34)collected the dusts with an efficiency of 97.99% and at a cost as low as $0.23 per cubic feet per minute per year. Dust loadings as high as 32 grains per cubic foot were encountered. Similar efficiencies were obtained with the low dust loadings of the more active process off-gases by glass \cool filters (50)and wet Cottrells ( 7 7 ) . According to Pring (67),~voolbag filters can lvithstand temperatures u p to 220' F.; Orlon? 275' F.; and glass cloth, 405' F. The latter requires impregnation with a silicone resin for prolonged life. Nylon? Vinyon. Dynel, and Dacron are unsatisfactory at elevated temperatures. Lapple and Kamack (-18) made a critical experimental stud!. of the performance of many types of \vet scrubbers on both laboratory and pilot-plant scales, evaluating the factors involved. They state that the "predominant mechanism which results in deposition of dust on the water drops i n a scrubber is believed to be that of turbulent circulation of dust laden gas over the water drops." Theoretical studies dealing Lvith filtration of aerosols have been revieLced by Chen (77), who gives equations for the interception of a particle by a cylindrical fiber due to inertial impaction, direct interception, Brownian diffusion settling, inertial and diffusion interception, and, finally, over-all collection efficiency of the fiber alone or in a filter bed with the interference of neighboring fibeis. T h e behavior of a filter may be calculated from these equations under many conditions of operation. Experimental values agree reasonably \sell Ivith the predicted performance. Kraemer and Johnstone (35) have calculated the motion of aerosol particles, with or without charge, in relation to charged and uncharged spherical and cylindrical collectors. T h e theoretical equations for many conditions were solved with an electronic digital computor. The collection efficiencies of dioctyl phthalate aerosols of known size
INDUSTRIAL AND ENGINEERING CHEMISTRY
and charge passing a spherical collector of known charge were measured and compared with the theoretical values. The results cvere in satisfactory agreement. As expected, the uncharged system had low collection efficiency which was increased on the average about 10 times by charging the sphere. A furthrr increase of 10 to 50 times resulted from charging both sphere and particles. T h e authors suggest that an 0.05micron aerosol charged in a corona Xvith 4 charges per particle would be completely collected by \cater spray of 50-micron droplets emitted from insulated nozzles charged a t 5000 volts. Another theoretically efficient collector of such charged particles Lvould be a pad made from a pair of S o . 36 varnished copper \vires tLvisted together and charged a t 100 volts. X combined mechanical and electrostatic filter is described ( 7 ) consisting of thin accordion-pleated filter cells supported by two grids, one grounded and the other charged. T h e edges of the pleats are coated with a metallic compound to distribute the 12-kv. charge over the filter. Collection efficiency for 3-micron and larger particles was S5Y0 without and 95y0 with charge; for l-micronplus particles it was 45yG without and 70% with charge.
Chemistry of Los Angeles Smog. Haagen-Smit and Fox (37) observed that organic compounds which have a significant vapor pressure a t ordinary temperatures, excepting the lower paraffins and saturated acids together with some tertiary compounds and a few others. combine lvith nitrogen dioxide under the influence of sunlight to yield ozone? along with oxygenated organic compounds-ozonides, peroxides, and eventually polymerized compounds. The most reactive substances \ and 3; and a t 4 P.M., 14: 6 : and 3 parts’100 million, respectively. -4ttendant high concentrations of carbon monoxide (4 to 16 p,p,m,) suggested that organic compounds \cere also present. I t is difficult to understand why higher oxidant Concentrations were not obtained unless the wind speed reduced the contact time below that required for appreciable reaction before dispersion occurred.
Auto Exhausts. It is generally agreed that, in Los Angeles. motor car exhausts constitute one of the principal sources of pollution. Hutchison and Holden (39). and Larson and others ( 4 9 ) analyzed the traffic volume and traffic patterns in Los Angeles. and estimated the amount of this pollution. To accomplish this, they determined the percentage of time spent by a n automobile during average city driving. i n each of its four cycles: accelerating. cruising? decelerating, and idling. They also analyzed the exhaust gases in each case. Emissions in 1954 \vex figured at 850 to 1000 tons per day of hydrocarbons. At least 607, of this material Lvould have to be burned or otherwisc removed from the exhaust gases in order to restore the conditions of the presmog period. hToting the fact that gasoline consumption is increasing about 77, per )-ear, Larson and othcrs (-19) urge a 90yc removal of these compounds from the exhaust gases. The exhaust gas analyses determined the different organic constituents, and also carbon monoxide and oxides of nitrogen, from many types of fuel. The laboratories of the automoti\re industry made a number of these smdies (76. - I : 73. 88. 96). Although tht. analytical data shoLc considerable variabilit)-, the type of fuel does not appear to cause a major difference in the composition of the exhaust. The decelerating cycle emits a large amount of unburned fuel. This can be sharply reduced by cutting off the fuel during deceleration or by admitting air to the intake manifold to prevent the vacuum exceeding 21 inches of mercury. Catalytic afterburners have thus far not operated satisfactorily on exhaust gases. Mader and others (56) observed that internally double bonded olefins and alpha olefins Lvith branched chains on the beta carbon readily yield oxidation products. including ozone, in sunlight, Catalytically cracked gasolines and their exhausts Lvere thought to contain more of these compounds than thermally cracked gasolines. It was suggested that this may account in part for the increase in smog symptoms since the trend toward catalytically cracked fuel began about 1942. However, Stephens and others (8’3) photolyzed mixtures of nitrogen dioxide with specially prepared authentic blends of thermally and catalyrically cracked gasolines and found no appreciable difference between the rate and extent of ozone formation from the t\vo types. Air Pollution and Health Greenxvald ( 2 8 ) has summarized the literature on the effects of the inhalation of low concentrations of sulfilr dioxide upon man and other mammals. This summary is timely. in vieiv of suspicions that sulfur dioxide might have been the principal culprit in the hleuse Valley and a t Donora and London. The question is not settled, but it seems unlikely that sulfur dioxide was a major factor in those episodes. Hemeon (3.5) suggested, on the basis of a dust sample VOL. 48, NO. 9
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taken from an air conditioner in a private home in Donora shortly after the episode, that an important irritant a t Donora was probably zinc sulfate, together with ammonium sulfate. In London, appreciable amounts of soluble ammonium salt have been found in such samples but the zinc content was low. La Belle and others (46) studied the synergistic effects of aerosols upon toxic gases. They found that the relative rates of penetration of these substances into the lungs determined the synergistic effects When aerosol penetration was greater than that of the gas, the toxicity of the latter was increased by addition of the aerosol. Conversely, if the gas penetration was greater, its toxicity was decreased by the aerosol. Amdur and others (2) showed a synergistic effect on guinea pigs with sulfuric acid aerosol (8 mg.,/cubic meter) on sulfur dioxide (89 p.p.m.). From a n air pollution standpoint, the concentrations used in all of these studies were unrealistically high. T h e results of the early investigations of the lethal London Smog were reviewed by McCabe (5g). Beaver (7) has summarized the findings of his committee, set up to evaluate the various factors involved and to make recommendations to prevent a recurrence of that disaster. Beaver ( 8 ) has also discussed the history of air pollution in Great Britain, characterized by the appointment of one commission after another, each of which made a n excellent scientific study and recommended effective action. However, nothing materialized from this work because of a reluctance to saddle industry ivith the burden of controlling the smoke. No*r that public opinion is fully aroused, the author is hopeful that his committee's recommendations will be fully implemented. Proposals include outlawing of black smoke, maximum use of smokeless fuel and close attention to burning other fuels smokelessly, establishment of smokeless zones in residential areas, and semismokeless zones i n industrial areas where the smoke would be reduced by 80%. Special precautions \rere set up to meet smog conditions such as those that existed in December 1952. Selson (62) and Watkinson (94) discuss the biological aspects of air pollution and the implications and interpretations of concentrations ordinarily found in urban air as contrasted with the concentrations that caused deaths in London and Donora. They conclude that in the "present state of our ignorance" (94) extrapolation from the high concentration effects to lower concentrations is very uncertain. Many expensive surveys like those under way in DetroitWindsor and Los Angeles, and perhaps also the development of new, highly sensitive techniques such as the respiration work of Amdur and others ( 3 ) > are needed to supply the necessary
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basic information. Study of lung cancer has made considerable progress due to chemical and statistical research, but much remains to be done in this area also (38). Breslow (7'3) and also Gafafer (27) report that preliminary attempts to find evidence for increased mortality, morbidity, and disabi1it)- in Los Angeles have yielded negative results. Three periods of heavy smog in September, October, and November 1954 were studied. No increase in deaths from selected cardiorespiratory diseases could be noted in the Los Angeles population 65 years of age or older a t the time of these episodes, though there was an obvious relationship in this group between mortality and daily temperature fluctuations. The mortality experience of a group of frail, elderly individuals in 16 Los Angeles nursing homes with a total of 358 beds was examined. The September and Sovember smogs had no effect, but there \cas a n increase in mortality in the Iveek folloiving the October smog. Pending further study, the significance of this observation is questionable. Infant mortality shoLved no effect due to the smog. All attempts to find effects on morbidity have so far yielded negative results. A household sickness survey, admissions to hospitals of persons with certain cardiac and respiratory diagnoses, school and industrial absenteeism, all show no immediate response to smog concentrations. The study is being continued, particularly with the idea of finding long-term effects, if any. In London variability of smog is sometimes great. O n January 19, 1955 (93), a 10-fold increase in smog occurred in 2 hours, and temporary deterioration in the clinical condition of some patients with chronic bronchitis and emphysema coincided with this incident. Kotin and coworkers (25, 42-44) have studied the aromatic hydrocarbons in the atmosphere of Los Angeles and also in Diesel and gasoline engine exhausts. Atmospheric samples of 2 to 3 million cubic feet \cere filtered to collect the aerosols. The latter were extracted with benzene and chromatographed. 3,4-Benzopyrene was found in concentration of about 0.8 to 0.9 mg. per million cubic feet (3 micrograms per 100 cubic meter). Other aromatic hydrocarbons which are not strongly carcinogenic, chrysene, pyrenc: 1,2-benzopyrene, 1,12-benzoperylene and a n unknown compound Y were also identified by their ultraviolet spectra. These compounds were also found in Diesel and gasoline engine exhausts. In addition, the latter contained anthanthrene, coronene, and another unidentified com': none of which could be pound A found in the atmospheric samples. The stability of these compounds was tested in a n atmosphere of artificial smoghexene plus ozone-representing about 100 times the amounts found in Los
INDUSTRIAL AND ENGINEERING CHEMISTRY
Angeles. After a 4-hour exposure, 55% of the 3,4-benzopyrene was recoverable. The other compounds Ivere destroyed to variable extents from 0 to 80%. The carcinogenicity of the benzene extracts from the atmospheric samples and exhaust gases to strain C57 mice \vas definitely demonstrated. A study of the aliphatic compounds in the atmosphere is being initiated by Kotin LU). The aerosol formed in artificial smog chambers, where aromatic compounds are presumably absent, is also carcinogenic. Some diepoxides are known to be carcinogenic. Epoxides have been identified in freeze-out samples by the mass spectrograph (95). In Great Britain, where coal smoke is the primary problem, carcinogenic subparticular, 3,4stances (21, 92)-in benzopyrene-~ have been isolated from urban atmospheres. It is well known that the incidence of lung cancer is greater among urban than among rural populations. This cannot be adequately assessed without a consideration of the smoking habits of the people. Cooper, Lindsey, and IValler (22) report 2.8 micrograms of 3,4-benzopyrene per 100 cubic meters as the average concentration in English toivnatmospheres. They found 1 ?/lo0 cigarettes (1.1 gram each). A person smoking 40 cigarettes daily \vould inhale 150 y of 3,4-benzopyrene yearly. H e would also inhale about 200 y from the atmosphere in the average British city. The authors suggest that the latter is absorbed on carbon particles and may be less active than the benzopyrene dissolved or suspended in droplets of solvent in cigarette smoke. In this connection, the 2-! ear interim report of Stocks and Campbell ( 8 J ) is of interest. They studied the urban and rural lung cancer death rates near Liverpool, for both smokers and nonsmokers. Rural death rate increased \vith number of cigarettes smoked. (Pipe smoking was equivalent to 25 cigarettes per week.) The urban death rate was 9 times the rural rate for nonsmokers, but for heavy smokers the ratio of the two rates approached unity. 'There was a nearly constant difference between corresponding urban and rural rates: suggesting a definite 'h-ban" factor. The conclusion is reached tentatively that half of the Liverpool lung cancer deaths are due to cigarette smoking and 3/8 to the urban factor. The urban factor, which increases the death rate of nonsmokers by a factor of 9, may well be associated with the fact that the urban 3,4-benzopyrene concentration is 8 to 12 times the rural concentration. literature Cited
(1 ) Air Controls Installations Ltd., Engineering (London) 179, 704 (1955). ( 2 ) .4mdur, M. O., Public Hcalth Reptr. ( U . S.) 69, 503-6 (1954).
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(1953). (4) Am. SOC. Testing Materials, Philadelphia, Pa., .4SThI Standards, Pt. 7, Desipation D1354-55T.. 1537-40 (1955). ( 5 ) .\ustin. R . R.. Proc. Third National Air Pollution Symposium, Stanford Research Institute. Los Xngeles. Calif., pp. 131-5, 1955. ( 6 ) Beard, G. V., Wilhelmsen. XI.. Division of Physical and Inorganic (Air Pollution Symposium). 128th Meeting, XCS, Xfinneapolis, Minn.. September 11-16, 1955. ( 7 ) Beaver. H. E. C., Final Report on Air Pollution, H. h.i. Stationer)Office, Cmd. 9322 (1954). London, 1955. ( 8 ) Braver. H. E. C.: in ”Air Pollution.” Chap. 1, p. 1-12, (F. C. Xfallette. editor) Reinhold, N e w York, 1955. ( 9 ) Benedict. H. X f . , Breen, W. H., Proc. Third National Air Pollution Symposium, Stanford Research Institute. Los Angeles, Calif., pp. 177-90, 1955. (10) Billings. C. E., Small. W.D.. Silverman, L.. J . d i r Pollution Control Assoc. 5 , 159-66 (1955). ( 11) Blasewitz, A . G.. Judson. B. F.. A i r Repair 4,223-9 (1955). (12) Bobrov, R. .4., Srimce 121, 510-11 (1955). ( 1 3) Breslow. L.: Public Health Repts. ( L . S . ) 70, 1140-2 (1955). 114) Cadle. R. D.. “Particle Size Determination,“ Interscience. New York. 19.5.5 ~.~ . . ( 1 5 ) Cadle. R. D.. Wiggins, E. J.. Arch. Ind. Health 1 2 , 584-91 (1955). ( 1 6 ) Chandler, J . hi.. Cannon, W. A . , Seerman: J. C . . Rudolph. A . J . ~
Air Pollution Control Assoc.
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VOL. 48, NO. 9
SEPTEMBER 1956
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