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1070 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 45, No. 5
Titanium and zirconium give zero or negligible corrosion rates in air aerated aniline hydrochloride solutions. Stainless steel ie unsatisfactory because of a tendency to form deep pits. The three materials are resistant to boiling chlorinated hydrocarbon- water mixtures. With the exception of stainless steel in carbon tetrachloride, these materials also have little or no catalytic effect on the decomposition of the hydrocarbon under such conditions.
LITERATURE CITED
(1) Am. Yoc. Testing Materials, Standards, Pt. I-B, 793-802 (1946). (2) Coriosion Handbook (H. H. Uhlig, ed.), p. 347, New York,
(3) Dean, R. S., Long, J. R., Wai tman, F. S., and Anderson, E. L., John Wley & Sons, 1948.
Met& Technol., 13, No. 2, 12-13 (1946); T e c h . Publ. 1961.
(4) E. I. Du Pont de Nemours and Go., Wilmington, Del., “Du Pont Titanium hfetal,” (Tech. Bull., 3rd ed.), pp. 9-10 (1951).
(8) Fieser, L. F., and Fieser, M., “Organic Chemistry,” abridged ed., p. 154, Boston, D. C. Heath and Co., 1944.
(6) Gee, E. A., Golden, L. B., and Lusby, I?’. E., Jr., IND. ENG. CHEM., 41, 1668-73 (1949).
(7) Gillett, H. IT., Foote Prints, 13, 5-7 (1940). (8) Golden, L. B., Lane, I. R., Jr., and Acherman, W. L., IND.
(9) Hoyt, S. L., “Metals and Slloys Data Book,” p. 286, New York,
(10) Hutchinson, G. E., and Permar, P. H.. Cor~os ion , 5, 322-3
(11) International Kickel Co., New York, Tech. Bull. T-23, pp. 3-4
(12) Titanium Metals Corp., New York, “Handbook on Titanium
RECEIVED for review September 24, 1952.
ENG. CHEM., 44, 1930-9 (1952).
Reinhold Publishing Corp., 1943.
(1 949).
(1 942).
Metal,” 4th ed., p. 33, 1981. ACCEPTED January 26, 1933.
Evaluating Sources of Air Pollution GORDON P. LARSON, GEORGE I. FISCHER, AND “ALTER J. H-4JIJIIXG
A i r Pollution Control District, County of Los Angeles, Los Angeles, Calif.
TUDIES of air pollution have been confined largely to the s development of atmospheric sampling methods and the meas- urement of the contaminants in the air. The data on air samplin’g for any locality must be related to the activities in that localitr which produce the pollution, if the information is to be of full value in a program for air pollution control. The purpose of this paper is to present methods for determining the quantities of the various pollutants created within an area and t o show how these emissions can be related to air sampling data. Methods shown in this study have been invaluable in promoting intelligent direc- tion of control and research programs, and if applied periodically, they should reveal the benefits of a program for control of air pollution.
The important pollutants of the Los Angeles atmosphere and their concentrations listed in Table I are representative of air sampling data obtained during clear and smog periods (10). Investigations covering these contaminants have led to a number of conclusions regarding the causes of the characteristic haze that often reduces visibility to less than 1 mile (11, 11), the causes of gas damage to vegetation (d,S, 8), the nature of the eye-irritating materials ( 6 ) , and the high rate of rubber cracking (6, 7). A com- plete discussion of these experimental studies is beyond the scope of this paper. A brief picture of the part each pollutant plays in caus- ing the effects observed during periods of smog is shown in Fig- ure 1. It can be seen that the essential materials for smog forma- tion are hydrocarbons, ozone, nitrogen dioxide, sulfur dioxide, and visible pollutants such as smoke, dusts, fumes, and mists.
METHODS APPLIED TO SOURCES
Two major problems are involved in an estimate of pollution discharged to the atmosphere. Production or consumption rates must be determined for each type of operation, and a corre- lation of the amount of a pollutant emitted to the amount of material processed or consumed must be established for each type of operation. This correlation is developed by analyses of the sources for the quantities and types of pollutants discharged.
More than 350 tests on sources of pollution in the Los Angeles area aere made. The collected samples were analyzed for mate- rials that previously had been found in the air. Extreme care was taken to ensure that the chemical and physical methods used on the source tests were equivalent to those used in the identifica- tion work on atmospheric samples. While testing procedures have not attained complete standardization. stack sampling follows procedures in use by others and provides reproducible results. All test information was related to the quantities of material processed or consumed during the sampling periods. The correlations developed are listed in Tables I1 and 111.
Pollution sources were surveyed to determine production and consumption rates for various operations. Some results of this survey are listed in Table 1 1 7 .
All hydrocarbon sources were not tested, because of the diffi- culties involved in quantitative determinations of this type. A literature survey indicated that refinery hydrocarbon losses are equivalent to from 1 to 2% of the refinery crude oil throughput (4, 6, I S ) . It is considered that the bulk of this loss is to the
TABLE I. CONCENTRATIONS OF POLLUTANTS IK LOS ANGELES ATMOSPHERE (Average values as measured over downtown Los Angeles on various days, 1951)
Concentrations, Mg. per Cubic Meter ~~
Concentrations, P.P.M. by Volume Periods of Periods of Periods of Periods of
Gases good visibilitya intense smog Aerosols good visibilitya inteme s m o g b Acrolein e Present Lower aldehydes 0 .07 0 . 4 Carbon monoxide 3 . 5 23.0 Formaldehyde 0 .04 0.09 Hydrocarbons 0 . 2 1 . 1 Oxidants‘ 0 . 1 0 . 5 Oxides of nitrogen 0.08 0 . 4 Ozonef 0 . 0 6 0 . 3 Bulfur dioxide 0 . 0 5 0 . 3
a Visibility approximately 7 miles. Visibility approximately 1 mile or less. No quantitative method known for measuring
d As determined by flame spectrophotometric an e As determined by liberated iodine method and f As determined by rubber cracking.
Aluminumd Calciumd Carbond Irond Leadd Ether-soluble
aerosols Silicond Sulfuric acid
low concentrations alysis. reported as ozone.
of a
0 003 0 008 0 006 0 007 0 035 0 132 0 003 0 010 0 002 0 042
0.012 0 ,120 0 . 0 0 7 0.028 0.00 0.110
tcrolein.
atmosphere, since many of the hydro- carbons involved are relatively volatile and extensive precautions are taken to restrict losses through effluent water sys- tems and ground seepage. One per cent of the 550,000-barrel daily crude oil throughput of Los Angeles County re- fineries corresponds to a daily hydrocar- bon loss to the atmosphere of 830 tons. Based on calculations, extrapolation of limited test data, and operating informa- tion from refiners, 80% of this over-all loss can be accounted for (Table V). The difference betwen the over-all losses and the losses that can be accounted for is attributed to leaks from pumps and fittings, storage losses for materials other than crude oil and gasoline,
May 1953 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 1071
TABLE 11. DATA DEVELOPED FROM SPECIAL STUDIES Losses to Atmosphere, Pounds per Unit of Consumption
Nonether- Ether- Total Lower Oxides Unit of soluble soluble Oil hydro- Acety- alde- of Organic
Consumption particulates wrticulates mista carbons lene hydesb nitrogenC acidsd Source of Pollution
,utomobile exhaust e 1 bbl. gasoline 1 bbl. gasoline 1 bbl. gasoline 1 bbl. fuel 1 ton rubbish 1 bbl. oil
0 .30 0.24 0 . 4 5 3 . 2
1 7 . 1 f
f 0 .14 0 . 3 7 1
29.2 f
3 . 2 0 .00 0 . 9 7 f
0.00 f
2 9 . 6 2 . 1
34 .3 Trace 0.00
Trace
13 .3 0 .31 0 .87
f 0.00
f
0 .30 0 .14 0 .30 0 . 4 6 5 . 1
Trace
0.00 5 . 2 3 . 3 9 . 4
10.6 5 . 2
0.09 0 . 2 2 0 .12 1 . 3
27 .4 0 . 5 6
At equilibrium conditions, approximately 90% of this mist will exist as vapor in atmosphere. b Calculated as formaldehyde: C Calculated as nitrogen dioxide. d Calculated as acetic acid.
Studebaker Champion 1947 odometer reading 40 000 miles: engine in average mechanical condition. Acceleration-deceleration conditions simulated on
f Not measured. Diesel bus 210-hp., two-stroke cycle used.
h Standard 3-cubic-foot domestic incinerator used. 29 pounds per h.our.
z Boiler, serving large power plant, consumed 100 barrels of fuel oil (9.2 API) per hour.
dynamometer by accelerating tohO miles per hour and'decelerating to 20 miles per hour continuously in high gear a t full and closed throttle, respectively.
Cruising conditions simulated on dynamometer by operating a t 30 miles per hour and 15 brake hp. Rubbish, composed of 46% leaves, 22% paper, 15% grass, 14% wood, and 3% rags, burned a t rate of
TABLE 111. DATA DEVELOPED FROM FIELD TESTS Emission of Nonether- Soluble Particulates,
Lb./Ton of Production 1 . 6 0 . 4 4 . 0 0 . 8 8 . 8
Industry Asphalt paving
Asphalt roofing
Chemicals Feed
Process Equipment Mixing plant
Asphalt saturator
Spray dryer
Product Control Equipment Paving material Cyclone
Roofing paper None
Detergent powder Cyclone
Cyclone and scrubber
Scrubber
Air cleaner Mill Mill Pulp dryer
Chaff-free wheat Cyclone Alfalfa meal Barley flour Cyclone Orange pulp Cyclone
Settling chamber and cyclone 0 . 2 4 . 0 3 . 1
11 .3 Fertilizer Frit Glass Metals
Reactor and mixer Rotary smelter Reverberatory furnace Cupola
Commercial fertilizer Scrubber Frit None Bottle glass None
7 .0 17 .0 3.0
14 .6 0.04
54 .0 34.0
9 . 2 3 . 7 4 . 0
17 .5 0 . 3
71.0 5 . 0
87.0 0.02
30.0
Gray iron None Baghouse None Scrubber None Type N Rotoclone None
Direct-fired rotary furnace Dross furnace Electric furnace
Yellow brass Lead Steel
Indirect-fired furnace Open-hearth furnace
Sweating furnace
Zinc oxide reduction furnace Fluid catalytic-cracking regenerator Cupola and blow chamber
Red brass Steel None
Aluminum None
Zino None Regenerated catalyst Rock wool insulation None
Electrostatic precipitator
With baghouse
Electrostatic precipitator and cyclone Petroleum refining Rock wool
TABLE IV. DAILY PRODUCTION AND CONSUMPTION IN LOS ANGELES COUNTY, 1951 (IO) and losses incurred in refinery shutdowns. Losses from gasoline
marketing were calculated from the vapor pressures, consump- tions, and storage capacities involved and are listed in Table VI.
Pollution passed the tolerance levels in 1942 and increased
A. Incineration Commercial and industrial incinerators Domestic incinerators Municipal incinerators Wood burners
Tons 1,000 4,000
400 1,500
B. Petroleum products Crude oil production Crude oil consumption refineries Diesel oil consumption: transportation Fuel gas consumption Fuel oil consumption summer Fuel oil consumption' winter Gasoline and naphth; distillate production Motor gasoline consumption Crude oil storage capacity, refineries Gasoline storage capacity, refineries
Barrels
REDUCED
HYDROCARBONS
IO
with the growth of population and expanded industrial activity. Losses to the atmosphere were estimated for 1940 with the expec- tation that differences between the daily emission rates of 1940 and subsequent years might reveal the significant sources contrib- uting to smog. The 1940 emissions were estimated by correct- ing the 1951 values in each category with appropriate factors- e.g., the 1940 to 1951 ratio of production workers was applied to the metals industry; the 1940 to 1951 ratio of gasoline consump- tion was applied to gasoline-powered transportation. Also, because the Btudy is to serve as an index of reductions made,
Figure 1. Schematic Reactions of Air Pollutants
Vol. 45, No. 5 1072 I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
TABLE I-. 1951 PETROI.EU~I REFINERY HYDROCARBON LOSSES, T O S S PER DAY
Source
Hydrocarbons, Olefinic Unsaturrn
Total ca, cs, c s Hydrocarbons Total molecules
Catalytic-cracking processes 20 2 0 separators and sewers 400 70 12 Storage crude oil 40 0 0
Treating processes 35 6 6 l-nnrnm iet,s i n n n Storage'and rundown, gasoline 160 24 23
~"... hIiscellaneousa
Total
~. 7
830 135 48 ~ - 165 33 __
a Includes losses from refineiy shutdown procedures, storage other than crude oil and gasoline, and pumps and fittings.
T.4BIX VI. 1951 G-4SoLISE ~ I A R K E T I X G HYDROCARBOS IAXSES,
Operation Total Olefinic Unsaturationa
Toxe PER DAY
2 . 5 1 . 5 2
:a Filling trucks at refineries Filling railroad cars at refineries Filling seagoing vessels 15 Marine terminal separators 43 6 Filling and breathing from bulk terminals 37 5 . 5 Filling trucks at bulk terminals 20 3 Filling retail station tanks 12 2
16 2 . 5 Filling vehicle tanks - Total 170 25
(c For each operation approximately 95% of losses are comporinds of 4, 5 , and 6 carbon atoms per molecule.
emissions were determined for 1948, the year 11 hen the present control program in Los Angeles was initiated. Careful checks on operational changes and control devices are made to keep the study up to date. A summation of the emissions for 1940, 1948, and 1951 is shown in Tables VI1 and VIII.
RELATION OF POLLUTION SOURCES T O AIR SAMPLING DATA
C.4SES AND Lrapo~s. Establishment of a relationship betwecn air sampling data and the pollution data of Tables VI1 and VI11 is comidered necessary as a measure of the survey's accuracy. In addition. such a relationship adds to the understanding of the dispersion of pollutants from source areas and aids in the interpre- tation of data obtained from air sampling programs.
The relation between the total quantity of a pollutant dis- charged from all sources in the area and the concentration of the pollutant in the air may be derived by considering the pollutant ae being uniformly dispersed throughout a given volume of air. This dispersion volume is calculated from the total emissions and atmospheric concentration of any chemically stable pollutant. I n this example, the concentration of carbon monoxide in the downtown Los Angeles area n-ac1 3 to 4 p.p.m. by volume during
clear periods (visibility, 7 milos; inversion height, 2000 feet; wind velocity, 7 miles per hour) (15 ) ; i t increased five- to eight- fold during average periods of intense smog and as much as ten- fold during the acut'e smog period of Kovember 28, 1950 (visibility, less than 1 inile; inversion height, 500 feet; wind velocity, 3 miles per hour) ( 2 4 ) . If the daily emissions of carbon monoxidt! or any other pollutant are assumed to be fairly constant, a pro- nounced increase in concentration can be explained only by a corresponding decrease in the dispersion volume. Therefore, the dispersion volume for a period of intense smog is one fifth t o one eighth the volume associat'ed with periods of good visibility and one tenth for the acute period of the above date.
Carbon monoxide emissions (standard cubic feet per day) are estimated as:
Gasoline-powered engines 127 X 106 Catalytic-cracking processes 17 X 106 Gas-powered engines 3 x 106 Metal-refining processes 1 x 105
Total 148 X 106
In order to give a concentration of 3.5 p.p.m. by voluni, 148 x 106 3.5 x 10-6'
or 4.2 X l O I 3 cubic feet of volume are required. This
represents the dispersion volume for a period oi good visibility. Wincl velocity and inversion height are the important factors
causing variation in the dispersion volume. The drcrease in dis- persion volume for November 28, 1950, is proportional to the product of the ratios of the inversion heights and wind velocities
2000 x 7 500 x 3
, or CJ.3. The for the clear and acute sniog periods-Le.,
close agreement of the two methods indicates that the dispersion volume concept is consistent with the meteorological data.
With the concentration calculated as if the pollutant were distributed uniformly throughout the dispersion volume, the air concentration for suIfur dioxide is calculated from Table VI1 ae follolvs:
300 2ooo 379 = 0.08 p.p.m. by volume during clear. 64 X 4.2 X 1013 period
300 2ooo 379 lo6 6.5 = 0.5 p.p.m. by volume during 64 X 4.2 X 10'3
intense smog ~- where 300 2ooo 64 379 - daily sulfur dioxide emissions. stanti-
ard cubic f e e t - 4.2 X l O I 3 = dispersion volume for clear period, cubic feet 4'2
= dispersion volume for intense smog period, cubic feet
6.5 = average ratio of disprrsion volumes for clear and intense 6.5
smog periods
TABLE 1-11. ~<\CISSIOluS TO L O S -4XGELCS C O U N T Y AT\.IOSPIIERE O F h R 0 9 0 L S . ACID GASES, AND h , D E H Y D E S
(Estimated tons per day)
Source Chemical, paint, roofing, rubber. and soap
industrips Food and fertilizer industries Fuel oil burning1 Incineration
Domestic Commercial, industrial, municipal, and
dumps Metals industries Mineral processing, stone, sand, grayel,
Oxides of Sulfur Lower Organic Particulatesa Nitrogen6 Dioxide 41de hydes C Aoidsd ~
1940 1948 1951 1940 1948 1451 1940 1948 1961 1940 1948 1951 1940 1948 1951
clay, etc. Petroleum refining Transportation
Gasoline Diesel
Total
a Includes smoke, dust, fumes, and mists b Reported as nitrogen dioxide. c Reported as formaldehyde.
6 7 3
60
85 12
30 0
14 3
13 '2 90
115 28
51 8
23 5
11 8 3
90
34 16
25 7
I S 21
20 27 0 0
0 0 0 0
71 120 4 7
N 0
85
21
7 0
0 0
132 10
10 0
100
N
S 1
A- 260
13 1
21 0
170
li
N 2
N 380
20 2
23 ti li S 0 0 0 0
170 S S N
s 8 10 10
N 70 14 4 2 0 0 0
K O 0 0 8 0 0 0 0
21 7 10 10 2 0 1 1
N 0 3
42
50 0
0 0
4 1
N K 0 0 7 7
5 3 55
69 19 0 0
0 0 0 0
7 7 2 2 __ __ __ __ -_ -_ -- -_ -_ - - - __ __ -
220 350 225 160 260 255 385 595 300 25 35 25 100 140 90
d Reported as acetic acid. e Less than 1 ton. I Includes fuel oil burned in all categories
except transportation. All values based on summer fuel oil usage, approximately on? half winter usage,
May 1953 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 1073
TABLE VIII. EMISSIOSS OF HYDROCARBONS TO Los ANGELES COUNTY ATMOSPHERE (Estimated tons per day)
Source Automobilesd 500 850 875 80 131 138 24 40 44 315 534 577 50 85 90 Chemical, paint, roofing, rubber, and
Petroleum marketing 97 165 170 15 24 25 14 23 24 82 141 145 Petroleum productionf 1700 270 270 N N N N N N 120 100 100
500 830 830 80 135 135 27 47 48 370 610 610 Petroleum refining@
Total 2810 2140 2180 175 290 305 65 110 120 900 1410 1460 Includes aromatics.
paint industries 13 25 35 N e N 7 N N 4 13 25 28
_ _ _ _ ~
Preliminary studies indicate that this group, with exception of branched-chain compounds, i s not a major factor b Preliminary studies indicate that this hydrocarbon is not a major factor in air pollution. C Oxidation products of these compounds considered to be a major factor in air ollution. d Includes all gasoline consumed in internal combustion engines; losses include greathing from gasoline tanks and carburetors.
Chemical, paint, roofing, rubber, and
Petroleum marketing 97 165 170 15 24 25 14 23 24 82 141 145 Petroleum productionf 1700 270 270 N N N N N N 120 100 100 Petroleum refinin~o 500 830 830 80 135 135 27 47 48 370 610 610
paint industries 13 25 35 N e N 7 N N 4 13 25 28
_ _ _ _ ~
~ . ~ . ~ ~ ~ ~
Total 2810 2140 2180 175 290 305 65 110 120 900 1410 1460 Includes aromatics, Preliminary studies indicate that this group, with exception of branched-chain compounds, i s not a major factor
b Preliminary studies indicate that this hydrocarbon is not a major factor in air pollution. C Oxidation products of these compounds considered to be a major factor in air ollution. d Includes all gasoline consumed in internal combustion engines; losses include greathing from gasoline tanks and carburetors.
N 0 N N - 50 in air
N N 0 0
N N N N _ _ 86 90
pollution.
Less than 1 ton. f Includes losses from production and field operations for ciude oil and natural gas.
g Includes evaporation losses from gasoline and crude oil storage.
1940 figure includes release of large quantities of natural gas directly to atmosphere.
Comparison of the measured sulfur dioxide concentrations of 0.05 and 0.3 p.p.m. by volume for clear and intense smog periods, respectively, with the calculated values indicates a close agree- ment. Table IX lists calculated and measured pollutant concen- trations.
TABLE IX. MEASURED AND CALCULATED CONCENTRATIONS OF POLLUTANTS AT DOWNTOWN Los ANGELES, 1951
Periods of Good Visi- Periods of Intense bilitya, P.P.IM. by Smogb, P.P.M. by
Volume Volume Pollutant Measured Calcd. Measured Calcd.
Carbon monoxide 3.5 3.5c 23.0 23.OC Oxides of nitrogen 0.08 0.10 0.4 0.6 Sulfur dioxide 0.05 0.08 0.3 0.5 Total bydrocarbonsd 0 . 2 0.40 1. 1 s 2.6 Lower aldehydes 0.07 0.02 0.4 0.1 Organic acids 0.07 0.03 0.4e 0.2
a Visibility approximately 7 miles. b Visibility approximately 1 mile or less. e Method defines that calculated value is same as measured value for CO. d Calculated as hexene. e Preliminary values.
Considering the factors involved in air sampling, the measured and calculated Concentrations are in good agreement for oxides of nitrogen and sulfur dioxide. The number and degree of disper- sion of pollution sources from any given sampling site influence the concentrations measured a t that point. It can be seen that higher measured concentrations are found at downtown Los Angeles for aldehydes and organic acids, while hydrocarbon con- centrations measure considerably less than the calculated values. These results confirmed earlier indications that some pollutants are formed by reactions in the air. The results obtained are understandable when it is realized that the calculations assume the pollutants to be chemically stable. Actually, some of the hydrocarbons are being oxidized continuously to form peroxides, aldehydes, and organic acids and these reactions account for the discrepancy in the hydrocarbon values and consequently, per- oxides, aldehydes, and organic acid concentrations are greater than can be attributed to industrial and other community sources.
Calculations similar to those above can be made for the particulate matter discharged from sources. It is advis- able to calculate the significance of aerosol concentrations as related to reduction of visibility. Having evaluated this rela- tionship, it is then possible to determine year-to-year improve- ments resulting from control measures.
However, comparison of quantities collected from the atmos- phere with amounts computed from sources reveals a higher cal- culated value than that measured by sampling. For instance, it is calculated that approximately 225 tons of aerosols are emitted to the air of Los Angeles County each day from industrial and public sources, but only about 100 tons are measured in the air.
A portion of the missing aerosol is composed of large particles
AEROSOLS.
which settle out soon after discharge. Filter-collected matter may include aerosols formed from reactions in t h e atmosphere as well as aerosols originating as such from sources. In view of the diverse sources of aerosols, it is obviously advisable to deter- mfne each substance quantitatively in the air sample.
Aerosols are determined according to three main classes: (1) solid particles in smoke, dusts, and fumes, (2) sulfuric acid mist, and (3) ether-soluble material. Visibility decreases as the con- centrations of all three of these materials increase.
Once concentrations of various aerosols are determined, it ia advisable to ascertain how effective each one is in reducing visi- bility. An evaluation of this function can be approximated by a relative pollution index for visibility.
The importance of each pollutant in aerosol form as it effects a reduction in visibility depends upon the radius of the particle, its index of refraction, and the quantity. Air sampling in Los Angeles has established the quantities of several aerosols and the fact that 95% of the particles in the smog are below 1 micron in diameter. It has also been shown that as the visibility decreases, the particles in the 0.5- to 0.8-micron range increase more rapidly than in other size ranges. With this information and certain as- sumptions, a relative pollution index can be determined from the following formula:
N P 6 W Relative pollution index for visiblity = - cc. = - D X - B N P where - = number of particles per cubic centimeter cc.
D = density, grams per cubic centimeter W = weight of material collected while sampling, micrograms V = volume of air sampled, cubic meters
In arriving at the constant of 6 in this formula, the index of refraction of the various materials which were identified was calculated in terms of effective scattering diameter, or considered as having the effect of changing the diameter of the particles. The changes in the dfameter in terms of the index of refraction fluctuate over very narrow limits. The mean value would result in a particle size of 0.682 micron. This value is then use3 in the formula:
to arrive a t the above constant. Table X gives the relative pollution index for the important aerosols which have been identi- fied. Other pollutants found in the lesser concentrations than calcium or iron give lower indexes (9).
It is apparent in this evaluation that the weights of materials found in the atmosphere are not necessarily significant unless studied on this or a similar basis. The use of such an index and‘ the studies relating total pollution quantities to the measured atmospheric concentrations are useful techniques.
1074 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 45, No, 5
TABLE X. RELATIVE POLLCTIOK INDEX FOR VISIBILITY W / v D
Pollutant y/Cu. d e t e r Grams’/Cc. R.P.I. Ether-soluble aerosols Sulfuric acid mist Carbon Silicon b Lead b Aluminum b Calcium b Ironb
120 110
132 ( B 3 ) a 28 42
8 7
10
0 . 8 1 . 4 2 . 1 2 . 4 9 . 1 2.0 2 .8 5.1
904 461
378 (15lla 69 28 24 14 12 - .
a It is known. by analysis and calculations, that approximately 60% of carbon is found in ether-soluble aerosol; therefore, relative pollution index for carbon should be reduced as indicated.
6 As determined by flame spectrophotometric analysis.
~~~
DISCUSSION OF SURVEY
BUILD-UP OF POLLUTIOK. Large increases in the emissions of most pollutants occurred in the period from 1940 to 1948. Smoke, dusts, fumes, and mists, grouped together as aerosols, increased from 220 to 350 tons per day, the oxides of nitrogen, from 160 to 260 tons per day, and sulfur dioxide, from 385 to 595. Alde- hydes and organic acids did not increase significantly, yet these materials exist in rather high concentrations in the atmosphcre. In this same period, however, the total hydrocarbon emissions decreased from 2810 to 2180 tons per day. This decrease \vas due to the utilization of natural gas, large amounts of which were released directly to the atmosphere in 1940. Compounds of olefinic unsaturation increased from 175 to 305 tons per day. Research has shown that among the most significant smog-form- ing materials are the unsaturates containing four, five, and six carbon atoms per molecule. In evaluating the known sources, the potentially harmful hydrocarbons must be considered apart from the total hydrocarbon emissions.
While the release of unsaturated hydrocarbons to the air increased in proportion to expanded refining activity and greater gasoline consumption, another change also occurred. Studies indicate that catalytic cracking forms more branched-chain paraffins, especially in the low-boiling range, than does thermal cracking. Bates et al. observe that, for the six-carbon fraction, the ratio of iso- to normal paraffins is approximately 10 to 1 in catalytic cracking and 0.5 to 1 in thermal cracking (1 ) ; for the five-carbon fraction the ratio is 18 to 1 in catalytic cracking (1 ). It is concluded that more branched-chain hydrocarbons are released to the Loa Angeles air since the advent of the catalytic-cracking processes. These compounds form stable peroxides in sunlight (16 ) ; and peroxides increase the rate at which olefins are oxidized (17 ) . Since the products of this oxidation have been shown to cause smog effects ( 6 ) , it follows that higher concentrations of eye-irritating, vegetation-damaging, and visibility-reducing compounds in the air have resulted from the increased emissions of olefins and branched-chain paraffins.
The hydrocarbon data listed in Table VI11 are preliminary and subject to revision when improved analytical methods are devel- oped. It is apparent, however, that the activities listed consti- tute the major hydrocarbon sources, and that the tonnages in this table must be kept current as new controls effect reductions in sources. This facilitates progressive evaluation of control measures after they have been invoked.
Comparisons of the figures for 1948 and 1951 in Table VI1 indicate the extent to which the pro- gram of control a t the source has reduced 8ome of the contam- inants. The reduction of 125 tons per day of visible smoke, dusts, fumes, and mists and 295 tons per day of sulfur dioxide since 1948 is a material contribution to improving the visibility. Emis- sions of sulfur dioxide were reduced below the 1940 level, while aerosol emissions were reduced to the 1940 level.
Because each pollutant has a different function in the forma- tion of smog, a change in the emission of one pollutant does not necessarily indicate a proportional change in all the effects of air pollution. Each source and each pollutant can be evaluated
TECHNOLOGICAL CHANGES.
REDUCTIONS IS POLLUTION.
only in terms of the individual si%og effects it influences. The amount of reduction in the concentrations of gases being con- trolled can be measured in the air. In the case of sulfur dioxide, the removal of 295 tons from the air since 1948 is a marked change. Concentrations during adverse smog periods dropped from 0.3 p.p.m. in 1948 to 0.15 p.p.m. in 1952. By the same token, confir- mation of the effectiveness of controls on aerosol sources can be obtained from measurements of appropriate air samples.
This study serves as a guide for planning future control measures. It indicates that future measures must control the major sources of hydrocarbon emis- sions and the uncontrolled aerosol sources. The contribution of refineries and automobile exhaust gases to the hydrocarbon problem must be investigated. Because only a portion of the hydrocarbon losses is oxidized and thereby contributes to smog, test methods must be developed to measure adequately the hydro- carbon contaminants. Successful control of smog-forming hydro- carbons, therefore, awaits the development of methods which will identify them.
These source studies indicate also that oxides of nitrogen, which are produced in most combustion processes, must receive further study. Current investigations are under way to deter- mine whether these play a role in smog formation other than through their ability to catalyze the oxidation of hydrocarbons.
If air sampling data are to have true significance, it is impera- tive that these data be related to emissions from sources which produce the pollutants. Data from sources are correlated with air sampling data to permit: (I) year-to-year comparisons of pollution levels; (2) a perpetual index of concentrations as a check against excessive emissions of a specific pollutant or group of pollutants; (3) a gage of progress in pollution reductions as controls are invoked; (4) understanding of the meteorological factors which influence the dispersion of pollutants from source areas; (5) detection of pollutants with atmospheric concentrations greater than their sources account for, indicating the influence of other mechanisms; and (6) a guide to the planning of future control measures. Aerosols must be evaluated in terms of their ability to reduce visibility. This can be determined by means of a relative pollution index for each material which is based upon the radius of the aerosol particle involved, its index of refraction, and the quantity. An example is cited whereby correlated stud- ies of source and air samples reflect technologica1 changes which alter pollution levels and delimit major smog-contributing sources that must be investigated for ultimate means of control.
FUTURE CONTROL MEASURES.
SUMMARY
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RECEIVED for review Auguat 25, 1952. ACCEPTED January 28, 1953.
