Environmental Health PerspectivesVol. 8, pp. 165-190, 1974

Potential Dilemma: The Methods ofMeeting Automotive Exhaust Emis-sion Standards of the Clean Air Actof 1970by Warren T. Piver *

This review attempts to provide an overview of the interconnected industrial changesassociated with compliance with the exhaust emission standards of the Clean Air Act of 1970. Tounderstand the complex nature of air pollution problems, Federal legislation, and compliancewith this legislation requires an understanding of automotive technology, petroleum refining,atmospheric chemistry and physics, economics, and public health. The endeavors of all of thesedifferent areas impinge to a greater or lesser extent on the final response to the Clean Air Actwhich is designed to safeguard public health.This overview begins by examining gasoline refinery practice and gasoline composition.

Included in this discussion are average values for trace contaminants in gasoline, and an ex-planation of the function of the many gasoline additives. Next, exhaust emissions arecharacterized, average values of exhaust components given, and a summary of important at-mospheric air pollution reactions presented. Emission control devices and sulfate emissionsfrom these devices are described. This is followed by a complete discussion of methyl cyclopen-tadienyl manganese tricarbonyl, a substitute antiknock for tetraethyllead. In the event TEL islegally banned from gasoline, or removed because it poisons the catalytic muffler surface, thismanganese antiknock is the most eff;caous replacement. In this discussion, the adverse healtheffects caused by exposure to manganese oxide particulates, the possible exhaust emissionproducts from this additive, are examined in detail. The review concludes with comments onautomotive engine and gasoline composition redesign as an approach to automotive air pollu-tion.

Introduction and Background

In 1952, Hagen-Smit (1) demonstrated thatsmog in Los Angeles was formed from twoautomotive exhaust gas pollutants, unburned

*National Institute of Environmental Health Sciences,National Institutes of Health, P. 0. Box 12233, ResearchTriangle Park, North Carolina 27709.

hydrocarbons and nitric oxides. In effect, thisstudy first showed clearly that the automobile,which had become an integral part of Americanculture, was a public health problem. The ironyof this was that the turn-of-the-century expec-tations for the automobile foresaw it as a solu-tion to many of the public health problemsengendered by the horse and carriage (2). Someselected expectations were reduction of city

August 1974 165

noise, restoration of frayed nerves, relief of traf-fic congestion, increased economy of operation,and the reduction of population movement fromrural to urban areas. In effect, the study byHagen-Smit stimulated much concern, debate,raised blood pressures, Federal agency creation,and pressure by different interest groups as towhat other pollutants were present inautomotive exhaust, what effect they had on theenvironment, and what could be done to removethe source of these pollutants. The combustionof leaded gasoline in the spark-ignitedautomotive engine, in particular was identifiedas the major mobile source of hydrocarbons,carbon monoxide, nitrogen oxides, lead halideparticulates, and other particulate matter.Presently, there are about 90 million passengercars in operation which use about 1011 gal gas-oline/yr. In 1968, 75 million cars produced 128 x109 lb of CO, 34 x 109 lb of hydrocarbons, and 16x 109 lb of nitrogen oxides (3).A portion of the discussions since the passage

of the 1970 Clean Air Act has centered on themethods to be used by automotive producers,gasoline refiners, and gasoline additiveproducers to achieve the exhaust emission stan-dards prescribed by this law for CO, hydrocar-bons, and nitrogen oxides. Lead particulateemissions are not regulated. The methods mostoften discussed are the use of catalytic mufflersto clean up exhaust emissions and the cor-responding removal of the lead antiknock ad-ditive since it would poison the catalytic surfaceof these mufflers. Others have advocated thecomplete redesign of the internal combustionengine, the development of new engines andfuels, and increased use of mass transit systemsas solutions to the pollution problem. What ismissing from all these discussions, however, isan assessment of these methods from the stand-point of environmental health. Such questionsas will the proposed solutions do the job, whatwill be the consequences for environmentalhealth if these methods fail, and what will bethe direct and indirect costs to the generalpublic are important and critical assessmentswhich are lacking at this time, and which willgreatly influence the final action on this issue.

This report addresses itself to a discussion ofthe methods proposed to meet the exhaust emis-

sion standards and an assessment of thesemethods from the standpoint of technologicalfeasibility of proposed fuel additives and emis-sion control devices, the economics of changes ofthis magnitude, and the implications for en-vironmental health. The question of whether ornot such as assessment can be made free frompersonal prejudices is real and can be answeredby saying that assessments by their very natureare judgments made by individuals with humanlimitations. This is not in support of the ideathat such assessments should not be made, butrather in support of the idea that suchassessments should be made and either used asstarting points for further discussions byothers, or made in conjunction with others as inthe Delphi Technique for TechnologyForecasting.The assessment of the implications of the con-

trol actions of the Clean Air Act of 1970 is lack-ing because it is difficult to predict the outcomeof such an action due to the complexrelationships between economics, public reac-tion, technology, and Federal intervention.However, the refusal to acknowledge thepossibility that what you propose to do to meet aset of regulations may contribute to the problemrather than solve it is not responsible either.This is not to say that human initiative in solv-ing problems should stop; far from it, however,recognition of one's actions and their im-plications is desperately required by not onlythe standard setter, but also those directlyaffected by the regulations of the Clean Air Actand also all segments of the general public.

Technology of Gasoline composition, com-bustion, and Exhaust Emission Profile

Gasoline Composition

In order to assess the developing technologyresulting from the Clean Air Act, it is necessaryto start with the state-of-knowledge about theexisting technology. In this analysis, the firstproblem is to characterize the composition ofgasoline. In this characterization, it must beremembered that the gasoline refining and blen-ding industry is highly competitive, with thereasoning for selection of various blends and ad-

Environmental Health Perspectives166

ditives bound up in science, secrecy, and intui-tion. The final composition is a function of thechemical composition of the crude oil startingmaterial, the design of process equipment, andthe economic value of the different crude frac-tionates. Other important variables are theclimatic conditions of the part of the country inwhich the gasoline is sold and the types ofchemical additives used. Given these manyvariables, it is not difficult to imagine a largenumber of different gasoline blends. Even so,gasoline composition and physical propertiesmust have definite ranges, since it mustsuccessfully function as a fuel for the internalcombustion engine. Remembering this, theproblem of characterization of gasoline composi-tion and an understanding of the use of ad-ditives is again manageable.A Task Force Report on Health Intelligence

for Fuel and Fuel Additive Registration (3)sponsored by the EPA began to' deal with theproblems of gasoline characterization andbiological test systems for evaluating the healtheffects of the exhaust emissions. In this exhaustemission characterization, both regulated andnonregulated emissions were considered equal-ly. In this report average compositions for 30commercial gasolines were given; these data arereproduced in Table 1. A flowsheet describinggasoline manufacture better explains how thedifferent fractions of gasoline are made in atypical refinery. This information is shown inFigure 1, and the gasoline composition is shownin Table 2. In Figure 1, FCCU stands for fluidiz-ed bed catalytic cracker unit, CRU meanscatalytic reformer' unit, and Udex is a li-quid-liquid extractor unit licensed by Univer-sal Oil Products. A catalytic cracker convertsthe large hydrocarbon molecules found in crudeoil to the smaller hydrocarbon molecules foundin gasoline. In operation, a fluidized bedcatalytic reactor forces the crude oil up througha bed of catalyst particles. The fluid motionagitates the catalyst particles creating a highdegree of turbulence and subsequent high ratesof mass transfer which converts the crude oilinto the C6-C8 gasoline hydrocarbons. This typeof reactor is preferred in this applicationbecause of high mass transfer rates and negligi-ble temperature gradients across the reactor.The catalytic reformer (CRU) cracks and

isomerizes straight-run gasolines and lightnaphthas to increase their octane number. Thisoctane upgrading is due to the production ofolefins, formation of low molecular weight com-pounds, and some isomerization. The Udexprocess is a liquid extraction with diethyleneglycol. This unit is used to separate aromaticssuch as toluene and benzene from the aliphatichydrocarbons and is an example of howpetroleum refiners can extract many valuableproducts from crude oil which can be used ingasoline blending and as starting materials forpetrochemical industries.

Function of Fuel Additives

A bewildering number of fuel additives isnecessary because of the variations in fuels, thevariation in engine designs, variations inseasonal temperatures in different regions ofthe country, and the economics of oil refineryoperations. If by the addition of small amountsof chemicals, it is possible to achieve high levelsof performance in the automotive engines, thenthe economic incentive for fuel additivesbecomes apparent. The use of fuel additives thusallows the oil refiner to divert large quantitiesof organic chemicals into other markets andthus increase the number of product optionsopen to him. Since most of these organicchemicals are major starting materials for otherchemicals industries, the use of fuel additives tofree.up basic chemicals for other markets is asound business practice.The variations in fuel composition and engine

designs makes the fuel additive business viablealso. For example, engines having lower com-pression ratios do not need deposit-modifyingadditives, and changes in olefin content of gas-oline requires different antioxidant compoundsfor these substances to be effective. The in-troduction of such a variety of compounds canpossibly lead to inhibition of function and someantagonism. Therefore, the trend will probablybe to develop multifunctional additives withmolecular structures capable of performing avariety of similar functions, such as moleculeswhich can function as antioxidants, corrosioninhibitors, and detergents, for example. Tables 3to 6 provide more information about gasolinecomposition. Table 3 lists key components in

August 1974 167

Table 1. Commercial gasoline properties.

Premium a Regular b Nonlead

Research octane 99.9-99.4 93.1-91.9 90.3

Motor octane 92.4-91.5 87.0-85.6 82.8

Reed vapor pressure 13.1-13.0 12.9-12.3 10.1

Olefins, % 4.4- 2.6 7.4-10.6 12.6

Aromatics, % 29.7-28.0 21.9-20.3 12.0

Saturates, % 65.9-69.4 70.7-69.1 75.4

Initial boiling point, °F 81-82 84-8g 94.0

Final boiling point, OF 410-398 420-390 368

Gravity (API) 60.5-59.9 60.7-63.0 67.5

aLiterature data (3).

bRange of several factors measured in 30 commercial fuel samples including premiums, regulars,and 91 octane low and nonleaded fuels.

C4 - C10 hydrocarbons - boiling point: 700F - 4000FNatural gas condensate C,g

butane, isobutane, C5's to gasoline ccl

Distillation OlefinicLight Straight Run Gasoline - RON: 40-70; 5-10%

0 1 Gases Cparaffins and cycloparaffins, C5-C7; B. P. <250°F

0 Lt. cyclw gas oil 20-50 DisFluid til Lt. rCCU -60%

30-40% CatCrude oil + Heavy cycle gas oil - Jet fuel Cracker B.P.< 250°FC5-C 35acid clayparaffins LDesulfur | No. 2 - No. 4 fuel catalystcyclo- oil, 'Diesel fuelparaffins and 1 Isome aromatics 10-20% Heavy FCCU4

II, 60% olef ins

Vac. II - butaneStill

F O Overall Mostly parFuel Oil Reformer CRU Lt. CRU - Regular ga

T CatalystDis HayCU--.Msl r> Residuum Asphalt til Heavy CRU Mostly ar

I oBottoms

Coker, Delayed Coker - Extract arUdex

Coke Raffinatec 1-c43 4Olef ins

I ~~~AlkylateIsobutane A branched paraffins

FIGURE 1. Gasoline manufacture.

'2 tohemicals

I-C 'I to4 3lkylation

olef ins

Premiumgasoline

romatics

paraffins

Environmental Health Perspectives168

Table 2. Refinery fractions used in gasoline.,

Gasoline Fraction

Premium 10-20% ButaneTypical 98-100 RONb

10-30% Light FCCU (olefins)

40-50% Overall reformate

10-20% Udex extract

10-40% Alkylate

+ 1000 ppm tetraethyllead

Regular 10-20% ButaneTypical 94-96 RONb

20-40% Heavy FCCU

10-20% Light straight run

0-10% Udex raffinate

20-40% Light CRU

30-50% Overall reformate

+400 ppm tetraethyllead

aLiterature data (3).bResearch octane number

gasoline and concentration ranges for tracemetal components. The concentration ranges ofthese trace elements have become an importantcomponent of the feasibility of catalyticmufflers. Tables 4 - 6 give information on thegeneral classes' of additives used in gasoline,their chemical groups, and their consumptionstatistics. The function of each additive type isgiven in the next section. The additive consump-tion statistics reveal that the major productionadditives for premium and regular gasolines aretetraethyllead (TEL) (72% by weight) and leadscavengers (20% by weight') such as ethylenedichloride and ethylene dibromide.

Function of Fuel Additives

Antiknock Action and Combustion inSpark-Ignited Engines: Knock is defined aspreignition of the fuel-air mixture during thecompression and ignition strokes of the internal

Table 3. Range of key components in gasoline. a

Element Concentration

Lead, g/gal

Chlorine, ppm

Bromine, ppm

Phosphorus, ppm

Sulfur, ppm

Carbon, wt-%

Hydrogen, wt-%

Trace elementsFe, wt-%Ca, wt-%Mg, wt-%Mn, wt-%

0.26-3.6

0.002-0.058

0.001-0.049

0.1-22.8

12.-1100

84.2-86.4

12.7-14.3

0.5-1.00.5-0.92-3

0.2-0.3

a Literature data (3).

combustion engine. In one theory of themechanism of knock, the compression of afuel-air mixture to 8-10 atm in fractions of asecond results mainly in the oxidation 'of thesaturated paraffinic portion of gasoline (ap-proximately 65-75% by weight) to peroxides,aldehydes, and alcohols, according to Downs etal. (4). If this group of parallel reactions isallowed to continue uninhibited,'the oxidationprocess will reach a rate at which ignition andheat release will occur spontaneously. The ex-plosive potential from peroxides has long beenrecognized by manufacturers and users of ether,since exposure of ether to air results in the for-mation of peroxides at an appreciable rate. Theresulting detonations 'of' this uncontrolledprocess, called knock occur before the pistonreaches the top of the compression stroke. Sincepreignition in the compression stroke does'notoccur at the maximum compression pressure,the knocking condition results in the inefficien-.cy of power derivation and instability in engineoperation Tetraethyllead (TEL) is added to com-pete for 02 in the fuel-air mixture during thecompression stroke. Since TEL oxidizes to PbOat a rate comparable to the rate of oxidation offuel paraffins, it can 'suppress the'amount ofperoxides, aldehydes, and alcohols formed'dur-ing the compression stroke. In this way, the-con-centrations of these paraffin oxidation products

August 1974 169

Table 4. Gasoline additives.

Additive Level, CommentPPM

AntiknocksTetraethylleadTetramethylleadMixtures lEquilibrated mixturesMethylcyclopentadienyl-manganese tricarbonyl

ScavengersEthylene dichlorideEthylene dibromide

DetergentsHTA (Esso)F-310 (Chevron)

LZ-580 (Mobile, Amoco)

DMA-4 (Shell)DMA-5A

Corrosion inhibitors

AntioxidantsDi-sec-butyl-p-phenylenediamineDi-tert-butyl cresol

1000 Best in paraffinic fuels; 106 lb/yrBest in aromatic fuels

Best in certain special blends

100-400 Best in aromatic fuels

100

>400 Mostly nitrogenousHydrogenated tallow aminesPrimary and secondary amines of

1400MW polybutene0 011 11

Ci5H31-N-C-CH2CH2-CI

Amine phosphateAmine phosphate (going out)

Mainly carboxylic acids

10-20

Deposit modifiersPhenyl dicresyl phosphate

Metal deactivatorsDisalicylpropanediamine

HydrocarbonsCarrier oilsPolymers

1000-5000100-300

do not reach the levels required for the rapidheat release process of preignition. Therefore,TEL allows the fuel-air mixture to be com-pressed to the volume at which optimal power isderived from the design of the engine.

In another theory of the mechanism of knock,Polss (5) suggest that uncontrolled combustiopin the ignition stroke is a multistage oxidationprocess and produces hydroperoxides in its firststages. The advancing flame front during com-bustion produces an increasing pressure andtemperature stress which causes hydroperox-

ides to decompose to free radicals. The freeradicals initiate chain-branching reactionswhich cause autoignition of the fuel-air mix-ture ahead of the flame front. The shock wavesfrom this process strike the cyclinder walls andresult in the knocking sound. TEL decomposesto lead oxides which scavenge free radicals fromhydroperoxide decomposition. The scavengersfor lead antiknock decomposition products areethylene dichloride and ethylene dibromide. Thereaction of these two compounds with lead ox-ides produces mixed lead halide particulates inthe exhaust emissions.

Environmental Health Perspectives170

Table 5. Additives used in premium grade automotive gasoline: 1969 consumption. a

Price, Use 1969Additive

$/blvl consumption, 106$$/lb level 101fbAntiknocks

TetraethylleadTetramethylleadMethylcyclopentadienyl-manganese tricarbonylc

Antioxidants2,4-Dimethyl-6-tert-butyl phenol2,6-Di-tert-butyl-4-methyl phenol2,6-Di-tert-butyl phenolN,N-Bis (1,4-dimethyl pentyl) p-phenylene-diamineN.n-Butyl-p-aminophenolN,N'-Diisopropyl-p-phenylenediamineN,N'-Di-sec-butyl-p-phenylenediamine

Corrcsion inhibitorsAlkyl and amine phosphatesAlkyldiamine naphthalene sulfonateFatty acid aminesFatty acid esters

Deposit modifiersCresyl diphenyl phosphateMethyl diphenyl phosphateMethyl phenyl phosphates, mixedTrimethyl phosphateTris(3-chloroisopropyl) thionophosphate'

DetergentsFatty acid amidesSurface-active alkyl ammonium dialkyl phosphates

Lead scavengersEthylene dibromideEthylene dichlorideCalcium sulfonate and dichlorotolueneCresyl diphenyl phosphate'

Metal deactivatorsN,N'-Disalicylidene-1,2-diaminopropaneN,N'-Disalicylal ethylenediamine c

Salicylal o-aminophenol

Rust inhibitorsAlkylamine salts of orthophosphoric acidsLinoleic acid derivativesAmmonium dinonylnaphthalene sulfonate CFatty acid amides c

Isononyl phenoxy tetraethoxy ethanol c

Isooctyl phenoxy tetraethoxy ethanol c

345.790 b0.35 2.34 cc/gal 285.1000.36 1.24 cc/gal 60.690

7.2420.59 7 lb/1000 bbl 1.6240.57 7 lb/1000 bbl 0.7380.37 6 lb/1000 bbl 2.9530.87 6 lb/1000 bbl 0.3160.66 6 lb/1000 bbl 0.1890.62 7 lb/1000 bbl 0.3680.97 5 lb/1000 bbl 1.054

10.958 b0.51 10 lb/1000 bbl 8.9660.20 50 ppm 0.6640.35 50 ppm 0.6640.25 50 ppm 0.664

6.328 b0.30 6 lb/1000 bbl 2.5310.33 6 lb/1000 bbl 1.8990.35 6 lb/1000 bbl 0.6330.55 6 lb/1000 bbl 1.265

4.904 b0.30 50 ppm 3.3220.41 2 lb/1000 bbl 1.582

96.897 b0.20 0.617 cc/gal 43.3150.09 0.653 cc/gal 53.582

1.40 1.5 lb/1000 bbl 1.580

5.273 b0.47 2 lb/1000 bbl 0.8430.15 7 lb/1000 bbl 4.430

Total 478.972 153.270a Literature data (3).b Subtotal.'Possible minor use.

August 1974

123.440 b101.29022.150

4.1180.9580.4201.0920.2740.1240.2281.022

5.102 b4.5720.1320.2320.166

2.301 b0.7590.6260.2210.695

1.644 b0.9960.648

13.485 b8.6634.822

2.120

1.060 b0.3960.664

171

Table 6. Additives used in regular grade automotive gasoline: 1969 consumption.

Price, Use 1969Additive $/blvl consumption, 106$$/lb level ~~~1061b.Antiknocks

TetraethylleadTetramethyllead

Antioxidants2,4-Dimethyl-6-tert-butyl phenol2,6-Di-tert-butyl-4-methyl phenol2,6-Di-tert-butyl phenolN,N'-Bis (1,4-dimethyl pentyl) p-phenylene-diamineN,n-Butyl-p-amino phenolN,N'-Diisopropyl-p-phenylenediamineN,N'-Di-sec-butyl-p-phenylenediamine

Corrosion inhibitorsAlkyl and amine phosphatesAlkyldiamine naphthalene sulfonateFatty acid aminesFatty acid esters

Deposit modifiersCresyl diphenyl phosphateMethyl diphenyl phosphateMethyl phenyl phosphates, mixedTrimethyl phosphateTris(f,-chloroisopropyl) thionophosphatec

DetergentsSurface-active alkyl ammonium dialkyl phosphateFatty acid amides

Lead scavengersEthylene dibromideEthylene dichlorideCalcium sulfonate and dichlorotoluenecCresyl diphenyl phosphatec

Metal deactivatorN,N'-Disalicylidene-1,2-diaminopropaneN,N'-Disalicylal ethylenediaminecSalicylalo-aminophenolc

Rust inhibitorsAlkyl amine salts of orthophosphoric acidsLinoleic acid derivativeAmmonium dinonyl naphthalene sulfonatecFatty acid amidescIsononyl phenoxy tetraethoxy ethanolcIsooctyl phenoxy tetraethoxy ethanolc

263.770b0.35 2.03 cc/gal 227.7500.36 0.8 cc/gal 36.028

6.686kb0.59 7 lb/1000 bbl 1.4990.57 7 lb/1000 bbl 0.6810.37 8 lb/1000 bbl 2.7260.87 6 lb/1000 bbl 0.2920.66 6 lb/1000 bbl 0.1750.62 7 lb/1000 bbl 0.3400.97 5 lb/1000 bbl 0.973

10.115b

0.51 10 lb/1000 bbl 8.2760.20 50 ppm 0.6130.35 50 ppm 0.6130.25 50 ppm 0.613

4.867 b0.30 5 lb/1000 bbl 1.9470.33 5 lb/1000 bbl 1.4600.35 5 lb/1000 bbl 0.4870.55 5 lb/1000 bbl 0.973

2.994b0.41 2 lb/1000 bbl 1.4600.30 25 ppm 1.534

73.863b

0.20 0.51 cc/gal 33.1140.09 0.538 cc/gal 40.749

1.40 2 lb/1000 bbl 1.946

0.47 2 lb/1000 bbl 0.7790.15 7 lb/1000 bbl 4.089

Total 369.109 119.392

"Literature data (3).bSubtotal.CPossible minor use.

Environmental Health Perspectives

94.060b,80.90013.160

38028b0.8840.3881.0080.2540.1150.2100.943

4.71lb

4.2200.1230.2150.153

1 .770b0.5840.4810.1700.535

1.057 b

0.5980.459

10.289b6.6223.667

2.724

0.3660.613

172

Detergents: Carburetor detergents are polarmolecules which adhere to the metal surfaces ofthe carburetor. This coating action preventsdeposition of materials which could build up onthese surfaces and thus change the dimensionsof the carburetor flow passages and ultimatelyplug the carburetor. Detergents are nitrogen-based compounds such as amines, amides,amine neutralized alkylphosphates, im-idazolines and succinimides. The molecules'polarity is a result of the nitrogen atoms. Thesurfactant qualities necessary for spreadingonto surfaces comes from the nature of theother components of the carburetor detergentmolecule.

Corrosion Inhibitors. Gasoline is transportedfrom the refinery to the distributors throughlong pipelines and storage tanks which are sub-ject to rust. Rust particles can plug fuel filters ifuncontrolled. Corrosion inhibitors which arefuel additives are high molecular weight sub-stances with at least one strong polar groupsuch as a carboxylic or phosphoric acid or theirneutralized derivatives. The polar group bindsto the metal surface and decreases the possibili-ty of water coming in contact with the metal.This eliminates the electrolyte necessary toeffect the electrochemical processes involved incorrosion. Diimides have also been shown to beeffective corrosion inhibitors for fuels. Again,the molecular requirements for effective corro-sion inhibitors are a polar group which binds tothe metal surfaces and coats them, and nonpolargroup which jutes out into the fuel.

Antioxidants: The ability of the olefinicportions of gasoline to oxidize and polymerize toform a decomposition product referred to asgum, obligates the need for antioxidant fuel ad-ditives. Phenylenediamines such as di-sec-butylp-phenylenediamine and hindered phenols suchas di-tert-butyl cresol are common antioxidantsfor gasoline. These compounds are also an-tioxidants for plastic and rubber products. An-tioxidants also scavenge peroxides formed dur-ing storage of gasoline and thus assist as an-tiknock compounds. The scavenging ability ofthese compounds originates from their functionof interrupting or terminating the oxidation andpolymerization reactions of the olefinic portion

of the gasoline. Generally the hindered phenolsare more effective antioxidants in lower olefincontent gasolines, and the phenylenediaminesare more effective antioxidants for higher olefincontent gasolines. However, phenylenediaminescatalyze the oxidation of mercaptans to dis-ulfides, the so-called fuel sweetening process.

Deposit Modifiers: High compression ratiosof 10:1 cause decomposed TEL and other resi-dues on cylinder walls to glow due to the hightemperatures of the compression stroke. Thisglowing phenomenon can cause surface ignitionto occur before normal spark ignition and thusresult in knock. Deposit modifiers such as cresyldiphenyl phosphate and methyl diphenyl phos-phate react with PbO and form lead phosphateswhich have higher glow temperatures. In effect,the volume of cylinder deposits is not reduced,but the thermal and electrical properties ofthese deposits are modified to reduce the fre-quency of surface ignition. Lower compressionengines do not require these additives since thecylinder wall temperatures do not reach theglow temperature of lead oxides.

Metal Deactivators: Because trace metalsin gasolines have the ability to catalyze decom-position of peroxides to free radicals and thuspromote decomposition of olefins, fuel additivescalled metal deactivators are necessary tochelate the metals and cause their deactivationas catalysts. The most widely used compoundfor this function is N,N'-disalicylidene-1,2propanediamine. An important question withthis particular additive is the nature of the ex-haust products of the chelated metal ions.Because of the 2000-2900°F temperaturesachieved during combustion, these chelatedmetals most probably are converted to oxides.What effect these substances will have on thecatalytic converter, and how they will react withother exhaust constituents, and what the finalexhaust products are, are unknown at this time.

Exhaust Emission Profiles

Federal regulations and changing enginedesigns have changed the exhaust emissionprofile substantially within the last six years.

August 1974 173

Minor engine modifications such as lower com-pression, leaner mixtures, spark retardation atidle, and limited use of air pumps have loweredhydrocarbon and carbon monoxide exhaust con-centrations of these atmospheric pollutantsto about 25% of what they were before the use ofthese devices. These facts are demonstrated byVoelz et al. (6) and are shown in Table 7.

Table 7. Average exhaust gas emissions for U.S.vehicles by age group.

Average exhaust emissions

2500 rpm IdleCity and

year group HC, ppm CO, % HC, ppm CO, %

Los AngelesPre-66 390 3.1 720 4.966-67 220 1.3 370 3.168-69 190 1.2 350 3.770 130 0.9 230 2.4

ChicagoPre-66 410 2.9 690 4.466-67 330 2.4 590 4.468-69 220 1.2 350 3.570 120 0.9 250 2.6

'These data are vehicles tested at the condition specifiedin the cities shown. Data of Voelz et al. (6).

These modifications, however, have had littleeffect on reducing nitrogen oxide emissions. It isthe nitrogen oxides which are involved with theformation of nitrogen dioxide (NO2). This com-pound then reacts with peroxyacyl free radicalsto form the eye irritant and plant damagingmaterial called peroxyacyl nitrate (PAN).There are two primary photochemical reac-

tions occurring in the lower atmosphere.Nitrogen dioxide decomposes photochemicallyto form nitric oxide and nascent oxygen. Theother primary photochemical reactions oc-curring in the lower atmosphere are thedegradation of aldehydes and ketones to formfree radicals. Once these two major reactionsare initiated, a large number of secondary reac-tions can occur which produce the major com-ponents of smog, eye irritants, and plantdamaging materials. A summary of these im-portant reactions (7) are given in eqs. (1)-(20).

Primary Photochemical Reactions:NO2+hu -,NO+ ORCHO + hv -R- + HOC-R-C-R' + hv -, R- + R'C-

II0

I,0

(1)(2)(3)

Secondary Chemical Reactions:O + O2 +Ml 03 + M (4)NO + 03- NO2 + 02 (5)NO2 +O NO+ O2 (6)R- + 02- ROO- (7)ROO- + N02- ROONO2 * peroxyalkyl nitrate (PAN) (8)ROO- + 03- RO- + 03 (9)ROO + SO-. ROOSO2 (10)

ROO- + Nd' RO- + NO2 (11)RC + O2. RCOOO- (12)

110

RCOOO- + NO2- RCOOONO2I PAN

RCOOO- + NO -- RCOOONO03 + RCH = CHR'-. RCHO + RO- + HC-

1103 + H2C =CH-CH = CH2 _4

(13a)

(13b)(14)

CH2=CHCHO + HCHO (15)CH3-CH = CH2 + NO2-CH-CH2NO2

Nitropropyl radical (plant damaging) (16)RO- + N02- RONO2 (17)RO- + NO - RONO (18)RONO + hu - RO- + NO (19)RONO + hv-R- + NO2 (20)

The types of hydrocarbons, oxygenatedhydrocarbons, and polynuclear or polycyclichydrocarbon particulates and their concentra-tion ranges in the exhaust from simplehydrocarbon fuels are shown in Tables 8-11. Itis not possible to determine the fractions ofthese substances contributed by the combustionof fuel additives since the product distributionof such a large number of simultaneous paralleland series reactions is unknown. Tables 8 and 9have been given by the EPA (3). In Table 8, it isinteresting to note that hydrocarbon (HC) andcarbon monoxide emissions for a hot startengine are about one-half of the concentrationsfor a cold start. Nitrogen oxides concentrationsare essentially unaffected by whether or not theengine is warm or cold.The analysis of exhaust emissions for

polycyclic hydrocarbon particulates for Euro-pean road tests with a VW 1300 is given in Table10. The chemical structures of these polynucleararomatics are given in Table 11.

Environmental Health Perspectives174

Table 8. Emission profiles; current systems, '71 Ford, LA-4 cycle.

Emissions, g/mile

Cold start Hot start

HCcbNOX

ParaffinOlefinAromatic

Dilution RatioExhaust Vol CF/Mile

MethaneEthaneAcetylene

ParaffinsIsobutanen-ButaneIsopentanen-PentaneHexanesHeptanes

Total

OlefinsEthylenePropyleneButenes2-Methyl-1-butene3-Methyl-1-buteneOthers

Total

AromaticsBenzeneTolueneEthylbenzeneo, p-Xylenem-XyleneMesitylene1,2,4-TrimethylbenzeneOthers

Total

The profile is given by Grimmer et al. (8) andshows the main components, their averageamounts in exhaust, their weight per cent in theexhaust, and their carcinogenic activity (Table10). Carcinogenic activity is defined as follows:a negative sign (-), inactive; plus sign (+) mild

carcinogen; three plus signs (+ + +), a strongcarcinogen. It is worthy of note, that 5.04 wt-%

of exhaust polycyclic aromatic hydrocarbon par-ticulates are carcinogens, and that the bulk ofthe particulates (87.14 wt-%) is composed ofphenanthrene, anthracene, pyrene,.and fluoran-thene. This type of distribution which favors thelower molecular weight polycyclic hydrocarbonsis quite possibly a function of the residence timeof combusted gasoline in the cylinder head and

August 1974

2.3239.304.02

± 0.065± 1.910± 0.41

1.81 ± 0.07815.60 + 2.2304.06 +±0.13

1.13 ± 0.0491.07 ± 0.0580.15 ±

10.11 ± 0.1592.87 ± 1.65

0.169 ± 0.0050.031 ± 0.0010.208 ± 0.004

0.90 ± 0.050.84 ± 0.0360.10 + 0.009

11.23 + 0.1482.27 ± 0.47

0.091 + 0.0100.021 + 0.0050.158 + 0.011

0.0040.045 ± 0.0060.051 ± 0.0050.0080.111 ± 0.0170.120

0.342 ± 0.087

0.0050.077 ± 0.0160.085 ± 0.0130.019 ± 0.0010.108 ± 0.0020.118

0.432 ± 0.083

0.212 ± 0.0020.117 ± 0.0060.026 ±0.011 ± 0.0020.0030.146 ± 0.039

0.572 ± 0.050

0.142 ± 0.0240.142 ± 0.0200.031 ± 0.0010.050 ± 0.0020.047 ± 0.0030.005 ±0.035 ± 0.0020.040 ± 0.002

0.504 ± 0.045

0.272 ± 0.0060.139 ± 0.0050.077 ± 0.0020.012 ± 0.0010.007 ± 0.0010.164 0.009

0.670 + 0.022

0.188 ± 0.0080.201 + 0.0070.046 + 0.0010.078 + 0.0050.070 + 0.0040.011 ± 0.0010.054 ± 0.0040.061 ± 0.003

0.724 + 0.023

175

Table 9. Oxygenates in exhaust from simple hydrocarbon fuels.

Oxygenate

AcetaldehydePropionaldehyde (+ acetone) bAcroleinCrotonaldehyde (+ toluene)CTiglaldehyde CH3CH = C(CH3)CHOBenzaldehydeTolualdehydeEthylbenzaldehydeo-Hydroxybenzaldehyde (+ Cio aromatic)dAcetone (+ propionaldehyde)bMethyl ethyl keton'eMethyl vinyl ketone (+ benzene)eMethyl propyl (or isopropyl) ketone3-Methyl-3-buten-2-one4-Methyl-3-penten-2-oneAcetophenoneMethanolEthano'lC5 alcohol (+ Cs aromatic)f2-Buten-1-ol (+ CsHsO)Benzyl alcoholPhenol + cresol(s)2,2,4,4-TetramethyltetrahydrofuranBenzofuranMethyl phenyl etherMethyl formnateNitromethaneC4HsOCsH6OC5HioO

Concentration range, ppma

0.8- 4.92.3-14.00.2- 5.30.1- 7.0

<0.1- 0.7<0.1-13.5<0.1- 2.6<0.1- 0.2<0.1- 3.52.3-14.0

<0.1- 1.00.1-42.6

<0.1- 0.8<0.1- 0.8<0.1- 1.5,<0.1- 0.40.1- 0.6

<0.1- 0.6<0.1- 1.1<0.1- 3.6<0.1- 0.6<0.1- 6.7<0.1- 6.4<0.1- 2.8

<0.1<0.1- 0.7<0.1- 5.0

<0.1<0.1- 0.2<0.1- 0.3

'Values represent concentration levels in exhaust from all test fuels.bData represent unresolved mixture of propionaldehyde + acetone. Chromatographic peak shape suggests acetone to be thepredominant corhponent.cToluene is the predominant component.

dThe Cio aromatic'hydrocarbon is the predominant component.

'Benzene is the.predominant component.f The aromatic hydrocarbon is the predominant component.

the exhaust manifold, and the rate constants as-sociated with the formation of this group ofpolycyclic compounds (9).

Gross (10) has examined the influence of fueland vehicle 'variables- on the formation ofpolycyclic hydrocarbons'in the exhaust gases.This comprehensive study measures benzo(a,-pyrene (BaP) and benz(a)anthracene (BaA) as afunction of fuel composition, engine deposits,and engine designs'which'includes studies withuncontrolled emission engines, modifiedengines, engines with thermal converters on the

exhaust, and engines with monel-platinumcatalytic converters on the exhaust. The resultsof this study are particularly good in clarifyingthe quantitative changes in the amounts of ben-zo(a)pyrene and benz(a)anthracene which areproduced during automotive operation as afunction of these many variables. Therefore,these 'results will be presented' in' detail. Table 12gives the key for each engine-exhaust systemdesign; Table' 13 defines the fuel and theresulting engine deposits; Tables 14 and 15 showhow'these variables affect the amounts of BaP

Environmental Health Perspectives176

and BaA in the exhaust. Figure 2 compares theemission output for each engine design with afuel containing 46 wt-% aromatics.Tables 14 and 15 show for the uncontrolled ex-

haust system of the 1966 Plymouth (P) thatamounts of dibenzo(a)pyrene and

Table 10. Polycyclic hydrocarbon profile in exhaustemissions from European road tests withVW 1300 a.

Emissions

Compound Total, gg Weight per cent

Phenanthrene

Anthracene

Pyrene

Fluoranthene

Benzo-(a)anthracene

Chrysene

Benzo(e)pyrene

Benzo(a)pyrene

AnthanthreneBenzo(ghi)-

peryleneDibenz(a,h)-anthracene

Coronene

2595.0

964.0

1168.4

822.1

102.6

67.8

54.1

83.8

42.7

253.2

64.9

146.1

40.74

15.15

18.33

12.92

1.63

1.07

0.86

1.32

0.68

3.98

1.02

2.30

aData of Grimmer et al. (8).

Table 1. Structure of polycyclic hydrocarbons.O8 X Al~~~~Carcinogenicactivity

Table 12. Emission test vehicles.

Emission-controlCode Model, year system

P 1966 Plymouth, No emission control318, V-8 (NC)

Q 1968 Chevrolet, Engine-modification307, V-8 (EM)

R 1970 Chevrolet, EM with spark retard350, V-8 (TCS System)

Q-RAM 1968 Chevrolet, Experimental air-injected307, V-8 RAM thermal reactor

R-CAT 1970 Chevrolet, Experimental monel cat-350, V-8 alyst + platinum cata-

lyst (Engelhard PTX-5)

_ 300,

+

- 200 I

100

m - benzo(a)pyrene

- benz(a)anthracene

* * l,,,1 RAM CAT

1966 1968 1970 EXPERIMENTALNC EM EM

FIGURE 2. Hydrocarbon emissions with various engines.Test. fuel, 46% aromatic, 3 ppm BaP; 3 g Pb/gal except inCAT design, in which 0 g Pb/gal used.

Anthracene Pyrene Flu

Chrysene Benzo (e)pyrene

0000

0

benz(a)anthracene increased as the weight perioranthene cent of aromatics in the fuel increased. Table 15

shows that for the uncontrolled exhaust system(P), the nature of the deposits on the cylinder

Y-?-b?-~ wall influehces the quantity of BaP- and BaAproduced. Apparently, leaded gasoline depositsgive more of these compounds, than. do the

Benzo(a)pyrene deposits,from unleaded gasoline. Table 14 showsalso that for car P, the BaP content of the ex-

,[ haust is essentially not a function of iead con-$A?~J~~J tent of t4e fuel, wher'eas the BaA content in-

creases slightly ,with lead content of the fuel.Coronene The two modified engines (EM), cars Q and R

essentially reduce BaP and BaA emissions by

August 1974

Phenanthrene

Benzo(a)anthracene

Anthanthrene Benzo(ghi)perylene Dibenz(a,h)-anthracene

k. kvAlvlj Llk

CC

I

177

Table 13. Fuel composition-Engine Deposit Relationship.

Code Deposit Fuel - deposit

A A Commercial lead-free premium used fromthe beginning of tests

A.5 A Commercial lead-free premium, + 0.5 gPb/gal

B3P B Commercial leaded (2-3 g TEL/gal) pre-mium with phosphorus additive

one fourth of the quantities shown for car Pfor all variations in fuel composition. Figure 2shows how all five engine designs compare onBaP and BaA emissions for test fuels containing46% aromatics and 3 ppm BaP. Engines P, Q, R,and Q-RAM were tested with fuel containing 3 gTEL/gal, and R-CAT with 0 g TEL/gal since thePb would poison the catalytic surface of the con-verter.

If it is assumed that a higher percentage ofaromatics is used as an alternative for leadedverters, it is possible to estimate the potentiallevels of benzo(a)pyrene and benz(a)anthracenereleased in the air. If gasoline consumption isassumed to be approximately 10ll gal/yr andtwice the present amounts of BaP and BaA ap-proximates the togal concentration of car-cinogenic material produced in exhaustemissions, then the concentration range of car-cinogenic material in the atmosphere couldrange from 1000 lb/yr for the catalytic exhaustsystem to about 200,000 lb/yr for the uncon-trolled exhaust system. Since these compoundsare resistant to degradation by environmentalprocesses, they will persist, their concentrationwill increase, and they will be widely distribu-ted.

Catalytic Converters and Thermal ConverterEmission Control Devices

Reduction-oxidation catalytic converters andthe thermal noncatalytic converter-lead trapsystem have been offered as solutions to the ex-haust emission control problem. The operatingprinciples of both designs are to reduce nitrogenoxides to N2 and 02, and to oxidize CO to C02 andhydrocarb6ns and polycyclic aromatics to C02and H20. The noncatalytic converter-lead trap

design offers the additional feature of lead par-ticulate trapping and can be used with presentlyavailable fuels. Leaded gasoline cannot be usedwith the catalytic mufflers. Of the two designs,it appears that the catalytic converter will beadopted as an interim solution to meet the 1976exhaust emission standards. For this reason, thethermal noncatalytic-lead trap system will notbe discussed. The design does have merit and inlieu of the present gasoline shortages, moreattention to the exhaust emission characteriza-tion from the device should be considered sinceexhaust lead particulates would be reduced by80% (11, 12) and the use of TEL in gasolinewould free up valuable aromatic feedstocks.The design of this catalytic system has a

reducing catalytic muffler on each exhaustmanifold pipe followed by one oxidationcatalytic muffler on the exhaust pipe precedingthe muffler. The feasibility of constructing sucha multipurpose catalytic converter to operateeffectively for extended periods of time and un-der such a wide variety of operating conditionsto which it will be subjected is questionable.Besides the obvious factors which will cause thecatalyst to break apart such as thermal shockfrom a hot exhaust on a cold catalyst at enginestartup, and mechanical breakup caused byoperation, other sources which can shortencatalyst life are the trace metals (10-20 ppmrange) which end up in gasoline as fractionationresidues. It is understood that lead must beremoved from gasoline for these devices toachieve their 50,000 mile life expectancy. Withleaded gasoline, the catalytic surface becomespoisoned after approximately 12,000 miles andthen the situation is one of the uncontrolled ex-haust. Other questions associated with thisdevice are increases in engine operatingtemperatures caused by increased back pressureof exhaust gas passage -through the catalyticmuffler with associated problems of lubricantdegradation and engine malfunction. Such asituation would result from using richer mix-tures which would produce better gas mileage,but may conceivably shorten engine life sub-stantially.

Presently, it appears that a Pt/Pd catalystwill be used in these mufflers. At one time al-most all of the transition metals were triedin this application since it had been shown that

Environmental Health Perspectives178

Table 14. BaP and BaA emissions as a function of engine design, aromatic content of fuel, and tel lead content of fuel.

Emissions, Ag/gal.BaP BaA

Aromatics 0 0.5 g 3.0 g 0 0.5 g 3.0 gVehicle in fuel, wt-% Pb Pb/gal Pb/gal Pb Pb/gal Pb/gal

P 11 56 - 56 126 - 15528 78 63 59 130 86 15728 36 18 29 49 30 4646 125 - 127 196 - 258

Q 28 11 8.9 36 28 20 7528 14 3.5 3.4 15 13 1546 30 - 32 55 - 63

R 28 48 36 26 70 61 5146 26 - 17 60 - 52

Table 15. Effect of deposit fuel composition on polycyclic hydrocarbon emissions.

BaP, Ag/gal BaA Mg/galTest Aromatics, Deposit Deposit Deposit Deposit

Vehicle wt-% A B A B

P 46 57 125 94 19628 39 78 51 13046 54 127 124 25828 36 78 49 13028 18 63 30 8628 29 59 46 157

Q 46 12 30 23 *5528 15 11 17 2828 14 11 15 2828 3.5 8.9 13 2028 3.4 36 15 75

NO was readily adsorbed onto these materials,a necessary step in the catalytic decompo-sition of NO to N2 and 02. Thermodynamic-ally, the equilibrium constant for the decom-position of NO is more favorable at lower tem-peratures (KNO = 3.236 x 102 at 1500°K;KNO = 1.208 x 104 at 1000°K; and KNO =1.413 x 1011 at 400°K). The reduction of NOproduces 02 which is then used to oxidizeCO and hydrocarbons, but the thermodynamicswould favor the reduction catalyst after theoxidation catalyst due to the lower tempera-tures and subsequent faster reaction rate ofNO decomposition. The proponents of the

thermal noncatalytic converter argue that thecatalytic converters are impractical and ex-pensive. The two main supporters of the ther-mal converters which could be used witheither leaded or unleaded gasoline are du Pontand Ethyl Corporation. Ethyl Corporation isthe main producer of TEL in the UnitedStates. The operating principle of the thermalconverter is to convert unburned hydrocarbonsand CO to C02 and H20, decompose NO toN2 and 02 and trap lead particulates. Theoperating temperatures range from 1200°K(du Pont design, KNO = 2 x 103) to 1500°K(Ethyl design, KNO = 3.24 x 102.

August 1974 179

It is the author's opinion that the catalyticemission control device is an example of a solu-tion for a problem after the fact. The mainquestions of how the design of the internal com-bustion engine and the composition of the fuelcan be changed to reduce levels of exhaustemissions which contribute to smog formationand associated health problems, are unad-dressed. It is realized, however, that suchsolutions require time to invent and implement,and require substantial monetary research com-mitments. Even so, the catalytic emission con-trol device is being sold as the method to meetthe standards of the Clean Air Act of 1970, eventhough it may be of questionable functioningability. The muffler has been shown by Campi-on (13) to catalyse the oxidation of sulfur occur-ring in gasoline as a residue, to S03 so thathigher concentrations of S03 are produced byuse of catalytic mufflers than without catalyticmufflers. In the atmosphere S03 is hydrolyzedto sulfuric acid mist which can be adsorbed ontoparticulates or fallout as acid rainfall.

The design of the catalytic muffler un-doubtedly will be improved to the point that theClean Air Act Standards or regulated exhaustemission levels for hydrocarbons, CO, andnitrogen oxides will be met. It is the nature andquantity of the unregulated emissions whichcause the most concern. The number of booksand journal articles dealing with the catalyticnature of platinum are extensive, because itschemical characteristics facilitate such a widevariety of gas-phase reactions. The ability of theplatinum catalyst to oxidize sulfur to S03 raisesthe real questions of what other reactions arepossible on this surface at exhaust gastemperatures and pressures. Then, what is thebreakup rate of these catalysts with theassociated questions concerning the discharge ofunregulated emissions into the environment ofplatinum metal, platinum compounds and com-plexes, and the refractory catalyst supportmatrix? If indeed the catalyst is breaking up at asignificant rate, how much of the catalyst can belost out the exhaust pipe before the catalystbecomes ineffective in reducing the regulatedemissions to the prescribed levels? In otherwords, how much catalyst can be lost before thesituation of the uncontrolled exhaust is reached?

Economics of a Ban on Leaded Gasoline

The economic impacts of the removal of leadfrom gasoline are significant and complex.These effects are significant because the totalsales of the major supplier of TEL would be cutin half and because the use of TEL frees up alarge quantity of aromatic feedstocks which arediverted into the petrochemical industry. Theban on lead in gasoline will not only affectseveral obvious interest groups, e.g., automobilemanufacturers, oil refiners, lead additiveproducers, and lead producers, but also otherchemical processors in a less well knownmanner.One very probable alternative to leaded gas-

oline if it is available, is the use of a higherpercentage by weight of aromatics. Chopey (14)has noted some of the economic implications ofsuch a switch to higher percentages of aromaticsin gasoline. The operations of the oil refiners,additive makers, automobile manufacturers,and lead producers are highly connected. Sinceall four deal with large volume products, largeamounts of capital and equipment are com-mitted by each industry. A change in theproducts of one industry, therefore, has a veryprofound effect on the products of the otherthree industries. In connection with these facts,it must be remembered that once a particularplant design has been decided on by industry, atimetable has been fixed which shows how muchtime is required for plant construction, and howlong the plant must operate at its rated capacityto pay for the investment and to realize a profit.Part of this profit is applied to the constructionof new plant facilities to perpetuate theoperations of the industry. The point here isthat a significant lead time is required to imple-ment a product change and that a change cannotbe affected immediately.

In leaded gasoline, the primary aromatics us-ed, benzene, toluene, and the xylenes, alreadyamount to approximately 20-30% by weight. Inunleaded gasolines, the weight percentage ofthese aromatics could be as high as 46% inpremium fuels. Even for engines designed torun on 91-92 Research Octane Number (RON)gasolines, the weight percentage of aromaticsmust be increased 5-10% above regular gaso-

Environmental Health Perspectives180

line compositions if this is the method chosento replace the octane boosting antiknock proper-ties of TEL. For the sake of illustration, as-suming that all gasolines will contain about 46%aromatics by weight, such a tremendous in-crease in demand by gasoline manufacturers forthese basic chemical feedstocks would have ec-onomic impacts on several obvious markets andseveral unexpected markets. Current con-sumption of gasoline according to EPA figuresamounts to approximately 1011 gal/yr. An in-crease of 10-20% by weight of aromatics in gas-oline would produce a demand for 10-20 billiongal/yr more of these chemicals. Several changeswould be in the product distribution of oil re-fineries because the major portion of these aro-matic chemicals are produced from the distillatestreams of crude oil refining. Already a majorportion of these aromatic feedstocks are beingdiverted into low-sulfur fuels for power genera-tion plants due to the S02 regulations of theClean Air Act. It is the increased demand foraromatics which would produce unexpectedeconomic results. For example, xylenes are ma-jor starting petrochemicals for phthalicanhydride and terephthalic acid which are usedrespectively to make PAE plasticizers and

polyester fibers (Dacron, Kodel, and Fortrel).Therefore, the increased demand for xylenewould eventually surface as an increase in theprice of flexible PVC plastics and polyester tex-tile products. Benzene is widely used in theproduction of styrene monomer for makingpolystyrene products, and for making phenols.Toluene is a valuable solvent and startingmaterial for the making of intermediates suchas nitrotoluene and toluenediamine. The pointhere is that there is a complex relationshipbetween economics, plant operations, products,legislation, and health, and that an action in oneof these areas does not occur independently asan isolated event.

The lead industry has been searching foralternative uses for the lead metal which wouldbe available for other uses if it is legally bannedfor the production of the octane boosting an-tiknock TEL (15). Research sponsored by theInternational Lead Zinc Research Organization,Inc. (ILZRO) is underway to divert this lead intonew organolead compounds, new or increaseduses of inorganic lead compounds, and newapplications of lead metal. The flowsheet inFigure 3 shows the present uses of lead in-

Worldwide Lead Production: 2.2 billion 1l

Tetraethyl lead Ionizing Radiation0.52 billion lbs/yr ShieWds

+-- - Use of Lead MetalJ - t ARCHITECTURAL APPL.UeoLedMetal- 1 - - - - -(Projected Uses as a Result Wall Panalsof Ban on Leaded Gasoline) Roofing

Construction Member

Storage* Battery

1.2 billion lb/yr

BIOCIDES AND MARINEPAINTS

(K6 )3-PbOCCH3(C4H9)3PbOCOH3

II

0

(C4H9)2Pb(OCCH3)2

0

LUBRICANTS CATALYST FOR MONOMER INPOLYURETHANE POLYMERIZATIOV

(CH)Pb FORM OF RIGID

4l 93 _Pb MC PLASTICS

_0

FIGURE 3. Lead production and distribution.

August 1974

Pigments(Minor Use)

181

dicated by solid lines, and projected uses forlead indicated by the broken lines.

Organolead derivatives have been tested fortheir use as biocides, lubricant additives,urethane polymerization catalysts andmonomers for polymerization. Inorganic leadderivatives continue to be used in paintpigments and lead acid storage batteries. Sincelead use in the storage battery accounts forabout half the production of lead, research is un-derway to use oxygen from the air as thecathode reactant. This design change would im-prove the operating range of the battery so thatit could compete more favorably with newer,more expensive, higher-energy densitybatteries. New markets for lead pigments wouldbe in paints for corrosion resistance for steel.Expanded use of lead metal in architecturalapplications has also been studied, particularlythe increased use of lead roofing shingles, wallpanels, and exterior building members.

Health Effects of the Alternatives for TELSubstitutes for TEL

The use of higher percentages of aromatics inthe gasoline to achieve the same octaneboosting, antiknock properties that TELsupplies apd the associated health problemswith the use of this alternative to TEL havebeen discussed previously. The incentive todevelop substitutes for TEL is high because ofthe market potential of the product. Metal car-bonyl compounds such as iron pentacarbonyland manganese carbonyl, and aromatic aminessuch as ethylaniline have been proposed as sub-stitutes for TEL (16). Iron pentacarbonyl hasbeen rejected because its combustion product,ferric oxide resulted in extensive engine wear.Manganese carbonyl was too expensive.Ethylaniline was rejected because it was 55times less efficient than TEL at providing an-tiknock characteristics to gasoline.

Efficacy of Manganese Antiknock Substitudefor TELA particular manganese antiknock additive,

methylcyclopentadienylmanganese tricarbonyl(MCMT) [CH3C5H4Mn (CO)3], has been singledout for detailed consideration because the majorproducer of TEL, Ethyl Corporation, has shown

that this additive at a concentration of 0.25 gMn/gal has the same octane boosting and an-tiknock characteristics as TEL (17). In currentleaded gasoline blends, TEL is present in theamount of 1.5 to 2.0 g/gal. Using U.S. TariffCommission unit price information for organicchemicals produced in 1970, TEL sold for$0.58/lb. At the present gasoline use level ofTEL, this cost adds about 0.2¢ to the price of agallon of gasoline. It is estimated that MCMTused at the rate of 0.25 g Mn/gal would addbetween 2.5 and 4¢ to the price of a gallon of gas-oline. Since the unleaded gasolines which use ahigher percentage of aromatics to obtain higheroctane ratings cost 2-4¢/gal more than leadedgasolines, the use of MCMT would beeconomically competitive with the higherpercentage aromatic no-lead gasolines. The ef-ficacy of MCMT was further substantiated by areport from HEW (18) in 1962 which cited thisparticular additive as being twice as effective inraising the octane number as TEL.MCMT is not a new compound. It is current-

ly being produced at the level of a 106 lb/yr. In1959, Ethyl Corporation announced higher oc-tanes could be obtained with this manganeseadditive in combination with TEL (19). MCMThas a synergistic effect with TEL on improvingantiknock properties of gasoline. The additivepromotes and extends the effect of TEL inraising octane number and preventing engineknock. Although the mechanism of action ofantiknock compounds is not completely known,it has been postulated by Girelli and Orlandi(20) that the manganese additive in thepresence of TEL decomposes to MnO at a fas-ter rate than TEL decomposes to PbO. It is thepresence of MnO which precedes the formationof PbO that breaks the chain of reactions ofgasoline combustion which in the presence ofTEL alone would continue unabated untilknocking occurred before the appearance ofPbO.

Preparation of Methylcyclopentadienlyman-ganese Tricarbonyl and Combustion Productsin the Exhaust

MCMT is one of the so-called "sandwich" com-pounds and is structurally similar to ferrocene,in that the methylcyclopentadiene ligand is ir-

Environmental Health Perspectives182

bonded to manganese. The methylcyclopen-tadienylmanganese tricarbonyl is furtherclassified as a penetration complex because dis-

similar ligands are bonded to the manganeseatom. MCMT has been synthesized by severalmethods. [eqs. (21) and (22)].

[Mn (CO)5]2 + excess [CH J I

100 parts 800 parts

Tetrahydrofuran

100 - 300 CCHT37

Mn

II III III0 0 0

Mg Cl2 + CH3C5H5 + Fe (CO)5 + N, N-dimethylformamide

CH 7

MnC C CIII III III0 0 0

Reaction (22) is run with the use of a Mn elec-trode, pressured to 1000 psi with C02; 25-30Vand current density of 0.1 A/cm2 at 195°C for 3hr.

Scavengers, such as ethylene dichloride andethylene dibromide, in the gasoline probablywould not be used with this Mn additive so thatthere could be some MnO, or other oxides ofmanganese such as MnO2, Mn2O3 and Mn2O4 inthe exhaust emissions of uncontrolled vehicles.These compounds would be particulate innature. Other possible gaseous exhaustemissions would be carbon monoxide (CO),methylcyclopentadienone (CH3C5H3O), andcyclopentadienecarboxaldehyde (CsH4CHO).There is also a possibility that methylcyclopen-tadiene could participate in the formation ofpolycyclic aromatic exhaust particulates.

Atmospheric Reactions of Exhaust Productsfrom Mn Additive

Methylcyclopentadienylmanganese tricar-bonyl has been used as an additive to fuel oil tosuppress the formation of S02 and N02 in theflue gases (16). Manganese dioxide, MnO2, form-

ed during combustion, readily reacts with S02and N02 to form soluble sulfates, dithionates,and nitrates, (21) by the reactions (23)-(25):

MnO2+ SO2 OMnSO4

2MnO2 + 382 MnS2O6 + MnSO4

MnO2 + 2N02 Mn(N03)2

(23)

(24)

(25)

Manganese sulfate, however, will catalyze theformation of sulfur trioxide from sulfur dioxide.Sulfur trioxide then reacts with water vapor toform sulfuric acid [eq. (26)].

MnSO4 2H202S°2+ °22S02 2 - 2S03 2H2S04 (26)

This reaction proceeds very rapidly in foggy at-mospheric conditions. It has been shown (21)that in a fog, on assuming a water vapor contentof 200,000 ,ug/m3, a Mn concentration of 0.2,ug/m3 and a S02 concentration of 1,750 Ag/m3

August 1974

(21)

(22)

183

produces about 25 ug/m3 of H2SO4 per hour. Therate of formation of H2SO4 triples when the Mnconcentration doubles, and increases linearlywith an increase in S02 concentration. It is alsosignificant that whereas other materials such asplatinum, graphite' charcoal, vanadium pen-toxide, chromic oxide, ferric oxide, and nitrogendioxide will catalyze the oxidation of S02 to S03,MnSO4 is the most active. EPA air quality datafor 1968 (22) indicate that the cities of Bir-mingham, Alabama; Covington, Kentucky;Detroit, Michigan; Cincinnati and Youngstown,Ohio; Allentown. Bethlehem, Philadelphia, andReading, Pennsylvania; Chatanooga, Knoxville,and Memphis, Tennessee; and Charleston, WestVirginia 'already have the 0.2,ug/m3 concentra-tion of Mn in the air.

Toxicity of MethylcyclopentadienylmanganeseTricarbonyl and CyclopentadienylmanganeseTricarbonyl

Both of these manganese compounds havebeen used as antiknocks, and both belong to theso-called "sandwich" compounds and are gtruc-turally similar to ferrocene. The toxicity ofcyclopentadienylmanganese tricarbonyl (CMT)has been studied extensively in Russia byArkhipova et al. (23-25) because CMT wassuggested as a replacement for TEL. Inhalationstudies with CMT on rats showed that vaporconcentrations of tenths of a milligram per literin air were lethal with a' one-time exposure.Acute inhalation studies with rats using concen-trations of 120 mg CMT/m3 showed vascularchanges such as increased permeability ofvessels, edema and hemorrhages and fallingblood pressure. Other manifestations of acutepoisoning from inhalation of CMT were atrophicchanges in the nerve cells, lowering of osmoticpressure of erthrocytes, and hypoxia, an effectcaused by molecules of CMT as a whole. Chronicinhalation exposure of rats to CMT at averageconcentrations of 1 mg/i3 produced poisoningcaused by accumulation of the substance in theorganism. Toxicity to the test animals wascharacterized by renal and nervous systemdamage, and by decreased resistance to infec-tion. It was concluded that the chronic toxicityof CMT was polytropic and was related to themetabolic decomposition of this compound to

give small quantities of carbon monoxide, andinorganic forms of manganese. The oral LD5otoxicity for CMT was 80 mg/kg body weight inwhite rats, and 3.2 mg/kg body weight in mice(24). The structrually similar compoundmethylcyclopentadienyl manganese tricarbonylhad an oral LD5o toxicity of 56 mg/kg bodyweight in mice (26).

Chronic exposure to this compound would bean occupation health problem to people involvedin manufacturing the additive and to gasolineattendants who would be involved in gasolinedistribution. It could become a health problemto the general public, however, because of the in-crease in popularity of self-service gasolinestations.

Toxicity of Exhaust Products of ManganeseAdditive

Exposure to high levels of manganese oxidedusts by manganese ore miners in Chile, Brazil,Morocco, and South Africa, manganese steelworkers in Pennsylvania, and manganeseworkers in dry battery plants in Egypt andGreat Britain have shown a high incidence of aneurological disorder similar to Parkinsonism,and a respiratory disease similar to acute lobarpenumonia (27 - 37). In both these diseases,manganese oxide dust particles in-the air of ex-posed workers, ranged between 5 mg/m3 and 60mg/m3. In many instances, the particle size ofmore than 50% of the manganese oxides was lessthan 1,u.

Both manganeae poisoning and manganicpneumonitis represent diseases which resultfrom excess manganese intake primarily via in-halation and ingestion (27). Manganese,however, is an essential nutritional element inman's diet and has a vital biochemical functionas a cofactor in many enzyme systems (38). Theconcentration of manganese in body tissues issteady, and fairly characteristic of each organ.Manganese levels in grains are substantial sinceit is a vital component of plant -growth. Inplants, manganese activates enzymes whichcatalyze various stages of plant respiration. Insoils in the northeastern U.S., manganese con-centration my be present in concentrations of 1g/m3 of soil (39). In plants, it is believed that

Environmental Health Perspectives184

manganese occurs in a chelated form. Thissituation would alter the availability ofmanganese in this coordinated complex formwith the strictly inorganic form of manganesein manganese oxide dust (37).

In the body, the highest concentration ofmanganese is in the bone (an average of 3.5mg/g of bone weight). The next highestmanganese concentration in the body occurs inthe glandular tissues, and the liver is consideredto be a storage site of manganese-; Lung, blood,and blood-forming tissue appear to haverelatively low manganese concentrations. It isbelieved that manganese concentrations in bodyorgans and tissues are homeostatically con-trolled, but the specific hormonal mechanismshave not been defined (38, 40, 41).The major portal of entry of manganese in the

air is the lung. From studies with radioactivemanganese tracers, however, evidence suggeststhat the bulk of inhaled manganese becomestransferred to the gastrointestinal tract fromwhich it is either absorbed or eliminated (27).The precise sites of gastrointestinal absorptionof manganese are unknown, but in studies withinorganic supplements, it appears that theamount absorbed is proportional to the amountsupplied for absorption. It has been suggestedthat gastrointestinal absorption of manganesefrom the lung is pertinent to the pathogenesis ofchronic manganese poisoning (38).Manganese is primarily excreted in the feces

via the bile. The gastrointestinal contents aretherefore both the source and sink formanganese. It has been shown that manganesein the bile is probably reabsorbed so that themetal is recycled several times through bodytissues before elimination. The rate ofmanganese elimination is insensitive to thepresence of other metals or changes in acid-basebalance, but sensitive to the body load. Insupplement studies with inorganic manganese,40-70% of the total dose is eliminated initiallyin the feces (38).The dynamics of transport and turnover of

manganese in body organs is different for eachorgan and may suggest how excess manganeseintake results in manganese poisoning.Therefore, the partition of manganese variesgreatly and is a function of the equilibrationdynamics of each organ. Manganese, however,

shows a distinct preference to accumulate inmitochondrian rich tissues (38). In studies with54Mn (27, 40, 42) it was showni that the rate ofloss of metal from blood was rapid and cor-related well with the rate of uptake by the liver.The transport pathway of manganese in humanplasma has been shown to be a fl-globulin,rather than transferrin, the transport proteinfor iron. Manganese has a long residence time inthe body after it has gained entry. The turnoverrate of manganese by the central nervoussystem, endocrine glands, and muscle tissue in-itially is rapid, but with time appears to level offto constant levels which are not dischargedreadily.One of the diseases which results from ex-

posure of manganese ore miners to high at-mospheric levels of manganese oxide dust ismanganic pneumonitis. There was a particular-ly high incidence of this respiratory disease dur-ing the winter of 1939-40 in Moroccanmanganese ore miners, with an associated highdeath rate (33). Reported cases of manganicpneumonitis averaged 65 per 1000 miners. Acomparable outbreak of this disease occurred inthe winter of 1947. Associated with these out-breaks were deplorable situations of nutrition,housing, and personal hygiene among theminers. It was concluded that manganese wasnot the sole etiological factor at work, but wascertainly an aggravating factor.

Clinical signs of manganese pneumonitis arefirst those of acute alveolar inflammation(32-34, 37). Breathing is markedly labored anddifficult, respiration shallow and gasping.Cough and expectoration are rare. The illnessalters, however, after the third day from frankpneumonia to less well defined localization anddiscrete pleural involvement. Fatality can ensuefrom heart failure between the fifth and tenthday. Fatality can also occur suddenly in patientsconsidered cured. Sulfonamides and antibioticshave very little effect on the disease. Amongpatients is observed a condition of leucopeniawith relative polynucleosis, an enormous rise inerythrocyte sedimentation rate (120 in the firsthour using a Westergren tube), and eosinophiliain the sputum. After observing these clinicalmanifestations of the disease, it was difficult todetermine whether the patient was sufferingfrom an ordinary pulmonary infection com-

August 1974 185

plicated and aggravated by manganese, or sub-acute edema, the pulmonary manifestation of atoxic state.The other disease resulting from an excess

respiratory intake of manganese oxide dust ischronic manganism or manganese poisoning.The major oxide of manganese found inmanganese ore is manganese dioxide, MnO2.Those who contract manganese poisoning ex-hibit a self-limiting psychiatric disorder, at theend of which permanent neurologicalmanifestations appear and persist even after ex-cess metal becomes cleared from body tissues.Again, the concentrations of manganese in theair were between 4 and 60 mg/m3, a situationwhich is four orders of magnitude greater thanwas found in U.S. city atmospheres in 1968.The neurological syndrome of chronic

manganism has three stages (27, 30, 33, 37, 38).The prodromal period is characterized by sub-jective disorders such as general asthenia andanorexia, staggering gait, times of incoherentspeech, periods of aggressiveness, general in-difference, lumbar pain and cramps, andperiods of insomnia. The intermediate phase ischaracterized by the development of more objec-tive symptoms. There are more acute distur-bances of speech, the assumption of a facial ex-pression which is jovial and fixed and gives thepatient a dazed appearance. Spasmodic laughterand weeping, increased clumsiness inmovements especially in upper limbs, andhyperemotionalism are characteristic clinicalsigns of the intermediate phase of manganesepoisoning. Walking backward is more difficultand may be accompanied by retropulsion andloss of balance. The established phase becomesreadily apparent after 2-3 months. The essen-tial symptom dominating the clinical picture ismuscular hypertonia in extension. This is mark-ed by increased muscular rigidity in the lowerlimbs and face. Movement is difficult andcharacterized by a "slapping" gate. Liftingweight is impossible and a slight push from thefront can topple the patient backward. Alongwith the muscular rigidity are either spon-taneous tremors, or tremors brought on by'fatigue, emotion or cold. The fixed facial expres-sion is more pronounced and facial emotion inspeech is lacking completely. Spasmodic laugh-ter is more frequent.

Susceptibility of individual exposed workersto chronic manganism in either manganese min-ing personnel or workers in industrialoperations which use manganese metals or ox-ides, is unpredictable. The latent period of thedisease can vary from 18 months to 20 years andthe most susceptible age is difficult to deter-mine (27). However, in studies with 54Mn, thetotal body turnover of manganese by healthy ex-posed miners was twice as rapid as by minerswith manganese -poisoning. In these samestudies, blood levels of manganese in healthy ex-posed miners was twice as high as in minerswith manganese poisoning. This confirms theindividual nature of the disease and how someindividuals who were exposed to the same at-mospheric concentrations of manganese asthose patients who contracted manganesepoisoning, have the ability to rapidly remove theexcess metal from their body tissues. Recently,modification of chronic manganism has beenachieved by gradually increasing doses of L-dopa, up to 8 mg/day, for patients withhypokinetic forms of this disease, and 5-hydroxytryptophane, 3 g/day (43, 44). Thesedrugs were used because of the similarity ofmanganese poisoning with Parkinson's disease.

Consequences of Manganese ExhaustProducts and Emission Control Devices

One of the more important questions to beanswered in determining the potential healthhazard from this replacement for TEL is whateffect will manganese exhaust products have onthe catalytic muffler emission control devicesfor both 1975 and 1976. Because there is no legalban on manganese gasoline additives, this com-pound may be used in gasoline as an antiknockadditive.

Presently, it is not possible to assess the im-pact of manganese oxides on this catalystsystem. Because manganese oxides are sucheffective oxidation catalysts, their presence mayactually enhance the effectiveness of the emis-sion control system. On the other hand, even ifhydrocarbons, CO, and nitrogen oxide emissionsare reduced, not all of the manganese oxides canaccumulate indefinitely in the exhaust emissioncontrol system and will be discharged as par-

Environmental Health Perspectives186

ticulates, probably as oxides, nitrates, and car-bonates. The fact that manganese oxides cancatalyze the conversion of sulfur to S03 isanother important aspect of this possible alter-native for TEL. In attempting to assess thepossible levels of atmospheric manganese due toa complete switch from leaded gasoline to thismanganese antiknock, use has been made of at-mospheric lead levels from 1968 EPA air qualitydata (22), and Ethyl Corporation's projected uselevel of Mn/gal of gasoline. Atmospheric leadabove cities is about 2 ,tg/m3 for a yearlyaverage. The use level of manganese/gal wouldbe about 1/6 of present Pb levels of gasoline. Ifit is assumed that lead in the air comes primari-ly as a result of the use of leaded gasoline, andthat the previously leaded gasoline will now bemanganesed gasoline, then the increase in at-mospheric manganese would be 0.35,g/m3 togive a total yearly average of about 1.2-1.5,Ug/M3.The levels of atmospheric manganese found in

connection with the incidence of manganicpneumonitis and chronic manganese poisoningwere 5-60 mg/m3, on the average. These samestudies on diseases from excess manganese ex-posure also showed that ambient weather con-ditions greatly influenced the manganese con-centration in the air. Foggy weather with nowind could easily increase the atmospheric con-centration of manganese to 10-20 times theaverage. In this respect, people caught in trafficjams and inner city dwellers could very possiblybe exposed to higher levels of manganese oxidesin the air than a yearly national average wouldshow. In assessing the potential health hazardfrom this antiknock compound, consideration ofthe individual susceptibility of this disease andthe difference in turnover and body loads of Mnmust be taken into account. Using the Air Quali-ty Data for 1968 from the EPA illustrates thatatmospheric concentrations of manganese couldbe about 1 g/m3 as compared with 5-60 mg/m3concentrations of manganese oxides associatedwith the incidence of manganese poisoning andmanganese pneumonitis. The threshold limitvalue (TLV) for manganese set by the AmericanConference of Government IndustrialHygienists in 1968 is a ceiling value of 5 mg/m3.It must be remembered that this value is forusually strong healthy workers who do not work

in this atmosphere all the time, and who may bemoved from jobs with high manganese levels inthe air, at regular intervals. Whether thegeneral population can tolerate chronic ex-posure to higher projected atmospheric levels ofmanganese and higher levels of sulfates as aresult of this manganese antiknock additive is aquestion which should be given serious con-sideration while there is still time to do so.

ConclusionsThe controversy on banning lead from

gasoline and the projected use of catalyticmufflers to achieve the standards of the CleanAir Act of 1970 has degenerated to a crisis situa-tion complete with uncompromising positionson the issues. This situation is due in part to theinability to answer fundamental aspects aboutthis question and the use of correlationsbetween exposure levels to lead and diseasewhich are difficult to substantiate. It is thiskind of atmosphere which has stifled criticaldiscussion and analysis of the economics andhealth effects of the methods proposed to meetthese standards. This is an important discussionbecause the alternatives are backed by interestgroups which would be most affectedeconomically by the outcome. The inclusion ofeconomics into a discussion on the alternativesto a problem historically has added to thegeneral confusion of the issues and resulted inoversimplified or wrong selection of an alter-native which is expedient, but may not solve theroot problem, and even may add to it. Withrespect to size and influence, the two interestgroups involved in the alternatives for leadedgasoline are not evenly matched. Indeed, itappears that the proposed alternative will be theuse of higher weight percentages of aromatics toachieve comparable octane boosting and an-tiknock capacity as TEL, coupled with the use ofthe dual catalytic converter system to clean upthe exhaust.These are alternatives which partially solve

the exhaust emissions problems but do not con-sider some of the fundamental aspects of notonly the pollution problem, but also the in-creased utilization of metallic and petroleumresources problem. Two of the root problems arethe design of the internal combustion engine

August 1974 187

and the composition of gasoline used. Until theair pollution crisis from automotive exhausterupted, automobile engines were being design-ed for higher and higher performance. Theachievement of this purpose manifested itself inshorter stroke engines, higher compressionratios, and the use of richer fuel mixtures. Ex-haust emission control regulations resulted inmodifications of engine design to meet thesestandards. Changes in engine design to solvepollution problems have to be evolutionary andcannot occur immediately. However, completeengine redesign must occur simultaneously andwould appear to attack the root problem in amore reasonable and acceptable manner. Themodification of engines with more sophisticatedemission control devices rapidly reaches thepoint of diminishing returns, as far as reducingthe rate of utilization of fossil fuels and theenhanced onset of the energy crisis are concern-ed. This is due to the fact that more horsepoweris diverted from running the engine to runningthe control devices. Therefore, more gasoline isrequired to travel the same distance, and theemission control devices must handle a largervolume of exhaust emissions. Compounding thisproblem still further, the National Academy ofSciences (45) raised serious doubts about notonly the performance of these catalyst systemsin actual use, but also the ability of maintenancepersonnel to properly repair these systems.The pollution problem from the automobile

exhaust is an engineering problem, and alwayshas been. The redesign of the internal combus-tion engine must be accompanied with asimultaneous redesign of gasoline composition.These design changes are a tremendouschallenge since the automotive engineer mustoperate now within efficiacy, environmental,fuel supply, and economic constraints.With respect to engine design, the stratified-

charge CVCC (complex vortex controlled com-bustion) engine by Honda (46), may be in theright direction. The operation of this engine in-itially involves ignition of a small amount of avery rich mixture in a small chamber above themain cylinder body. The flame then spreads to alarger quantity of a very lean mixture in thelarger main cylinder and completes the work ofcombustion with the downward stroke of thepiston. This design has the effect of not allowing

cylinder gas temperatures to reach the highertemperatures (2900°F range) required forsignificant formation of nitrogen oxides. Theuse of lean mixtures in the larger chamber hasalready cut down on the quantities of CO andhydrocarbons produced so that the engine canachieve the 1975 U.S. Standards for ExhaustEmissions without control devices. The averageresults with a 1955-cc 4-cylinder CVCC enginecompared with U.S. Standards are shown inTable 16.

Table 16. Comparison ofemissions from CVCCengine with 1975 U.S. standard.

Emissions from Honda Emissions 1975 U.S.engine, g/mi Standards, g/mi

HC 0.23 0.41CO 2.41 3.40NO. 0.95 3.00

This design was achieved without loss of per-formance (9.1 compression ratio 72 mm bore,and 88 mm stroke), and without drastic changesto present engine block design such as theWankel engine would be. The developments byHonda require watching and more completeanalysis than can be given here to determinewhether or not the CVCC engine completelysolves the air pollution problem.

It can be seen that the methods used toachieve the standards of the Clean Air Act haveaffected many industrial endeavors which atfirst may not have appeared to have any connec-tion at all with these proposed alternatives.However, it is hoped that discussion of theseproposed alternatives and control devices hasbeen stimulated so that they may be given dueconsideration for their impact on environmentalhealth.

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