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' ! ' Automotive Emissions JOHN H. JOHNSON Michigan Technological University Pollution from Automobiles Problems and Solutions / 40 Emissions Standards and Control Approaches / 40 Fuel Economy / 40 In-Use Passenger Car Emissions / 41 Emissions Regulations / 42 Emission Test Procedures / 43 Emission Standards / 45 U.S. Fuel Economy Standards / 46 Vehicle and Emission Control System Technology / 46 Spark-Ignition Gasoline-Powered Vehicles / 47 Diesel-Powered Passenger Cars: Particulate Control / 48 Diesel-Powered Heavy-Duty Vehicles / 49 In-Use Vehicle and Engine Characteristics / 50 Gasoline-Powered Passenger Cars and Trucks / 50 Diesel-Powered Passenger Cars / 52 Diesel-Powered Trucks / 52 Models for Predicting Future Emissions / 53 Fuels and Fuel Additives / 54 Trends in Gasoline Fuel Properties / 54 Fuel Usage Trends / 56 Methanol-Fueled Vehicles / 56 Trends in Diesel Fuel Properties / 59 Refueling Emissions / 59 Additives / 60 Methods for Measuring the Unregulated Pollutants / 61 Sampling / 62 Analytical Methods / 63 Current Regulated and Unregulated Emissions / 64 Regulated Emissions / 64 Unregulated Emissions / 64 Summary of Research Recommendations / 70 Air Pollution, the Automobile, and Public Health. (it) 1988 by the Health Effects Institute. National Academy Press, Washington, I).C. 39

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40 Automotive Emissions Pollution from Automobiles-Problems and Solutions Concern about the automobile as a source of air pollution has been expressed period- ically, but national concern was first evi- denced in the 1960s when California estab- lished the first new car emission standards. The scientific basis of this effort is the pioneering atmospheric chemistry research of A. I. Haagen-Smit, who showed that photochemical reactions among hydrocar- bons (HC) and nitrogen oxides (NOX) pro- duce the many secondary pollutants that reduce visibility and cause eye and nose irritation in the Los Angeles area. This paper reviews our current knowl- edge of automotive emi~cion~ in~l',rlin~ standards, control technology, fuel econ- omy, fuels and additives, in-use emissions, measurement methods for unregulated pol- lutants, and models for predicting future automotive emissions. Fuel economy is in- cluded because achieving high fuel econ- omy and low emissions together makes the engineering effort more difficult. Emissions and fuel economy are interrelated because both are influenced by the engine combus- tion system design. In practice, the strin- gency of emission standards determines the importance of this interrelationship. After current knowledge in each area has been reviewed, important gaps in our knowl- edge are identified and research needed to fill these gaps is described. Emissions Standards and Control Approaches MA ~ _^ _% If- ~ Evolving emission standards have resulted in three levels of stringency, and in turn, three types of control technology. Figure 1 describes the technologies applied in each of the three phases and the general time periods in which they were applied to cars, light-duty trucks, and heavy-duty trucks (Ford Motor Co. 1985a). The percent re- duction in the HC, carbon monoxide (CO), and NOX emissions are also shown. Air/fuel (A/F) ratio, which is controlled by the carburetor or fuel injection system, is the most important variable in determin- ing emissions and in applying catalyst tech- nology. Figure 2 (Heinen 1980) is a plot of NOX, HC, and CO concentrations in the exhaust versus A/F ratio for a typical gas- oline engine. It is impossible to achieve the low emissions demanded by federal stan- dards by A/F ratio control alone since the concentrations of the three pollutants are not minimums at the same A/F ratio. In fact, when CO and HC concentrations are a minimum, at an A/F ratio of around 16:1, NOX production is close to a maximum. Also shown is the A/F ratio for maximum power (13.5:1) and maximum fuel economy (17:1~. The region where A/F ratio exceeds 17.5:1 is the lean bum region where misfires can occur along with slow flame speeds, causing increased HC concentration. The A/F ratio effects are used in all phases of control. The stoichiometric ratio of 14.7:1 is necessary in the Phase III control using three- way catalysts since the A/F ratio must be in a narrow window within + 0.05 of the stoi- chiometric ratio to achieve high HC, CO, and NOX control efficiencies simultaneously. Exploring the lean burn region is an impor- tant area of research and development be- cause of the potential of improved fuel econ- omy and adequate emission control with only an oxidation catalyst. Fuel Economy Federal regulations also mandate automo- tive fuel economy. The period from 1968 to 1974 resulted in primary emphasis on emission control with loss of fuel economy from lower compression ratios, changes in spark timing, A/F ratio and axle ratio changes, and exhaust gas recirculation. Fig- ure 3 (Heavenrich et al. 1986) shows the U. S. fleet combined, city, and highway fuel economy data for each model year since 1974. The figure also includes infor- mation on average vehicle weight. The fuel economy from 1977 to 1980 improved al- most exactly in proportion to the decreas- ing weight of vehicles. If the data in figure 3 were normalized to the 1978 weight mix, it would show that fuel economy improve- ments leveled out in 1982. With the intro

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John H. Johnson Major Emission Reduction Phases REDUCTION (%) FROM UNCONTROLLED TIME Light Heavy FRAME Car Truck Truck pre 1968 1 975 1 979 1981 1984 1 987 and beyond 41 TECHNOLOGY APPLICATIONS _ Phase I Uncontrolled to INITIAL CONTROL LEVELS HCs CO NOx Closed crankcase controls (HCs) 72% 67% 24% Evaporative emission controls (HCs) Engine modifications for improved combustion (HCs and CO) Air injection (thermactor) systems _ ,. .~ ~ ^~ Ones and ~V) Exhaust gas recirculation (NOx) _ Phase 11 HCs CO NOx INTERMEDIATE"TECHONOLOGY-LIMITED" 86% 82% 24% LEVELS .................................. . 1st-Phase controls _....................................... ........... .. . . Oxidation catalysts (HO & CO control) .......................... . .. . . . ....... ................................... _ . Early-stage electronic engine controls ................................................ ............................. . . (optimized fuel economy, driveability, .... ................. ............................. _ . . emissions control performance) ...................................... ............................. ~.................... .............................. ............. , ................................................. Phase 111 HCs CO NO ULTIMATE CONTROL LEVELS ...................................... ............ x . . . ( ar) 1 st Phase controls ............................... ............................................. ......................... . . . . . 90% 90% 50% (Truck) Three way catalyst systems (HCs' CO1 ................. ...... ,., ... . . ......... A . Nux) ............................. , , .............. ... .................... .. .. , ,., .............................................. .,, .................... , . ............... . . Particulate traps (diesels) ............................. . ..................................................... ......................................................... ....... .................... , , : . . . . . , . Figure 1. Major phases in the reduction of automotive emissions. (Adapted with permission from Ford Motor Co. 1 985a. ) auction of the oxidation catalytic converter in 1975, improved fuel economy and re- duced emissions occurred simultaneously. Further emission reduction with simulta- neous fuel economy improvement contin- ues through application of new technology, especially computer engine control. In-Use Passenger Car Emissions The in-use emissions from passenger cars exceed the new car standards mandated by law. Nonetheless, emissions continue to decrease in spite of high tampering rates and fuel switching (that is, using leaded fuel in engines developed to run on unlead . Figure 5 shows EPA emission factors data as analyzed by General Motors Corp. (1985a). The measured emission concentra tions for various model years are compared to the standards that were in effect during those years. The measured NO, concentra tions follow the standards fairly well. Al though the measured HC and CO concen trations are higher than the standards, the difference between the actual emissions and the standards appears to be narrowing (al though the ratio is not decreasing) as im proved technology, more frequent inspec tion and maintenance, and better training of mechanics has occurred. Even though the overall trend of emissions is down, a ed fuel). From field surveys in 14 cities,few vehicles have high emission levels, as Greco (1985) found the overall tamperingshown in figure 6, probably because of rates and catalyst tampering rates shown in figure 4. electronic problems rather than catalyst re- moval or misfueling problems.

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42 Emissions Regulations In the 1960s, motor vehicles were identified as one of the primary sources of air pollu- tants in urban areas. Emission standards for passenger cars were first imposed in Cali- - fornia in 1965. These were followed by U.S. federal standards in 1968. The 1970 Clean Air Act further imposed stringent HC, CO, and NOX reductions for 1975 and 1976. These reductions were subsequently delayed and changed by the 1974 Energy 40r ~ 35 - O 30 8 J 25 LL Lu 20 LL 11 ~ 15 Automotive Emissions Maximum power IStoichiometric mixture Maximum fuel economy Lean burn area 400C 300C Q x 200C o 1 OOC o - 800 . - 600 ~CO / _~ 400 \ \\/ -200 _ \/\ i'" ~ O ___~' I 8 10 12 lo 'A 14 16 18 20 22 AIR/FUEL RATIO c' o - 4 ~ - - Figure 2. Concentrations of HC, CO, and NOX emissions as a function of air/fuel ratio in a typical gasoline engine. (Adapted with permission from Heinen 1980, and the Society of Automotive Engineers, Inc.) and Environmental Coordination Act and the 1977 Clean Air Act Amendments. Rec- ognition of the motor vehicle as a major source of pollutants has spread to other countries, of which many have imposed diverse standards and test procedures re- flecting various degrees of stringency. The differences have come about because of dif- ferent regulatory philosophies and air quality goals, in combination with concerns about the conflicting goal of improved fuel eff~- ciency (Barnes and Donohue 1985~. Coo 4500 10L = 0 Highway 0< a` ~o Combined '~ ~ City Weight l 75 76 77 78 79 80 81 82 83 84 85 86 MODEL YEAR Figure 3. U.S. fleet fuel economy and average vehicle weight by model year. (Adapted with permission from Heavenrich et al. 1986, and the Society of Automotive Engineers, Inc.) 4000 imp :I1 m 3500 ~ m I 3000 2500 J 2000

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John H. Johnson 50 A 0- 30 a 20 llJ ~ 10 rig o Overall tampering ~ Catalyst tampering v In. 84 83 82 81 80 79 78 77 76 75 VEHICLE MODEL YEAR Figure 4. Overall and catalyst tampering rates by vehicle model year, based on 1984 survey. (Adapted from Greco 1985.) Emission Test Procedures Passenger Cars. Emissions come princi- pally from three automotive sources: the ex- haust, the fuel system (evaporative), and crank- case ventilation gases. To give the standard (maximum allowable level of emission in grams per mile) operational meaning, two ma- jor aspects must be defined: the driving cycle and the emissions sampling method. Driving cycles are discussed below and sampling meth- ods will be covered in a later section. 12 _ HO 10 _ 8 _ 6 _ 4 _ ~ 2 _ ~ O z 100 _ in 80 _ cn _ 60 _ 40 _ ~20 E u.l o ~ 5 lo: 4 3 2 _ 1 _ O ~To a-" 's80 81-82 83-8s o_ control ): VEHICLE MODEL YEAR 0 Figure 5. Average vehicle lifetime HC, CO, and NOx emissions compared with standards (STD), by model year for all industry passenger vehicles. (Adapted with permission from General Motors Corp. 1985a.) 43 Regulations require exhaust emission measurements during the operation of the vehicle (or engine) on a dynamometer dur- ing a driving cycle that simulates vehicle road operation. The approach to driving cycles by various regulatory authorities represent two basic philosophies. Accord- ing to the first, the driving cycle is made up of a series of repetitions of a composite of various vehicle operating conditions repre- sentative of typical driving modes. The European Economic Community and Jap- anese cycles reflect this philosophy. Ac- cording to the second, the composite of driving modes is an actual simulation of a road route. The United States, Canada, Australia, Sweden, and Switzerland all use a version of the federal test procedure (FTP). The FTP cycle is divided into a "transient" portion and a "stabilized" por- tion with a total cycle time of 1,372 see, a driving distance of 7.5 miles, and an aver- age speed of 19.7 miles per hour (mph). Two such cycles are run: one with the vehicle at an ambient temperature of 1~30C before start ("cold" cycle), and one with the engine control system hot ("hot" cycle) after a 10-min shutdown after running the cold cycle. Trucks. Many of the light-duty trucks intended primarily for the carrying of goods are also capable of use as passenger vehicles. The gross vehicle weight for light-duty trucks in the United States is less than 8,500 lb; trucks heavier than 8,500 lb 300- 200 : 100 .~_ ~ no. ... I~ CAL ~ ' 1 ' 1 ' -r ' 1 1 20,000 40,000 60,000 80,000 ODOMETER MILES Figure 6. Scatter plots of CO emissions from 703 1981 model-year federal cars. (Adapted with permis- sion from General Motors Corp. 1985a.)

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44 Automotive Emissions Table 1. Motor Vehicle Emission Standards in the United States Emission Ratesa Federal California Evap Partic- Evap Partic Model HC CO NOX (g/ ulatesb HC+ HC CO (g/ NO.` (g/ ulatesb HC+ Year (g/mi) (g/mi) (g/mi) test) (g/mi) NOy (g/mi) mi) (g/mi) test) (g/mi) NOr Passenger Cars Pre control 10.60C 84.0 4.1 47 10.60' 84.0 4.1 47 1966 6.30 51.0 (6.0) 1968 6.30 51.0 (6.0)d 6.30 51.0 1970 4.10 34.0 4.10 34.0 6 1971 4.10 34.0 4.10 34.0 4.0 6 1972 3.00 28.0 2.90 34.0 3.0 2 1973 3.00 28.0 3.0 2.90 34.0 3.0 2 1974 3.00 28.0 3.0 2.90 34.0 2.0 2 1975 1.50 15.0 3.1e 2 0.90 9.0 2.0 2 1977 1.50 15.0 2.0 2 0.41 9.0 1.5 2 1978 1.50 15.0 2.0 be 0.41 9.0 1.5 6 1980 0.41 7.0 2.0 6 0.39f 9.0 1.0 2 1981 0.41 3.4 1.0 2 0.39 7.0 0.7 2 1983 0.41 3.4 1.0 2 0.398 7.0 0.4 2 1984 0.41 3.4 1.0 2 0.39 7.0 0.4 2 0.60 1985 0.41 3.4 1.0 2 0.39 7.0 0.4 2 0.40 1986 0.41 3.4 1.0 2 0.60 0.39 7.0 0.4 2 0.20 1987 0.41 3.4 1.0 2 0.20 0.39 7.0 0.4 2 0.20 1989 0.41 3.4 1.0 2 0.20 0.39i 7.0 0.4 2 0.08 Light-Duty Trucks 1975 2.00 20.0 3.1 2 2.0 1976 2.00 20.0 3.1 2 0.90 17.0 2.0 1978 2.00 20.0 3.1 6 0.90 17.0 2.0 6 1979 1.70 18.0 2.3 6 0.50j 9.0 2.0' 6 1980 1.70 18.0 2.3 6 0.50/ 9.0 2.0' 2 1981 1.70 18.0 2.3 2 0.50 9.0 1.5 2 1983 1.70 18.0 2.3 2 0.50 ~9.0 1.0P 2 1984 0.80 10.0 2.3 2 0.50 9.0 1.0P 2 1986q 0.80 10.0 2.3 2 0.50 9.0 1.0 2 1988 0.80 10.0 1.7 2 0.50 9.0 1.0 2 (Table continued next page.) NOTE: Evap = evaporative HC. a Emission rates for HC, CO, NOB by (or adjusted to equivalent) 1975 Federal Test Procedure. b Diesel passenger cars only. c Crankcase emissions of 4.1 g/mi not included; fully controlled. NOX emissions (no standard) increased with control of HCs and CO. e Change in test procedure. f NMHC standard (or 0.41 g/mi for total HC). g 0.7 NO.~ optional standard 1983 and later, but requires limited recall authority for 7 yr/70,()00 mi. h Optional standard, 0.3 g/mi, requires 7 yr/75,000 mi limited recall authority. ' Primary standard = 0.4 g/mi required on 90% of production after 1989. 0.41 for <4,000 lb. k 1.5 for <4,000 lb. 0.39 for <4,000 lb (nonmethane) and in following years. m 0.6 for >6,000 lb and in following years. n 2.0 for >6,000 lb. California: 1.0 NOR optional standard for 1983 and later, but requires limited recall authority for7 yr/75,000 mi. Primary standard = 0.4 g/mi.

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John H. Johnson 45 Table 1. Continued Emission Rates Federal California Partic- Partic HC CO NOX ulates HC ulates (g/ (al (g/ Evap (g/ (g/ CO NO. ~Evap (g/ Model bhp- bhp- bhp- (g/ bhp- HC+ bhp- (g/bhp- (g/bhp- (g/ bhp- HC+ Year hr) hr) hr) test) hr) NOy hr) hr) hr) test) hr) NO. Heavy-Duty Truck and Bus Engines' 1969 " '' 1972 . v 1973 40.0' 16.0 1974 40.0 16.0 40.0 16.0 1975 40.0 16.0 30.0 10.0 1977 40.0 16.0 1.0 25.0 7.5 5.0 1978 40.0 16.0 1.0 25.0 7.5 6 5.0" 1979 25.0 10.0 1.5 25.() 7.5 6 5.0 1980 1.5 25.0 10.0 1.0 25.0 7.5 2 6.0 1984 1.5 25.0 10.0 0.5 25.0 7.5 2 4.5"' 1985 1.9 37.1- 10.6Z 3cia 0 5 25.0 7.5 2 4 5i''bb 1987 1.1 14.4 10.6 3 0.5 25.0 7.5 2 4.5 1988 1.1 14.4 6.0 3 0.6 0.5 25.0 7.5 2 4.5 1991 1.1 14.4 5.0 3 0.25 0.5" 25.0" 7.5" 2 4.5 NOTE: Evap = evaporative HC. P 1.5 for >6,000 lb. q Full useful life requirement = 11 yr/120, 000 mi (was 5 yr/50,000 ml). r NOX federal standard = 1.2 g/mi under 3,751-lb loaded vehicle weight (LVW), 1.7 g/mi for 23,751 lb L~W, and 2.3 g/mi for '6,000 lb LVW. s 1.2 for <3,751 lb. ' Various test methods, values are not strictly comparable. U275ppmHC, 1.5% CO. v 180 ppm HC, 1.0% CO. w A combined standard is optional in lieu of separate HC and NO.~ standards (for example, 1 g HC + 7.5 g NO~ or 5 g tHC+NOxi). x 1.3 for diesel. Y 15.5 for diesel. Z 10.7 for diesel. aa 4.0 for >20,000 lb. bb Gasoline only and in following years. cc 1988 federal standards for NO y have been postponed until 1990. Separate standard of 0.1 for all 1991 urban buses and all 1994 engines. ee 1.3 HC, 16.5 CO, 5.1 NO~ for diesel. SOURCE: Adapted with permission from General Motors Coro. 1986. are classified as heavy-duty vehicles. The driving-cycle philosophies for the light commercial vehicles follow those for pas- senger cars. For heavy commercial vehi- cles, engine dynamometers are used, not chassis dynamometers; that is, the enp;ine rather than the vehicle is certified. The new (effective 1985) U.S. transient test proce- dure for heavy-duty vehicles combines the two philosophies just described in that the cycle is made up in a random way from actual driving cycle data. The use of this cycle replaces the 13-mode steady-state cy- cle in use since 1973 in California and since 1974 nationally (U.S. Environmental Pro- tection Agency 1972~. Emission Standards United States. Emissions standards and test procedures in the United States have changed significantly since the first auto- mobile emission standards were imposed in California in 1966 (see table 1) (General

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46 Automotive Emissions Motors Corp. 1986~. Light-duty truck stan- dards are somewhat higher than the car stan- dards because of the differences in weight. The U.S. passenger car regulations re- quire that the vehicle comply with the emission standards for five years or 50,000 miles, whichever occurs first. Certification testing of prototype vehicles for 50,000 miles of use is based on the Automobile Manufacturers' Association (AMA) 40.7- mile durability cycle. The cycle consists of numerous stops, acceleration, and high/ medium-speed driving (maximum of 55 mph) (U. S. Environmental Protection Agency 1973~. Europe. The European Economic Com- munity, an inter-Europe regulatory body, has announced future model standards for passenger cars based on three engine size (displacement) categories. Large-car (> 2- liter engine displacement) standards are roughly equivalent to current U.S. stan- dards although there is no valid correlation between the distinct U.S. and European emission test cycles. Standards for medium cars (1.~2.0 liters) are considered to fall in the Phase I/Phase II range shown in figure 1. Requirements for small-car levels (< 1.4 liters) are comparable to Phase I require- ments. The standards include diesels; how- ever, large diesel cars are only required to meet medium-car levels. Japan. Catalyst forcing standards cur- rently in effect for passenger cars are 0.25 HC/2.1 CO/0.25 NOX g/km for the unique 10-mode hot start and 7.0 HC/60 CO/4.4 NOX g/test for the 11-mode cold- start test procedures. These standards are generally considered to be equivalent to current U.S. California levels (Ford Motor Co. 1985a). U.S. Fuel Economy Standards There have been passenger car and light- truck fuel economy standards since 1978 and 1979, respectively. The manufacturers are required to conduct passenger car fuel economy tests according to the U.S. Envi- ronmental Protection Agency (EPA) urban or "city" driving cycle the FTP for emis sion testing described earlier. The EPA also has a suburban or "highway" cycle that includes a significant amount of simulated highway driving. A combined fuel econ- omy number based on these two tests is published by the EPA and the U. S. Depart- ment of Energy and used by manufacturers in their sales literature. Manufacturers each have to meet the Corporate Average Fuel Economy (CAFE) standards for their sales-weighted fleet. Car standards started at 18 miles per gallon (mpg) in 1978, went to 27.5 mpg in 1985, but were reduced to 26 mpg by the U. S. De- partment of Transportation for 198~1988. Vehicle and Emission Control System Technology The technology used for emission control in cars changed rapidly in the 1970s as the automotive industry spent considerable re- search and development funds to meet the stringent emission standards originally set by the 1970 amend 1977 Clean Air Act Amendments. This technology is now be- ing optimized to reduce the product cost associated with emission controls while im- proving the in-use durability of the emis- sion control systems. Heavy-duty gasoline- powered vehicles have used this technology as allowable emissions have progressively decreased. Control technology is being developed to meet proposed standards and anticipated changes in fuels. Proposed 1988, 1991, and 1994 particulate standards require new con- trol systems for heavy-duty diesels. For the United States to become less dependent on imported petroleum fuels, there is interest in using methanol in passenger cars and diesel-fueled buses. There are continued efforts to develop stratified-charge engines for passenger cars because of their potential for better fuel economy at equivalent emis- sions. There is also a demand for develop- ment of direct-injection diesels that give 15 percent better fuel economy than pre- chamber or swirl-chamber engines with equivalent or better emissions. An addi- tional demand exists for an adiabatic diesel

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John H. Johnson 47 engine (more precisely, a low-heat-re- jection engine) that would have improved fuel economy and lower emissions with a simpler cooling system, particularly for vehicles in the heavy-duty class. Spark-Ignition Gasoline-Powered Vehicles During the past 15 years, emissions have been significantly lowered by improved design of the engine and fuel system while still achieving the high fuel economy de- manded by the federal standards and the consumer market. These reductions have come about by A/F ratio control, cylinder- to-cylinder distribution of air and fuels choke operation, combustion chamber de- sign, fuel injection, exhaust gas recircula- tion (EGR), ignition systems, spark tim- ing, valve timing, and many additional design details. The computer scheduling of spark timing, EGR, A/F ratio, and trans . . . . . . mission gear ratio as a tunctlon ot engine operating conditions are done very pre- cisely with sensors and actuators. This scheduling is referred to as the engine cali- bration. With all of this technology, ve- hicles still do not meet HC/CO/NOX standards of 0.4/3.4/1 g/mi without after- treatment devices. The period after 1983 has seen better optimization of systems and removing of components to reduce costs, but nevertheless, catalysts are still neces sary. Catalyst Control Systems. Meeting the 1975 MC/CO standards of 1.5/15 g/mi and at the same time increasing the fuel econ- omy was achieved through the broad intro- duction of the oxidizing catalytic con- verter. The catalyst is cold (1~30C) at the start of the FTP cycle and must warm up to 250-300C before oxidation of CO and HC occurs. The time required for this is a function of catalyst design and position but can be from 20 to 120 sec. The HC emitted during this period can be one-fourth to three-fourths of the allowable limit (Hil- liard and Springer 1984~. The amount of NOX emitted during the cold start is only about 10 percent of the allowable limit. The time period from 1975 to 1984 saw ~ 00 ~ ' NOx ,, CO z t) 60 _ IL z an _ o En cr o 80 40 20 _ ~ Window O , ~ , // I I 13 14 15 16 AIR/FUEL RATIO Figure 7. Conversion efficiency characteristics of a three-way catalyst. (Adapted with permission from Amann 1985.) increased fuel economy and improved emission control through exploitation of the high HC and CO removal efficiency of the oxidizing catalytic converter, so that the engine calibration could be optimized for efficiency. Progress was made by de- creasing the cold-start engine-out HC and CO emissions, by achieving faster con- verter light-off, by reducing heat loss from the exhaust system, and by reducing the deterioration of catalyst performance with cumulative driving distance (Amann 1985~. Reducing combustion temperature by spark retard and/or diluting the incoming mixture with EGR provided NOX control during the time period from 1973 to 1980. The 1981 standards stipulate no more than 1 g/mi NOX, which could not be achieved either by EGR or engine design and cali- bration. Two additional catalytic ap- proaches have gained widespread applica- tion along with the microprocessor control system, to provide the necessary control: the "three-way" catalyst and the "dual" catalyst. Three-way catalysts are capable, within a narrow range of exhaust stoichiometry, of simultaneously decreasing NOX, HC, and CO, as shown in figure 7. Within a narrow range of values of the A/F (approximately + 0.05 from the optimum), all three emis- sions are decreased with a reasonably high efficiency. An oxygen sensor is used in the . . . . . . ex Bust in conjunction Wit ~ a mlcroproces sor to make this technology feasible.

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48 Automotive Emissions CARBURETOR Al R FU EL DRIVER ~ AIR 1 l ETERIN l:' ELECTRONIC SIGNAL ITHROTTLE I DEVICE I 1 CONTRA LEA ENGINE mu\ 1 \ - V ~ OXYG EN SENSOR Figure 8. System for closed-loop control of A/F ratio. The oxygen sensor inserted in the exhaust pipe ahead of the catalyst measures oxygen concentration and signals the electronic controller to adjust fuel rate continuously. (Adapted with permission from Amann 1985.) In a dual catalyst, two catalysts are used in series- a three-way catalyst followed by an oxidizing catalyst. Air is injected into the exhaust gas between the two catalysts to provide the oxygen necessary for the oxidizing catalyst to operate efficiently. Once more, precise A/F ratio control is required to make the three-way catalyst function. During the cold-start portion of the FTP cycle, the air supply to the oxidiz- ing catalyst can be diverted to the exhaust ports to add oxygen to the combustion products of the rich start-up mixture for faster catalyst light-off and to achieve higher HC and CO control efficiencies in the three-way catalyst. The dual-bed con- verter is more complex than the single-bed three-way catalyst, because it requires an . . extensive air management system. To maintain A/F ratio control within the narrow window, closed-loop control (feed- back control of fuel delivery on oxygen level in exhaust) was introduced on many cars in 1981. The schematic of a typical system is shown in figure 8 (Amann 1985~. The key element in the closed-loop system is the oxygen sensor inserted in the exhaust pipe ahead of the catalyst. It measures exhaust oxygen concentration and signals an electronic controller to adjust fuel rate continuously so that the mixture is main- tained at the stoichiometric ratio. Current Control Approaches. Since 1983 the number of engines with some type ot No particular trend in emission systems is evident except for the use of heated oxygen sensors to initiate closed-loop operation faster and more predictably and to maintain it during long idling periods. The heated sensors also deteriorate less with extended mileage (Way 1985~. Most cars use closed loop control with a three-way catalyst; many also have an oxidation catalyst that is a dual catalyst and one of three air supply systems (pulse air, air pump, or pro grammed pump). Lean-Burn Combustion Systems. An im portant engine emission control system un der development is the lean combustion system. This system uses a closed-loop microprocessor in conjunction with lean mixture sensor and an oxidation catalyst. This alternate emission control approach achieves good fuel economy (potential 10-15 percent improvement) and also meets the emission standards by operating beyond 22:1 A/F where NOX emission is low enough to meet the 1-g/mi standard. In this lean operating region, the engine needs a different sensor design to provide feedback, and also a highly turbulent fast burn combustion system so that slow flame speed and misfires do not cause emissions and driveability problems. Toyota has de veloped and marketed such a system in Japan but not yet in the United States (Kimbara et al. 1985~. It may be possible to introduce this type of system into the U. S. market, but dura bility and driveability under hot and cold conditions need to be examined further (Kimbara et al. 1985~. The other important technological limit might be that lean burn could be restricted to cars under 2,500 3,000 lb because NOX generally increases with vehicle weight. Diesel-Powered Passenger Cars: Particulate Control There has been a major research and devel opment effort during the past seven years to develop aftertreatment devices for diesel passenger cars to meet the federal 0.2 g/mi tuel Injection has grown drastically, but standard first proposed for 1985 and later carburetors are still used on many engines. put offuntil 1987. California has a 0.2-g/mi

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John H. Johnson r G'owp~ug Controller ~ driver to Battery _~ RPM ~ Power ~ control Pressure box ') to Glowplug driver / ~signal '\bielow) Fox. ,~ ~ Pressure /__~/' \ transducer Glowplug igniter (air Figure 9. Diesel particulate trapping system utiliz- ing a ceramic fiber trap, a fuel additive, glow plug igniters, and exhaust backpressure regeneration con- trols. (Adapted with permission from Simon and Stark 1985, and the Society of Automotive Engineers, Inc.) standard that was initiated in 1986, and will be lowered 0.08 g/mi in 1989. A number of prototype systems have been built and field tested to meet the 0.2 g/mi standard. Mer- cedes-Benz (Abtoff et al. 1985) introduced a catalytic trap oxidizer in 1985, in conjunc- tion with careful modification of the engine (in particular, the turbocharger). The sys- tem meets and is certified to the 1986 49 California standards and has been sold in the 11 western states. Volkswagen has de- veloped a prototype system that uses a Corning ceramic particulate filter in con- junction with Lubrizol 8220 manganese (Mn) additive. The additive consists of nonstoichiometric Mn fatty acid salts dis- solved in naphtha, which is metered from a separate fuel-additive storage tank on the vehicle (lifetime filling) and mixed with the fuel (Wiedemann and Neumann 1985~. Emissions of Mn oxide of all valence states, as well as MnSO4, may occur. Data sug- gest that most of the Mn residue is in the form of sulfate. General Motors has also tested a system, shown in figure 9, with on-board tank- blending, additive dispensing, and ceramic fiber trap (Simon and Stark 1985~. This system uses pressure and engine speed to provide a measure of particulate loading for triggering the glow plug igniters for regen- eration. Simon and Stark (1985) investi- gated three different additives: cerium (0.13 g Ce/liter), manganese (0.07 g Mn/liter), and cerium plus manganese (0.07 g (Ce + Nln)/liter). Their tests showed that vehicles equipped with properly tuned 4.3-liter en- gines and operated using a fuel additive would not, on a production basis, be able to meet the 1987 federal emissions stan- dards at sea level or at altitude. Equipped with particulate traps, however, the vehi- cles would probably meet the 1987 federal standards and might, with further engine tailoring, be able to meet the 1989 Califor- nia standards on a production basis. Diesel-Powered Heavy-Duty Vehicles Diesel-powered heavy-duty vehicles use direct-injection turbocharged engines of two-cycle as well as four-cycle design. Die- sel engines are designed for a commercial market and hence durability, reliability, and fuel economy drive their development. The approaches enforced to date to meet the standards for particulates, HCs, and NOX have involved improved turbocharg- ers, intercooling, improved fuel systems and nozzles, and electronic fuel injection control. To reduce NOX emissions and improve fuel economy, some manufactur

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66 Automotive Emissions Table 10. Qualitative Analysis of Nonpolar and Moderately Polar Fractions of Diesel Particulate Extract Compound Approximate Concentration in Oldsmobile Extract (ppm) Nonpolar fractions Phenanthrenes and anthracene Methylphenanthrenes and methylanthracenes Dimethylphenanthrenes and dimethylanthracenes Pyrene Fluoranthene Methylpyrenes and methylfluoranthenes Chrysene Cyclopenta|cdlpyrene Benzotghi]fluoranthene Benz~ajanthracene Benzota~pyrene Other PAHs, heterocyclics HCs and alkylbenzenes Total nonpolar fractions Moderately polar fractions PAH ketones Fluorenones Methylfluorenones Dimethylfluorenones Anthrones and phenanthrones Methylanthrones and methylphenanthrones D imeth ylan thrones and dim eth ylp hen anthro nes Fluoranthones and pyrones Benzanthrones Xanthones Methylxanthones Thioxanthones Methylthioxanthones Total PAH carboxaldehydes Fluorene carboxaldehydes Methyl fluorene carboxaldehydes Phenanthrene and anthracene carboxaldehydes Methylanthracene and methylphenanthrene carboxaldehydes Dimethylanthracene and dimethylphenanthrene carboxaldehydes Benz~ajanthracene, chrysene, and triphenylene carboxaldehydes Naphthalene dicarboxaldehydes Dimethylnaphthalene carboxaldehydes Trimethyluaphthalene carboxaldehydes Pyrene and fluoranthene carboxaldehydes Xanthene carboxaldehydes Dibenzofuran carboxaldehydes Total PAH acid anhydrides Naphthalene dicarboxylic acid anhydrides Methylnaphthalene dicarboxylic acid anhydrides Dimethylnaphthalene dicarboxylic acid anhydrides Anthracene and phenanthrene dicarboxylic acid anhydrides Total (Table continued next page.) 600 1,400 3,000 1,700 1,400 800 100 20 100 500 40 30,000 500,000 539,700 4,000 400 200 1,600 1,600 1,300 1,200 200 300 200 1,600 900 13,500 1,600 400 2,600 1,600 400 400 300 300 1,000 1,600 600 400 1 1,200 3,000 1,000 500 600 5,100

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John H. Johnson 67 Table 10. Continued Compound Approximate Concentration in Oldsmobile Extract (ppm) Hydroxy PAHs Hydroxyfluorene Methylhydroxyfluorene Dimethylhydroxyfluorene Hydroxyanthracenes and hydroxyphenanthrenes Hydroxymethylanthracenes and hydroxymethylphenanthrenes Hydroxydimethylanthracenes and hydroxydimethylphenanthrenes Hydroxyfluorenone Hydroxyxanthone Hydroxyxanthene Total PAH quinones Fluorene quinones Methylfluorene quinones Dimethylfluorene quinones Anthracene and phenanthrene quinones Methylanthracene and methylphenanthrene quinones Fluoranthene and pyrene quinones Naphthot1,8-cdlpyrene 1,3-dione Total Nitro-PAHs Nitrofluorenes Nitroanthracenes and nitrophenanthrenes Nitrofluoranthenes Nitropyrenes Methylnitropyrenes and methylnitrofluoranthenes Total Other oxygenated PAHs PAH carryover from nonpolar fraction Phthalates, HC contaminants Total, moderately polar fractions 1,400 400 1,500 600 900 1,300 2,000 1,300 1,000 10,400 700 600 500 1,900 2,000 200 600 6,500 30 70 10 150 20 280 8,000 6,000 30,000 91,000 SOURCE: Adapted with permission from the National Research Council 1983b. The particulate-extract in the high-per- formance liquid chromatograph (HPLC) eluent can be separated into nonpolar, moderately polar, and highly polar frac- tions. The fractions can then be further analyzed by gas chromatography/mass spectrometry (GC/MS). Table 10 lists the results of such an analysis of the nonpolar and moderately polar fractions of a partic- ulate extract from an Oldsmobile diesel vehicle, including the approximate extract concentrations for this particular vehicle. The highly polar fraction has not been fully characterized. It contains the PAH carbox- ylic acids, acid anhydrides, and probably sulfonates and other highly polar species (National Research Council 1983b). Most (75 percent) of the direct bacterial mutagenicity resides in the moderately po- lar fraction. The remaining direct mutage- nicity is in the highly polar fraction. These aspects are discussed further in the National Research Council's report (1983b). Over 50 chromatographic peaks of nitro- PAH compounds have been identified in diesel particulate extracts, as listed in table 11. The most abundant of the nitro-PAHs is 1-nitropyrene, ranging from 25 to 2,000 ppm in the vehicle extracts studies. The other nitro-PAHs are present at concentra- tions from below the ppm range to a few ppm. The nitropyrenes have been studied in greater detail than other PAH com- pounds. They are released in diesel and

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68 Table 11. Nitroarenes in Diesel Exhaust Particulate Extracts Mononitroarenes N i tro in den e Nitroacenaphthylene Nitroacenaphthene Nitrobiphenyl Nitrofluorene Nitromethylacenaphthylene Nitromethylacenaphthene Nitromethylbiphenyl Nitroanthracene Nitrophenanthrene Nitromethylfluorene Nitromethylanthracene Nitromethylphenanthrene Nitrotrimethylnaphthalene Nitrofluoranthene Nitropyrene Nitro (C2-alkyl) anthracene Nitro (C2-alkyl) phenanthrene Nitrobenzofluorene Nitromethylfluoranthene Nitromethylpyrene Nitro (C3-alkyl) anthracene Nitro (C3-alkyl) phenanthrene Nitrochrysene Nitrobenzoanthracene Nitronaphthacene Nitrotriphenylene Nitromethylnaphthacene or nitromethylchrysene Nitromethylbenzanthracene Nitromethyltriphenylene Nitrobenzopyrene Nitroperylene Nitrobenzofluoranthene Automotive Emissions Polynitroarenes Dinitromethylnaphthalene Dinitrofluorene Dinitromethylbiphenyl Dinitrophenanthrene Dinitropyrene Trinitropyrene Trinitro (C5-alkyl) fluorene Dinitro (C6-alkyl) fluorene Dinitro(C4-alkyl)pyrene Nitro-oxyarenes Nitronaphthaquinone Nitrodihydroxynaphthalene Nitronaphthalic acid Nitrofluorenone Nitroanthrone Nitrophenanthrone Nitroanthraquinone Nitrohydroxymethylfluorene Nitrofluoranthone Nitropyrone N itro fl u o ran theneq uin one Nitropyrenequinone Nitrodimethylanthracene carboxaldehyde N it rodi m eth yl p henan t hrene ca rb o x aldeh y de Other nitrogen compounds Benzocinnoline Methylbenzocinnoline Phenylnaphthylamine (C2-alkyl) phenyloaphthylamine SOURCE: Adapted with permission from the National Research Council 1983b. gasoline exhaust (according to particulate extracts) at rates of approximately 8.0 (diesel fuel), 0.30 (leaded gasoline), and 0.20 mg/mi (unleaded gasoline) (National Research Council 1983b). 1-Nitropyrene has been the only ni- tro-PAH detected in spark-ignition par- ticulate extracts. Very low 1-nitropyrene particulate extract concentrations have been found recently in on-road heavy- duty diesel and light-duty spark-ignition vehicles (National Research Council 1 983b). Gasoline-Powered Vehicle Refueling Hydro- carbons. Williams (1985) has reported the concentration of HCs in the breathing zone of individuals during vehicle refueling. Gas chromatographic data for gasoline and the refueling vapor indicate that only the lower molecular weight, more volatile com- pounds are emitted. Williams concluded that: 1. Vapor composition does not equal 1- . . gaso~ne compos~t~on; 2. Range of total HC concentrations varied widely with the environmental con- ditions, resulting in exposures from 8 to 3,000 ppmC; and 3. Propane, butane, and pentane provide more than 80 percent of total exposure.

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John H..Iohnson 69 Areas in Need of Additional Research. To do efficient particulate control develop- ment work and to better understand emis- sion characteristics, there is a need for a fast-response real-time particulate mass measurement instrument. The tapered ele- ment oscillating microbalance (TEOM) holds the most promise, but there is a gap between what is known about its principle of operation and the reality of making its use practical for measuring par- ticulates. The other instrument gap involves ~ea- suring methanol accurately. Formaldehyde has also been identified as a potentially important unregulated pollutant that needs careful real-time measurement and control because it is generally considered to be a carcinogen. Measurement of particulate emissions from heavy-duty diesel engines using the EPA test procedures with dilution tunnels is inadequate. The current reneatabilitv of measurements is poor. Barsic (1984) showed trom a round-robin test that the root mean square of the 2-~ standard devi- ations were 76 percent of a 0.25 g/bhp-hr standard for six heavy-duty diesel engines tested in seven laboratories. For measure- ments intended to implement the 0.25 g/bhp-hr or the 0.1 g/bhp-hr standard, this variation is unacceptable. It is uncertain whether particulate emis- sion standards should be based on amount of total particulate matter, on which cur- rent standards are based, or amount of soluble organic component extracted from the particulates. The soluble organic com- ponent is the portion of the particulate that has been shown to be mutagenic and pos- sibly carcinogenic (Claxton 1983), suggest- ing that future health-related regulations should be based on this fraction. Basing standards on the soluble organic compo- nent poses the problem of separating and quantifying the specific toxic components by one of the present methods solvent extraction, vacuum sublimation, or ther- mogravimetric analysis. Variability associ- ated with the separation methods and sam- pling condition affects the mass of the soluble fraction collected, compounding the previously stated measurement vari ability problem for the total particulate matter. Present measurement methods for the collection of vapor-phase HCs from diesel engines do not collect all the compounds. Characterization of potentially toxic HCs is not possible if they cannot all be col- lected. There is need to continue the develop- ment and use of advanced HPLC and GC/MS techniques In conjunction warn separation methods to more accurately measure the amounts of key biologically active HCs in the particulate as well as the vapor phases. The nitroaromatics are im- portant compounds whose concentrations in diesel exhaust with and without partic- ulate traps should be measured more accu- rately. There is a need to investigate and de- velop measurement methods that quantify diesel odor. Pioneering work was carried out in the late 1960s and early 1970s, but was dropped around 1978 because of the potential health effects of diesel particulate emissions. Diesel odor, along with partic- ulates, is still the typical person's percep- tion of the diesel pollutants that are of concern. There is a need to apply odor measurement methods to new engines used in light-duty and heavy-duty vehicles and advanced engines that use particulate traps or incorporate advanced high-temperature materials. Refined organic compound measure- ment is particularly important to advance the development of low-heat-rejection (or commonly called adiabatic, as an ideal goal) diesel engines because their combustion chamber wall and gas temperatures will be higher. This elevated temperature will in- crease the amount of lubricating oil appear- ing as particulate emissions and has the potential of producing reactions between the HCs and oxygen/HNO3/NOx and other such gaseous mixtures to form toxic and biologically active species. A particular need in unregulated pollu- tant characterization data for gasoline en- gines is additional nitrous acid (HNO2) data as an extension to Pitts et al. (1984~. That paper showed higher levels of HNO2 from older (1974 and earlier) light-duty

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70 Automotive Emissions vehicles than from 1982 and newer cars that use three-way catalyst systems. The data show that even though the number of older cars is small, their HNO2 emission levels are so high that they may be the major source of all gaseous HNO2 from automo- tive emissions. HNO2 is a key precursor to photochemical air pollution and is also an inhalable nitrite. There is little known about how and when the nitro-PAHs are formed in the exhaust system (or the dilution tunnel) of diesel engines. Flow reactor studies with the basic species NO, NO2, CO, CON, N2, 02, S02, HCs present in the ex- haust, along with detailed engine studies that include the effects of the particles in the reactions, could help resolve this issue. Recommendation 9. PAH Measure- ments. There is a need for a program of comparative measurements of PAHs in partial-exhaust sampling systems and in full-flow dilution tunnel systems, with measurements made in the atmosphere downwind from the plume, for the pur- pose of determining how well laboratory data reflect the true composition of emis- sions into the atmosphere. Recommendation 10. Kinetics of Ni- tro-PAH Formation. Research is recom- mended to discover how and when nitro- PAHs are formed in the diesel engine exhaust system and dilution tunnel. This work can best be done by flow reactor studies of the basic gases in conjunction with detailed engine studies that include the actual HCs and particles. Recommendation 11. Particulate Mea- surement Variability. Research is required to reduce the variability in heavy-duty die- sel particulate measurements. Work needs to be undertaken to determine how to better control the parameters that influence this variability. a Recommendation 12. HC Character- ization. There is a need for research on the complete characterization of particulate- phase and gas-phase HCs in diesel exhaust. a Recommendation 13. Diesel Odor. There is a need to investigate and develop analytical methods that quantify diesel odor. This research should take advantage of the knowledge gained in the past eight years about measuring particulate-bound and vapor-phase HCs. Recommendation 14. Nitrous Acid. Additional data should be obtained about HNO2 emissions from older gasoline- powered vehicles. The literature shows high levels of HNO2 from older cars that may be contributing significantly to in- creased photochemical smog and direct ef- fects. . . Summary of Research Recommendations HIGH PRIORITY Based upon current information, the following research studies are most likely to yield useful data. Recommendation 1 Tampering and misfueling statistics are fairly well developed but Tampering and their effect on emissions is not as well known. Therefore, work Misfiteling should be done to better characterize the effect of tampering and misfueling on emissions from vehicles and to better assess their effect on ambient pollutant concentrations.

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John H..Iohnson 71 Recommendation2 There is a need for continued research on particulate control Diesel Particulate technology, including the regeneration systems, to reduce the cost Emissions and and complexity of these systems and the associated fuel economy Control penalties. Work needs to continue with various additives, substrate materials, regeneration systems, and controls to develop optimum systems that are able to decrease the diesel particulate emissions to the levels of 0.1 ~/bho-hr for heavy-duty diesels and 0.08 Mimi - ~ ---r ~~~ ~~ ' for light-duty vehicles required in California. In conjunction with this research there is a need to measure the metal species and the size distribution of the particles coming from diesel particulate traps. Recommendation 4 Real-time measurements of formaldehyde concentration should Formaldehyde be performed under transient and extreme conditions such as Measurements acceleration and deceleration, low temperature, light load, and extended idling with restricted ventilation. This research work should be done with and without catalysts since worst-case condi tions in the field will occur with catalysts removed. Similar measurements should be made on bus engines. Recommendation 7 Data should be obtained about the size distribution of particles in Diesel Fuel diesel exhaust and about the metal species they contain with and Additives without a particulate trap, with a diesel fuel containing a typical additive under consideration for production use. Data on the HCs bound to the particles and the vapor-phase HCs should also be obtained. Recommendation 10 Research is recommended to discover how and when nitro Kinetics of Nitro- PAHs are formed in the diesel engine exhaust system and dilution PAH Formation tunnel. This work can best be done by flow reactor studies of the basic gases in conjunction with detailed engine studies that include the actual HCs and particulates. Recommendation 11 Particulate Measurement Variability Research is required to reduce the variability in heavy-duty diesel particulate measurements. Work needs to be undertaken to deter- mine how to better control the parameters that influence this variability. Recommendation 12 There is a need for research on the complete characterization of HC Characterization particulate-phase and gas-phase HCs in diesel exhaust. MEDIUM PRIORITY Recommendations An improved vehicle evaporative emissions model should be Evaporative developed that is valid over various types of operating conditions Emission Model for a variety of ambient temperatures. At the same time, changes should be made in the EPA test procedure to obtain the data necessary to properly design and size the evaporative system for the high-temperature soak situation, and data should be sought that can be used in EPA's MOBILES computer model for other use patterns of cars.

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72 Automotive Emissions Recommendation 5 An automotive quality No. 2 diesel fuel with low sulfur and low Automotive Quality aromatics is necessary if low particulate emissions are to be No. 2 Diesel Fuel achieved. Research should be undertaken in cooperation with the automotive and petroleum industries to decide on effective and economical cetane number, sulfur and aromatic content, and 90 percent boiling point temperature specification limits for automo tive quality No. 2 diesel fuel, and to formulate fuels that meet the specifications. The need for this research becomes more urgent as diesel fuel usage continues to increase. Improved emissions and more control options require low-sulfur diesel fuel. Recommendation 6 Some combination of field RVP control along with a test fuel Evaporative with typical RVP (or calculation corrections for RVP differences) Emissions Control should be developed. Controlling RVP in motor gasoline, an approach successfully applied in California, is needed generally for controlling field evaporative.emissions. The question of whether car manufacturers should be testing with a worst-case RVP test fuel or a typical fuel needs further study. Recommendations Studies should begin immediately with an evaluation of the Emissions best available emissions data on engines operating with and with Measurement out emission control devices, to determine which of the unregu Methods lated pollutants really pose a potential threat to human health. Other unregulated pollutants might be added to this list if their concentrations reflect engine or emission control device perform ance. Next, every effort should be made to improve the analytical procedures presently used to measure the concentrations of those pollutants, to the point where they can be readily carried out by technicians. This may require that packaged sets of reagents and equipment be marketed for a specific analysis. For example, pre packed traps might be available for collecting gaseous HCs prior to thermal desorption onto a gas chromatograph with a specified capil lary column for the analysis of specific HCs at predetermined condi tions. Recommendation 9 There is a need for a program of comparative measurements of PAH measurements PAHs in partial-exhaust sampling systems and in full-flow dilution tunnel systems, with measurements made in the atmosphere down wind from the plume, for the purpose of determining how well laboratory data reflect the true composition of emissions into the atmosphere. Recommendation 13 There is a need to investigate and develop analytical methods that Diesel Odor quantify diesel odor. This research should take advantage of the knowledge gained in the past eight years about measuring partic ulate-bound and vapor-phase HCs. Recommendation 14 Additional data should be obtained about HNO2 emissions from Nitrous Acid older gasoline-powered vehicles. The literature shows high levels of HNO2 from older cars that may be contributing significantly to increased photochemical smog and direct effects.

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lohn H..Iohnson Acknowledgment I would like to thank Peter V. Woon for all of his assistance in the preparation of this paper. References Abtoff, J., Schuster H. C., and Langer, J. 1985. The trap oxidizers an emission control technology for diesel engines, Society of Automotive Engineers Paper 850015, Warrendale, Pa. Alson, J. 1985. EPA methanol vehicle emissions test programs, talk at EPA Region VI Methanol Work- shop, May 1985, Dallas, Tex. Amann, C. A. 1985. The powertrain, fuel economy and the environment, General Motors Corp. Research Publication 4949, Warren, Mich. Austin, T. C., and Rubenstein, G. S. 1985. A com- parison of refueling emissions control with onboard and Stage II systems, Society of Automotive Engi- neers Paper 851204, Warrendale, Pa. Barnes, G. J., and Donohue, R. J. 1985. A manufac- turer's view of world emissions regulations and the need for harmonization of procedures, Society of Automotive Engineers Paper 850391, Warrendale, Pa. Barsic, N. J. 1984. 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