Factors Influencing Vehicle Idle Emissions. Statistical Analysis of New York State Data Marcia P. Helme” and Walter J. Pienta New York State Department of Environmental Conservation, Division of Air, 50 Wolf Road, Albany, N.Y. 12233
administered by the DEC Division of Air in Albany, N.Y. The test vans were scheduled into the major cities and associated suburban areas across the state. Testing was conducted a t high vehicle use areas such as shopping center parking lots. The testing procedures and data gathered on each vehicle were similar for all 5 years of the testing program. For each vehicle tested, the following variables were recorded: model year, manufacturer, number of cylinders, mileage, concentration of hydrocarbons a t idle, and concentration of carbon monoxide a t idle. Vehicles with automatic transmissions were tested in “drive” with the brake applied, while manual transmission equipped vehicles were tested in “neutral”. The exhaust analyzers used in the program were dual-beam nondispersive infrared analyzers with the hydrocarbon sample referenced to hexane. The instruments were “garage type” analyzers as opposed to laboratory grade instrumentation. For the first year of the program (1972), Sun Electric Corporation EET-910 exhaust emissions analyzers were used exclusively. T h e ranges on this equipment were 0-7.5% carbon monoxide (CO) and 0-2000 ppm of hydrocarbons (HC). In 1973, the EET-910 instruments were used as well as Sun Electric’s then-new prototype “EPA-75” analyzer. One test van was used for the program during these 2 years. For the 1974 season, the department purchased six modified EPA-75 units from S u n Electric, similar to the units used by the California Highway Patrol for their roadside enforcement program. T h e modifications consisted of self-contained battery pack units, allowing operation on either conventional AC power or the battery pack. There were no modifications made to the emissions measurement system and associated electronics. T h e use of battery-powered instruments broadened the number of sites across the state into which the test vans could be scheduled, and also improved the actual location of the test vans a t a given site. This EPA-75 equipment had ranges of 0-10% CO and 0-2000 ppm of HC. The 1975 and 1976 programs used the same exhaust analysis equipment. T h e instrumentation used had both a mechanical/electronic span adjustment (simulating 100% of scale) and an inlet for gas calibration. Mechanical calibration was checked and adjusted periodically during a test day. The frequency of mechanical checks ranged from prior to testing each vehicle to checking i t after seven to ten vehicles.
Which general vehicle variables influence idle emissions? New York State operated a voluntary idle emissions test program for vehicles across the state during the 5-year period 1972-1976. Approximately 25 000 vehicles were inspected. The test program recorded model year, manufacturer, number of cylinders, and vehicle age as easily measured variables possibly affecting the idle emissions of carbon monoxide and hydrocarbons. Statistical analyses, including multiple range tests, indicate that all four factors significantly influence a vehicle’s emission levels, but t h a t the influences are not simple. For example, it is not universally true that emission levels decrease with succeeding model years, although trends are apparent for particular vehicle types. T h e most dramatic differences occur among manufacturers. T h e paper presents a n analytic methodology t o separate and judge the influence of certain easily determined vehicle variables. Vehicle idle emission levels are important to the study of mandatory inspectiodmaintenance systems as more and more states opt for idle emissions inspection tests. T h e reduction of idle emissions is important to the air quality of congested urban areas, where vehicles spend a large proportion of their operation a t idle. More importantly, idle testing-while being relatively easy and inexpensive compared to other types of emissions and diagnostic tests-is a n effective short test in identifying vehicles with the best potential for large mass emissions reductions ( I , 2). The New York State Department of Environmental Conservation (DEC) has conducted a roadside emissions measurement program since April of 1972. From then until November of 1976, approximately 25 000 motor vehicles were tested hy DEC technicians. This report summarizes the general trends and characteristics of these vehicles. The purposes for this characterization are twofold. T h e first is to see if the data support the following expectations: Idle emissions increase with increasing vehicle age. Idle emissions among manufacturer groups are approximately equal. Idle emissions decrease with increasing engine size. Idle emissions decrease with more recent model years. With the exception of the third point, the above behavior of idle emissions was anticipated when the department promulgated the standards in 1972. The second purpose is to look a t the implications for a state emission inspection/maintenance program.
Statistical Description and Analysis
Program Operation Program Development. The voluntary vehicle emissions measurement program ran from April to November for each year from 1972 through 1976. The 1975 and 1976 programs varied from the 1972-1974 programs. In 1975, tests using a portable dynamometer were commenced. This program, called the Simulated Driving Conditions (SDC) Test Program, had-as a major goal-the study of emissions from vehicles subjected to steady-state engine loads. T h e program used the Clayton Key-Mode (Copyright 1971, Clayton Manufacturing Co., El Monte, Calif.) system of emissions evaluation. For this report, only idle mode data from those tests are used. Data Acquisition and Test Procedures. The program was 306
Environmental Science & Technology
Purpose and Method. New York State’s program of voluntary testing could introduce potential bias into the sample statistics. The program may have tended to attract (a) drivers who are interested in good vehicle maintenance and (b) owners of newer vehicles. Additionally, the fact t h a t the program operated predominantly in shopping areas may have affected the number of high-mileage, commuter trip vehicles. Since vehicle age and model year are part of the data base, the effect of too many new vehicles can be separated out of the data and is discussed later in this section. T h e bias which may be created by owner maintenance as well as t h a t created by a potential lack of high-mileage commuter vehicles cannot be judged or eliminated using current data. However, these biases are likely to occur uniformly throughout the sample and our analysis here does not draw conclusions about absolute emissions levels but compares emissions among vehicle groups.
0013-936X/80/0914-0306$01 .OO/O
@
1980 American Chemical Society
In order to characterize idle emissions of vehicles on the road, a total of four factors are considered: model year, age, manufacturer, and number of cylinders. Age is defined as the difference between the model year of the vehicle and the year in which the vehicle was tested (Le., 1976 model-year vehicles tested in 1976 were age zero). Previous reports (see ref 3-5) have investigated the impact of such factors upon emission levels by stratifying (grouping) the sample vehicle population by each factor singly and comparing mean values between groups. For example, to investigate the effect of manufacturer upon emission levels, the sample was divided into several manufacturer groups and the means for each group computed and compared. In this analysis, however, the total sample was sufficiently large to subdivide by all four factors a t once. Each four-way subdivision is called a cell. Subdivisions were made as follows: Six Model-Year Groups: Pre-1968, 1968-1969, 19701971,1972,1973--1974,1975-1976. These groupings are based on the years in which changes were made in federal new car certification standards. Three Age Groups: 0-2 Years, 3-5 Years, 6 or More Years. This coarse grouping keeps the tot,al number of cells from being too large, while allowing comparisons between new, old, and “middle-aged” vehicles. Fioe Manufacturer Groups: General Motors, Ford, Chrysler, American Motors, and foreign. Three Cylinder Groups: 4, 6, and 8. This subdivision was chosen as an indicator of engine size. Our first step in this analysis was to perform an analysis of variance. A standard 6 X 3 X 5 X 3 factorial analysis is not possible because there are too many empty cells. For example, the sample contains no new 1969 vehicles and no old 1975 vehicles. The four-way stratification actually results in 127 cells out of a possible 270. Table I shows the four-way cell description and the number of vehicles obs’erved in each cell. One can then clompare mean emission levels among cells. Odometer mileage, the fifth factor from our data base, is not considered here: since to do so would necessitate a five-way subdivision of the sample, resulting in an unmanageably large number of cells and in cells with too few observations. For those familiar with analysis of variance (7,9, l o ) ,Table I indicates that an analysis using nested cells is possible. Accordingly, model year was nested within iage, both of these were crossed with manufacturer, and number of cylinders was nested within the other three factors. The HMDP2V program was used ( 9 ) .The results show all interactions to be significant. This indicates the need for a more disaggregated approach. In other words, the results of the analysis of variance show that, in order to observe the influence of any one of the four factors, each of the other three factors must be held constant. Accordingly, multiple-range tests were performed. Multiple-range tests are appropriate when the sample population is not representative of the total population, as is the case in a voluntary testing program. According to this method, one does not, for example, consider the mean CO emission for all six-cylinder vehicles compared with the mean for all fourcylinder vehicles. The percentage of four-cylinder vehicles which are foreign is large compared with the percentage of six-cylinder vehicles which are foreign. It would then be questionable whether we were, in fact, investigating the effect of the number of cylinders or the effect of manufacturer. Only in the case where neither age, manufacturer, nor model year significantly affects CO emissions could we compare the two groups of all four-cylinder vehicles and all six-cylinder vehicles. Results. I t is generally considered t h a t either the normal or the log norma.1 distribution provides a good fit to CO and
Table 1. Cell Frequenciesa model year
no. of
age
cyls.
GM
Ford
Chrysler
AMC
0, 1, 2
70-71
4 6 8
41 59 579
43
**
**
85 278
113 223
36 58
**
**
155 340
50
**
**
452 711
129 109
**
**
72
73-74
75-76
3, 4, 5
pre-68
68-69
70-7 1
72
73-74
6+
pre-68
68-69
70-7 1
4 6 8 4 6 8 4 6 8
84 75 880 149 134 1472
67 73 447 174 133 581
37
66 103 445
34 82 165
163 194
44 24
**
**
**
29 81
18 46
11 30
4 6 8
**
**
**
** * * **
161 926
102 465
129 390
71 33
4 6 8
39 152 1269
48 180 555
**
**
261 508
82 72
**
**
106 155
19 17
**
**
60 108
11
4 6 8
4 6 8
29 35 446
36 28 176
4 6 8
257
4 6 8
**
**
**
**
474 1301
303 610
325 478
140 40
**
**
**
**
109 62 1
58 243
101 254
43 25
**
**
**
16 145
22 67
34 42
** *
4 6 8 4 6 8
14
15 13 122
forelgn
20
12
253 20
**
366 31
**
555 63
**
153 13
**
30
*
** 298 21
**
463 37
**
103 24
**
44
* **
370 22
**
147 10
**
31
* **
a *, too few observations to be significant (less than 10). * * , no observations.
HC emissions [5 (p 16), 6 ( p ll)].Kolmogorov-Smirnov tests were applied to 15 cells, and the results (not shown here) indicate that the normal is the better distribution for CO emissions, while the log normal is preferable for HC. a. T h e Effects of the Number of Cylinders. Figure 1 presents some of the sample means and confidence limits of idle CO emissions. Cells are grouped together in blocks. Each block represents a given age-model year-manufacturer group. The several cells within each block represent vehicles with different numbers of cylinders. By comparing the means within each block, one can discern whether the number of a vehicle’s cylinders significantly influences its emission levels when the other three factors (age, model year, manufacturer) are held constant. For example, the lower left block of Figure 1 represents CO emissions for new 1975-1976 General Motors vehicles and shows a definite decrease. The confidence intervals within a given block provide a visual picture of the extent to which vehicles in different cells have different emission levels. Nonoverlapping confidence intervals within a block suggest t h a t the means within that block are significantly different. In addition, a multiple-range test was performed on each Volume 14, Number 3, March 1980
307
::i FORD
CHRYSLER
AMC
el
Ea
B e
FOREIGN
n E
1
AGE 6t MODEL YEAR PRE-68
20 10
-z --P 0 V
1
5.04.0
3.0: 2.0-
8
39:~~
MODEL YEAR 70-71
E
e
1.0-
E l ' El
E P 4
6
8
4
6
8
Ir 4
6
8
leR 4
6
8
NUMBER OF CYLINDERS *SIGNIFICANT DIFFERENCE
Figure 1. Effects of number of cylinders: mean CO values, with 9 5 % confidence limits
block. All blocks where the differences are significant are so labeled. T h e mathematics of the test are as follows: Mean carbon monoxide confidence limits are derived from the standard expression for a normal distribution:
x f s,tl\/n
(1)
w
where = sample mean value for cell; .s, = sample standard deviation for cell; t = table value of student's distribution based on 95% confidence; n = number of observations in cell. Hydrocarbon confidence limits are derived from the expression for a log normal distribution: exp
(7f s , t / t / n )
(2)
where ?T; = sample arithmetic mean of logarithms; s j = sample standard deviation of logarithms. The multiple range test is described by Winer ( 7 ,p p 191-5) and by Mood and Graybill ( 8 . p p 267-71). The test is applied here as follows: Differences among cell means are significant if, and only i f -
- Xrnm
Xmax
x,,,
S,~,ltG
>4
(3)
x,,,
where = maximum cell mean within the block; = minimum cell mean within the block; Sx,p= pooled staudard deviation for the block. This reflects the standard deviation of each cell in proportion to the cell's size. 6 = harmonic mean for t h e number of observations for t h e block, Le., 6 = k / Z f = l ( l / n Lwhere ), n, represents the number of observations in the i t h cell, and h represents t h e number of cells in the block. Winer recommends the harmonic mean when not all cells contain the same number of observations (7, p p 215-8). q = table value of studentized range statistic for a 5% level of significance. Tables are available in Winer (7) and in Mood and Graybill (8). The inequality (3) refers to carbon monoxide. In the case of hydrocarbons, it becomes: -
- Ymm >4 pl\ijl
Ymax
s, 308
Environmental Science & Technology
where Pmax, ymin, and Sl,prefer to the means and standard deviations of the logarithms. The multiple-range test will usually find differences among emission levels within a given block to be significant when the confidence intervals of the maximum and minimum have little or no overlap. The fact that the difference between the maximum and minimum is significant does not guarantee that the differences between intermediate values are significant. For example, Figure 1 shows that idle CO emissions of new 1975-1976 General Motors vehicles vary significantly between four and eight cylinders, but there is little distinction between the emissions of four- and six-cylinder vehicles. Significant differences do not necessarily guarantee a trend. For example, in Figure 1, six blocks indicate significant within-block differences. Four of these six blocks indicate a decrease in emissions with an increase in engine size, while two of them indicate the opposite. In other words, the presence of a significant difference tells that some effect is present but not the nature of the effect-Le., whether it is upward, downward, or U-shaped. T h e nature of the effect is determined from the visual presentation of the means and their confidence intervals. In general, we infer t h a t a trend is present when a large percentage of the blocks exhibit the same nature (e.g., downward) as well as exhibiting significant differences. Does Figure 1 support the hypothesis t h a t vehicles with more cylinders tend to have lower idle emissions? Note t h a t this holds true in only 4 of the 15 blocks. In fact, Figure 1 suggests that there is no universal relationship between idle CO emission levels and number of cylinders. An analysis of all 56 age-manufacturer-model year blocks for both CO and HC (not shown here) indicated that emissions decrease with increasing engine size in only 1 2 blocks in the case of CO and in 7 blocks in the case of HC. The blocks where this occurred tended to be among t h e 0-2 age group.of vehicles. Thus, there is a tendency for idle CO emissions and, t o a lesser extent, HC emissions to decrease as the number of cylinders increases, but this trend is present only for new cars. In any event, the results thus far show t h a t one cannot
CHRYSLER
FORD
FOREIGN
AMC
AGE 6t
40 30 20
3.0 2.0
BE
1.0
a w m I
a
1
C I
1
n ln?crld ~ c + ~ (
? a 0 n u +
~ I
~ I
n cm t d d
I
n m t d d ~ C + - L ~ P
D
MODEL 0 SIGNIFICANT
a
1
S
~
r AC d~ ? Cd d~
- I
~ I
~
~
~
,
m m +Pr - -
YEAR
DIFFERENCE
Figure 2. Effects of model year: mean CO values, with 95% confidence limits, for six-cylinder vehicles
FORD
GM
r,ooo1
I
I
CHRYSLER
AMC I
II I
FOREIGN
900 AGE 6t
500 400 300 2 00
E
MODEL 0 SIGNIFICANT
YEAR
DIFFERENCE
Flgure 3. Effects of model year: geometric mean HC values, with 95% confidence limits, for six-cylinder vehicles
discount number of cylinders as an influential factor, even though there is 110 universal trend which carries through vehicle age. Consequently, the remainder of this analysis will consider six-cylinder vehicles only. (Were we to consider only eight-cylinder vehicles, we could not make comparisons between foreign and American manufacturers. Were we t o a n alyze only four-cylinder vehicles, we could not compare Chrysler and Arnerican Motors vehicles with t h e other manufacturers.) Cells can then be compared with t h e assurance
t h a t no cell has higher emissions just because it contains a disproportionate amount of vehicles with the “wrong” number of cylinders. b. The Effects o f h l o d e l Year. T o investigate t h e effects of model year, we grouped all of the six-cylinder vehicles into age-manufacturer blocks. T h e appropriate means and confidence intervals for CO and HC are shown in Figures 2 and 3, respectively. The cell means within each block represent different model years. T h e same methods explained in the Volume 14, Number 3, March 1980 309
a
Pre.68 Model Yrs
3.04
1968-69
It3
--
1970-71
1973.74
1972
1975-76
UIU '
*
I
*
I
I
Figure 4. Effects of manufacturer: mean CO values, with 9 5 % confidence limits, for six-cylinder vehicles
previous section are used in this section and in succeeding sections to explore the effects of each of t h e three remaining factors: model year, manufacturer, and age. If the changes in the design of vehicle emission systems were producing a significant decrease in idle CO emissions, all t h e blocks in Figure 2 should look like the middle left block (General Motors. age 3 t o 5 years). The block shows a significant decrease in CO with succeeding model years; however, such a decrease is not universal. Older Fords and Chryslers of age less than 6 years show no effect. One concludes that the decrease in idle CO emission levels for succeeding model years is far from universal, although it exists for particular manufacturers and for particular model years. In contrast to idle CO, t h e idle HC emissions show significant differences among model years in almost all blocks. Like the CO emissions, the H C emissions often show a significant decrease between only two successive model year groups within a block. T h e H C decrease between 1967 and 1968 is universally significant, Le., it is present in nearly all blocks. We conclude, then, t h a t a significant decrease in idle HC emissions for succeeding model years is universal in that it applies to almost all age-manufacturer groups. However, the levels do not decrease with every change in federal standards. The most pronounced decreases occur between 1967 and 1968 and between 1971 and 1972. c. T h e Effects of Manufacturer. Figures 4 and 5 show the effects of manufacturer. In this case, each block represents all six-cylinder vehicles in a given age-model year group. Cell means within a block represent different manufacturers. Since all manufacturers should have met the same standards in production, the expected result is t h a t there should be no difference in idle emissions among manufacturers. From 1970 on, every block in Figure 4 shows significant differences among manufacturers for vehicles less than 6 years old. For model years 1970 through 1974, General Motors vehicles consistently have the lowest idle CO emissions, while Chrysler and foreign vehicles have the highest emissions, particularly when vehicles are new. Vehicles of age 3 through 5 years show fewer differences among manufacturer groups, but General Motors is still definitely below the rest. The most 310
Environmental Science & Technology
pronounced difference is in t h e block of new 1975-1976 vehicles, where Chrysler vehicles are significantly higher than all of the others. When this block is compared with the block of new 1973-1974 vehicles, we see that, of the four higher emitters in 1973-1974, all but Chrysler show a marked improvement by 1975-1976. Of course, these data cannot show whether these improvements will continue as the vehicles age. In Figure 5, there are significant differences in nearly all blocks. Foreign vehicles are consistently the higher HC emitters through 1972. By 1975, the most pronounced difference is between Fords, which are the lowest emitters, and all other manufacturers. Unlike the CO emissions, differences in HC between manufacturer groups do not necessarily diminish as the vehicles age. d The Effects of Age Figures 6 and 7 present the effects of vehicle age. Here, a block represents all six-cylinder vehicles of a given model year-manufacturer group. Cell means within a block represent different vehicle ages. While almost all blocks in Figure 6 show a tendency for emissions to increase with vehicle age, in only 3 out of the 19 blocks are these differences significant; therefore, while the trend is universal, it is not dramatic. Figure 7 shows that the same holds true for hydrocarbons.
Conclusions Each of the four factors studied (model year, age, manufacturer, and number of cylinders) has been shown to be associated with a statistically significant influence on either idle CO, idle HC, or both. Although, in many cases, there are no consistent universal trends cutting across all model years, vehicle ages, manufacturers, or numbers of cylinders, still each of the factors must be weighed as to its impact upon emissions inspection standards. Although the more recent model years show improvement in idle emissions levels, the trend is not consistent across all manufacturers. Thus, although idle emissions characteristics for the vehicle population as a whole tend to follow the trend of new car standards, quantitative idle emissions reductions fall short of the potential of control technology and manu-
Pn-68Modrl Yrr. 1968-69
is70 - 71
i972
1973-74
1975- 76
AGE 6+
L 3,495
500 - 400 V
300 200 100
Figure 5. Effects of manufacturer: geometric mean HC values, with 95 YOconfidence limits, for six-cylinder vehicles
CHRYSLER
GM
AMC
FOREIGN
?r
3.0
m
r-
E
[E
6.0
4.0
E, a W
> 0 0
d6.0
n 0
I
3.0 2.0 I.o
4.0
BE
3.0 2.0 0
SIGNIFICANT DIFFERENCE
VEHICLE AGE
Figure 6. Effects of age: mean CO values, with 95% confidence limits, for six-cylinder vehicles
facturers' specifications. In particular, for catalyst technology in 1975-1976 vehicles, the improvement is not as large as might be expected. Among model year groups, there are more significant differences in idle I-IC than in the idle CO emissions. This might be because CO emissions are more sensitive to maladjustments t h a t do not significantly affect t h e perceived performance of t h e vehicle, whereas malfunctions related to HC, indicative of ignition problems, would tend to be repaired more quickly
since their effect on performance is more pronounced. However, without data on the state-of-tune of these vehicles, this remains merely conjecture. The most dramatic differences occur among manufacturers. T h e method of analysis used separates out t h e effects of age, number of cylinders, and model year. Thus, the reasons for t h e vehicles of a particular manufacturer having lower emissions cannot be ascribed to its sample set having a lower percentage of older (and higher emitting) vehicles or having fewer Volume 14, Number 3, March 1980 311
FORD
GM
CHRYSLER
AMC
FOREIGN
F
m
r-
I
@I
400
500
I
4
:::L I V”
300 200 io0
z-
‘u! y?
*+
*SIGNIFICANT DlFfERENCE
VEHICLE AGE
Figure 7. Effectsof age: geometric mean HC values, with 95% confidence limits, for six-cylinder vehicles
vehicles with a particular number of cylinders. The between-manufacturer differences diminish as the vehicles age, but the relative rank remains the same. Thus, the hypothesis t h a t idle emissions among manufacturers are approximately equal cannot be supported by our data. Age is the most universal factor influencing emissions, but not the most dramatic. It is, along with model year, the easiest of the influences to understand, and certainly age is a variable from which one would expect the clearest trends. After all, it is the deterioration of in-use vehicles which a state inspectiodmaintenance system seeks to control and lessen. T h e universality of the influences of age is, therefore, not surprising. What is surprising is that the influence of age is less dramatic than the influence of manufacturer. However, age is t h e only one of the components of what is commonly referred to under the general terms of vehicle “deterioration” or “degradation”. Mileage and the care of vehicles received-the effects of maintenance and repair-were ignored. One might expect decreases in idle emissions as the number of cylinders increases. This trend does exist for newer vehicles (age 0, 1, 2 ) for both idle CO and idle HC. This trend is not apparent for vehicles of age three or more. Further analysis is needed to determine why the trend continues for some vehicles as they age, and is either absent or masked for other types.
Implications for Setting Emission Standards for a n Inspection S y s t e m New York State began its pilot program and has continued voluntary testing using emissions standards varying with model year alone. As pointed out in the introductory statement, these standards were based upon a n implicit assumption of uniformity among manufacturers and their various engine families. The results in this report indicate that use of such standards in a n inspection system would yield significantly differing failure rates among different manufacturers and among vehicles with different numbers of cylinders. In particular, small engine vehicles would have a higher failure rate than large engine vehicles. Chrysler Corporation vehicles and, to a lesser extent, cars of foreign manufacturers would have higher failure rates than those of other manufacturers. (However, recent analysis of 1977-1979 model year vehicles 312
Environmental Science d Technology
indicates that for newer model years, Ford vehicles, not Chryslers, are the major polluters. For example, analysis of 1233 vehicles of model year 1978, tested in 1978, shows that a CO standard of 4.5 vol 97, and a HC standard of 420 ppm would fail 16.5% of all 1978 vehicles, 15.2% of all 1978 GM vehicles, 24.9% of all 1978 Ford vehicles, 13.8% of all 1978 Chrysler vehicles, 10.2% of all 1978 AMC vehicles, and 8.4% of all 1978 foreign vehicles.) An alternative would be to account for these differences among manufacturers and among various engine sizes by setting standards to reject the same proportions of vehicles in each manufacturer-engine size group. Focusing only on differences among manufacturers, t h e data presented here would certainly allow system design for failure rates by a specific manufacturer to meet the overall emissions reduction goals of a n inspection system. However, even though the data suggest large variations in idle emissions among manufacturers, it does not necessarily follow that standards must reflect these variations. Although the original assumption that all manufacturers met the same new car standards and should have approximately equal idle emissions proved incorrect, the idea of uniform standards need not be completely discarded. In fact, the inspection/maintenance system may be used to promote rectification of problems associated with particular models. In some cases, intermanufacturer differences in failure rates can be accounted for through specific idle system design elements. It certainly is not reasonable to expect an inspection system (or this paper) to account for all the differences in emissions levels that were found to exist. The main thrust of the paper is to explore intergroup differences in emissions where t h e groups are well defined by variables easily and accurately measured. Certainly the four factors (engine size, model year, manufacturer, age) are not meant to be an all-inclusive list of factors which might influence emissions. Vehicle state-of-tune (or vehicle maintenance) may have more impact upon emissions than any of the factors considered. Indeed, an inspection program has as its target those vehicles which are not properly maintained-or not maintained a t all (merely repaired when the vehicle is no longer driveable). Nevertheless, without accounting for or detailing specific design or maintenance problems, it is reasonable that standards be set to fail the highest emitters in order to fail a minimum number of vehicles
while maximizing the air quality benefit. A distinction probably should be made between taking sanctions against a vehicle owner who does not properly maintain his or her vehicle and thereby has excessive emissions, and one who makes every attempt to maintain the vehicle “properly” but still has high emissions. A case in point is the poor idle emissions performance of 1975-1976 vehicles in general and 1975-1976 Chrysler Corporation vehicles in particular. Chrysler recommends t h a t vehicles with idle CO in excess of 0.3% a t the tailpipe need repair or adjustment. Yet, the mean idle carbon monoxide of all 1975 Chrysler vehicles with up to 1year of use was 3.2% ( 3 ) . This slippage between design and production vehicles in their first year of use is one which must be addressed by EPA and the manufacturers before the further deterioration of vehicles comes under the purview of state agencies. EPA is essentially trying to establish that dealers are agents of the manufacturers in terms of emissions related servicing and t h a t the responsibility of manufacturers t o build vehicles t h a t will comply with standards for their useful life extends beyond production and assembly. Thus, a fine line remains in distinguishing between improper design and maintenance for which the manufacturer is liable and improper maintenance or negligent lack of maintenance for which the owner is directly responsible. It is hoped that i,his fine line will be better defined, and there will be smaller variations among manufacturers, which will ultimately simplify the task of reducing emissions from in-use vehicles. Although inspection system design raises many questions in addition to those the analysis of the data had tried to resolve, these are basic issues which must be contended with in the process of setting inspection standards. T h e data collection and analysis presented herein provide an indispensible base upon which further work of designing optimal standards can proceed.
We appreciate the suggestions and assistance of Dr. .John Hawley, Mr. Robert hlajewski. and Dr. John Wilkinson in reviewing this paper. We also appreciate the efforts of Mrs. Kathy McMillen in preparing the typed manuscript and of Mr. Gary Lanphear, Mrs. Carol Clas. and Mrs. Mary Kelly in preparing the graphs.
Literature Cited (1) E P A Report IMS-004/PS-2,”‘PortlandStudy Interim Analysis: Update with Nine l l o n t h s of Vehicle Operation”, May 1979. ( 2 ) State of Oregon, Department of Environmental Quality, “Report on Motor Vehicle Emission Inspection Program 1977-1978”, February 1979, Appendix G. (3) Pienta. W.J., “Steady State Emission Characteristics of 1975 and 1976 Model Year Vehicles Tested in New York State”, New York State Department of Environmental Conservation. (4) Elston, J. C., “A Comparison of Nationwide Inspection Program Idle Emission Data”, New Jersey State Department of Environmental Protection. (5) Berens, A, P., Hill, h1. H., ”Automobile Exhaust Emission Surveillance Analysis of t h e FY 1974 Program”. EPA-160/3-76-019. Ann Arbor, 1976. (6) EPA Report EPA-460/%-74-001,“Automobile Exhaust Emission Surveillance Analysis of the FY 1972 Program”. (7) LViner. B. J . , “Statistical Principles in Experimental Design”, McGraw-Hill. New York. 1971. (8) Mood. A. M., Graybill, F. A,. “Introduction to t h e Theory of Statistics”: hIcGraw-Hill. S e w York. 1963. (9) Dixon, LV, J., Ed., ” B M D P , Biomedical Computer Programs”, Vniversity of California Press. Los Angcles. 1975. (10) ffalpole, R. E., Myers, R. H., “Probability and Statistics f o r Engineers and Scientists”. LLlacMillan, New York, 1972. (11) Lindgren, B. n’.. “Statistical Theory”, 2nd ed., MacMillan. Toronto, 1968.
Receiced for recieic, ,Vfarch 12, 1979. ..lccepted December 21, 1979.
Ac k n ow1edgmerits
Supplementary Material Available: Table I I showing the effec ts of number of cyiinders using the results of mrritiple range t e s t s , Figure 8 shoaing the effects of number C J cylinders ~ using geometric m e a n H C calues, u,ith 9J‘r confidence limits. and Figures 9-12,
The authors wish to acknowledge the role of the 18 technicians who have been with the Mobile Source Section (Bureau of Source Control, Division of Air) a t various times since 1972, as well as the vehicle owners whose cars were tested. Because of their efforts and cooperation, New York State has a strong data base upon which to develop an inspection system. We would also like to acknowledge the contributions of Eric Holt, who directed the test programs from 1972 t o 1973.
normal und log norma/ plots of cumulatice frequencies for ris-c>linder 1972 Chrlslers cifagr 0, 1. and 2 (1p a g e s ) , will appearfollouing these pages in the microfilm edition of this coiunx of the journal. Photocopies of the supplementar>,material fr(Jl?Ithis paper or microfiche (105 X 118 mm, 24X reduction, negatices) may be obtained from Business Operations, Rooks and :Journals Diiiision, American Chemical Society, 1155 16th S t . , .V. W., Wmhington, D.C. 20036. Full bibliographic citation Gournai, t i t i p of article, a u t h o r ) and prep u y m e n t , check or money order for $‘.?..50f o r photocopy ($7.00foreign) or S3.00 for microfiche (S1.00 foreign), are reqriired.
Volume 14, Number 3, March 1980
313
