EPA-AA-SDSB-84-2
Technical Report
An Evaluation, of the Particulate Levels Occurring
Under 1.0/1.2 g/mi NOx standards for LDDVs and LDDTS
By
Rebecca Kanner
May 1984
NOTICE
Technical Reports do not necessarily represent final EPA
decisions or positions. They are intended to present
technical analysis of issues using data which are
currently available. The purpose in the release of such
reports is to facilitate the exchange of technical
information and to inform the public of technical
developments which may form the basis for a final EPA
decision, position or regulatory action.
Standards Development and Support Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air, Noise and Radiation
U. S. Environmental Protection Agency
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I. Introduction
The Diesel Particulate Study (DPS)[1] examined the level
of NOx and particulate emissions that would be present for
three different NOx scenarios: 1) l.f)/1.2 g/mi, 2) 1.5/1.7
g/mi, and 3) 2.0/2.3 g/mi NOx standards for LDDVs and LDDTs,
respectively. Chapter 1 of the study estimated the particulate
emission level as a function of a changing NOx emission level.
This relationship was based on the certification test results
for LDDVs and LDDTs from 1982 and 1983 model years. The
methodology to estimate the particulate levels will be
described in the following section-. The purpose of this report
is to compare the particulate emissions estimated under the low
NOx level (i.e., 1.0/1.2 g/mi) to the actual 1984 California
and 50-state certification particulate levels that are now
available at these low NOx levels.
It is important to make this comparison because the
particulate emissions at low NOx emission levels were based on
data at higher NOx levels. Thus, the derived NOx/particulate
relationship was extrapolated to obtain the low. NOx levels.
The 1984 California standard is at a 1.0/1.2 g/mi NOx level,
allowing the opportunity to examine the particulate emission
levels of certified LDDVs and LDDTs at these NOx standards.
Without accurate estimates, it is not possible to project what
the manufacturers' corporate average particulate standard
levels will be with a 1.0/1.2 g/mi NOx standard. Nor will it
be possible to judge just how many vehicles will require traps
for this scenario. This report will examine the accuracy of
the estimates and the resulting projections.
II. Previous Methodology
In order to estimate particulate standard levels under a
NOx standard of 1.0 g/mi for LDDVs and 1.2 g/mi for LDDTs, a
NOx/particulate relationship was developed through the use of
NOx/particulate tradeoff curves. The data for these curves
were supplied by 1983 model year low mileage levels. (Test
results from 1982 were used when 1983 results were not
available.) Light-duty diesel vehicles were divided into three
categories based on engine size: 1) small (1.6-4.3 liters
displacement), 2) medium (2.0 to 2.8 liters displacement) and
3) large (3.0 to 5.7 liters displacement). The tradeoff curves
for these engine sizes resulted in three respective slopes for
NOx values less than 1.35 g/mi: 1) -.033, 2) -.201, and 3)
-.400 g/mi particulate/g/mi NOx. Light-duty diesel trucks were
divided into only two categories: 1) small (1.6 to 2.5 liters
displacement), and 2) full-size (6.2 liters displacement). The
slopes 'for LDDTs are the same as for small and large LDDVs,
respectively.
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The low-mileage LDDV particulate and NOx emission values
are listed in Table 1; the LDDT data are -in Table 2. These
values were projected by using the known 1983 certification
emission data for each engine, family and the appropriate
NOx/particulate tradeoff curve slope (applied down to a
low-mileage NOx level of 0.90 g/mi).
The standard levels for both NOx and particulates were
determined by multiplying the low-mileage emission levels by
their deterioration factors (DF) - and the safety factor. The
deterioration values (DF) were the certification DFs for the
1983 model year. A safety margin of 10 percent was used for
this study. The estimated LDDV particulate standard levels
under the 1.0 g/mi NOx standard are listed in Table 3, the LDDT
values are included in Table 4.
III. 1984 Certification Levels
The methodology just described is potentially biased in
its accuracy of predicting particulate standard levels at low
NOx levels because the emission data that were used in the DPS
were 1983 certification values (i.e., emission values under a
1.5/2.3 g/mi NOx standard). At the time of the study, there
were no other data available, nor was the effect technology
changes would have on the NOx/particulate relationship known.
Since that time, the 1984 California standards of 1.0 g/mi NOx
for LDDVs and 1.2 g/mi for some LDDTs have gone into effect and
the projections can be evaluated. It should be noted that the
majority of the LDDV engine families that were certified
federally in 1983 were not certified in 1984 in California.
Only those 1983 federal engine families which had identical, or
nearly identical, 1984 California counterparts were included in
this evaluation.
The certification levels were obtained from the 1984
summary sheets of the California and 50-state certification
applications. The actual emission levels listed in Tables 1
and 2 were calculated by dividing the certification emission
levels by their DF's and adjusting for the 10 percent safety
factor.
It's difficult to make a comparison of these particulate
values to the estimated particulate emission values because the
actual NOx emission levels are less than the .9 g/mi
low-mileage level of a 1.0 g/mi NOx standard for LDDVs. In
order to make a comparison it was necessary to adjust the
actual emission levels so that the NOx low-mileage level was
also equal to 0.90 g/mi. To do this, ideally, new
NOx/particulate tradeoff curves should be plotted and new
slopes measured from the 1984 emission data. This procedure
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Table 1
Comparison of LDDV Low-Mileage,
Low-NOx, Particulate Emissions (g/mi)
Estimated - DPS
Mfr.
CM
GM
Isuzu
Isuzu
Mercedes
Benz
Nissan
Peugeot
Volks-
wagen
Volks-
wagen
Engine
Disp.
1.8L
4.3L
1.8L
1.8L
3.0L
1.7L
2.3L
1.6L
1.6L
ConfigU--
ration
M5,2500
L3*,3500
M5,2750
A3 ,2750
A4,4000
M5,2500
A3, 3500
M5,2250**
5A,2250
NOx
Test Level
.90
.90
.90
.90
.90
.90
.90
.90
.90
Particulate
Test Level
.18
.33
.19
.17
.51
.23
.32
.19-. 23
.18
Actual
NOx
Test Level
.56
.74
.72
.70
.80
.52
.69
.65-. 90
.87-. 9
Particulate
Test Level
.18
.26
.21
.24
.50
.23
.34
.13-. 28
.15-. 18
Volvo 2.4L M4***3500 .90 .38 .65 .27
* The transmission of the 1984 GM 4.3L is L4.
** The inertia weight of the 1984 1.6L, MS Volkswagen varies
from 2375-2500.
*** The transmission of the 1984 Volvo is L4.
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Table 2
Comparison of LDDT Low-Mileage,
Low-NOx, Particulate .Emissions (q/mi)
Estimated
Mfr.
GM
GM
Isuzu
Isuzu
Mitsu-
bishi
Mitsu-
bishi
Nissan
Toyota
Toyo-
Kogyo
Engine
Disp.
6.2L
6.2L
2.2L
2.2L
2.3L
2.3L
2.5L
2.4L
2.2L
Trans-
mission
L4
L4
M4
M5
M5
M5
M5
M5
M5
NOx
Test Level
1.08
1.08
1.08
1.08
1.08
1.08
1.08
1.08
1.08
Particulate
Test Level
.51
.53
.27
.26
.39
.37
.30
.27
.27
Actual
NOx Particulate
Test Level Test Level
1.16
1.60
.68
.76
.60
.70
.68
.68
.75
.46
.34
.28
.26
.30
.22
.16
.20
.14
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was not followed because there were not enough data points
available; the slopes from the 1983 N0x/part"iculate curves were
used to, adjust the emission levels. The particulate standard
levels under a 1.0 g/mi NOx standard were calculated using the
1984 DFs and the safety factors; these values are listed in
Table 3. A similar procedure was followed for LDDTS; the
results are listed in Table 4.
IV. Comparison
The difference between the estimated and the adjusted
actual LDDV particulate standard levels is listed in terms of
percent for each engine family in Table 3; the corresponding
percentages for LDDTs are presented in Table 4. The estimated
LDDV particulate levels are greater than the values derived
from the 1984 low NOx data for all but three engine families.
The range is quite large, varying from a five to a fifty
percent difference; the comparison of the two particulate
levels for LDDTs is similar.
From this analysis it is clear that the DPS generally
overestimated the manufacturers' corporate average particulate
standard levels at low NOx standards for both LDDVs and LDDTs,
based on the 1983 standard levels. The difference is an
average of approximately 5 percent for LDDVs and nearly 25
percent for LDDTs. For LDDTs, the differences occur nearly
entirely with small LDDTs. (The projection for the GM 6.2L
engine was very accurate.) It follows that the projected
number of vehicles requiring traps for this scenario is also
overestimated, particularly for LDDTs, if the same engine
families and the same number of engine families are certified
under a 1.0/1.2 g/mi national NOx standard as were certified
for the California and the 50-State standard in 1984. The
estimated values in the DPS should, thus, be considered as
somewhat conservative for LDDVs, but very conservative for
LDDTs.
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Table 3
Comparison of Estimated vs. Adjusted "Actual" LDDV
Particulate Standards Levels Under the 1.0 g/mi NOx Standard
Mfr.
GM
GM
Isuzu
Isuzu
MB
Nissen
Peugeot
VW
VW
Volvo
Engine
Disp.
1.8L
4.3L
1.8L
1.8L
3.0L
1.7L
2.3L
1.6L
1.6L
2.4L
Conf ig.
M5,2500
L3,3500
M5,2750
A3, 2750
A4,4000
M5,2500
A3, 3500
M5,2250
SA,2250
M4,3500
Est. Particulate
Standard (g/mi)
.21
.37
.23
.21
.57
.29
.36
.21-. 29
.21
.47
Adjusted "Actual"
Particulate
Standard (g/mi)
.20
.24
.24
.27
.51
.31
.34
.14-. 36
.18-. 21
.24
Percent
Difference
-4.8
-35.1
+4.3
+28.6
-10.5
+6.9
-5.6
-33.3-+24.1
-14.3-0.0
-48.9
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Table 4
Comparison of Estimated vs. Adjusted "Actual" LDDT
Particulate Standard Levels Under the 1.2 g/mi NOx Standard
Mfr.
GM
GM
Isuzu
Isuzu
Mits
Mits
Nissan
Toto
Toko
Engine
Disp.
6.2L
6.2L
2.2L
2.2 L
2.3L
2.3L
2.5L
2.4L
2.2L
Trns.
M4
L4
M4
M5
M5
M5
M5
M5
M5
Est. Particulate
Standard (g/mi)
.56
.59
.34
.33
.43
.41
.37
.30
.30
Adjusted "Actual"
Particulate
Standard (g/mi)
.54
.61
.32
.30
.31
.23
.18
.25
.14
Percent
Difference
-3.6
+3.3
-5.9
-9.1
-27.9
-43.9
-51.4
-16.7
-53.3
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1983
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References
1. "Diesel Particulate Study," U.S. EPA, ECTD, October
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