EPA-AA-TEB-EF-8 4-1
Proposal for 1980 and Earlier Light-Duty
Gas Vehicle Emission Factors for MOBILE3
by
Thomas L. Darlington
May 1984
Test and Evaluation Branch
Emission Control Technology Division
Office of Mobile Sources
U.S. Environmental Protection Agency
-------
Table of Contents
Page
1.0 SUMMARY 3
2.0 BACKGROUND 6
2.1 MOBILE2 Approach 6
2.2 MOBILES Approach 6
2.3 Other Items Pertaining to LDGV Emission Rates 6
3.0 BASIC EXHAUST EMISSION RATES 8
3.1 Identification of Tampered and Misfueled Vehicles 8
3.2 EGR Tampered Vehicles 8
3.3 Vehicles with High Lead Fuel Values 9
3.4 Low Altitude Emission Rates 11
3.4.1 HC and CO Emission Rates 11
3.4.2 NOx Emission Rates 12
3.4.3 Summary of All Pre-1981 Low Altitude Rates 13
3.5 High Altitude Emission Rates 14
3.5.1 HC and CO Emission Rates 14
3.5.2 NOx Emission Rates 15
3.5.3 Summary of All Pre-1981 High Altitude Rates 16
4.0 CORRECTION FACTORS 17
4.1 Normalized Bag Fractions 17
-------
1.0
SUMMARY
New HC, CO and NOX emission rates were developed for 1975-1980
light-duty gasoline vehicles (LDGV's) at low and high altitudes. The
rates were not updated for the California region. The HC and CO rates
were developed from a sample of vehicles that excluded those with
evidence of air pump tampering, catalyst removal and misfueling. The
NO emission rates were developed from a sample that excluded the same
vehicles plus those with evidence of EGR tampering. The new rates are
shown in Table 1 below. The HC and CO rates for 1980 are substantially
lower than MOBILE2, while the HC, CO, and NOX rates for 1975-79 and the
NOX rates for 1980 are little changed from MOBILE2. The effect of
these new rates on HC and CO emission factors for light-duty vehicles at
low altitude is shown in Figures 1 and 2. Only the 1975-80 emission
rates have been changed for these figures; all other rates are the same
as in MOBILE2. It should also be noted that the 1975-80 emission rates
used did not reflect misfueling, whereas the 1981 and later emission
rates did. Including MOB1LE2 misfueling effects in these new 1975-80
emission rates would have had the effect of narrowing the gap between the
hOBIjJi2 and hObILE3 lines.
Table 1
Emission Rates of 1975-80 LDGV's
Region
Low Alt.
wYR Group
1975-76
1977-79
1980
HC
ZML* DR**
1.07
1.07
0.36
0.27
0.27
0.10
CO
ZML i)R
18.23 2.59
18.23 2.59
6.09 0.73
NOx—
ZML
2.44
1.70
1.50
DR
0.03
0.09
0.07
High Ait.
1975-76
1977
j.978-79
1980
2.02
0.95
2.10
0.78
0.27
0.27
0.27
0.10
43.07
16.97
39.78
22.80
2.59
2.59
2.59
0.73
1.70
1.42
1.00
0.82
0.03
0.09
0.09
0.07
* ZML = Zero mile level, gin/mi.
** DR = Deterioration rate, gm/mi/lOK miles.
-------
NOTE:
FIGURE 1
Effect of Using MOBILE3
1975-80 Emission Rates
on LDGV HC Emissions
The MOBILES emission factor
curve uses MOBILE2 emission
rates for all years except
1975-80.
Legend
A MOBILE2
X MOBILE3
1980
1985 1990
CALENDAR YEAR
1995
2000
-------
50-i
NOTE:
FIGURE 2
Effect of Using MOBILES
1975-80 Emission Rates
on LDGV CO Emissions
The MOBILE3 emission factor
curve uses MOBILE2 emission
rates for all years except
1975-80.
Legend
A MOBILE2
X HOBILE3
20
1980
1985 1990
CALENDAR YEAR
1995
2000
-------
2.0 BACKGROUND
2.1 MOBILE2 Approach
The 1979 and earlier LDGV emission rates for MOBILE2 were developed from
an analysis of covariance on all available low altitude, high altitude
and California data in which mileage was the covariate and the regions
were the strata. The analysis supported the assumption of equal
deterioration rates and separate zero-mile levels for the regions.
For the 1980 model year, the deterioration rate was assumed to be the
same as for 1975-79 LDGV's. The zero-mile level, however, was adjusted
to reflect the fact that most 1980 LDGV's would be equipped with air
pumps, and to reflect the fact that the HC and CO standards were lower
for 1980.
The regressions obtained from the analysis of covariance were used as
emission rates in MOBILE2 with one modification. Emission rates of
predominately catalyst model year groups (i.e., 1975 and later) were
compensated for misfueling effects, since it was felt that the Emission
Factor (EF) test sample did not adequately reflect national average
misfueling rates and effects. No adjustments were made for any other
type of tampering such as catalyst removal or air pump disablement.
2.2 MOBILES Approach
The MOBILES analysis of pre-1981 LDGV emission rates will focus primarily
on 1975-79 and 1980 emissions, since no new data have been collected on
pre-1975 vehicles. The concept for MOBILES is to develop basic emission
rates which reflect a no misfueling and tampering scenario, and then add
the tampering and misfueling effects on separately. As a result,
tampered vehicles must be identified and removed from the EF sample prior
to performing analysis of covariance. This will be discussed further in
Sections 3.1 through 3.3.
Analysis of covariance has been used to develop the 1975-79 emission
rates for MOBILES. Also, there was now enough data to use this same
technique on 1980 model year vehicles. The California data were used to
develop deterioration rates where technologies and emission standards
were similar to the non-California low-altitude case. However, a
specific analysis of California emission rates was not performed.
2.3 Other Items Pertaining to LDGV Emission Rates
Other items pertaining to the estimation of LDGV emission rates are also
being updated as a part of MOBILES. These items are identified in the
list below, but will not be presented in this document. Documents on the
humidity correction factor for NOX and nonmethane hydrocarbon emissions
-------
have already been published, and other analyses are under way either by
EPA or under a support contract. It should be noted that the air
conditioning and trailer towing correction factors will not be updated
for MOBILE3.
1. VMT vs. age distribution.
2. Kegistration vs. age distribution.
3. Diesel sales fractions.
•4. Speed correction factors.
5. Temperature correction factors.
6. Evaporative emissions.
7. Idle emissions.
-------
3.0 BASIC EXHAUST EMISSION RATES
Sections 3.1 through 3.3 discuss tampered vehicles identified in the
1975-80 emission factor sample and their emissions. However, estimates
of the emission impacts of tampering for MOBILE3 were not necessarily
developed from these vehicles. For more information on the manner in
which the effects of tampering were included in MOBILE3, refer to the
"Anti-Tampering and Anti-Misfueling Program to Reduce In-Use Emissions
From Motor Vehicles" report (December 31, 1983, EPA-AA-TSS-83-10).
3.1 Identification of Tampered and Misfueled Vehicles
The 1975 and later light-duty vehicle data base was searched for vehicles
with signs of air pump tampering, missing catalysts, widened fuel tank
filler necks, lead values in gasoline above 0.05 g/gal, and EGR
tampering. Vehicles with missing air pumps, belts, or disabled air pump
hoses were considered to have tampered air pump systems. Vehicles with
widened filler necks or lead fuel values exceeding 0.05 g/gal or both
were considered to be misfueled vehicles. Vehicles with disconnected EGR
vacuum hoses or missing EGR valves were considered to be EGR tampered
vehicles. The number of tampered and misfueled vehicles found in the EF
sample is shown in Table 2.
Table 2
Number of Tampered or Misfueled Light-Duty Vehicles
1975-80 Vehicles, All Regions
Number
Tampering/Misfueling Type Tampered
EGR 208
Lead above 0.05 gms/gal 66
Filler Neck 39
Air Pump 11
Catalyst Removed 9
Total Number of 1975-80
Vehicles Searched 4171
The two predominant types of tampering, EGR tampering and fuel lead
values above 0.05 g/gal, are discussed in the following paragraphs.
3.2 EGR Tampered Vehicles
The number of vehicles with EGR tampering and their average NOX
emissions as compared to the vehicles without EGR tampering are shown in
Table 3.
-------
Table 3
Number of EGR Tampered
Vehicles and Average NOX
Emissions, Low and High
Altitude
Tampered Untampered
Mean Mean
Region Group N % NOx (gpm) N_ NOx (gpm)
Low Altitude 1975-76 42 2.3 3.91 1825 2.49
(Non-Calif.) 1977-79 77 4.5 4.37 1632 1.98
1980 11 1.9 3.62 584 1.71
High Altitude 1975-76 10 3.8 2.49 251 1.79
1977-79 8 1.9 3.00 412 1.24
1980 4 3.2 0.92 120 0.89
The data in Table 3 indicate that EGR tampering rates in the EF sample
are within the 2-5% range, and that EGR tampered vehicles have
significantly higher NOX emissions than those without EGR tampering.
3.3 Vehicles With High Lead Fuel Values
Not all 1975-80 EF vehicles had tests for lead content of the fuel. In
fact, very few of the i975-79 vehicles had lead tests, while many more
1980 vehicles had lead tests.
The number and percentage of vehicles with high lead values (exceeding
0.05 grams/gal) is shown in Table 4. ihe low and high altitude regions
seem to have about the same rate (5-10%).
Table 4
Number and Percentage* of Catalyst Vehicles With
High Lead Values ( greater than .05 g/gal)
—Low Alt.— —High Alt.—
N . % N %
1^75-79 19 7.8 2 5.6
1980 36 7.7 8 10.5
* The percentage is calculated as the number of catalyst vehicles with
high lead values divided by the total number of catalyst vehicles
with lead tests.
-------
10
The average emissions of vehicles with low and high lead fuel content is
shown in Table 5. For 1975-79 vehicles, HC and CO emissions are higher
in the high lead vehicles. For 1980 vehicles, the average HC and CO
emissions of vehicles with high lead values are slightly lower than the
low lead vehicles.
Table 5
Average Emissions of Cars with Low and High Fuel
Lead Values: Low Altitude, Non-California
Pollutant
HC
CO
MYR Group
1975-79
1980
1975-79
1980
1975-79
1980
Low: Less
than .05 g/gal
2.10
0.76
25.52
9.43
2.42
1.75
High: Greater
than .05 g/gal
2.80
0.59
36.47
8.22
2.71
1.54
The 1980 cars have lower emissions in the high lead group because that
group contains no high emitting HC/CO vehicles. For example, the maximum
HC value of the high lead cars is 2.79 gm/mi. In contrast to this, the
low lead group contains seven vehicles over 4.1 gm/mi, with one at 13.7
gm/mi. A similar comparison could be made for CO.
A better comparison of the emission effects of misfueling for 1980 EF
vehicles would be to focus on the emissions of high lead versus low lead
cars in the sample of vehicles that omits all low lead cars with
emissions above the highest emission value of the high lead cars. This
technique removes those low lead cars that have high emissions for
factors other than misfueling. The comparison is shown in Table 6.
Table 6
Average Emissions of 1980 Cars
with Low and High Lead Fuel Values
without High-Emitting Low Lead Cars
Pollutant
HC
CO
—Emissions (gm/mi)—
Low Lead High Lead
0.56
7.30
0.59
8.22
-------
11
The data in Table 6 indicate that the emissions of high-lead cars are
higher than low lead 1980 cars, but only slightly. One explanation for
the small difference in emissions of high and low lead cars is that the
owners with the high lead cars that have agreed to participate in
emission factor programs may only infrequently misfuel with • leaded fuel.
This type of infrequent misfueling does not damage the catalyst as much
as persistent misfueling with leaded fuel.
3.4 Low Altitude Emission Rates
3.4.1 HC and CO
The low altitude HC and CO 1975-79 and 1980 emission rates for vehicle
samples with and without the tampered and misfueled vehicles are
presented in Table 7. Model year groups are the same as those used in
MOBILE2. The "all" code under Tamp/Mfuel status means that no vehicles
are excluded. The "no tamp" status means that vehicles with evidence of
air pump tampering> filler neck tampering, lead values above 0.05 gms/gal
or with catalysts removed are excluded. Vehicles with EGR tampering were
included for the HC and CO emission rates, since EGR tampering has been
demonstrated to not influence HC and CO emission rates significantly.*
The emission rates in Table 7 are somewhat lower than the MOBILE2
emission rates, which are presented in Table 8.
Table 7
Low Altitude Emission Rates of 1975-80 LDV's — Current Analysis
Tamp/Mfuel HC CO
Status N_ ZML DR ZML DR
1975-79 All 3576 1.09 0.26 18.33 2.16
No Tamp 3512 1.07 0.27 18.23 2.59
1980 All 595 0.36 0.10 6.10 0.74
No Tamp 556 0.36 0.10 6.09 0.73
Removal of tampered and misfueled vehicles seems to have little impact on
the emission rates. This was expected, since the frequency of tampering
in the EF sample was found to be low (each item with the exception of EGR
tampering is less than 3.5%).
This was a conclusion in "Light Duty Driveability Investigation",
EPA/460-3-78-012, Dec., 1978. When fourteen 1978 cars underwent EGR
disconnections, average HC decreased 1.4%, average CO increased 0.9%,
and average NOX increased 210%.
-------
12
Table 8
MOBILE2 HC and CO Exhaust Emission Rates
for 1975-80 LDGV's at Low Altitude
HC C0;
MYR Group ZML DR ZML DR
1975-79 1.29 0.29 20.16 2.86
1980 0.29 0.29 6.14 2.86
The most notable differences between MOBILE2 and MOBILE3 are in the HC
and CO deterioration rates for 1980 vehicles: the new estimates are about
one-third of the MOBILE2 estimates. The 1980 EF sample includes the 1980
GM vehicles which have sealed carburetors.* Recent regressions of 290
1980 GM vehicles have estimated the HC and CO DR's to be 0.06 gm/mi/lOK
and 0.42 gm/mi/lOK, respectively. These are lower than the DR's
developed ror the 1980 EF sample which includes all manufacturers.
3.4.2 NOX Emission Rates
The low altitude NOX emission rates for 1975-80 vehicles are shown in
Table 9. These were estimated after the same tampered and misfueled
vehicles were removed as were removed for the HC/CO analysis, with the
addition that EGR tampered vehicles were also removed. Removal of the
EGR tampered vehicles had a small impact on the emission rates. Also
shown are the MOBILE2 NOX emission rates.
Table 9
Low Altitude
NOX Emission Rates for 19/5-80 LDGV's
Current
—Analysis— —MOBILE2—
MYR Group N ZML DR ZML DR
1975-76 1815 2.44 0.03 2.43 0.04
1977-79 1582 1.70 0.09 1.69 0.10
1980 544 1.50 0.07 1.56 0.10
The emission rates from the current analysis in Table 9 are changed very
little from the MOBILE2 emission rates.
Although GM used sealed carburetors on most 1979 models, their
proportion of the 1975-79 sample is much smaller than their
proportion of the 1980 sample.
-------
13
3.4.3 Summary of all Low Altitude Pre-1981 Rates
The proposal is to use the new estimates as presented in Tables 7
(without tampering) and 9 for 1975-79 and 1980 emission rates at low
altitude for MOBILE3. The pre-1975 emission rates would be the same as
in MOBILE2. This ignores the effect of tampering on pre-1975 emission
rates. However, the current analysis has demonstrated a rather small
impact on the emission rates from the low level of tampering in the EF
sample* Also, pre-1975 vehicles had few emission controls to be tampered
(catalysts, for example), so tampering was likely a smaller problem on
these vehicles. Therefore, ignoring pre-1975 tampering very likely does
not pose a problem of accuracy with respect to the pre-1975 emission
rates.
The new rates for all pre-1981 years are presented in Table 10. The
MOBILE2 50K emission levels are presented for comparison.
Table 10
MOBILE3 Exhaust Emission Rates for 1980
and Earlier Low Altitude 49-State
Light-Duty Gasoline Powered Vehicles
Model 50K Mile MOBILE2 50K
Pollutant Years ZML PR Emission Level Emission
HC Pre-1968 7.25 0.18 8.15 8.15
1968-69 4.43 0.25 5.68 5.68
1970-71 3.00 0.37 4.85 4.85
1972-74 3.36 0.17 4.21 4.21
1975-79 1.07 0.27 2.42 2.74
1980 0.36 0.10 0.86 1.74
CO Pre-1968 78.27 2.25 89.52 89.52
1968-69 56.34 2.55 69.09 69.09
1970-71 42.17 3.13 57.82 57.82
1972-74 40.78 2.44 52.98 52.98
1975-79 18.23 2.59 31.18 34.46
1980 6.09 0.73 9.74 20.44
NOX Pre-1968 3.44 0.0 3.44 3.44
1968-72 4.35 0.0 4.35 4.35
1973-74 2.87 0.04 3.07 3.07
1975-76 2.44 0.03 2.59 2.63
1977-79 1.70 0.09 2.15 2.19
1980 1.50 0.07 1.85 2.06
-------
14
3.5 High Altitude Emission Rates
3.5.1 HC and CO Emission Rates
Analysis of covariance yielded the high altitude zero mile levels and
deterioration rates in a manner similar to low altitude.
In the MOBILE2 analysis, a test of equal DR's for all three pollutants at
low and high altitudes was rejected only once (1970-71 CO emissions) at
the 5% level of significance. Therefore, the low and high altitude DR's
were assumed to be the same. Since then, more data have been collected
at low and high altitude. The new data is showing that the assumption of
equal low and high altitude Dk's is being rejected also for .HC and CO
emissions of 1978-79 vehicles. The significance levels are shown in
Table II. By the MOBILE2 criteria a significance level greater than .05
indicates that the hypothesis that the DR's are equivalent is accepted.
Significance levels less than .05 indicate that the hypothesis is
rejected.
Table 11
Significance Levels of the
Assumption of Equal DR's
Between Low and High Altitude:
1978-79 Vehicles
Pollutant Region N[ DR Significance
HC Low ' 1027 0.23 .004
High 290 0.44
CO Low 1027 1.92 .0002
High 290 5.87
An examination of the scatter plots of emissions versus mileage of
1978-79 vehicle at low and high altitudes reveals that there are many
more high mileage vehicles (i.e., 60-100K) in the low altitude sample
than in the high altitude sample. This Leaves the imprv-ssion that if
more high mileage high altitude vehicles had been tested, the DR's would
have been similar. However, an examination of the CO data in the high
altitude mileage range (0-68K miles) for both altitudes revealed
significantly more gross emitters in the high altitude sample than the
low altitude sample. At high altitude, 4.5% of the vehicles were between
100 and 150 gin/mi CO. At low altitudes, the percentage of vehicles
between 100 and 150 gm/mi CO was 0.7%.
The data on balance indicates that separate DR's should be used for
1978-79 vehicles at low and high altitude. However, since only one group
is involved it was decided to preserve the consistency of the model
(i.e., DR's of all model year groups at low and high altitude are equal)
rather than to make an exception for one model year group. Also, using
-------
15
different DR's for this group would not have much impact on the fleet
emission rates. For example, on January 1, 1988, the 1978 and 1979 model
year groups accumulate less than 8% of the fleet VMT. Therefore, the
data at all altitudes and all regions will be used to establish DR's
(where technologies and standards are similar between Ca-1 Eornia and
non-California vehicles), while the non-California altitude-specific data
will be used to establish the low and high altitude zero mile levels.
For MOBILE2, the emission rates of 1977 vehicles at high altitudes were
separated from the 1975-79 group creating three groups: 1975-76, 1977,
and 1978-79. The reason for this was to adequately reflect the situation
in 1977 in which manufacturers were required to meet the new vehicle
emission standards at low and high altitudes. Manufacturers responded by
selling very few models at high altitudes, and the requirement for
meeting standards at high altitude was relaxed for the 1978 model year.
Consequently, the MOUILE2 emission rates for high altitude are lower for
the 1977 model year than for the surrounding model year groups.
The new HC and CO emission rates for LDGV's at high altitudes are shown
in Table 12. Vehicles that were misfueled or had evidence of tampering
(except for EGR tampering) were removed. Also shown are the MOBILE2 high
altitude emission rates.
Table 12
High Altitude LDGV HC and CO Emission Rates
HC CO
Current MOBILE2 Current MOBILE2
N ZML DR ZML DR ZML DR ZML DR
1975-76
1977
1978-79
1930
255
124
290
114
2.02
0.95
2.10
0.78
0.27
0.27
0.27
0.10
2.41
1.07
2.10
0.46
0.29
0.29
0.29
0.29
43.07
16.97
39.78
22.80
2.59
2.59
2.59
0.73
50.46
19.55
39.39
18.22
2.86
2.86
2.86
2.86
3.5.2 NOX Emission Kates
The new NOX emission rates for LDGV's at high altitude are shown in
Table 13. The data set that was used in the preceding HC/CO analysis was
used, except that EGR-tampered vehicles were also reuoved.
-------
16
Table 13
High Altitude NOX Emission Rates
Current.-— MOBILE2
MYR Group N ZML DR ZML DR
1975-76 247 1.70 0.03 1.70 0.04
1977 121 1.42 0.09 1.42 0.10
1978-79 285 1.00 0.09 1.02 0.10
1980 110 0.82 0.07 1.02 0.10
3.5.3 Summary of Pre-1981 High Altitude Emission Rates for MOB1LE3
Using the data from the current analysis, the high altitude emission
rates for pre-1981 LDGV's for MOBILE3 are presented in Table 14. The
MOBILE2 50K emission levels have also been presented for comparison.
Table 14
Exhaust Emission Rates for High Altitude
49-State Light-Duty Gasoline Powered Vehicles
Model 50K Mile MOBILE2 50K
Pollutant Years ZML DR Emission Level Emission Level
HC Pre-1968 9.35 0.18 10.25 10.25
1968-69 5.60 0.25 6.85 6.85
1970-71 4.58 0.37 6.43 6.43
1972-74 4.58 0.17 5.43 5.43
1973-76 2.02 0.27 3.37 3.86
1977 0.95 0.27 2.30 2.52
j.978-79 2.10 0.27 3.45 3.55
1980 0.78 0.10 1.28 1.91
CO Pre-1968 -117.70 2.25 128.95 128.95
98.29
95.29
87.83
64.76
33.85
53.69
32.52
NOX Pre-1968 1.96 0.0 1.96 1.96
1968-72 2.91 0.0 2.91 2.91
1973-74 1.91 0.04 2.11 2.11
1975-76 1.70 0.03 1.85 1.90
1977 1.42 0.09 1.87 1.92
1978-79 1.00 0.09 1.45 1.52
1980 0.82 0.07 1.17 1.52
Pre-1968
1968-69
1970-71
1972-74
1975-76
1977
1978-79
1980
-117.70
85.54
79.64
75.63
43.07
16.97
39.78
22.80
2.25
2.55
3.13
2.44
2.59
2.59
2.59
0.73
128.95
98.29
95.29
87.83
56.02
29.92
52.73
26.45
-------
17
4.0
CORRECTION FACTORS
The speed and temperature correction factors are being updated under a
support contract from EPA data generated in FY83. The NOX vs. humidity
correction factor relationship was presented in another analysis*. The
trailer towing and air conditioning correction factors used in MOBILES
will be the same as those used in MOBILE2.
4.1 Normalized Bag Fractions
Normalized bag fractions are ratios of a bag's emissions to the FTP
composite zero mile levels. They are used to predict the emissions if a
user selects operating mode characteristics that are different from
standard conditions (20.7% cold start, 52.1% stabilized, 27.3 hot
start). New normalized bag fractions were computed from the new data for
1975-80 model years. The same values are used at both low and high
altitudes. The new bag fractions are presented in Table 15.
Table 15
Normalized Bag Fractions for
LDGV's
Pol
HC
CO
Model Year
1975-79
1980
1975-79
1980
—Seg. 1
Bl Dl
1.856 0.345
2.200 0.714
1.792 0.177
2.403 0.278
—Seg. 2
Bl D2
0.765 0.233
0.571 0.171
0.882 0.157
0.649 0.061
—Seg. 3
B3 D3
0.802 0.196
0.914 0.143
0.628 0.109
0.612 0.076
-Total Test-
Bo Do
1.000
1.000
1.000
1.000
0.246
0.274
0.148
0.110
NOx 1975-76 1.297 0.012 0.781 0.004 1.194 0.016
1977-79 1.371 0.040 0.766 0.046 1.166 0.063
1980 1.313 0.047 0.810 0.034 1.125 0.054
1.000 0.009
1.000 0.049
1.000 0.042
Memo from C. Shih to R. Stahman, September 1, 1983, "New Humidity
Correction Factors for MOBILE3."
------- |