**EPA420-R-01-024**

**Evaporative Emissions of**

**Gross Liquid Leakers in MOBILE6**

**Larry C. Landman**

**Document Number M6.EVP.009**

**April 2001**

**U.S. EPA**

**Assessment and Standards Division**

**National Vehicle Fuel and Emissions Laboratory**

**2000 Traverwood Drive**

**Ann Arbor, Michigan 48105-2425**

**734-214-4939 (fax)**

**mobile@epa.gov**

NOTICE

> These 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 release of
> these 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.

**ABSTRACT**

In six parallel documents (M6.EVP.001, M6.EVP.002, M6.EVP.004,
M6.EVP.005, M6.EVP.006, and M6.EVP.008), EPA noted that a potentially
significant portion of evaporative emissions (from the in-use fleet) may
be the result of a small number of vehicles leaking liquid gasoline
(rather than gasoline vapors). This document describes EPA\'s approach
(in MOBILE6) to estimating both the frequency of occurrence vehicles
with these significant leaks of liquid gasoline and the magnitude of the
emissions resulting from those leaks.

This report was originally released (as a draft) in June 1999. This
current version is the final revision of that draft. This final revision
incorporates suggestions and comments received from stakeholders during
the 60-day review period and from peer reviewers.

*i*

**TABLE OF CONTENTS**

**[Page Number]{.underline}**

1.0 Introduction . . **. . . . . . . . . . . . . . . . . .** 1

2.0 Characterizing GLLs **. . . . . . . . . . . . . . . .** 1

2.1 GLLs on RTD Test **. . . . . . . . . . . . . . .** 3

2.2 GLLs on Hot Soak Test **. . . . . . . . . . . . .** 8

2.3 GLLs on Running Loss Test **. . . . . . . . . . .** 12

2.4 Summary of Magnitudes of Evaporative Emissions 15

3.0 Frequency of Occurrence of GLLs **. . . . . . . . . .** 16

3.1 First Approach to Estimating Frequency **. . . .** 17

3.1.1 On the RTD Test **. . . . . . . . . . . .** 17

3.1.2 On the Running Loss Test . **. . . . . . .** 19

3.1.3 On the Hot Soak Test **. . . . . . . . . .** 21

3.2 Second Approach to Estimating Frequency **. . . .** 23

3.3 Selection of Approach to Estimating Frequency . 25

3.4 Overall Occurrence of GLLs

in the In-Use Fleet **. . . . . . . . . . . . . .** 28

4.0 References **. . . . . . . . . . . . . . . . . . . . .** 30

**[APPENDICES]{.underline}**

A. RTD Emissions of 11 Vehicles with Liquid Leaks **. . .** 31

B. Hot Soak Emissions of 14 Vehicles with Liquid Leaks 32

C. Running Loss Emissions of 10 Vehicles with

Liquid Leaks **. . . . . . . . . . . . . . . . . . . .** 33

D. Predicted Frequency of Occurrence of

GLLs **. . . . . . . . . . . . . . . . . . . . . . . .** 34

E. Peer Review Comments from Sandeep Kishan . . . . . . 35

F. Comments from Stakeholders **. . . . . . . . . . . . .** 43

*ii*

**Evaporative Emissions of**

**Gross Liquid Leakers in MOBILE6**

**Report Number M6.EVP.009**

Larry C. Landman

U.S. EPA Assessment and Standards Division

1.0 INTRODUCTION

In four parallel reports **\[1,2,3,4\]\*** the US Environmental
Protection Agency (EPA) noted that for a small number of vehicles, the
primary mechanism of evaporative emissions was the substantial**\*\***
leakage of liquid gasoline (as opposed to simply vapor leaks). In each
of those reports, such vehicles were referred to as \"Gross Liquid
Leakers\" (GLLs). One consistent feature of these vehicles is that their
evaporative emissions far exceed the evaporative emissions of the
vehicles that were not gross liquid leakers (non-GLLs). In this report,
EPA:

> develops a set of criteria to define GLLs,
>
> determines the evaporative emissions produced by these GLLs, and
>
> determines the occurrence (i.e., frequency) of these GLLs as a
> function of vehicle age.

2.0 CHARACTERIZING \"GROSS LIQUID LEAKERS\" (GLLs)

The term \"gross liquid leaker\" (GLL) identifies vehicles having
substantial leaks of liquid gasoline, as opposed to simply vapor leaks.
But, this term has been used in different contexts and it is, therefore,
likely that some vehicles that behave as GLLs based on one type of
evaporative emissions test might not behave as GLLs on another type of
test. In this analysis, EPA makes use of four different types of testing
programs to identify

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

**\*** The numbers in brackets refer to the references in Section 4
(page 31).

**\*\*** Throughout this report, we use adjectives such as
\"substantial\" and \"severe\" to describe the leaks that produce GLLs.
Quantitative estimates of that type of leak can be obtained using the
emissions (in grams per hour) from Table 2-1 (page 17).

those vehicles with substantial liquid leaks:

> a real-time diurnal (RTD) test **\[1,2\]** in which evaporative
> emissions are measured for stabilized test vehicles that are enclosed
> in a sealed housing with the temperatures cycling over a 24-hour
> period to simulate the pressure-driven evaporative HC emissions that
> result from the daily increase in ambient temperature,
>
> a hot soak test **\[3\]** in which evaporative emissions are measured
> for one hour following a driving cycle for test vehicles that are
> enclosed in a sealed housing,
>
> a running loss test **\[4\]** in which evaporative emissions are
> measured during a driving cycle for test vehicles that are enclosed in
> a sealed housing, and
>
> a visual inspection **\[5\]**.

In this report, EPA first estimates the mean evaporative emissions of
these GLLs for each type of test (Section 2), and then estimates the
likelihood of those types of leaks occurring (Section 3).

Generally, when EPA predicts evaporative emissions (either resting loss,
diurnal, hot soak, or running loss**\***) these two variables are
critical:

> **1)** the ambient temperature and
>
> **2)** the fuel volatility as measured by the Reid vapor pressure
> (RVP) of the test fuel.

However, for vehicles that are classified as GLLs, most (but, not
necessarily all) of the evaporative emissions are the result of the leak
of liquid gasoline. Since it is unlikely the rate of leakage is a
function of either the temperature or the fuel volatility, EPA will
treat (in MOBILE6) the evaporative emissions of these vehicles as
independent of ambient temperature and RVP.

An additional source of data was a 1998 test program conducted for the
Coordinating Research Council (CRC) in which 50 late-model year vehicles
(1992 through 1997, with a mean age of 4.5 years) were tested using the
hot soak, running loss, and RTD tests.**\[6\]** However, none of those
50 vehicles had detected liquid leaks. Thus, the results from these
tests were not used in the analyses in Section 2. The observation that
no GLLs were identified among this sample of 50 vehicles will be
considered in the analysis in Section 3.

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

**\*** MOBILE6 will not consider GLLs in its estimates of evaporative
emissions from crankcase losses or refueling. The methodology for
estimating these emissions has not changed from that in MOBILE5.

2.1 [GLLs on the RTD Test]{.underline}

The category of vehicles identified as GLLs was first discussed in a
report dealing with evaporative emissions during resting losses and
diurnals. **\[1\]** In that report, the term \"gross liquid leaker\" was
used to refer to vehicles which had resting loss emissions of at least
2.0 grams per hour. Those analyses were performed on 119 vehicles tested
in various EPA programs plus 151 vehicles tested for the Coordinating
Research Council (CRC).

The analyses in that report were based on tests in which the ambient
temperature cycled over 24 hours to simulate (in real-time) a full
day\'s temperature pattern. The results of those real-time diurnal (RTD)
tests were used to estimate both resting loss and diurnal emissions. In
that analysis, the diurnal emissions were calculated by subtracting the
resting loss emissions from the total RTD test results.

Since the 151 vehicles in the CRC program were randomly recruited
(within each of three model year ranges), EPA will use that random
sample to estimate the means of the resting loss and diurnal emissions
of vehicles that had liquid leaks of gasoline. The mechanics who
inspected the test vehicles identified 32 of those vehicles as having
evidence of some fuel leakage (from damp hoses and connectors to visible
leaks).

Since our intention is to only estimate the mean of the emissions of the
vehicles having only substantial leaks (i.e., GLLs), we first limited
our sample to vehicles:

**1.)** whose resting loss emissions (i.e., the mean emissions during
the last six hours of the 24-hour RTD test) were at least 0.25 grams per
hour and

**2.)** whose total RTD emissions were at least 30 grams per day.

These limitations produced a set of vehicles whose gasoline leaks had an
observable effect on the evaporative emissions (even if that effect was
not sufficient to create a GLL). Eleven such vehicles were found among
the 32 having identified liquid leaks. The emissions from those 11
vehicles are given in Appendix A. It is important to note that while all
of these vehicles leaked liquid gasoline, less than half of them were
eventually classified as GLLs (i.e., having resting loss emissions of at
least 2.0 grams per hour). All of these 11 vehicles are carbureted. In
the absence of evidence to the contrary, EPA will treat fuel injected
and carbureted vehicles with liquid leaks the same for the purposes of
resting loss and diurnal emissions.

The usual approach that EPA has followed in estimating emission levels
is to simply calculate the mean of the sample of applicable test
results. However, the number of vehicles identified as GLLs (i.e.,
having resting loss emissions of at least 2.0 grams per hour) is
relatively small, and the range of their emissions is relatively large.
From a statistical standpoint, the combination of these two conditions
may lead to a high degree of uncertainty in the calculated mean. An
alternate approach is to fit an assumed type of distribution curve to
those limited number of observations. The type of distribution that has
historically been used for emissions is the lognormal distribution
**\[7\]** (i.e., the logarithms of the emissions, rather than the
emissions themselves, are assumed to be normally distributed). EPA will
use this approach in MOBILE6.

Prior to modeling the estimated diurnal emissions, we reexamined the
data in Appendix A. Since our intent was to model the distribution of
diurnal emissions from vehicles with the severest leaks, we dropped from
the analysis the results of vehicle number 9042 due to its relatively
low diurnal emissions (suggesting that it was not a GLL relative to its
diurnal emissions). Additionally, we assumed that if a valid estimate of
the diurnal emissions from vehicle 9129 had been obtained**\***, then
that estimated diurnal would have been less than the emissions from the
two highest emitting vehicles but higher than the emissions from the
remaining eight vehicles. Using these two assumptions, we ranked the
diurnal emissions and assigned a percentile to each. The plot of those
percentiles versus the corresponding diurnal emissions is given in
Figure 2-1, on the following page. The solid line in that figure is the
graph of the cumulative distribution obtained by assuming that the
logarithms of the emissions are normally distributed. (The mean of the
logarithms of the emissions is 3.812; the corresponding standard
deviation is 1.075.) (Distributions other than the lognormal were
examined, but none came as close to approximating the observed
distribution.) We then used that lognormal distribution to estimate the
frequency associated with each possible diurnal emission level.

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

**\*** In Reference **\[1\]**, EPA noted that the hourly diurnal
emissions from vehicle number 9129 suggest that the leak actually
developed around the tenth hour of the test. Hence, that vehicle was a
GLL for only the second half of the RTD test. Trying to precisely
estimate the emissions during the first half of the RTD test, assuming
the vehicle had been a GLL for the entire test, is questionable.
However, based on the vehicle\'s emissions for the last 14 hours of the
RTD, it appears that its 24-hour RTD emissions would have fallen between
the emissions of vehicles number 9054 and 9087.

**[Figure 2-1]{.underline}**

**Cumulative Distribution of Estimated Diurnal Emissions**

**For Vehicles Exhibiting Liquid Fuel Leaks**

**With Diurnal Emissions Over 15 grams per day**

![](media/image1.emf){width="6.194444444444445in"
height="3.7916666666666665in"}

Although the lognormal distribution predicts that a small number of
vehicles would have impossibly high diurnal emissions, EPA chose to
limit the maximum emissions based on the assumption that a truly severe
leak would result in the quick repair of the vehicle. Since one (real
world) test vehicle (in our sample) had diurnal emissions of almost 400
grams per day, EPA assumed that the limit of the maximum emissions
should be higher than that value. EPA will use 1,000 grams per day as
the maximum for the purpose of estimating fleet averages.

The lognormal distribution also predicts that some leaking vehicles will
have diurnal emissions of close to zero. To separate the GLLs from
vehicles having only minor or moderate leaks, we again examined the
estimated diurnal emissions in Appendix A. A visual inspection of those
data indicated a relatively large discontinuity (i.e., a break) between
24.86 and 62.64 grams per day. Based on that observation, EPA will use
25 grams per day as the minimum value. For a group of leaking vehicles
whose diurnal emissions were between 25 and 1,000 grams per day, the
lognormal distribution predicts that the mean diurnal emissions of that
group of leakers would be 104.36 grams per day. (Doubling the maximum
possible diurnal to 2,000 grams per day would result in increasing the
estimated group average only to 107.41 grams daily.)**\***

EPA will use 104.36 grams per day as the average full-day\'s diurnal
emissions from GLLs over a day for which the maximum daily temperature
is exactly 24°F above the daily low temperature. (See report number
M6.EVP.002 to use temperature cycles with ranges other than 24°F.)
Earlier versions of MOBILE limited diurnal emissions to times when the
ambient temperature was at least 40°F. However, we suspect that, at
temperatures below 40°F, the diurnal emissions would still continue.
However, at those low temperatures, the likelihood of ozone exceedences
would be small.

**[Figure 2-2]{.underline}**

## Cumulative Distribution of Resting Loss Emissions

**For 11 Vehicles Exhibiting Liquid Fuel Leaks**

**And Having Resting Loss Emissions Over 0.25 grams / hour**

![](media/image2.emf){width="6.014583333333333in" height="3.68125in"}

The preceding approach was repeated (using the data in Appendix A) for
resting loss emissions. The resting loss emissions from the 11 vehicles
in Appendix A are plotted in Figure 2-2.

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

**\*** The more traditional approach would have been simply to average
the diurnal emissions of the four vehicles in Appendix A having RTD
emissions of at least 100 grams with the diurnal emissions of two other
leakers from the EPA testing programs. The mean of those six diurnals is
100.29 grams per day, which corresponds to using the lognormal
distribution with the maximum diurnal emissions set to 675 grams per
day.

As with the previous figure (Figure 2-1), the solid line in Figure 2-2
is the graph of the cumulative distribution obtained by assuming that
the logarithms of the resting loss emissions are normally distributed.
(The mean of the logarithms of the resting loss emissions is 0.841; the
corresponding standard deviation is 1.528.) A visual inspection of that
figure suggests that the lognormal model does not fit the resting loss
emissions of leaking vehicles as well as it fit the diurnal emissions.
In fact, a straight line (i.e., a \"uniform\" distribution) is the curve
that best fits the resting loss emissions for vehicles having at least
1.0 grams per hour (therefore, covering all GLLs). However, it also
predicts that forty percent of the vehicles with leaks have zero resting
loss emissions.

In previous analyses (see M6.EVP.001), EPA determined that the lower
bound of the resting loss emissions of the GLLs would be 2.0 grams per
hour. Since one (real world) test vehicle (in our sample) had resting
loss emissions of about 16 grams per hour, EPA assumed that the limit of
the maximum emissions should be higher than that value. EPA will use 50
grams per hour as the maximum for the purpose of estimating fleet
averages. For a group of leaking vehicles whose hourly resting loss
emissions were between 2.0 and 50 grams, the lognormal distribution
predicts that the mean resting loss emissions of that group of leakers
would be 9.163 grams per hour.**\*** (Doubling the maximum possible
resting loss to 100 grams per hour would result in increasing the
estimated group average only to 10.875 grams hourly.) The linear fit
(i.e., uniform distribution) predicts the mean of the resting losses
from vehicles emitting at least 2.0 grams per hour would be 10.518 grams
per hour. Thus, all of those approaches produce similar estimates of the
average hourly resting loss emissions from GLLs.

Although the uniform distribution produces a superior estimate of the
observed data compared to the lognormal distribution, both approaches
produce similar estimates of the mean resting loss emissions. Therefore,
EPA will use the lognormal distribution for consistency among the
various evaporative models in this report. EPA will use the estimate
based on the lognormal model (i.e., 9.16 grams per hour) as the average
hourly resting loss emissions from GLLs. Since the mechanism responsible
for the vast majority of the resting loss emissions from these vehicles
is the fuel leaking out of the vehicle, and since this process is not
dependent upon the ambient temperature or fuel volatility, EPA had
proposed (reference **\[1\]**)

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

**\*** The more traditional approach would have been to simply average
the resting loss emissions of the five vehicles in Appendix A having
resting loss emissions of at least 2.0 grams per hour with the resting
loss emissions of two other leakers from the EPA testing programs. The
mean of those seven resting losses is 8.84 grams per hour, which
corresponds to using the lognormal distribution with the maximum hourly
resting loss emissions set to 45.2 grams per hour.

considering resting loss emissions from GLLs as independent of fuel
volatility and temperature.

2.2 [GLLs on the Hot Soak Test]{.underline}

The category of vehicles identified as GLLs based on evaporative
emissions during a hot soak, are discussed in a report prepared for EPA
by one of its contractors **\[8\]**. In that report, the term GLLs was
used to refer to \"vehicles which produce abnormally high evaporative
emissions as a result of a fuel leak and which have hot soak emissions
of over 10 grams per test.\" Since the hot soak test is one hour in
duration, \"grams per test\" is equivalent to \"grams per hour\" for the
hot soak. (See reference **\[8\]** to calculate hot soak emissions for
time periods less than an hour.) Since the hot soak test measures total
evaporative emissions during that hour, the results also include resting
loss emissions which must be subtracted to obtain the (net) hot soak
emissions.

In the analyses for that report, hot soak test results on 493 vehicles
were used. Of those 493 vehicles, the mechanics identified 14 as having
evidence of some fuel leakage (from damp hoses and connectors to visible
leaks). Those 14 vehicles (along with their hot soak test results) are
listed in Appendix B. The hot soak emissions of those 14 leaking
vehicles ranged from 2.00 to 88.57 grams per test (averaging 22.47
grams). For the remaining 479 vehicles that did [not]{.underline} have
liquid leaks detected, their hot soak emissions ranged from 0.04 to
88.35 grams per test (averaging 1.77 grams).

A quick inspection of the emissions listed in Appendix B suggests that
the port fuel injected (PFI) vehicles that have leaks exhibit higher hot
soak emissions than the carbureted (CARB) vehicles that have leaks.
Since the fuel delivery systems in the PFI vehicles operate at a higher
pressure than do the systems in the carbureted vehicles, a hole in the
fuel system of a PFI vehicle will leak more fuel than a hole of the same
size in a carbureted vehicle.**\*** Therefore, the observation that the
PFIs with liquid leaks have (on average) higher hot soak emissions than
the corresponding carbureted vehicles is reasonable. There was an
insufficient sample of leaking vehicles with throttle body injection
(TBI) systems to analyze. Therefore, the hot soak emissions from this
technology grouping will be estimated using a theoretical rather than
statistical approach.

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

**\*** Bernoulli\'s equation indicates that the leak rate will be
proportional to the square root of the ratio of operating pressures.

In Figure 2-3 (below), we plotted the hot soak emissions (in grams per
test) of the six carbureted vehicles (from Appendix B) versus the
corresponding percentiles. The solid line in that figure is the graph of
the cumulative distribution obtained by assuming that the logarithms of
the emissions are normally distributed. (The mean of the logarithms of
the hot soak emissions is 1.9644; the corresponding standard deviation
is 0.6963.)

######### Figure 2-3

**Cumulative Distribution of Hot Soak Emissions**

**For 6 Carbureted Vehicles Exhibiting Liquid Fuel Leaks**

![](media/image3.wmf){width="6.197916666666667in"
height="3.8958333333333335in"}

As was done in Section 2.1 with diurnal emissions, that lognormal
distribution was used to estimate the frequency associated with each
possible hot soak emission level. Although the lognormal distribution
predicts that a small number of carbureted vehicles would have
impossibly high hot soak emissions, EPA chose to limit the maximum
emissions based on the assumption that a truly severe leak would result
in the vehicle being quickly repaired. In Appendix B, we can see that
one owner tolerated a vehicle having hot soak emissions of almost 90
grams per test. Based on that observation, EPA will assume that, for the
purpose of estimating the mean hot soak emissions, the hot soak
emissions of the GLLs range between 10 and 300 grams per test.

Using the lognormal distribution in Figure 2-3, we can predict the mean
hot soak emissions for the GLL carbureted vehicles assuming hot soak
emissions ranging between 10 and 300 grams per test. The mean hot soak
emissions of that group of leakers would be 16.9549 grams per test (or
per hour). (That average emission level was not very sensitive to the
assumption of the emissions of the highest possible leaker. Lowering the
assumed level of the highest emitting carbureted vehicle to 50 grams
reduced the average only to 16.5503. Similarly, raising the assumed
level of the highest emitting vehicle to 1,000 grams increased the
average only to 16.9550.) EPA, therefore, will use 16.95 grams per test
as the estimate of hot soak emissions from GLL carbureted vehicles.

To estimate the mean of the hot soak emissions from the PFI vehicles
that had liquid leaks, we proceeded in the same fashion that we employed
for the carbureted vehicles. In Figure 2-4 (on the following page), we
plotted the hot soak emissions (in grams per test) of the seven PFI
vehicles (from Appendix B) versus the corresponding percentiles.

The solid line in Figure 2-4 is the graph of the cumulative distribution
obtained by assuming that the logarithms of the emissions are normally
distributed. (The mean of the logarithms of the hot soak emissions is
2.8830; the corresponding standard deviation is 1.5822.)

**[Figure 2-4]{.underline}**

**Cumulative Distribution of Hot Soak Emissions**

**For 7 PFI Vehicles Exhibiting Liquid Fuel Leaks**

![](media/image4.wmf){width="6.177083333333333in"
height="3.8958333333333335in"}

A visual inspection of that figure suggests that the lognormal model
does not fit the hot soak emissions of leaking PFI vehicles as well as
it fit the carbureted vehicle. In fact, a straight line (i.e., a
\"uniform\" distribution) provides almost as good a fit to the hot soak
emissions for the six PFI vehicles having at least 2.25 grams per test.
(We are considering the lognormal distribution to be a better fit
because the sum of the squares of the residuals is lower than for the
linear fit.) EPA will use the lognormal distribution because it is the
better fit and for consistency among the various evaporative models in
this report.

Using the lognormal distribution in Figure 2-4, we can predict the mean
hot soak emissions for the GLL PFI vehicles assuming hot soak emissions
ranging between 10 and 300 grams per test. The mean hot soak emissions
of that group of leakers would be 57.1425 grams per test (or per hour).
(That average emission level is only slightly sensitive to the
assumption of the emissions of the highest possible leaker. Lowering the
assumed level of the highest emitting carbureted vehicle to 250 grams
reduces the average to 53.3468. Similarly, raising the assumed level of
the highest emitting vehicle to 400 grams increases the average only to
63.0990.) The linear fit (i.e., uniform distribution) predicts the mean
of the hot soak emissions for PFI vehicles emitting at least 10 grams
per test would be 52.2481 grams per test. Thus, all of those approaches
produce similar estimates of the mean hourly resting loss emissions from
GLLs. EPA, therefore, will use 57.14 grams per test as the estimate of
hot soak emissions from GLL PFI vehicles.

Due to a lack of data (see Appendix B), we were not able to perform a
similar analysis for the TBI vehicles. This situation was addressed in
the report on hot soak emissions (M6.EVP.004), in which the author
stated:

> \"While there is no data on TBI liquid leakers in the data sets,
> Bernoulli\'s equation indicates that the leak rate for TBI systems
> would be about one half that for PFI systems (the square root of the
> ratio of operating pressures). Therefore, without further data, the
> author suggests assuming that TBI liquid leakers might emit
> approximately half the emissions of PFI systems.\"

EPA assumes (in MOBILE6) that the frequency of having a hole of a given
size is the same for both the TBI and PFI vehicles. Based on that
assumption, Bernoulli\'s equation predicts that at each frequency in the
cumulative distribution curve for PFIs (i.e., Figure 2-4), the
corresponding TBI curve would predict only one-half the hot soak
emissions. Thus, since the median (i.e., the 50 percentile point)
corresponds to a PFI vehicle with a hot soak test of 17.868 grams, the
median hot soak test result for a TBI vehicle would be one-half of that
(8.9339 grams). Pictorially, the effect would be to maintain the
distribution curve (in Figure 2-4) while changing the horizontal scale
from zero to 100 to a scale from zero to 50. That transformation is
performed in the following graph (Figure 2-5). Also, in that figure, we
plotted the single result for TBI vehicles in our data base (from
Appendix B).

Using the lognormal distribution in Figure 2-5, we can predict the mean
hot soak emissions for the GLL TBI vehicles assuming hot soak emissions
ranging between 10 and 300 grams per test. The mean hot soak emissions
of that group of leakers would be 44.9990 grams per test. Therefore, EPA
will use 45.00 grams per test (or grams per hour) as the estimate of hot
soak emissions from GLL TBI vehicles. (It is encouraging, but not
statistically significant, that the actual test result of 8.28 from
Appendix B is quite similar to the predicted median hot soak test value
of 8.9339 grams per test.)

**[Figure 2-5]{.underline}**

**Estimated Cumulative Distribution of Hot Soak Emissions**

**For TBI Vehicles Exhibiting Liquid Fuel Leaks**

![](media/image5.wmf){width="6.166666666666667in"
height="3.9166666666666665in"}

2.3 [GLLs on the Running Loss Test]{.underline}

In 1997, running loss tests were performed on 150 vehicles as part of a
testing program conducted for the Coordinating Research Council (CRC).
The mechanics who inspected those test vehicles identified 40 of those
vehicles as having evidence of some fuel leakage (from damp hoses and
connectors to visible liquid leaks). The running loss emissions from
these vehicles were measured over a single LA-4 driving cycle, using
tank fuel (RVP about 6.8 psi), and ambient temperature about 95 degrees
Fahrenheit. **\[9\]**

Since our intention is to estimate the mean of the emissions of the
vehicles having only substantial leaks, we first limited our sample to
leaking vehicles whose running loss emissions were at least 5.0 grams
per mile over the single LA-4 driving cycle. (Five grams per mile
appears to be a reasonable break point since the next highest running
loss emissions for a leaking vehicle was only 3.52 grams per mile.) Ten
such vehicles were found among those 40 having identified liquid leaks.
The emissions from those 10 vehicles (reported as grams per mile, grams
per test, and grams per hour) are given in Appendix C. It is important
to note that while all of these vehicles leaked liquid gasoline, not all
of them are classified as GLLs (using the criteria developed in this
section). All of these 10 vehicles are carbureted. (Two of the original
40 leaking vehicles were fuel injected; however, their running loss
emissions were each less than 0.4 grams per mile.)

The approach used in the preceding sections (for diurnal, resting loss,
and hot soak) was repeated for running loss emissions (using the data in
Appendix C). The running loss emissions from the 10 vehicles in Appendix
C are plotted in Figure 2-6. As with the previous figures, the solid
line is the graph of the cumulative distribution obtained by assuming
that the logarithms of the emissions are normally distributed. (The mean
of the logarithms of the emissions is 4.2; the corresponding standard
deviation is 0.88.)

**[Figure 2-6]{.underline}**

## Cumulative Distribution of Running Loss Emissions

**For Vehicles Exhibiting Liquid Fuel Leaks**

**With Running Loss Emissions Over 5 grams per mile**

![](media/image6.emf){width="6.166666666666667in"
height="3.888888888888889in"}

To determine the appropriate range of running loss emissions for these
GLLs, we reexamined the running loss test results on all 150 vehicles.
All of the vehicles that did not have an identified liquid leak had
running loss emissions (for the single LA-4 cycle) of less than 4.2
grams per mile. EPA selected 7.0 grams per mile as the value that
distinguished between vehicles that have liquid leaks and those defined
as GLLs.**\*** Since one (real world) test vehicle (in the CRC sample)
had emissions on the running loss test of about almost 43 grams per
mile, EPA assumed that the limit of the maximum emissions should be
higher than that value. EPA will use 200 grams per hour as the maximum
for the purpose of estimating fleet averages. For a group of leaking
vehicles whose running loss emissions were between 7.0 and 200 grams per
mile, the lognormal distribution predicts that the mean running loss
emissions of that group of leakers would be 17.649 grams per mile. (As
with the emissions on the hot soak and diurnal tests, that average
emission level was not very sensitive to the assumption of the emissions
of the highest possible leaker. Lowering the assumed level of the
highest emitting carbureted vehicle to 90 grams/mile reduced the average

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

**\*** This 7.0 grams per mile test result over a 19.6 mile per hour
driving cycle is equivalent to 137.2 grams per hour (which includes
resting loss emissions).

only to 17.181. Similarly, raising the assumed level of the highest
emitting vehicle to 500 grams/ mile increased the average only to
17.696.) As previously stated, this analysis of running loss emissions
of GLLs is based solely on carbureted vehicles. Using the logic (and
Bernoulli\'s equation) from Section 2.2, it could be argued that the
running loss emissions from PFI GLLs would be four times that amount.
However, it does not seem reasonable to assume such a high emissions
rate based on no data. Therefore, in the absence of evidence to the
contrary, (for the purposes of running loss emissions of GLLs) EPA will
treat fuel injected and carbureted vehicles the same.

Thus, EPA will use 17.65 grams per mile as the estimate of the emissions
from a running loss test from [ALL]{.underline} GLLs over a single LA-4
driving cycle. Since all of those GLLs were tested over only that single
cycle, an approach needed to be found to estimate running loss emissions
over different cycles (i.e., speed correction factors were needed). EPA
assumed (for MOBILE6) that the magnitude of the leaks were essentially
independent of speed. Thus, the 17.65 grams per mile (at 19.6 miles per
hour) results in a running loss (test) rate of 345.94 grams per hour
which includes resting loss emissions of 9.16 grams per hour (from
Section 2.1, page 8).

Therefore, the running loss emissions (in MOBILE6) were obtained by
subtracting the mean resting loss (hourly) emissions from the total mean
running loss (hourly) test emissions to obtain the rate of 336.78 grams
per hour.

2.4 [Summary of Magnitudes of Evaporative Emissions]{.underline}

For the full-day diurnal emissions (based on the temperatures cycling
over a 24 degree Fahrenheit range) of GLLs, EPA will use 104.36 grams
per day. (See report number M6.EVP.002 to use other temperature cycles
or to estimate hourly diurnal emissions.)

For the resting loss emissions of all GLLs, EPA will use 9.16 grams per
hour.

To estimate the result of a hot soak [test]{.underline} on GLLs:

> EPA will use 16.95 grams per [test]{.underline} for carbureted
> vehicles,
>
> EPA will use 45.00 grams per [test]{.underline} for TBI vehicles, and
>
> determine the occurrence (i.e., frequency) of these GLLs as a function
> of vehicle age.

To calculate the actual hot soak emissions per hour, the resting loss
emissions must be subtracted from the hot soak [test]{.underline}
emissions.

To estimate the result of a running loss emissions on all GLLs, EPA will
use 336.78 grams per hour. The resting loss emissions have already been
subtracted to obtain this value.

These average (mean) emissions as well as the minimum (threshold) values
are summarized in the Table 2-1 (on the following page).

+----------------------------------------+-------------+---------------+
| ###### Table 2-1                       |             |               |
|                                        |             |               |
| **Summary of Emissions from Vehicles   |             |               |
| with Gross Liquid Leaks**              |             |               |
+----------------------------------------+-------------+---------------+
|                                        | #######     |               |
|                                        | Emissions b |               |
|                                        | y Test Type |               |
+----------------------------------------+-------------+---------------+
| #### [Type of Emissions]{.underline}   | ##          | ##### Average |
|                                        | ### Minimum |               |
+----------------------------------------+-------------+---------------+
| > **Hot Soak (grams per test)**        |             |               |
+----------------------------------------+-------------+---------------+
| > **Carbureted Vehicles**              | >           | > 16.95**\*** |
|                                        |  10.0**\*** |               |
+----------------------------------------+-------------+---------------+
| > **TBI Vehicles**                     | >           | > 45.00**\*** |
|                                        |  10.0**\*** |               |
+----------------------------------------+-------------+---------------+
| ####  PFI Vehicles                     | >           | > 57.14**\*** |
|                                        |  10.0**\*** |               |
+----------------------------------------+-------------+---------------+
| > **Resting Loss (grams per hour)**    | > 2.0       | > 9.16        |
+----------------------------------------+-------------+---------------+
| > **Diurnal (grams per day)**          | > 25.0      | > 104.36      |
+----------------------------------------+-------------+---------------+
| > **Running Loss (grams per hour)**    | > 13        | > 336.78      |
|                                        | 7.2**\*\*** |               |
+----------------------------------------+-------------+---------------+
| > **\* The Hot Soak [test]{.underline} |             |               |
| > emissions (both Minimum and Average) |             |               |
| > include resting loss emissions which |             |               |
| > must be subtracted.**                |             |               |
| >                                      |             |               |
| > **\*\* The Minimum Running Loss      |             |               |
| > [test]{.underline} emissions include |             |               |
| > resting loss emissions which must be |             |               |
| > subtracted.**                        |             |               |
+----------------------------------------+-------------+---------------+

3.0 FREQUENCY OF OCCURRENCE OF \"GROSS LIQUID LEAKERS\"

In Section 2, the magnitude of each type of evaporative emissions from
liquid leakers was estimated independently using lognormal
distributions. Also, EPA believes the data can be linked when estimating
the frequency of the GLLs. However, due to the lack of data on the
occurrence of GLLS on the hot soak test for vehicles over the age of 10,
EPA made the following two basic assumptions in predicting the frequency
of GLLs:

**1.)** For each test of evaporative emissions (i.e., RTD, hot soak, and
running loss tests), the frequency of GLLs increases as a function of
only age. This model of the frequency is based on the assumption that
modern technology vehicles will show the same tendency toward developing
these severe liquid leaks as do the older technology vehicles at the
same age.**\*** EPA modified this assumption (in reference number
**\[10\]**) for the 1996 and newer vehicles certified to the new
enhanced evaporative standard.

**2.)** The vehicles classified as GLLs on the hot soak test are the
same vehicles identified as GLLs on either the running loss or RTD
tests. (That is, the set of vehicles classified as GLLs on the hot soak
test is the union of the set of vehicles classified as GLLs on the RTD
test with the set of vehicles classified as GLLs on the running loss
test.) Therefore, the rate of GLLs as identified on the hot soak test
would be the sum of the two rates for the RTD testing and the running
loss of the two rates for the RTD testing and the running loss testing
minus the number of double counted vehicles (i.e., the product of those
two rates assuming these two categories are independent of each other).

Implicit in this assumption is EPA\'s belief that these three tests of
evaporative emissions do not identify the same vehicles as being GLLs.
For example, if there were a leak in the fuel line of a vehicle, that
leak may be severe when the fuel system is under pressure (i.e., when
the engine is on). Thus, a running loss or a hot soak test would
identify the vehicle as a GLL, but the RTD test might not (since the
engine would be off).

EPA considered the following two different approaches to predicting the
occurrence of GLLs. (See footnote on page 22.)

3.1 [First Approach to Estimate Frequency]{.underline}

The first approach involved two basic steps:

> **1.)** Find two logistic growth functions that separately predict the
> rate of GLLs on the RTD test and on the running loss test,
> respectively.
>
> **2.)** Verify that the union of those two functions approximate the
> results observed on the hot soak test.

3.1.1 First Approach Estimating Frequency of GLLs on the RTD Test

In the report dealing with evaporative emissions measured during the RTD
tests (M6.EVP.001), EPA used the results from a

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

**\*** An alternative approach that EPA is [not]{.underline} proposing
(due to lack of data) assumes that the modern technology vehicles
exhibit a lower tendency to leak (due to the more stringent demands
imposed by the new evaporative emissions certification procedure as well
as heightened attention to safety, such as, fuel tank protection and
elimination of fuel line leaks). This approach would result in replacing
each single logistic growth function with a family of two or more
curves.

test fleet of 270 vehicles (i.e., the combined EPA and CRC samples) to
estimate the occurrence of GLLs within each of the three model year
ranges used in the recruitment process (the pre-1980, 1980-85, and
1986-95 vehicles). The estimated rate of occurrence of the GLLs is
reproduced in the following table (Table 3-1). The large confidence
intervals are the result of the relatively small sample sizes.

+------------+--------+----------+-----------+-----------+-----------+
| **Table    |        |          |           |           |           |
| 3-1**      |        |          |           |           |           |
|            |        |          |           |           |           |
| *          |        |          |           |           |           |
| *Frequency |        |          |           |           |           |
| of Gross   |        |          |           |           |           |
| Liquid     |        |          |           |           |           |
| Leakers**  |        |          |           |           |           |
|            |        |          |           |           |           |
| **Based on |        |          |           |           |           |
| RTD        |        |          |           |           |           |
| Testing**  |        |          |           |           |           |
+------------+--------+----------+-----------+-----------+-----------+
| ## Vehicle | **Sa   |          | **S       | **90%     |           |
|            | mple** |          | tandard** | C         |           |
|            |        |          |           | onfidence |           |
|            |        |          |           | I         |           |
|            |        |          |           | nterval** |           |
+------------+--------+----------+-----------+-----------+-----------+
| **[Age     | **[S   | **[      | **[Deviat | **[Lo     | **[Up     |
| (yea       | ize]{. | Frequenc | ion]{.und | wer]{.und | per]{.und |
| rs)]{.unde | underl | y]{.unde | erline}** | erline}** | erline}** |
| rline}\*** | ine}** | rline}** |           |           |           |
+------------+--------+----------+-----------+-----------+-----------+
| 6.12       | 85     | 0.20%    | 1.41%     | 0.00%     | 2.52%     |
+------------+--------+----------+-----------+-----------+-----------+
| 13.00      | 50     | 2.00%    | 1.98%     | 0.00%     | 5.26%     |
+------------+--------+----------+-----------+-----------+-----------+
| 21.79      | 51     | 7.84%    | 3.76%     | 1.65%     | 14.03%    |
+------------+--------+----------+-----------+-----------+-----------+
| **\***     |        |          |           |           |           |
| \          |        |          |           |           |           |
| "**Vehicle |        |          |           |           |           |
| Age**\"    |        |          |           |           |           |
| was        |        |          |           |           |           |
| calculated |        |          |           |           |           |
| by         |        |          |           |           |           |
| s          |        |          |           |           |           |
| ubtracting |        |          |           |           |           |
| the model  |        |          |           |           |           |
| year from  |        |          |           |           |           |
| the test   |        |          |           |           |           |
| year and   |        |          |           |           |           |
| then       |        |          |           |           |           |
| adding     |        |          |           |           |           |
| one-half   |        |          |           |           |           |
| to         |        |          |           |           |           |
| simulate   |        |          |           |           |           |
| the rate   |        |          |           |           |           |
| as of      |        |          |           |           |           |
| January    |        |          |           |           |           |
| first.     |        |          |           |           |           |
+------------+--------+----------+-----------+-----------+-----------+

In one of the parallel reports (M6.EVP.001), EPA derived a logistic
growth curve that exactly fit those three data points (from Table 3-1).
The equation of that function is given below:

**Rate of Gross Liquid Leakers**

**Based on RTD/Resting Loss Testing =**

The predicted occurrences of GLLs based on this equation are given in
Appendix D. The frequencies from Table 3-1 are plotted in the following
figure (Figure 3-1). Also graphed in that figure are the 90 percent
confidence intervals (as dotted lines) from Table 3-1 and the predicted
frequencies (as the solid line) from Appendix D (or from the preceding
equation).

After EPA had created the preceding equation, additional test data were
provided by CRC (project number E-41). Specifically, a test program run
during 1998 found [no]{.underline} GLLs on the RTD test in a sample of
50 late-model year vehicles (1992 through 1997, with a mean age of 4.5
years). (See reference **\[6\]**.) Those results are consistent with
that preceding equation.

**[Figure 3-1]{.underline}**

**Predicted Frequency of Gross Liquid Leakers**

**With Observed Frequencies and 90 Percent Confidence Intervals**

**Based on RTD Testing**

![](media/image7.wmf){width="6.0625in" height="3.5208333333333335in"}

3.1.2 First Approach Estimating Frequency of GLLs on the Running Loss
Test

For the 150 vehicles in the CRC running loss testing program, the
occurrence of GLLs (i.e., the six vehicles in Appendix B whose running
loss emissions exceeded 7.0 grams/mile), the occurrence of GLLs was
calculated within each of the three model year ranges used in the
recruitment process (the same model year ranges used in the RTD
testing). Those estimated rates of occurrence of the GLLs appear in the
following table (Table 3-2). The large confidence intervals are again
the result of the relatively small sample sizes.

+------------+--------+----------+-----------+-----------+-----------+
| Table 3-2  |        |          |           |           |           |
|            |        |          |           |           |           |
| *          |        |          |           |           |           |
| *Frequency |        |          |           |           |           |
| of Gross   |        |          |           |           |           |
| Liquid     |        |          |           |           |           |
| Leakers**  |        |          |           |           |           |
|            |        |          |           |           |           |
| **Based on |        |          |           |           |           |
| Running    |        |          |           |           |           |
| Loss       |        |          |           |           |           |
| Testing**  |        |          |           |           |           |
+------------+--------+----------+-----------+-----------+-----------+
| *          | **Sa   |          | **S       | **90%     |           |
| *Vehicle** | mple** |          | tandard** | C         |           |
|            |        |          |           | onfidence |           |
|            |        |          |           | I         |           |
|            |        |          |           | nterval** |           |
+------------+--------+----------+-----------+-----------+-----------+
| **[Age     | **[S   | **[      | **[Deviat | **[Lo     | **[Up     |
| (y         | ize]{. | Frequenc | ion]{.und | wer]{.und | per]{.und |
| ears)]{.un | underl | y]{.unde | erline}** | erline}** | erline}** |
| derline}** | ine}** | rline}** |           |           |           |
+------------+--------+----------+-----------+-----------+-----------+
| 8.84       | 50     | 2.00%    | 1.98%     | 0.00%     | 5.26%     |
+------------+--------+----------+-----------+-----------+-----------+
| 14.24      | 39     | 5.13%    | 3.53%     | 0.00%     | 10.94%    |
+------------+--------+----------+-----------+-----------+-----------+
| 22.48      | 61     | 4.92%    | 2.77%     | 0.36%     | 9.47%     |
+------------+--------+----------+-----------+-----------+-----------+

It was not possible to [exactly]{.underline} fit the frequencies in
Table 3-2 with an increasing function (since the observed frequencies
seem to drop after age 14.24 years). EPA derived a logistic growth curve
that best fit those three data points. The equation of that function is:

########  Rate of Gross Liquid Leakers

**Based on Running Loss Testing =**

The predicted occurrences of GLLs based on that equation are also given
in Appendix D. The frequencies from Table 3-2 are plotted below in
Figure 3-2. Also graphed in that figure are the 90 percent confidence
intervals (as dotted lines) from Table 3-2 and the predicted frequencies
(as the solid line) from Appendix D (or from the preceding equation).

######### Figure 3-2

**Predicted Frequency of Gross Liquid Leakers**

**With Observed Frequencies and 90 Percent Confidence Intervals**

**Based on Running Loss Testing**

![](media/image8.wmf){width="6.0625in" height="3.5208333333333335in"}

Again, the newly acquired data (noted at the end of Section 3.1.1) in
which [no]{.underline} GLLs were found during running loss testing in a
sample of 50 late-model year vehicles (mean age of 4.5 years) are
consistent with that preceding equation.

3.1.3 First Approach Estimating Frequency of GLLs on the Hot Soak Test

To estimate the rate of occurrence of GLLs on the hot soak test, we
first referred to the second assumption on page 18, which states that
the collection of vehicles that are GLLs on the hot soak test is the
union of the collection of vehicles identified as GLLs on the running
loss test with the collection of vehicles identified as GLLs on the RTD
test. Thus, we were able to estimate the rate of GLLs on the hot soak
test based solely on the rates of GLLs on the running loss and RTD
tests. In the last column of Appendix D, the rate of GLLs on the hot
soak was calculated by adding the two preceding columns and then
subtracting the product of those two columns. (As stated at the
beginning of Section 3.0, due to the lack of data at ages over 10 years,
we were not able to use the same approach to predict GLLs on the hot
soak as we did on the other two tests.)

To test the reasonableness of the results of the above assumption, we
identified the six vehicles (in the hot soak testing program of 300
vehicles conducted for Auto Oil) that had hot soak test emissions in
excess of 10 grams per test. In this testing program, the test fleet was
again stratified into three model year ranges, but they were different
groupings (1983-85, 1986-90, and 1991-93). This resulted in a sample of
newer vehicles than were used in the RTD or running loss testing
programs.**\*** Those estimated rates of occurrence of the GLLs within
each of the three new model year ranges appear below in Table 3-3. The
large confidence intervals are again the result of the relatively small
sample sizes. We then compared those observed rates (in Table 3-3) with
the predicted rates in Appendix D.

+------------+--------+----------+-----------+-----------+-----------+
| **Table    |        |          |           |           |           |
| 3-3**      |        |          |           |           |           |
|            |        |          |           |           |           |
| *          |        |          |           |           |           |
| *Frequency |        |          |           |           |           |
| of Gross   |        |          |           |           |           |
| Liquid     |        |          |           |           |           |
| Leakers**  |        |          |           |           |           |
|            |        |          |           |           |           |
| ###        |        |          |           |           |           |
|  **Based o |        |          |           |           |           |
| n Hot Soak |        |          |           |           |           |
|  Testing** |        |          |           |           |           |
+------------+--------+----------+-----------+-----------+-----------+
| *          | **Sa   |          | **S       | **90%     |           |
| *Vehicle** | mple** |          | tandard** | C         |           |
|            |        |          |           | onfidence |           |
|            |        |          |           | I         |           |
|            |        |          |           | nterval** |           |
+------------+--------+----------+-----------+-----------+-----------+
| **[Age     | **[S   | **[      | **[Deviat | **[Lo     | **[Up     |
| (y         | ize]{. | Frequenc | ion]{.und | wer]{.und | per]{.und |
| ears)]{.un | underl | y]{.unde | erline}** | erline}** | erline}** |
| derline}** | ine}** | rline}** |           |           |           |
+------------+--------+----------+-----------+-----------+-----------+
| 1.98       | 66     | 1.04%    | 1.25%     | 0.00%     | 3.10%     |
+------------+--------+----------+-----------+-----------+-----------+
| 5.55       | 166    | 1.20%    | 0.85%     | 0.00%     | 2.60%     |
+------------+--------+----------+-----------+-----------+-----------+
| 9.38       | 64     | 6.25%    | 3.03%     | 1.27%     | 11.23%    |
+------------+--------+----------+-----------+-----------+-----------+

The observed frequencies from Table 3-3 are plotted in Figure 3-3
(below). Also graphed in that figure are the 90 percent

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

**\*** Since none of the mean ages in Table 3-3 exceeded 10 years, EPA
chose approaches different from those used with the diurnal or running
loss emissions. Rather than predicting the occurrence on the hot soak
test of GLLs among older vehicles based only on data from newer
vehicles, EPA estimated those rates based on the rates of GLLs on both
the RTD an running loss tests.

confidence intervals (as dotted lines) from Table 3-3 and the predicted
frequencies (as the solid line) from Appendix D. Those predicted
occurrences from Appendix D are based [not]{.underline} on hot soak test
results, but on results of running loss tests and RTD tests.

Comparing, in Figure 3-3, the predicted rates of GLLs occurring with the
observed rates of GLLs on the hot soak test, we observe:

> the predicted rates are all lower than the observed rates which were
> based on relatively small samples, but
>
> the predicted rates are all within the 90 percent confidence intervals
> of the observed rates (at each of the three points).

These differences between the predicted and observed rates may simply be
the result of the small sample sizes.

**[Figure 3-3]{.underline}**

**Predicted Frequency of Gross Liquid Leakers**

**With Observed Frequencies and 90 Percent Confidence Intervals**

**On the Hot Soak Test**

**(Based on RTD and Running Loss Testing)**

![](media/image9.wmf){width="6.0625in" height="3.5208333333333335in"}

Again, the newly acquired data (noted at the end of Sections 3.1.1 and
3.1.2) in which [no]{.underline} GLLs were found during hot soak testing
in a sample of 50 late-model year vehicles (mean age of 4.5 years) are
consistent with the preceding hot soak predictions.

3.2 [Second Approach to Estimate Frequency]{.underline}

The second approach employed by EPA was to use all of the observations
(in Tables 3-1 through 3-3) to find logistic functions that optimize
(simultaneously) all of the predictions. This approach produced the
following two equations:

########  Rate of Gross Liquid Leakers

**Based on RTD/Resting Loss Testing =**

**Rate of Gross Liquid Leakers**

**Based on Running Loss Testing =**

These two equations (and their union which estimates GLLs on hot soak
tests) predict rates of occurrence that are all within one-half of the
corresponding standard deviations at each of the nine observations (in
Tables 3-1 through 3-3). We can again graph those data (i.e., observed
rates and confidence intervals) from Tables 3-1 through 3-3, but now in
figures with curves from these new predictions (Figures 3-4 through
3-6). The only differences between the three figures in Section 3.1 and
these new corresponding figures are the solid lines designating the
predicted frequencies.

**[Figure 3-4]{.underline}**

## Predicted Frequency of Gross Liquid Leakers Using Second Approach

**With Observed Frequencies and 90 Percent Confidence Intervals**

**Based on RTD Testing**

![](media/image10.wmf){width="6.0625in" height="3.5208333333333335in"}

######### Figure 3-5

## Predicted Frequency of Gross Liquid Leakers Using Second Approach

**With Observed Frequencies and 90 Percent Confidence Intervals**

**Based on Running Loss Testing**

![](media/image11.wmf){width="6.0625in" height="3.5208333333333335in"}

**[Figure 3-6]{.underline}**

## Predicted Frequency of Gross Liquid Leakers Using Second Approach

**On the Hot Soak Test with Observed Frequencies and 90 Percent
Confidence Intervals**

**(Based on RTD and Running Loss Testing)**

![](media/image12.wmf){width="6.0625in" height="3.5208333333333335in"}

A visual inspection of these three figures (3-4 through 3-6) indicates
that this approach produces predicted rates (of the occurrence of GLLs)
that are all well within the 90 percent confidence intervals of the
observed rates (at each of the nine points). In fact (as noted earlier
in this section), all nine predicted rates are within one-half of the
corresponding standard deviations at each of the observations.

3.3 [Selection of Approach to Estimate Frequency]{.underline}

In choosing between these two methods (which in EPA\'s opinion are the
two best candidates) of predicting the frequency of GLLs, we first
observed that the greatest difference between these two methods was in
estimating the rate of GLLs on the hot soak test. In Figure 3-7 (on the
following page), we reproduced the estimated frequency curves from
Figures 3-3 and 3-6. In this figure, the \"dashed\" line is the estimate
produced using the first method (i.e., from Figure 3-3 in Section
3.1.3), and the solid line is the estimate produced using the second
method (i.e., from Figure 3-6 in Section 3.2).

**[Figure 3-7]{.underline}**

**Comparing Predicted Frequency of Gross Liquid Leakers**

**On the Hot Soak Test**

![](media/image13.emf){width="6.069444444444445in"
height="3.513888888888889in"}

A visual inspection of this figure indicates that:

> The two predicted rates are similar for vehicles at least 17 years of
> age or older.
>
> For vehicles newer than 17 years of age, the second method predicts a
> substantially higher occurrence of GLLs. (For vehicles up through the
> age of 10, the second method predicts more than twice as many GLLs as
> does the first method.)

To decide between these two models, EPA made use of a recent testing
program run jointly by the CRC and the American Petroleum Institute
(API). **\[5\]** This program was specifically designed to determine the
frequency of vehicles with liquid leaks. Since actual measurements of
evaporative emissions were not performed in this program, we cannot
determine which of those vehicles identified as having liquid leaks
would have met our criteria for GLLs.

In that API/CRC program, 1,000 vehicles were inspected for any signs of
leaks with the engine operating (during at least a portion of the visual
inspection). (This protocol was expected to permit identification of
vehicles exhibiting fuel leaks on the RTD, hot soak, or running loss
tests.) The vehicles were then classified by the mechanic according to
the severity of the observed leaks. The visible liquid leaks were
classified as either:

> small liquid leaks (e.g., single drops) or
>
> larger leaks (e.g., steady flow of drops).

This classification was based on a visual inspection rather than on the
results of a test of the actual evaporative emissions. The results of
that study are summarized in the following table:

+------+--------+-------+-------+-------+-------+---------+---------+
| T    |        |       |       |       |       |         |         |
| able |        |       |       |       |       |         |         |
| 3-4  |        |       |       |       |       |         |         |
|      |        |       |       |       |       |         |         |
| **F  |        |       |       |       |       |         |         |
| requ |        |       |       |       |       |         |         |
| ency |        |       |       |       |       |         |         |
| of   |        |       |       |       |       |         |         |
| Lea  |        |       |       |       |       |         |         |
| king |        |       |       |       |       |         |         |
| Ve   |        |       |       |       |       |         |         |
| hicl |        |       |       |       |       |         |         |
| es** |        |       |       |       |       |         |         |
|      |        |       |       |       |       |         |         |
| **In |        |       |       |       |       |         |         |
| API  |        |       |       |       |       |         |         |
| /CRC |        |       |       |       |       |         |         |
| Tes  |        |       |       |       |       |         |         |
| ting |        |       |       |       |       |         |         |
| P    |        |       |       |       |       |         |         |
| rogr |        |       |       |       |       |         |         |
| am** |        |       |       |       |       |         |         |
+------+--------+-------+-------+-------+-------+---------+---------+
|      |        |       |       |       |       |         |         |
+------+--------+-------+-------+-------+-------+---------+---------+
|      |        |       | **    | **    | **To  | **90%   |         |
|      |        |       | Vehic | Vehic | tal** | Conf    |         |
|      |        |       | les** | les** |       | Int     |         |
|      |        |       |       |       |       | erval** |         |
+------+--------+-------+-------+-------+-------+---------+---------+
| *    | **     |       | **w   | **w   | **w   |         |         |
| *Mod | Mean** |       | ith** | ith** | ith** |         |         |
| el** |        |       |       |       |       |         |         |
+------+--------+-------+-------+-------+-------+---------+---------+
| **Ye | *      | **Sam | **Sm  | **Lar | **    |         |         |
| ar** | *Age** | ple** | all** | ger** | Any** |         |         |
+------+--------+-------+-------+-------+-------+---------+---------+
| **[  | *      | **[   | **[   | **[   | **[   | **      | **      |
| Rang | *[(yea | Sizes | Leaks | Leaks | Leaks | [Lower] | [Upper] |
| e]{. | rs)]{. | ]{.un | ]{.un | ]{.un | ]{.un | {.under | {.under |
| unde | underl | derli | derli | derli | derli | line}** | line}** |
| rlin | ine}** | ne}** | ne}** | ne}** | ne}** |         |         |
| e}** |        |       |       |       |       |         |         |
+------+--------+-------+-------+-------+-------+---------+---------+
| Pre  | 22.329 | 70    | 5     | 2     | 7     | 4.10%   | 15.90%  |
| -80s |        |       |       |       |       |         |         |
+------+--------+-------+-------+-------+-------+---------+---------+
| 8    | 14.394 | 155   | 10    | 1     | 11    | 3.70%   | 10.49%  |
| 0-85 |        |       |       |       |       |         |         |
+------+--------+-------+-------+-------+-------+---------+---------+
| 8    | 9.429  | 352   | 2     | 2     | 4     | 0.21%   | 2.07%   |
| 6-91 |        |       |       |       |       |         |         |
+------+--------+-------+-------+-------+-------+---------+---------+
| 9    | 3.979  | 423   | 0     | 0     | 0     | 0.00%   | 0.49%   |
| 2-98 |        |       |       |       |       |         |         |
+------+--------+-------+-------+-------+-------+---------+---------+

The 90 percent confidence intervals in Table 3-4 are based on the
(total) number of vehicles with either small or large visible leaks.
Those vehicles which were identified as having [large]{.underline}
visible liquid fuel leaks were almost certainly GLLs, and many of the
vehicles which were identified as having [small]{.underline} visible
liquid fuel leaks were possibly GLLs as well. Thus, EPA considers the
upper bound of the confidence intervals as a conservative estimate of
the occurrence of the GLLs. If we reproduce Figure 3-7, and include the
90 percent confidence intervals from Table 3-4 (as dotted lines), we
produce Figure 3-8.

**[Figure 3-8]{.underline}**

**Comparing Predicted Frequency of Gross Liquid Leakers**

**On the Hot Soak Test**

**(New Confidence Intervals from Table 3-4)**

![](media/image14.emf){width="6.069444444444445in"
height="3.513888888888889in"}

A visual inspection of Figure 3-8 strongly suggests the second method
for predicting the frequency of GLLs over predicts the actual occurrence
of GLLs for vehicles under the age of 13 years. (The conclusion that the
second method \"**OVER PREDICTS**\" the frequency is based on EPA\'s
choice of basing the confidence intervals on Table 3-4 instead of Table
3-3. That choice reflects primarily the relatively large sample sizes in
Table 3-4 compared with those in Table 3-3.)

Therefore, EPA will use the first method (Section 3.1) to estimate the
frequencies of the occurrence of GLLs on the three types of tests for
evaporative emissions. The results of that method are given in Appendix
D.

3.4 [Overall Occurrence of GLLs in the In-Use Fleet]{.underline}

The equations in Section 3.1 (or the results in Appendix D) predict the
occurrence of GLLs identified on the RTD test to range between 0.02 to
8.55 percent by vehicle age, and for those identified on the running
loss test to range between 0.05 and 5.97 percent by vehicle age. It is
reasonable to ask what is the overall percentage of these vehicles in
the entire in-use fleet. To answer that question, we referred to another
report which provides an estimate of the national distribution by age of
light-duty vehicles (LDVs) and light-duty trucks (LDTs). (See reference
**\[11\]**.) Applying the percentages from Appendix D to those estimated
vehicle counts produces Table 3-5 (on the following page). The predicted
total counts in Table 3-5 suggest that GLLs represent approximately 1.2
to 1.6 percent of the entire in-use fleet.

+-----------------+----------------+----------------+----------------+
| **Table 3-5**   |                |                |                |
|                 |                |                |                |
| **Predicted     |                |                |                |
| Occurrence of   |                |                |                |
| Gross Liquid    |                |                |                |
| Leakers**       |                |                |                |
|                 |                |                |                |
| **In the        |                |                |                |
| National In-Use |                |                |                |
| Fleet of LDVs   |                |                |                |
| and LDTs**      |                |                |                |
|                 |                |                |                |
| (as of January  |                |                |                |
| 1995)           |                |                |                |
+-----------------+----------------+----------------+----------------+
| **Calendar**    |                | **GLLs**       |                |
+-----------------+----------------+----------------+----------------+
| **Year Minus**  | **Vehicle**    | **[Identified  |                |
|                 |                | on:]           |                |
|                 |                | {.underline}** |                |
+-----------------+----------------+----------------+----------------+
| **[Model        | **[Counts]     | **[RTD]        | **[Running     |
| Year            | {.underline}** | {.underline}** | Loss]          |
| ]{.underline}** |                |                | {.underline}** |
+-----------------+----------------+----------------+----------------+
| 0               | 9,581,160      | 2,052.19       | 4,750.99       |
+-----------------+----------------+----------------+----------------+
| 1               | 12,690,223     | 3,924.61       | 9,349.56       |
+-----------------+----------------+----------------+----------------+
| 2               | 12,595,718     | 5,621.77       | 13,760.93      |
+-----------------+----------------+----------------+----------------+
| 3               | 12,479,871     | 8,033.14       | 20,159.55      |
+-----------------+----------------+----------------+----------------+
| 4               | 12,328,489     | 11,433.59      | 29,321.45      |
+-----------------+----------------+----------------+----------------+
| 5               | 12,124,815     | 16,178.24      | 42,197.16      |
+-----------------+----------------+----------------+----------------+
| 6               | 11,850,006     | 22,702.78      | 59,817.53      |
+-----------------+----------------+----------------+----------------+
| 7               | 11,484,110     | 31,499.85      | 83,045.60      |
+-----------------+----------------+----------------+----------------+
| 8               | 11,007,677     | 43,050.78      | 112,104.66     |
+-----------------+----------------+----------------+----------------+
| 9               | 10,404,139     | 57,685.81      | 145,891.73     |
+-----------------+----------------+----------------+----------------+
| 10              | 9,663,040      | 75,350.55      | 181,302.31     |
+-----------------+----------------+----------------+----------------+
| 11              | 8,783,860      | 95,286.08      | 213,090.08     |
+-----------------+----------------+----------------+----------------+
| 12              | 7,508,980      | 111,677.02     | 226,678.25     |
+-----------------+----------------+----------------+----------------+
| 13              | 6,076,245      | 121,573.75     | 219,360.63     |
+-----------------+----------------+----------------+----------------+
| 14              | 4,896,767      | 128,727.45     | 203,502.92     |
+-----------------+----------------+----------------+----------------+
| 15              | 3,929,300      | 131,947.97     | 181,708.71     |
+-----------------+----------------+----------------+----------------+
| 16              | 3,140,650      | 130,511.75     | 157,112.78     |
+-----------------+----------------+----------------+----------------+
| 17              | 2,503,094      | 124,468.78     | 132,479.39     |
+-----------------+----------------+----------------+----------------+
| 18              | 2,030,454      | 116,862.35     | 111,810.15     |
+-----------------+----------------+----------------+----------------+
| 19              | 1,710,242      | 110,464.75     | 96,801.22      |
+-----------------+----------------+----------------+----------------+
| 20              | 1,451,096      | 102,385.03     | 83,696.51      |
+-----------------+----------------+----------------+----------------+
| 21              | 1,240,664      | 93,514.33      | 72,483.90      |
+-----------------+----------------+----------------+----------------+
| 22              | 1,069,132      | 84,580.52      | 63,008.21      |
+-----------------+----------------+----------------+----------------+
| 23              | 928,705        | 76,080.74      | 55,054.76      |
+-----------------+----------------+----------------+----------------+
| 24 and older    | 3,724,043      | 312,764.31     | 221,641.23     |
+-----------------+----------------+----------------+----------------+
| **TOTALS:**     | 175,202,480    | 2,018,378      | 2,740,130      |
+-----------------+----------------+----------------+----------------+

**4.0 REFERENCES**

**1)** Larry Landman, \"Evaluating Resting Loss and Diurnal Evaporative
Emissions Using RTD Tests,\" Report numbered M6.EVP.001, April 2001.

**2)** Larry Landman, \"Modeling Hourly Diurnal Emissions and
Interrupted Diurnal Emissions Based on Real-Time Diurnal Data,\" Report
numbered M6.EVP.002, April 2001.

**3)** Louis Browning, \"Update of Hot Soak Emissions Analysis\"
prepared by Louis Browning of ARCADIS Geraghty & Miller, Inc. for EPA,
Report numbered M6.EVP.004, September 1998

**4)** Larry Landman, \"Estimating Running Loss Evaporative Emissions in
MOBILE6,\" Report numbered M6.EVP.008, April 2001.

**5)** D. McClement, \"Raw Fuel Survey in I/M Lanes\", Prepared for the
American Petroleum Institute and the Coordinating Research Council, Inc.
by Automotive Testing Laboratories, Inc., June 10, 1998.

**6)** D. McClement, \"Real World Evaporative Testing of Late Model
In-Use Vehicles, CRC Project E-41\", Prepared for the Coordinating
Research Council, Inc. by Automotive Testing Laboratories, Inc.,
December 17, 1998.

**7)** Melvin Ingalls, \"Mobile Source Exposure Estimation,\" prepared
by Southwest Research Institute for EPA, EPA Report Number
EPA460/3-84-008, March 1984, Appendix A.

**8)** Edward L. Glover, \"Hot Soak Emissions as a Function of Soak
Time,\" Report numbered M6.EVP.007.

**9)** D. McClement, \"Measurement of Running Loss Emissions from In-Use
Vehicles (CRC Project E-35)\", CRC Report No. 611, Prepared for the
Coordinating Research Council, Inc. by Automotive Testing Laboratories,
Inc., February 1998.

**10)** Larry Landman, \"Modeling Diurnal and Resting Loss Emissions
from Vehicles Certified to the Enhanced Evaporative Standards,\" Report
numbered M6.EVP.005, April 2001.

**11)** Tracie R. Jackson, \"Fleet Characterization Data for MOBILE6:
Development and Use of Age Distributions, Average Annual Mileage
Accumulation Rates, and Projected Vehicle Counts for Use in MOBILE6,\"
Report numbered M6.FLT.007.

**Appendix A**

**RTD Emissions of 11 Vehicles with Liquid Leaks**

**With RTD \> 30 and Resting Loss \> 0.25**

**(Arranged in Increasing Order of Estimated Resting Losses)**

**(ALL of the Leaking Vehicles Were Carbureted)**

+-------------+-------------------+---------------+-------------------+
|             | **Real-Time**     | **Estimated** |                   |
+-------------+-------------------+---------------+-------------------+
|             | **Diurnal**       | **Rst Loss**  | **Estimated**     |
+-------------+-------------------+---------------+-------------------+
| **Vehicle** | **(RTD) Test**    | **(at 72°F)** | **Diurnal**       |
+-------------+-------------------+---------------+-------------------+
| **          | **[(grams /       | **[(grams /   | **[(grams /       |
| [Number]{.u | da                | hr)]{         | da                |
| nderline}** | y)]{.underline}** | .underline}** | y)]{.underline}** |
+-------------+-------------------+---------------+-------------------+
| 9095        | 32.26             | 0.28          | 24.85             |
+-------------+-------------------+---------------+-------------------+
| 9037        | 33.44             | 0.47          | 21.47             |
+-------------+-------------------+---------------+-------------------+
| 9046        | 33.76             | 0.62          | 18.21             |
+-------------+-------------------+---------------+-------------------+
| 9042        | 30.88             | 0.89          | 8.83              |
+-------------+-------------------+---------------+-------------------+
| 9098        | 45.21             | 0.90          | 22.91             |
+-------------+-------------------+---------------+-------------------+
| 9148        | 47.97             | 1.27          | 16.63             |
+-------------+-------------------+---------------+-------------------+
| 9049        | 181.35            | 4.87          | 64.55             |
+-------------+-------------------+---------------+-------------------+
| 9054        | 316.59            | 10.58         | 62.64             |
+-------------+-------------------+---------------+-------------------+
| 9129        | 181.79            | 10.77         | **IGNORE\***      |
+-------------+-------------------+---------------+-------------------+
| 9087        | 478.16            | 14.12         | 139.22            |
+-------------+-------------------+---------------+-------------------+
| 9111        | 777.14            | 16.51         | 380.79            |
+-------------+-------------------+---------------+-------------------+
| > **\*** An |                   |               |                   |
| >           |                   |               |                   |
| examination |                   |               |                   |
| > of the    |                   |               |                   |
| > hourly    |                   |               |                   |
| > RTD data  |                   |               |                   |
| > from this |                   |               |                   |
| > vehicle   |                   |               |                   |
| > (in       |                   |               |                   |
| > reference |                   |               |                   |
| >           |                   |               |                   |
|  **\[1\]**) |                   |               |                   |
| > suggests  |                   |               |                   |
| > that the  |                   |               |                   |
| > leak      |                   |               |                   |
| > actually  |                   |               |                   |
| > developed |                   |               |                   |
| > around    |                   |               |                   |
| > the tenth |                   |               |                   |
| > hour of   |                   |               |                   |
| > the       |                   |               |                   |
| > 24-hour   |                   |               |                   |
| > test.     |                   |               |                   |
| > While the |                   |               |                   |
| > resting   |                   |               |                   |
| > loss      |                   |               |                   |
| > estimate  |                   |               |                   |
| > (based on |                   |               |                   |
| > hours 19  |                   |               |                   |
| > through   |                   |               |                   |
| > 24) is    |                   |               |                   |
| > most      |                   |               |                   |
| > likely    |                   |               |                   |
| > valid,    |                   |               |                   |
| > the       |                   |               |                   |
| > estimate  |                   |               |                   |
| > of        |                   |               |                   |
| > diurnal   |                   |               |                   |
| > emissions |                   |               |                   |
| > is        |                   |               |                   |
| >           |                   |               |                   |
|  unreliable |                   |               |                   |
| > (in fact, |                   |               |                   |
| > it is     |                   |               |                   |
| >           |                   |               |                   |
|  negative). |                   |               |                   |
|             |                   |               |                   |
| Note that   |                   |               |                   |
| while       |                   |               |                   |
| [all]{      |                   |               |                   |
| .underline} |                   |               |                   |
| 11 of these |                   |               |                   |
| vehicles    |                   |               |                   |
| have liquid |                   |               |                   |
| leaks most  |                   |               |                   |
| of them do  |                   |               |                   |
| **[NOT]{.u  |                   |               |                   |
| nderline}** |                   |               |                   |
| qualify as  |                   |               |                   |
| *           |                   |               |                   |
| *[Gross]{.u |                   |               |                   |
| nderline}** |                   |               |                   |
| Liquid      |                   |               |                   |
| Leakers     |                   |               |                   |
| (only the   |                   |               |                   |
| five        |                   |               |                   |
| highest     |                   |               |                   |
| emitting    |                   |               |                   |
| vehicles    |                   |               |                   |
| meet the    |                   |               |                   |
| necessary   |                   |               |                   |
| criteria).  |                   |               |                   |
+-------------+-------------------+---------------+-------------------+

**Appendix B**

**Hot Soak Emissions of 14 Vehicles with Liquid Leaks**

**(With Hot Soak Emissions At Least 2.0 grams / test)**

**Sorted by Fuel Delivery System**

**In Increasing Order of Emissions**

+-----------+----------+-----------+--------+---------+--------------+
| > **[Prog | **V      | **Fuel**  | **     | **RVP** | **Hot Soak** |
| ram]{.und | ehicle** |           | Temp** |         |              |
| erline}** |          | **[Sys    |        | **      | **[(grams    |
|           | **[Numbe | tem]{.und | **[(   | [(psi)] | HC)]{.       |
|           | r]{.unde | erline}** | °F)]{. | {.under | underline}** |
|           | rline}** |           | underl | line}** |              |
|           |          |           | ine}** |         |              |
+-----------+----------+-----------+--------+---------+--------------+
| > Auto    | 134      | CARB      | 94     | 6.0     | 2.54         |
| > Oil     |          |           |        |         |              |
+-----------+----------+-----------+--------+---------+--------------+
| > EPA     | 177      | CARB      | 95     | 6.1     | 4.63         |
+-----------+----------+-----------+--------+---------+--------------+
| > EPA     | 122      | CARB      | 105    | 6.1     | 5.53         |
+-----------+----------+-----------+--------+---------+--------------+
| > Auto    | 79       | CARB      | 92     | 7.0     | 9.49         |
| > Oil     |          |           |        |         |              |
+-----------+----------+-----------+--------+---------+--------------+
| > EPA     | 173      | CARB      | 92     | 6.7     | 14.53        |
+-----------+----------+-----------+--------+---------+--------------+
| > EPA     | 97       | CARB      | 110    | 6.7     | 14.66        |
+-----------+----------+-----------+--------+---------+--------------+
|           |          |           |        |         |              |
+-----------+----------+-----------+--------+---------+--------------+
| > **[Prog | **V      | **Fuel**  | **     | **RVP** | **Hot Soak** |
| ram]{.und | ehicle** |           | Temp** |         |              |
| erline}** |          | **[Sys    |        | **      | **[(grams    |
|           | **[Numbe | tem]{.und | **[(   | [(psi)] | HC)]{.       |
|           | r]{.unde | erline}** | °F)]{. | {.under | underline}** |
|           | rline}** |           | underl | line}** |              |
|           |          |           | ine}** |         |              |
+-----------+----------+-----------+--------+---------+--------------+
| > EPA     | 143      | TBI       | 94     | 6.4     | 8.28         |
+-----------+----------+-----------+--------+---------+--------------+
|           |          |           |        |         |              |
+-----------+----------+-----------+--------+---------+--------------+
| > **[Prog | **V      | **Fuel**  | **     | **RVP** | **Hot Soak** |
| ram]{.und | ehicle** |           | Temp** |         |              |
| erline}** |          | **[Sys    |        | **      | **[(grams    |
|           | **[Numbe | tem]{.und | **[(   | [(psi)] | HC)]{.       |
|           | r]{.unde | erline}** | °F)]{. | {.under | underline}** |
|           | rline}** |           | underl | line}** |              |
|           |          |           | ine}** |         |              |
+-----------+----------+-----------+--------+---------+--------------+
| > Auto    | 35       | PFI       | 104    | 6.7     | 2.00         |
| > Oil     |          |           |        |         |              |
+-----------+----------+-----------+--------+---------+--------------+
| > Auto    | 199      | PFI       | 96     | 6.5     | 2.26         |
| > Oil     |          |           |        |         |              |
+-----------+----------+-----------+--------+---------+--------------+
| > Auto    | 47       | PFI       | 93     | 6.1     | 11.56        |
| > Oil     |          |           |        |         |              |
+-----------+----------+-----------+--------+---------+--------------+
| > EPA     | 33       | PFI       | 113    | 6.0     | 46.95        |
+-----------+----------+-----------+--------+---------+--------------+
| > Auto    | 276      | PFI       | 87     | 6.3     | 49.39        |
| > Oil     |          |           |        |         |              |
+-----------+----------+-----------+--------+---------+--------------+
| >         | 372      | PFI       | 106    | 9.0     | 54.18        |
| EPA**\*** |          |           |        |         |              |
+-----------+----------+-----------+--------+---------+--------------+
| >         | 266      | PFI       | 105    | 9.0     | 88.57        |
| EPA**\*** |          |           |        |         |              |
+-----------+----------+-----------+--------+---------+--------------+
| **\***    |          |           |        |         |              |
| These two |          |           |        |         |              |
| vehicles  |          |           |        |         |              |
| were      |          |           |        |         |              |
| tested    |          |           |        |         |              |
| using a   |          |           |        |         |              |
| subs      |          |           |        |         |              |
| tantially |          |           |        |         |              |
| more      |          |           |        |         |              |
| volatile  |          |           |        |         |              |
| fuel.     |          |           |        |         |              |
+-----------+----------+-----------+--------+---------+--------------+

**Appendix C**

**Running Loss Emissions of 10 Vehicles with Liquid Leaks**

**(With Running Loss Emissions At Least 5.0 grams / mile)**

**(Arranged in Increasing Order of Estimated Resting Losses)**

**(ALL of the Leaking Vehicles Were Carbureted)**

  -------------------------- ---------------------- ---------------------- ----------------------
                             **Running**            **Running**            **Running**

  **Vehicle**                **Loss HC**            **Loss HC**            **Loss HC**

  **[Number]{.underline}**   **[(grams /            **[(grams /            **[(grams /
                             mile)]{.underline}**   LA-4)]{.underline}**   hour)]{.underline}**

  35044                      5.009                  37.47                  98.32

  35125                      5.297                  39.44                  103.49

  35099                      5.649                  42.17                  110.65

  35085                      6.880                  51.18                  134.29

  35045                      7.469                  55.79                  146.39

  35071                      9.175                  68.84                  180.63

  35047                      13.480                 100.19                 262.89

  35129                      13.566                 100.72                 264.28

  35054                      24.841                 184.96                 485.32

  35091                      42.973                 318.90                 836.76
  -------------------------- ---------------------- ---------------------- ----------------------

**Appendix D**

**Predicted Frequency of Occurrence of GLLs**

  --------------------------- --------------------------- ------------------------ ------------------------
  **Vehicle**                 **Resting**                                          

  **Age**                     **Loss /**                  **Running**              **Hot**

  **[(years)]{.underline}**   **[Diurnal]{.underline}**   **[Loss]{.underline}**   **[Soak]{.underline}**

  0                           0.02%                       0.05%                    0.07%

  1                           0.03%                       0.07%                    0.10%

  2                           0.04%                       0.11%                    0.15%

  3                           0.06%                       0.16%                    0.23%

  4                           0.09%                       0.24%                    0.33%

  5                           0.13%                       0.35%                    0.48%

  6                           0.19%                       0.50%                    0.70%

  7                           0.27%                       0.72%                    1.00%

  8                           0.39%                       1.02%                    1.41%

  9                           0.55%                       1.40%                    1.95%

  10                          0.78%                       1.88%                    2.64%

  11                          1.08%                       2.43%                    3.48%

  12                          1.49%                       3.02%                    4.46%

  13                          2.00%                       3.61%                    5.54%

  14                          2.63%                       4.16%                    6.67%

  15                          3.36%                       4.62%                    7.83%

  16                          4.15%                       5.00%                    8.95%

  17                          4.97%                       5.29%                    10.00%

  18                          5.75%                       5.51%                    10.94%

  19                          6.46%                       5.66%                    11.75%

  20                          7.05%                       5.77%                    12.42%

  21                          7.54%                       5.84%                    12.94%

  22                          7.91%                       5.89%                    13.34%

  23                          8.19%                       5.93%                    13.63%

  24                          8.40%                       5.95%                    13.85%

  25                          8.55%                       5.97%                    14.00%
  --------------------------- --------------------------- ------------------------ ------------------------

**Appendix E**

### Response to Peer Review Comments from Sandeep Kishan

This report was formally peer reviewed by one peer reviewer (Sandeep
Kishan). In this appendix, comments from Sandeep Kishan are reproduced
in plain text, and EPA's responses to those comments are interspersed in
indented italics. Each of these comments refer to page numbers in the
earlier draft version (dated June 30, 1999) that do not necessarily
match the page numbers in this final version.

\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*

This memorandum provides peer review comments on two EPA documents:
\"Estimating Running Loss Evaporative Emissions in MOBILE6,\" Document
No. M6.EVP.008, June 28, 1999, and \"Evaporative Emissions of Gross
Liquid Leakers in MOBILE6,\" Report Number M6.EVP.009, June 30, 1999.
Both of these are draft reports.

Overall, we think that the reports are good, and they present some new
data analysis techniques that are attractive. Since, in the past, we
have had to do similar data analyses and modeling for evaporative
emissions from vehicle test data, we can appreciate many of the
difficulties and data limitations you are subject to. We hope the
comments below help you with this effort.

[Document No. M6.EVP.009 (June 30, 1999)]{.underline}

We have the following questions, comments, and recommendations on this
draft report. For each item we give the page number and paragraph that
the comment refers to, if it is a specific comment.

We found that the first half of the report, which estimates the average
emissions rate of gross liquid leakers, was well written and, in
addition, we thought that the technique of fitting the sparse data to
log-normal distributions was excellent. However, in the second half of
the report which estimates the frequency of gross liquid leakers of
different types in the vehicle population, we had difficulty
understanding the distinction between the first approach and the second
approach. We did understand the development of the logistic growth
curves for each emission type. However, we think that there is no reason
to average this data, which causes loss of important information, before
building the logistic models. More defensible relationships could easily
be built using the individual car data rather than averages of data.

1\. In general, the report presents the final story of the analysis and
shows how the data fits that story. In many cases, we are more
accustomed to a method of analysis reporting that demonstrates how the
data reveals what the most likely story is. Consequently, we have looked
to see if the data have been presented in a way so that the story holds
together.

2\. Page 2, Second paragraph from bottom -- We agree with the EPA
proposed treatment of considering evaporative emissions for gross liquid
leakers as independent of ambient temperature and RVP.

*EPA, of course, agrees with its own methodology.*

3\. Page 3, Paragraph 3 -- The report seems to begin the discussion of
substantial leakers and gross leakers in a manner that is confusing to
the reader. We suggest, and perhaps this is the intended meaning of the
author, that substantial leakers are those leakers which have a lower
limit of liquid leak rates than do gross liquid leakers. For each type
of emission a set of substantial liquid leakers are analyzed. Then, at
some point in the development, only the gross liquid leakers are
analyzed. For example, later in the report for the hot soaks tests, the
substantial liquid leakers have rates of greater than 2 grams per hour
and the gross liquid leakers have rates of greater than 10 grams per
hour. Consequently, we suggest that beginning in Section 2.1, a
distinction between substantial and gross liquid leakers be made. The
parenthetical comments in Section 2.1 seem to say that substantial
liquid leakers and gross liquid leakers are synonymous. We think that
these parenthetical comments only serve to cloud the distinction between
substantial and gross liquid leakers and, therefore, they should be
removed. These comments appear in the third, fourth and fifth paragraphs
on Page 3.

*No, there was no attempt to define a \"substantial\" leaker category.
The word \"substantial\" only refers to the magnitude of the leak. Our
intent was to define a \"Gross Liquid Leaker\" (GLL) as a vehicle having
a substantial leak of liquid gasoline. The exact magnitude of a
\"substantial leak\" (in terms of drops of gasoline per hour) was left
vague. However, the reader could use the lower bounds specified for GLLs
(see Table 2-1) to calculate such hourly rates. The text has been
revised to avoid this confusion.*

4\. Page 3, Paragraph 5 -- We agree with the approach of using a
log-normal fit of the sparse data to estimate the gross liquid leaker
average emission rates to avoid simply calculating the mean of the
sparse values which are available.

5\. Page 4, Second Paragraph -- It took me a while to recognize that the
estimated diurnal emissions, which are referred to in the second
paragraph, is equal to the RTD emissions minus 24 times the resting loss
emissions. We think it would be helpful to the reader to insert a short
paragraph before this paragraph to remind the reader of this
relationship.

*We added that explanation to the beginning of Section 2.1.*

6\. Page 5, Paragraph 1 -- We agree with the technique of trimming the
upper tail off the log-normal distribution for the purposes of
calculating the mean gross liquid leaker emission rate; it reflects an
engineering reality. We also like the technique of determining the
sensitivity of the mean to doubling the value of the upper cutpoint.
However, we were curious about how much the mean would change if no
upper cutpoint were used, and we suspect that other readers would have
the same curiosity. Our gut feel is that, if the upper cutpoints were at
+infinity, the average emission rate would be only slightly increased.

*The RTD test of the vehicle with the highest diurnal (380.79 grams per
day) was aborted after 16 hours because the technicians were concerned
that the SHED was approaching an explosive concentration level. In this
report we calculated an average diurnal using a maximum of 5 times that
potentially explosive rate. Even that maximum seems too high. By using
still higher values, we risk reducing the credibility of the analysis.
The reader is of course free to perform that calculation.*

7\. Page 5, Paragraph 2 -- Choosing the value of the lower cutpoint of
the lognormal distribution is more problematic then choosing the upper
cutpoint. We felt that the discontinuity argument of values between 25
and 62 grams per day in the second paragraph was pretty weak since there
are larger discontinuities at larger emission values. We think we agree
that a lower limit is needed (on the other hand, it may be possible that
calculating the average value using the lower tail of the log-normal
distribution may not change the average value much) to avoid double
counting of emissions from gross liquid leakers and the diurnal
emissions of non-gross liquid leakers which will be estimated from a
different routine in a MOBILE code. We think that a more defensible
approach to selecting the lower cutpoint would be to consider the range
of normal (not leakers) diurnal emission values for the fleet using the
existing routines in MOBILE. In other words, could an analysis of the
diurnal emissions emitter model in MOBILE be done to verify that the
lower cutpoint chosen for the diurnal emission gross liquid leaker
distribution does not produce a gap or a bump in the distribution
between the normal and the gross liquid leaker models?

*We agree that the selection of the lower bound (threshold) for the
gross liquid leakers is a weak point. It is highly sample dependent. If
a higher threshold value were selected, the effect would be to increase
the estimated average diurnal emissions (from these GLLs). For example,
doubling the threshold from 25 to 50 grams per day would increase the
estimated average by almost 35 percent. While this seems to be a large
change, the actual effect on total evaporative hydrocarbon is in
consequential. As more data become available, we may revise these
threshold values.*

8\. Page 5, Paragraph 2 -- It would be beneficial to the reader to have
an appendix to show how the average emissions for the log-normal
distribution with the cutpoints on the upper and lower end are
calculated. Most readers won\'t want to or won\'t be able to go through
this tricky calculation.

*These averages were calculated by computing the area under curves using
Riemann sums (from first semester Calculus). We see no need to include
these calculations in this report.*

9\. Page 6, Second full paragraph -- Comments 4, 6, 7, and 8 above apply
generally to all of the different types of gross liquid leaker
calculations in Section 2. From this point forward, the comments will
apply only to specific issues on individual gross liquid leaker types.

10\. Page 7, Paragraph 1 -- The last sentence talks about a uniform
distribution. We think that this is a relatively minor comment but it
did take me a while to understand what the author was referring to. In
the last paragraph on the page, the report mentions that the uniform
distribution would have a better fit but the only reason that the report
gives to not chose the uniform distribution was for consistency with
other models in the report. However, there is another reason that could
be considered, and perhaps mentioned, is that the uniform distribution
would imply that 40% of the vehicles would have zero resting loss
emissions. We think that you will agree this is probably not the case.
The third paragraph on Page 7 also has a typo in the third line: the
word approached should be approaches.

*Good point, the material has been revised to include this.*

11\. Page 11, Second full paragraph -- The reference to the other report
suggests that the relative fuel pressures between TBI and PFI systems
are a factor of 4 different. This is not explicitly stated in this
report. Perhaps it should be if the author believes it still to be
correct.

*We believe that the critical assumptions were stated. Going off into a
detailed discussion of relative pressures might only cloud the issue.*

12\. Page 15, Table 2-1 -- The footnote at the bottom of Table 2-1
brings up an issue. For the RTD data analysis, the resting losses were
removed from RTD to get diurnal emissions. But the same approach was not
used to separate resting losses from hot soak emissions and running loss
emissions. Why is there a difference in analysis methods? Perhaps, it
would have been just as easy to determine the average RTD emissions per
day and then Table 2-1 would have had an entry for RTD in place of
diurnal.

*Since we estimated resting loss emissions by averaging the emissions
during last six hours of the RTD test (i.e., the hours corresponding to
the period from midnight to 6 AM), the resting loss values were
available for each RTD test. This permitted us to easily calculate for
each RTD test a resting loss / diurnal pair. This was not true of the
hot soak or running loss tests. Therefore, different approaches were
used.*

The footnote at the bottom of Table 2-1 also is a surprise to the
reader. At a minimum, we suggest that the reader be warned that this
subtraction will occur by placing an appropriate statement at the
beginning of the analysis sections for hot soak and running loss average
emission rate determinations.

*As the reviewer suggested, an explanation has been added to both the
hot soak section and to the running loss section.*

13\. Page 15, Table 2-1 -- One of the problems that we had in following
the discussion in the previous sections about the determination of
average gross liquid leaker emission rates was the values used to
determine substantial leakers, gross leakers, lower cutpoints, and upper
cutpoints of the log-normal distributions. A table placed somewhere in
the report such as the following would help guide the reader through
these different values.

+---------------------+----------+-------+---------------+-----------+
|                     | **Liquid |       | # Av          | **GLL     |
|                     | L        |       | eraging Range | Average** |
|                     | eakers** |       |               |           |
+---------------------+----------+-------+---------------+-----------+
|                     | **Subst  | **Gr  |               |           |
|                     | antial** | oss** |               |           |
+---------------------+----------+-------+---------------+-----------+
| Hot Soak Test       | \>2      | \>10  |               |           |
| (g/hr)\*            |          |       |               |           |
+---------------------+----------+-------+---------------+-----------+
| > Carbureted        |          |       | 10-300        | 16.95     |
+---------------------+----------+-------+---------------+-----------+
| > TBI               |          |       | 10-300        | 45.00     |
+---------------------+----------+-------+---------------+-----------+
| > PFI               |          |       | 10-300        | 57.14     |
+---------------------+----------+-------+---------------+-----------+
| Resting Loss (g/hr) | \>0.25   | \>2   | 2-50          | 9.16      |
+---------------------+----------+-------+---------------+-----------+
| Diurnal (g/day)     | RTD\>30  | \>25  | 25-1000       | 104.36    |
+---------------------+----------+-------+---------------+-----------+
| Running Loss        | \>5      | \>7   | 7-200         | 17.65     |
| (g/mile)\*          |          |       |               |           |
+---------------------+----------+-------+---------------+-----------+

*We agree that such a revised table would be useful. We replaced Table
2-1 with a revised table, similar to this one. (We noted, in response to
the third comment, that there is no category of \"substantial leakers.\"
Therefore, the revised table is different from this one.)*

14\. Page 15, Second paragraph -- The first assumption states that for
each test of evaporative emissions (RTD, hot soak, and running loss
tests)... Immediately we thought, where are the resting losses? Aren\'t
the frequencies of occurrence for gross liquid leaker resting losses
going to be estimated? This seems to be a glaring omission.

*The second paragraph of Section 2.1 explains that the RTD test is used
to obtain both the diurnal emissions and the resting loss emissions.*

15\. Page 15, Paragraph 3 -- In the second assumption, we think that it
is important to bring in engineering concepts about how gross liquid
leaks are related to the different types of evaporative emissions. For
example, if gross liquid leaks are related to fuel pressure, they could
occur for running losses and hot soaks but not occur for resting losses
and diurnals. We think that this type of discussion would lend
engineering support to Assumption 2.

*We have added that assumption (and example) to Section 3.0.*

16\. Page 15, Paragraph 3 -- We think that we can understand what
Assumption 2 says. However, we do not follow the reasoning behind the
assumption. It seems to us that there should be gross liquid leakers for
each of the four types of emissions. We do not understand why the report
suggests using two types to estimate the third type (that is, the
running loss and the RTD results to determine the hot soak results).
Because we could not understand the reasoning behind this assumption, we
did not understand why, on Page 16, the second step in Section 3.1 was
necessary and, of course, when it came to understanding the distinction
between Approach 2 and Approach 1, we were lost.

*The approach was necessary because EPA lacked data on GLLs on the hot
soak test at ages over 10 years. This statement has been added to the
beginning of Section 3.0.*

17\. Page 16, Section 3.1.1 -- We think that using averages of
frequencies of occurrence of gross liquid leakers for the three model
year groups used in recruitment causes a large amount of information to
be lost from the data. Additionally, since Assumption 1 states that
gross liquid leaker frequencies will be assumed to be the same for older
and newer technologies, there is no need to divide vehicles into model
year groups. A better and more defensible approach for determining the
logistic growth functions would be simply to use logistic regression on
the gross liquid leak leaker indicators for each vehicle that was
tested. A logistic regression procedure, which is simple to use, is
available in SAS. For each logistic regression, the input variable would
be vehicle age and the response variable would be an indicator variable
that would have a value of zero for a non-gross liquid leaker and one
for a gross liquid leaker. The procedure would fit the data to a model
with the same shape as shown in Figure 3-1. The procedure also has
options for outputting the confidence limits of the predicted values.

*True. However, we believe that Figure 3-1 (and the similar figures that
follow) illustrating the resulting equation (curve) closely
approximating the three averaged rates (frequencies) is far more
informative than having the same cumulative distribution curve drawn
through a cloud of data. Additionally, the stratification into model
year groups was based upon the stratified (targeted) recruitment that
was used, not on potential differences in the rates of GLLs.*

18\. Page 17, Figure 3-1 -- The figures such as Figure 3-1 could still
be used to show trends in the data and the model results when logistic
regression is used to build the models. For example, the plot could be
made to have the average frequency for every five years of age and the
model resulting from logistic regression and the confidence limits could
be drawn as curves on the plot. The confidence limits provided by the
model would span the entire range of the data.

*That approach would produce a graph similar to the existing Figure 3-1,
with the exception that the individual points would be equally spaced,
but with more variance at each point. We see no advantage to this, but
the reader is free to reanalyze the data.*

Use of logistic regression would also appropriately solve the logistic
growth expression for gross liquid leakers based on running loss
testing, which is shown on Page 19 in Figure 3-2. In this instance,
using the average values for the three model year groups caused a
problem which has probably occurred by chance alone, in that the oldest
model year average had a lower value than the middle model year value.

*This approach only solves the \"problem\" by obscuring the fact that
the calculated rate of occurrence of GLLs in this sample is slightly
lower for the older vehicles. We still believe (as noted in our response
to comment 17) that this graphical approach is more useful to the
readers.*

19\. Page 19, Section 3.1.3 -- This section starts with the phrase \"to
estimate the rate of occurrence of gross liquid leakers on the hot soak
test...\" since we did not understand Assumption 2 fully, we do not
understand why the gross liquid leaker rate of hot soak needs to be
estimated when it could have been modeled just like it was for RTD and
running loss. We think that perhaps a Venn diagram would help in
clarifying the gross liquid leakers. We think the report is using the
following Venn diagram with two overlapping circles for diurnal and
running loss with the union of the circles being hot soak gross liquid
leakers.

*The explanation that was added to the beginning of Section 3.0 (in
response comment 16) was repeated (in the beginning of Section 3.1.3)
for emphasis.*

We think that the Venn diagram for the gross liquid leakers should start
with the following Venn diagram which has four overlapping circles for
resting loss, diurnal, running loss, and hot soak emissions. Then the
report should consider engineering relationships to see if it is
possible to simplify the diagram.

*We do not believe that Venn diagrams are necessary.*

20\. Page 21, Section 3.2 -- The only clue that we have as to how the
second approach differs from the first approach are the two words
\"optimize simultaneously.\" If the frequency of gross liquid leakers in
the fleet is calculated simultaneously (we assume this means a vehicle
would be a gross liquid leaker for all types of emissions) then
wouldn\'t there be just one equation to predict the gross liquid leaker
rate of occurrence? Because we could not understand Assumption 2 and the
distinction between Approach 1 and Approach 2, we could not comment
intelligently on Section 3.3.

*As the reviewer pointed out (in comment 15), a vehicle might qualify as
a GLL on only one or two the three evaporative tests that we used. (An
explanation of that was added to the end of Section 3.0.) Thus, it is
not only possible, it is likely that there would be three distinct
equations (curves) for the frequency of the different types of GLLs.*

**Appendix F**

### Response to Comments from Stakeholders 

[No]{.underline} comments were submitted in response to EPA's posting a
draft of this report on the MOBILE6 website.