United States Air and Radiation EPA420-R-02-035
Environmental Protection December 2002
Agency
<>EPA Sensitivity Analysis of
MOBILE6.0
) Printed on Recycled Paper
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EPA420-R-02-035
December 2002
Sensitivity Analysis of MOBILE6.0
R.A. Giannelli, J.H. Gilmore, L. Landman, S. Srivastava,
M. Beardsley, D. Brzezinski, G. Dolce, J. Koupal, J. Pedelty, G. Shyu
Assessment and Standards Division
Office of Transportation and Air Quality
U.S. Environmental Protection Agency
NOTICE
This technical report does not necessarily represent final EPA decisions or positions.
It is intended to present technical analysis of issues using data that are currently available.
The purpose in the release of such reports is to facilitate the exchange of
technical information and to inform the public of technical developments which
may form the basis for a final EPA decision, position, or regulatory action.
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ABSTRACT
The Assessment and Standards Division (ASD) of the U.S. Environmental Protection Agency's
(USEPA) Office of Transportation and Air Quality (OTAQ) has recently completed an update of its
emissions model, MOBILE61. This model estimates emissions of carbon monoxide (CO), hydrocarbons
(HC), and nitrogen oxides (NOx) from roadway use of gasoline and diesel fueled automobiles,
motorcycles, busses, and trucks. MOBILE6 is used by local and state governments to determine their
compliance with the Clean Air Act2. Hence, the emissions results can have large impacts on
transportation planning and budgeting.
MOBILE6 has the option for allowing the user to enter local data in lieu of default national data for
several parameters. And, of course, resources are required to determine this local data. Hence, a prior
knowledge of the relative importance of different MOBILE6 input parameters with respect to emission
results can be an important factor in determining whether or not local data should be collected. This
report presents a systematic study of the relative importance of various MOBILE6 input parameters.
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TABLE OF CONTENTS
LIST OF FIGURES v
LIST OF TABLES vii
Section
INTRODUCTION 1
METHODS 2
RESULTS 4
A. PARAMETERS WITH MAJOR EFFECTS ON EMISSIONS (GREATER
THAN 20% CHANGES) 5
A.I HC Emissions
Registration Distribution Command
Average Speed Command
Min/Max Temperature Command
Speed VMT command
Fuel RVP (Reid Vapor Pressure)
A.2 CO Emissions
Min/Max Temperature
Fuel RVP (Reid Vapor Pressure)
Registration Distribution command
Average Speed Command
A.3 NOx Emissions
Registration Distribution command
Average Speed Command
Min/Max Temperature Command
A.4 Major Parameter Summary
B. PARAMETERS WITH INTERMEDIATE EFFECTS ON
EMISSIONS (5% TO 20%) 27
B.I HC Emissions
Altitude
Speed VMT Command
Starts per Day
B.2 CO Emissions
Air Conditioning
Altitude
Mileage Accumulation
iii
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Vehicle Starts Per Day
B.3 NOx EMISSIONS
Absolute Humidity
Air Conditioning
Altitude
Mileage Accumulation
C. PARAMETERS WITH MINOR EFFECTS ON EMISSIONS
( LESS THAN 5%) 45
CONCLUSIONS 46
APPENDIX 47
REFERENCES 56
IV
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LIST OF FIGURES
Figure Page
1. MOBILE6 daily temperature cycles 3
2. 1975 All Vehicles NOx emissions and daily temperature cycles 4
3. 1975 All Vehicles NOx emissions and daily temperature cycles; percent differences 4
4. MOBILE6 light duty gasoline vehicle registration fractions 7
5. All vehicles hydrocarbon emissions and vehicle registrations 8
6. All vehicles hydrocarbon emissions and vehicle registrations; percent differences 8
7. Volatile organic compound emissions and area wide average speed 9
8. All vehicles volatile organic compound emissions and average speed 9
9. Light duty gasoline vehicle volatile organic compound emissions and freeway
average speed 10
10. Light duty gasoline vehicle volatile organic compound emissions and area wide
average speed 10
11. All vehicle hydrocarbon emissions and average daily temperature 12
12. All vehicle hydrocarbon emissions and average daily temperature; percent differences .... 12
13. All vehicle hydrocarbon emissions and average daily temperature; percent differences .... 12
14. Light duty gasoline vehicle hourly arterial roadway speed fractions 14
15. Variation of light duty gasoline vehicle hourly arterial roadway speed fractions 14
16. Average speed of vehicles on arterial roadways by time of day 14
17. Light duty gasoline vehicle hydrocarbon emissions and average daily arterial speed 15
18. All vehicle hydrocarbon emissions and average daily arterial speed 15
19. All vehicle hydrocarbon emissions and average daily arterial speed; percent differences. . . 15
20. All vehicle hydrocarbon emissions and fuel RVP 16
21. All vehicle hydrocarbon emissions and fuel RVP; percent differences 16
22. Light duty gasoline vehicle carbon monoxide emissions and average daily temperature. . . .17
23. All vehicle carbon monoxide emissions and average daily temperature 17
24. Light duty gasoline vehicle carbon monoxide emissions and average daily
temperature; percent differences 18
25. All vehicle carbon monoxide emissions and fuel RVP 19
26. All vehicle carbon monoxide emissions and fuel RVP; percent differences 19
27. All vehicles carbon monoxide emissions and vehicle registrations 20
28. All vehicles carbon monoxide emissions and average speed 21
29. Carbon monoxide emissions and average speed; percent differences 22
30. All vehicles oxides of nitrogen emissions and vehicle registrations 23
31. All vehicles oxides of nitrogen emissions and vehicle registrations; percent differences. . . 23
32. Oxides of nitrogen emissions and freeway average speed 24
33. Light duty gasoline vehicle oxides of nitrogen emissions and arterial roadway
average speed 24
34. All vehicles oxides of nitrogen emissions and arterial roadway average speed 24
35. Light duty gasoline vehicle oxides of nitrogen emissions and area wide average speed. ... 25
36. All vehicles oxides of nitrogen emissions and area wide average speed 25
37. Oxides of nitrogen emissions and average daily temperature 26
38. Oxides of nitrogen emissions and average daily temperature; percent differences 26
39. Hydrocarbon emissions and altitude 29
40. Hydrocarbon emissions and altitude; percent differences 30
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41. Light duty gasoline vehicle hydrocarbon emissions and variation of light duty
gasoline vehicle hourly freeway roadway speed fractions 31
42. Light duty gasoline vehicle hydrocarbon emissions and variation of light duty
gasoline vehicle hourly freeway roadway speed fractions; percent differences 31
43. All vehicles hydrocarbon emissions and variation of vehicle hourly freeway
roadway speed fractions; percent differences 31
44. Light duty gasoline vehicle hydrocarbon emissions and vehicle starts per day 32
45. Light duty gasoline vehicle hydrocarbon emissions and vehicle starts per day;
percent differences 32
46. All vehicle hydrocarbon emissions and vehicle starts per day; percent differences 33
47. Light duty gasoline vehicle carbon monoxide emissions and air conditioning 34
48. All vehicle carbon monoxide emissions and air conditioning 34
49. Carbon monoxide emissions and air conditioning; percent differences 34
50. Light duty gasoline vehicle carbon monoxide emissions and altitude 35
51. All vehicle carbon monoxide emissions and altitude 35
52. Carbon monoxide emissions and altitude; percent differences 35
53. Variation of MOBILE6 light duty gasoline vehicle mileage accumulation rates 36
54. Light duty gasoline vehicle carbon monoxide emissions and vehicle mileage 37
55. All vehicle carbon monoxide emissions and vehicle mileage 37
56. Light duty gasoline vehicle carbon monoxide emissions and vehicle starts per day 38
57. Light duty gasoline vehicle carbon monoxide emissions and vehicle starts
per day; percent differences 38
58. All vehicle carbon monoxide emissions and vehicle starts per day; percent differences ... 38
59. Oxides of nitrogen emissions humidity correction factor and light duty gasoline
vehicle oxides of nitrogen emissions 40
60. Light duty gasoline vehicle oxides of nitrogen emissions and absolute
humidity; percent differences 40
61. All vehicle oxides of nitrogen emissions and absolute humidity; percent differences 40
62. Absolute humidity and barometric pressure 41
63. Light duty gasoline vehicle oxides of nitrogen emissions and air conditioning 42
64. All vehicle oxides of nitrogen emissions and air conditioning 42
65. Oxides of nitrogen emissions and air conditioning; percent differences 42
66. Light duty gasoline vehicle oxides of nitrogen emissions and altitude 43
67. All vehicle oxides of nitrogen emissions and altitude 43
68. Oxides of nitrogen emissions and altitude; percent differences 43
69. Light duty gasoline vehicle oxides of nitrogen emissions and vehicle mileage 44
70. Light duty gasoline vehicle oxides of nitrogen emissions and vehicle
mileage; percent differences 45
71. All vehicle carbon monoxide emissions and vehicle mileage; percent differences 45
VI
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LIST OF TABLES
Table Page
1. Summary of major effects parameters 6
2. Summary of intermediate effects parameters 28
3. Summary of minor effects parameters 45
A.I Description of variation of parameters and resulting affects on LDGV emissions 47
A.2 Description of variation of parameters and resulting affects on all vehicle emissions 50
A. 3 Affects of the variations of the relative fraction of heavy and light duty trucks
on emissions from heavy and light duty trucks 53
A.4 Summary and description of minor effects parameters and their effects on
LDGV emissions 54
Vll
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INTRODUCTION
Recently, the Assessment and Standards Division of the USEPA released its latest version, MOBILE6,
of a computerized model which facilitates the determination of HC, CO, and NOx inventories from
mobile sources for a given locale. MOBILE6 is a significant revision of the previous version, MOBILES3, both in the style
and the type of user inputs. These inputs include a set of default data, based on national averages, which produce default
emission results. However, these national input data differ between specific localities and regions of the country. Hence, the
resulting MOBILE6 default emissions will not necessarily represent the mobile source emissions for a specific locale.
Efficient use of MOBILE6 will depend on the user's familiarity with the many different MOBILE6
input parameters and the USEPA's usage guidance4'5, the location specific mobile source statistics (e.g.,
vehicle registrations, vehicle usage in terms of mileage, roadway types, fuel types, inspection and
maintenance programs, etc.), and knowledge of the input parameters that make significant impacts on
MOBILE6 emissions results. So, in an effort to expedite the use of MOBILE6 and its inputs, a
systematic study has been done which allows users to compare the relative impact of each individual
parameter on emissions results.
Because of the number of individual inputs and the many dimensional aspects of many of the inputs, the
emissions results (except for temperature and humidity) were studied individually and, except for
humidity and temperature, the interdependences between parameters were not studied. That is,
emissions changes due to variations of a single input parameter were calculated and then compiled. The
results are listed in terms of percent increase or decrease in the MOBILE6 input with the ensuing
percent increase or decrease in the emissions for Light-Duty Gasoline Vehicles (LDGV) and fleet wide
vehicles (All Vehicles or emissions of all 28 MOBILE6 vehicle types weighted by vehicle mileage)
relative to the MOBILE6 national default inputs and the resulting emissions. (For a complete description
of the MOBILE6 vehicle classifications see the MOBILE6 users' guide5.) For parameters without a
default value, a single base value was used. Also, for some inputs the emissions in grams/mile are
displayed as a function of the specific input parameter or the percent change in the input parameter
relative to the default value. Calendar years from 1975 through at least 2020 in increments of 5 to 20
years were considered for each input studied.
This report summarizes the complete results for MOBILE6 LDGV and the All Vehicle categories
"composite" emission results. "Composite" emissions for carbon monoxide and nitrogen oxide
emissions means cold start emissions plus hot, stabilized running emissions. For hydrocarbon emissions
the "composite" emissions are comprised of evaporative emissions plus cold start emissions and hot,
stabilized running emissions.
The emissions results presented in this work are from a draft version (September 10, 2001) of
MOBILE6. So, the absolute magnitudes of the emission results in this work may vary slightly from
updated versions of MOBILE6. However, in general, the trends presented here will be consistent with
emissions estimations being produced by current versions of MOBILE6.
Because of the breadth of inputs, all of the MOBILE6 input parameters were not considered in this
report. Some of the parameters not considered here are inspection and maintenance program parameters,
diesel and natural gas vehicle fractions, engine start soak times, trip lengths, and hot soak durations. (A
complete list of the parameters considered is given in the Appendix, Table A.I.)
The input parameters are grouped, in this report, by the magnitude of their effects. We divided the
effects into three groups: major effects, moderate effects, and minor effects. In order to develop working
definitions of those somewhat vague terms, we examined the effects on emissions (HC, CO, and NOx
separately) when we varied the input values by 20 percent (from the default values). (The choice of that
size of change, 20 percent, was arbitrary.) We then defined:
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(1) An input parameter will be said to have a "major" effect on one of the three pollutants (HC, CO,
or NOx) if that (arbitrary) 20 percent change in that input parameter resulted in at least a 20
percent change in the emissions of that pollutant (relative to the emissions when the default
values were used). Thus, a change in one of the input parameters that has a "major" effect will, in
general, produce a change in emissions that is at least as great (proportionately) as the change in
that parameter. In general, the ratio between the change in emissions to the change in input value
needed to be greater than or equal one and the emission changes needed to reach a value of 20%.
(2) An input parameter will be said to have a "minor" effect on one of the three pollutants if that
(arbitrary) 20 percent change in that input parameter resulted in less than a 5 percent change in
the emissions of that pollutant. Thus, a change in one of the input parameters that has a "minor"
effect will, in general, produce a change in emissions that is much smaller (proportionately) than
the change in that parameter.
(3) An input parameter will be said to have an "intermediate" effect on one of the three pollutants if
that (arbitrary) 20 percent change in that input parameter resulted in a change of between 5 and
20 percent in the emissions of that pollutant. Thus, a change in one of the input parameters that
has an "intermediate" effect will, in general, produce a change in emissions that is somewhat
smaller (proportionately) than the change in that parameter.
Since the factors affecting the presence of HC, CO, and NOx are different, it is reasonable that these
groupings (major, intermediate, and minor) will be different for each pollutant. The details of the
analysis methodologies and the results for these parameters are presented below.
METHODS
MOBILE6 inputs have a variety of formats and requirements. They could consist of a single
number/character, sets of numbers, or simply the input command acting as an "on/off switch. Hence,
there was no single standard method of changing the inputs to get understandable and useful information
from the resulting changes in emissions. However, once a method of changing the inputs was decided
upon, the results were quantified in terms of a percentage change in the input relative to the MOBILE6
default values versus a percentage change in emissions relative to emissions calculated from the default
input values.
As mentioned above, many of the MOBILE6 inputs consist of a set of numbers. And determining how
to make changes to the input so that the resulting changes in emissions could be quantified and useful to
potential users of MOBILE6 varied from input to input. For example, the hourly temperature values or
daily minimum and maximum temperature inputs determine a daily temperature cycle which is based on
24 standard temperature increments/ decrements from the National Weather Service. MOBILE6 uses
these 24 values with the MIN/MAX TEMP input command to construct a daily temperature cycle
(scaled according to the user supplied minimum and maximum temperatures) with the minimum and
maximum temperatures occurring between 6am and 7am and 3pm and 4pm, respectively. The
temperature inputs can thus vary the average daily temperature, the 24T temperature cycle, and the
individual hourly temperatures. All of these input variations have different effects on the emissions
results. As a result, each of these variations were analyzed independently to determine their individual
effects on the emissions. Figure 1 (below) illustrates the base (i.e., default) temperature cycle in which
hourly temperatures rise and fall over a 24° Fahrenheit range (i.e., cycling between 72°F and 96°F), as
well as three alternate cycles with variations in the daily temperature of 34°F daily temperature rise and
fall (i.e., a 42 percent increase from the default), a 14°F daily temperature rise and fall (i.e., a 42 percent
decrease from the default), and a constant temperature for each hour of the day (i.e., a 100 percent
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decrease from the default). Figures 2 and 3 (below) illustrate the changes in NOx emissions that
correspond to those daily temperature cycles.
In Figure 2, each of the lines represents one of the four different temperature cycles at 5 different
average daily temperatures. Different average daily temperatures were determined by varying the daily
minimum and maximum temperatures of the four different daily temperature cycles. In other words, the
temperature cycles were moved up and down the temperature axis of Figure 1 to determine the NOx
emissions values at average daily temperatures of 101T, 92T, 82T, 72T, and 42 T. Note that each of
the lines decrease with increasing temperature; higher composite NOx emissions at lower (average
daily) temperatures.
For this part of the work (i.e., temperature cycle induced changes on emissions), the emissions
comparisons made were relative to the standard 24 degree Fahrenheit temperature cycle. Emissions
differences were found and then the percentages relative to the standard cycle were determined. The
graphs in Figure 3 illustrate these results for a number of different calendar years and average daily
temperatures. Because the input variations never lead to emissions variations (increases or decreases) of
more than 5%. The temperature cycles were considered to have minor effects on MOBILE6 emissions
results.
Similar methods were determined for each MOBILE6 input which would make possible a practical
quantification of the changes in MOBILE6 emissions output.
-standard 24 degree temperature cycle, max
-14 degree cycle
34 degree cycle
-constant temperature
10
of day
Figure 1. To determine how differences in the 24 hour temperature
cycle affects emissions, four cycles were considered. The cycles had
minimum and maximum temperatures which differed by 0°F (or a
constant temperature), 14°F, 24°F, and 34°F over the entire day. The
average daily temperature of each of the curves is kept at 82°F.
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| 6,5
«
I
All Vehicles1975 NOx Emissions
NOx Composite Emissions 4
All Vehicle Types
100% corresponds to constant daily temperature ,-
-42% corresponds to 14 degree temperature cycle T
+42% corresponds to 34 degree temperature cycle |
(The lines are drawn to guide your eyes.) t
itiitaril temp. cycle(24 ilegrei
-^-constant temperature cycl
-a-H degree cycle
-*-34 degree cycle
60 70
average daily temperaturef F)
- » -1975,42 degrees
Fahrenheit
-61975,82 degrees
Fahrenheit
-^1975,102 degrees
Fahrenheit
2000,42 degrees
Fahrenheit
- 20DD. 02 degrees
Fahrenheit
2000,102 degrees
Fahrenheit
2005,42 degrees
Fahrenheit
x 2005,82 degrees
Fahrenheit
0 2005,102 degrees
Fahrenheit
2025,42 degrees
Fahrenheit
2025,82 degrees
Fahrenheit
- -2025,102 degrees
Fahrenheit
Figure 2. This graph illustrates 1975 All
Vehicle NOx emissions as a function of
average daily temperature for each of the four
different temperature cycles in Figure 1 . The
different average daily temperatures were
defined by varying the minimum and
maximum temperatures of the four different
daily temperature cycles.
Figure 3. This figure shows the relationship
between All Vehicles NOx emissions and
changes in the hourly temperature cycles
depicted in Figures 1 and 2. It shows that NOx
emissions are not highly dependent on the shape
of the temperature cycle. As indicated in the
graph each curve is associated with a calendar
year and an average daily temperature.
In Figure 2, each of the lines represents one of the four different temperature cycles at 5 different
average daily temperatures. Different average daily temperatures were determined by varying the daily
minimum and maximum temperatures of the four different daily temperature cycles. In other words, the
temperature cycles were moved up and down the temperature axis of Figure 1 to determine the NOx
emissions values at average daily temperatures of 101T, 92°F, 82°F, 72°F, and 42 °F. Note that each of
the lines decrease with increasing temperature; i.e., higher composite NOx emissions at lower (average
daily) temperatures.
For this part of the work (i.e., temperature cycle induced changes on emissions), the emissions
comparisons made were relative to a 24 degree Fahrenheit temperature cycle. Emissions differences
were found and then the percentages relative to the standard cycle were determined. The graphs in
Figure 3 illustrate these results for a number of different calendar years and average daily temperatures.
Because the input variations never lead to emissions variations (increases or decreases) of more than
5%. The temperature cycles were considered to have minor effects on MOBILE6 emissions results.
Similar methods were determined for each MOBILE6 input which would make possible a practical
quantification of the changes in MOBILE6 emissions output.
RESULTS
In the Appendix, Tables A.I and A.2 contain full summaries of the LDGV and All Vehicle sensitivity
analysis results, respectively. They list the MOBILE6 input considered, an abbreviated description of
how its values were changed relative to the default values, and the percent changes in emissions for each
of the three pollutants, i.e., non-methane hydrocarbons (NMHC) [volatile organic compounds (VOC) for
the Average Speed command], carbon monoxide (CO), and oxides of nitrogen (NOx). Results in these
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tables were derived from the standard MOBILE6 descriptive output. As mentioned above, the emissions
values are the "composite" emission results which are cold start emissions plus hot, stabilized running
emissions for NOX and CO. For hydrocarbon emissions the "composite" emissions include evaporative
emissions along with cold start emissions and hot, stabilized running emissions.
This report will describe both the methodologies used to change the inputs and the impacts these
changes have on emissions (relative to the default MOBILE6 values or some standard value) for the
three MOBILE6 pollutant types, i.e., HC, CO, and NOx. (As mentioned above, except for the results of
the Average Speed command the hydrocarbon emissions considered are all in the form of non-methane
hydrocarbons or NMHC. The Average Speed command results are in terms of hydrocarbon volatile
organic compounds or VOC.)
A. PARAMETERS WITH MAJOR EFFECTS ON EMISSIONS (GREATER THAN 20%
CHANGES)
Table 1 (below) lists those input parameters which have the greatest effect on both LDGV and All
Vehicle emissions. It also contains a short description of the input changes and the magnitude of
emissions changes relative to MOBILE6 default results. Changing any one of those parameters will have
relatively large affects on the emission rates, i.e., an emissions change-to-input change ratio of one or
greater and at least a 20% change in emissions. This section will discuss these results in detail.
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Table 1. Summary of LDGV and All Vehicle results with input parameters which have a "major"
effect on emissions. (The parameters are sorted in alphabetic order not in order of the
magnitude of their effect on emissions.)
HC
CO
NOx
Average Speed Command - low speeds
(15mph), Arterial roadways , Area Wide
roadways and Freeways : 20% to 80% emissions
increases
Average Speed Command - low speeds
(lOmph), Arterial roadways , Area Wide
roadways and Freeways : 15% to 40% emissions
increases
Average Speed Command - low speeds
(lOmph), Arterial roadways , Area Wide
roadways and Freeways : 20% to 50% emissions
increases
Fuel Reid Vapor Pressure(RVP) (The RVP was
increased from 6.51b/in2 to 11.51b/in2 for a
number of calendar years between 1975 and 2050
with minimum and maximum temperatures 72°F
and 92°F, respectively. Percent differences were
determined relative to 7.51b/in2)
Emissions decreases of-3%(1985) to -6%(2005)
at6.51b/in2
Emissions increases of 77%(2005) to 38%(1985)
atll.51b/in2
Fuel Reid Vapor Pressure(RVP) (The RVP was
increased from 6.51b/in2 to 11.51b/in2 for a
number of calendar years between 1975 and 2050
with minimum and maximum temperatures 72°F
and 92°F, respectively. Percent differences were
determined relative to 7.51b/in2)
No emissions changes at6.51b/in2
Emissions increases of 101%(2050) to 2%(1975)
atll.51b/in2
Mm/Max Temperature Command - Average
daily temperature (vary the average daily
temperature from 12°F to 107°F by shifting the
standard temperature cycle) emissions increases
up to 20% to 50% at low average daily
temperature (12°F); this variability decreases with
increasing calendar year and increasing
temperatures
Mm/Max Temperature Command - Average
daily temperature (vary the average daily
temperature from 12°F to 107°F by shifting the
standard temperature cycle) emissions increases
up to 25% for calendar years around 1995 (the
variability lessens with increasing calendar years)
Mm/Max Temperature Command - Average
daily temperature (vary the average daily
temperature from 12°F to 107°F by shifting the
standard temperature cycle) emissions increases
up to 200%( average daily temperature of 12°F )
with temperature decreasing below 55°F; this
variability increases with increasing calendar year
Registration distribution (decrease newer
vehicle fractions and increase older vehicle
fractions) 20% age shift to older vehicles can
yield about a 50% increase in emissions
depending on the calendar year of evaluation
Speed VMT Command(Arterial Roadways):
-3% - null low speed vehicle fractions;
9% - equal vehicle fractions for all speeds
14% - increase low speed vehicle fraction by 10%
21% - increase low speed vehicle fraction by 20%
29% - increase low speed vehicle fraction by
30%) : emissions change on at least a 1-to-l ratio
up to 44% increase in emissions with a 30%
change in the fraction of vehicles from higher
non-congested speeds to lower speeds; the 3%
change from lower speeds to higher speeds
yielded a 3% reduction in emissions
Registration distribution (decrease newer
vehicle fractions and increase older vehicle
fractions) 20% age shift to older vehicles can
yield about a 50% increase in emissions
depending on the calendar year of evaluation
Registration distribution (decrease newer
vehicle fractions and increase older vehicle
fractions) 20% age shift to older vehicles can
yield about 40% increase in emissions depending
on the calendar year of evaluation
A.1 HC EMISSIONS
MOBILE6's estimation of hydrocarbon emissions are most affected by the age distribution of the fleet
(Registration Distribution command; see Figures 4, 5, and 6), low vehicle speeds (Average Speed and
Speed VMT commands; see Figures 7 through 10), high average daily temperatures (Min/Max
temperature or Hourly Temperature commands; see Figures 11 and 12), and fuel RVP (Reid Vapor
Pressure).
Registration Distribution Command
The vehicle age distributions (Registration Distribution command) were changed by increasing the
fraction of vehicles with ages greater than 13 years old and subtracting the same fraction from the
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vehicles which are younger than 13 years old. Each vehicle age had an equal fraction added to or
subtracted from it. Figure 4 displays the MOBILE6 default age distribution (the dark blue line with
diamond shaped symbols) and how it was modified to obtain age distributions shifted by 5, 10, 15, and
20 percent. Figures 5 and 6 show the relationship between vehicle age and hydrocarbon emissions. They
show the impact of the main MOBILE6 assumption, i.e., the emission rates deteriorate with vehicle age
or mileage together with shifting vehicles to less restrictive emissions standards and older emissions
reduction technologies.
Note that the for calendar years greater than 1975 these MOBILE6 all (or fleet wide) vehicle types have
at least a 1-to-l emissions-to-input percentage rate response for changes in the emissions due to changes
in vehicle age. Again this demonstrates that as lower emissions standards and better emissions
technologies are taken out of the fleet the emissions increases are substantial. In fact the changes are
greater than a one-to-one ratio. LDGV numbers are similar to the All Vehicles type age and NMHC
emissions relationship.
0.08 T
e MOBILE6 DEFAULT
n- 5% AGE SHIFT
A-10% AGE SHIFT
-15% AGE SHIFT
* -20% AGE SHIFT
10 15
VEHICLE AGE
25
Figure 4. The MOBILE6 default vehicle registration fractions were shifted
from newer to older vehicles in increments of 5%. The age thirteen vehicle
fractions were unchanged. Although All Vehicle registration fractions
were changed, this figure illustrates the Light-Duty Gasoline Vehicle
fractions.
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All Vehicles HC Emissions and Vehicle Registration
0-
All Vehicles HC Emissions and Vehicle Registration
20 25 30
% shift in vehicle fractions
20 25 30
/.Shift in Vehicle Fractions
Figure 5. All Vehicle hydrocarbon emissions as
a function of the percent change in the
MOBILE6 vehicle type registration fractions.
Figure 6. The same as Figure 5 except the
percent differences in emissions are given as a
function of the percent change in the All
Vehicle type registration fractions. For each of
the different MOBILE6 vehicle types the
fractions were shifted from newer to older
vehicles as illustrated for Light-Duty Gasoline
Vehicles in Figure 4 above.
Average Speed Command
Next in importance for hydrocarbon emissions is the dependence on vehicle speed through the Average
Speed command. This relationship is due to both an activity factor, i.e., the fraction of vehicles driving
at a particular speed (MOBILE6 has a set of 14 different speeds, i.e., 2.5, 5, 10, 15, 20, 25, 30, 35, 40,
45, 50, 55, 60, and 65 miles/hour) for each hour of the day (see e.g., Figures 14, 15, and 16), and a
functional vehicle emissions-vehicle speed relationship6. For each roadway type (freeways, local
roadways, arterial roadways, and freeway ramps) in MOBILE6 a cycle was developed to model driving
behavior and the resultant emissions6. Emissions from these cycles were then used to determine
"7 R
corrections to the LA4 cycle. Hourly vehicle fractions for the different roadway types apportion the
vehicles traveling at different speeds on the different roadways and hence the speed corrections applied
to the particular roadway type. (The sum of the fractions for each roadway type is one.) Both of the
above factors come into play when considering the difference between default emissions and those
emissions resulting from changing the MOBILE6 defaults by using the Average Speed and Speed VMT
commands.
The Average Speed command (and the Speed VMT command) set(s) the fraction of vehicles which are
operating at a given speed on the different MOBILE6 roadway types. The graphs in Figure 7 show the
LDGV and All Vehicle hydrocarbon volatile organic compound (VOC) emissions dependence on speed
using the Average Speed command for area wide roadway types at speeds ranging from 10 to 35 mph.
Figure 8 shows a similar dependence for Light-Duty Gasoline Vehicles on freeways with speeds varying
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LDGV VOC Emissions and Area Wide Average Speed
i14
|e
25 30 35 40
average area wide vehicle speed(milesfhour)
Figure 7.
a. Light-Duty Gasoline Vehicle hydrocarbon
volatile organic compound (VOC) emissions
as a function of Area Wide speed supplied in
the Average Speed command.
Effect of Average Speed on Composite VOC Emissions
All Vehicle Types, Arterial/Collector Roadways
25 35 45
Average Speed (miles per hour)
b. All Vehicles hydrocarbon volatile organic
compound (VOC) emissions as a function of
Area Wide speed supplied in the Average Speed
command.
20
18
16
14
12
10
Effect of Freeway Average Speed on LDGV VOC Emissions
1 1 MI 1 1 ill 1 1 MI 1 1 ill 1 1 1 1 1 1 1 ill rm .....
o 1 1 1 1 1 i 1 1 1 in 1 1 1
10 15 20 25 30 35 40 45 SO 55 60 65 70
Average Speed (miles per hour)
Figure 8. Light-Duty Gasoline Vehicle hydrocarbon
volatile organic compound (VOC) emissions as a
function of Freeway speed supplied in the Average
Speed command.
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from 10 to 65 miles per hour. There are results for five calendar years, i.e., 1975, 1995, 2000, 2005, and
2025.
The emissions results from Figures 7 and 8 above can be used to establish how the VOC emissions
differ from emissions calculated using the default speed data. MOBILE6 default results are based on an
average speed distribution rather than a single average speed. The average daily speed of these default
distributions for all (or area wide) roadway types is about 28mph8. Figures 14 and 15 display the
MOBILE6 default vehicle speed-roadway fractions for arterial roadways between the hours of 4am to
Sam, 7am-8am, and 4pm to 5pm. Changing average vehicle speeds using the Average Speed command
changes the proportion of vehicles travelling on MOBILE6 roadway types and has relatively large
effects on emissions when compared to MOBILE6 emissions results calculated with the default vehicle
roadway-average speed fractions. Figures 9 and 10 display the percent changes in VOC emissions
relative to default MOBILE6 results as a function of vehicle speeds via the Average Speed command.
These figures display results for VOC from all MOBILE6 vehicle types using the Average Speed
command for Area Wide roadways and Freeways.
Effect of Freeway Average Speed on LDGV VOC Emissions
40 45 50 55 60 65 70
Average Speed (miles per hour)
90 T
Figure 9. Percent change in LDGV VOC
emissions relative to MOBILE6 default
emissions as a function of average freeway
using the MOBILE6 Average Speed
command. (The All Vehicle emission results
are similar.)
-10"
20 J-
LDGV VOC Emissions and Area Wide Average Speed
10 15 20 25
Average AreaWide Vehicle Speed(mph)
Figure 10. Percent change in LDGV VOC
emissions relative to the MOBILE6 default
results as a function of LDGV average area
wide speed supplied in the Average Speed
command. (The All Vehicle emission results
show similar trends.)
10
-------
Min/Max Temperature Command
The third input parameter that has substantial effects on hydrocarbon emissions when changed from a
base value (of 82T) is the average daily temperature (Min/Max Temperature command). As mentioned
above (see e.g., Figure 1) each hour of the day has a unique temperature value and is determined by the
Min/Max Temp or the Hourly Temperature commands. These inputs determine a set of 24 hourly
temperature differences. By shifting the maximum and minimum daily temperatures to higher or lower
temperatures the average daily temperature can also be changed. The All Vehicles hydrocarbon
emissions dependence on the average daily temperature is displayed in Figurel 1. Percent differences in
All Vehicle emissions due to changes in temperature as a function of the percent difference in average
daily temperature relative to a base value of 82T with a temperature range of 70.6T to 94.6T are
displayed in Figure 12. Each figure has results for calendar years of 1975, 1995, 2000, 2005, and 2025.
Figure 13 illustrates the same results in terms of the percent change in average daily temperature and
percent change in emissions relative to emissions estimated with an average daily temperature of 82°F.
Because MOBILE6 estimates tailpipe emissions and evaporative emissions, low temperatures and
higher temperatures yield relatively higher emissions compared to more moderate temperature range.
The emissions at lower temperatures should reflect catalyst driven cold start emissions. Because the air
conditioning correction is automatically applied, the higher temperatures will be exhibiting effects due
to both air conditioning usage and higher evaporative emission rates. Actually, the emissions effects of
air conditioning will be discussed later in this report. More importantly, however, the MOBILE6
temperature correction9 has an exponential dependence on ambient temperature. So, for temperatures
above about 75°F the emissions reflect this exponential increase and this characterizes the emissions at
higher temperatures.
Although the emissions dependence on the average number of vehicle starts per day is listed in the
intermediate effects section, at lower temperatures (temperatures less than 45*F) the start emissions
increase dramatically (e.g., a 5*F increase in temperature yields about a 5% to 15% increase in
emissions) with temperature decreases. Thus, at lower temperatures they become a larger fraction of the
composite [start plus running (plus evaporative for HC)] emissions. Hence, the ratio of the change in
emissions to the change in starts per day will also increase at these lower temperatures and may be
considered to have a major effect parameter.
11
-------
'
j:
m 6
All Vehicles HC (constant absolute humidity=75grains/lb)
All Vehicles HC (constant absolute humidity=75gralnsJlb)
Temperature(T)
Figure 11. All Vehicle NMHC emissions as
a function of average daily temperature.
The daily temperatures were changed by
shifting the average daily temperature, but
keeping the default 24T temperature cycle
(e.g., Figure 1). (The LDGV results are
similar.)
Figure 12. Percent changes in All Vehicles
NMHC emissions as function of the percent
change in average daily temperature relative to
the MOBILE6 default 24T temperature cycle
with an average daily temperature of 82T (e.g.,
Figure 1). Each of the different average daily
temperatures undergo a 24°F daily temperature
cycle.
All Vehicles HC (constant absolute humidity=75grains/lb>*0;;
Figure 13. All Vehicle percent changes in NMHC emissions as a function
of percent change in the average daily temperature relative to 82°F with a
24°F daily temperature cycle. This graph is derived from the two Figures
above. (The LDGV results are similar.)
12
-------
Speed VMT command
Next, the SPEED VMT command for arterial roadway types can yield relatively large changes in
hydrocarbon emissions when varied from the MOBILE6 default values. The SPEED VMT command
allows users to input the fraction of vehicles travelling at 14 different speeds (2.5, 5, 10, 15, 20, 25, 30,
35, 40, 45, 50, 55, 60, and 65 miles/hour) for each hour of the day on arterial roadways and freeways.
Figure 14 illustrates two (4am to Sam and 4pm to 5pm) of the twenty-four hours of MOBILE6 default
vehicle fractions at the 14 different speeds on arterial roadways.
Next, Figures 15 and 16 depict how the vehicle fractions were changed relative to the MOBILE6
defaults. Vehicle fractions from two "congested" or "rush" hour intervals (7am to Sam and 4pm to 5pm)
were averaged together. Then, from this average congested hourly interval of vehicle fractions, fractions
of vehicles were moved from the middle range of speeds (30, 35, 40, 45, and SOmph) and distributed
amongst the lower speeds (2.5, 5, 10, and 15mph). These vehicle fraction shifts of 10, 20, and 30 percent
resulted in 14, 21, and 29 percent reductions in the daily average of hourly speed, respectively (see
Figure 16). A fourth set of fractions were constructed by shifting 17percent of the vehicle fractions from
the lower speeds (2.5, 5, 10, 15, 20, and 25 mph) to the higher speeds (30, 35, 40, 45, 50, 55, 60, and 65
mph) (the 17 percent decrease in lower speeds). This fourth redistribution yielded a 3 percent increase in
daily average of hourly speed. The fifth set of fractions were all set equal to 1/14. That is, all speeds had
an equal fraction of vehicles. This resulted in a 9 percent decrease in average hourly speed. These
vehicle fractions for different speeds on arterial roadways were used for each hour of the day. The
MOBILE6 default values, of course, varied for each hour of the day as can be inferred from Figure 14.
Emissions were determined from the changed arterial vehicle fractions and compared to the MOBILE6
defaults. Figures 17 and 18 depict Light Duty Gasoline Vehicle (LDGV) and All Vehicle emissions
relative to the MOBILE6 default values as a function of the percent change in the daily average of
hourly arterial roadway vehicle speeds. Figure 19 illustrates the percent change in All Vehicles HC
emissions as a function of the change in the daily average of hourly vehicle arterial roadway speeds.
(Again, the lines are drawn to guide the reader's eyes.) Except for the flat distribution of speeds which
shows about a 9 percent reduction in the daily average of hourly arterial vehicle speeds, the emissions
percent differences from the default values have a nearly linear relationship with changes in these
average speeds. In general, the results show that a mixing of vehicles at different speeds yield higher
emissions, especially when more vehicles are in the lower speed ranges.
13
-------
0.35 T
-$- MOBILES non-rush hour speeds,
4am to 5am
-4-MOBILES rush hour speeds,
4pm to 5pm
20
30 40 50
speedjmiles/hour)
70
Figure 14. Each hour of the day has a set of 14
fractions, one for each of the 14 different
speed values. The two default MOBILE6
values illustrated above are for arterial
roadways during a "rush" hour, 4pm to 5pm,
and during a "non- rush" hour, 4am to Sam.
-H-4.4% reduction of low speeds
10% more low speeds
-6-20% more low speeds
30% more low speeds
flat
20
30 40 50
speed(miles/hour)
70
Figure 15. The. 5 curves represent how the
MOBILE6 default values were changed.
Fractions of vehicles from an average of hours
2(7am-8am) and ll(4pm-5pm) were shifted
from the lower speeds to the higher speeds and
vice versa. Also, each hour of the day had the
same vehicle fractions, whereas the default
hourly fractions varied (see e.g., Figure 16
below).
35
30
average speed(miles/hr
-i -i NJ NJ
D cn o cn o cn
Hi i r
^s
**
- L.
^'
^ ^^^^^-^ *
HI I I II I
^4. ' ,x^
^^^f
i^^^^^^^^^^^^^^^^^^,.
.. n _ _
O default average hourly speeds
10%(daily average hourly speed, 30.9mph)
-© 20%(daily average hourly speed, 28.2mph)
i 30%(daily average hourly speed, 25.5mph)
flat(daily average hourly speed, 32.6mph)
^T non-rush/ 1 7%(daily average hourly speed, 37.0mph)
default daily average of hourly speeds, 35.9mph
f ! ! SI
hour
Figure 16. This illustrates the effective (vehicle fraction weighted)
average speed of the vehicles on arterial roadways for each hour of
the day. The default hourly and daily average of the hourly values
are shown along with the values from the 5 curves of Figure 15.
14
-------
-3% - null low speed vehicle fraction
9% equal vehicle fractions for all speeds
14% - increase low speed vehicle fraction by 10%
21% - increase low speed vehicle fraction by 20%
29% increase low speed vehicle fraction by 30%
30 -25
20 -15 -10 -5
!. change in average daily arterial speed
all vehicles
-3% - null low speed vehicle fraction
9% - equal vehicle fractions for all speeds
14% increase low speed vehicle fraction by 10%
21% - increase low speed vehicle fraction by 20%
29% increase low speed vehicle fraction by 30%
15 IB 5 0
% change in average daily arterial speed
Figure 17. Hydrocarbon emissions as a
function of the change in vehicle fraction
weighted speed on arterial roadways.
Figure 18. Hydrocarbon emissions as a function
of the change in vehicle fraction weighted speed
on arterial roadways.
-1975 all vehicles HC
-1995 all vehicles HC
-2000 all vehicles HC
2005 all vehicles HC
-2020 all vehicles HC
all vehicles
-3% - null low speed vehicle fraction
9% - equal vehicle fractions for all speeds
14% - increase low speed vehicle fraction by 10%
21% - increase low speed vehicle fraction by 20%
29% - increase low speed vehicle fraction by 30%
change in daily average of arterial speed
Figure 19. Percent change in All Vehicles hydrocarbon emissions from
MOBILE6 default values as a function of percent change in the daily
average of hourly arterial vehicle speeds relative to the MOBILE6 default
values.
15
-------
Fuel RVP (Reid Vapor Pressure)
As with temperature and calendar year, fuel RVP is a required input. For exhaust emissions the RVP
dependence is actually intertwined with the temperature correction factor5'9. In other words, the
MOBILE6 temperature correction is a function of RVP (and temperature) and hence any variation of
fuel RVP varies the temperature correction factor at a specific temperature and thus changes the exhaust
emissions. There are also, of course, evaporative emissions dependencies on RVP. However, at
temperatures below 45*F, fuel evaporation becomes negligible and RVP is assumed to have no effect on
emissions.
Figures 20 and 21 display results for the emissions and the percent difference in emissions relative to a
standard RVP value of 7.5psi, respectively. The main effects are for RVP values above 9 pounds per
square inch (psi). There is a steep increase in emissions for RVP values above 9psi. This is indicative of
the exponential dependence of the temperature correction factor on fuel RVP. However, RVP effects are
the same for all RVP values greater than 11.7psi. Hence the curves would flatten out from 11.7psi
through 15.2psi (15.2psi is the maximum value of RVP allowed in MOBILE6).
All Vehicles HC Emissions and Fuel RVP
-«-1975
'1985
2005
-2025
All Vehicles HC Emissions and Fuel RVP
11 12
RVP(lb/in2)
Figure 20. Hydrocarbon emissions as a function
of the fuel Reid Vapor Pressure (RVP).
Figure 21. Percent change in hydrocarbon
emissions relative to the emissions at 7.5psi as a
function of the fuel Reid Vapor Pressure (RVP).
16
-------
A.2 CO EMISSIONS
Average daily temperatures below SOT (Min/Max Temperature or Hourly Temperature commands)
have a very significant effect on carbon monoxide emissions (see Figures 22, 23, and 24 below). So,
average daily temperature has a major effect on CO emissions. Also, the age distribution of the fleet
(Registration Distribution Command; see Figure 27), Reid Vapor Pressure (Figures25 and 26), and low
vehicle speeds (Average Speed command; see Figures 28 and 29) have effects on emissions which are
relatively large and can reach values greater than 20 percent with input changes of the same or smaller
magnitude.
Min/Max Temperature
As described above for hydrocarbon emissions the average daily temperature can be varied with the
Min/Max Temperature or the Hourly Temperature commands. Furthermore, as with HC emissions, these
CO emission results were compared to CO emissions that were determined with an average daily
temperature of 82°F over a 24°F daily temperature cycle, i.e., 70.6T to 94.6T. Figures 22 through 24
display the affect of temperature on CO emissions. The average daily temperatures ranged from 12°F to
107T and the absolute humidity was held constant at 75 grains/pound. [Of course, humidity and
temperature (and atmospheric pressure) are interrelated. At higher temperatures the atmosphere can
more readily contain higher proportions of water vapor, whereas at cooler temperatures, water vapor will
more easily condense out of the air. In MOBILE6 ambient humidity mainly affects NOx emissions.
As mentioned in the HC temperature dependence section, the start emissions increase with decreasing
temperature. However, the start CO emissions affects due to the average number of vehicle starts per
day is listed in the intermediate effects section. But, at decreasing temperatures (temperatures less than
60*F) the start emissions begin to increase and begin to be the major influence on CO emissions. For
example e.g., a 5*F decrease in temperature yields about a 10% to 20% increase in emissions depending
on the model year. And just as in the case for HC, the CO start emissions will become a larger fraction
of the composite [start plus running (plus evaporative for HC)] emissions at these lower temperatures.
In fact, as illustrated in Figure 24 the effect is more pronounced than in the case of HC emissions.
_ 150 -
LDGVCO (constant absolute humidity=75grainsflb)
10 20 30 40 50
90 100 110
temperature ('F)
Figure 22. LDGV CO emissions as a function of Figure 23. MOBILE6 All Vehicle types CO
average daily temperature using the MIN/MAX emissions as a function of average daily
Temperature command. temperature using the MIN/MAX Temperature
command.
17
-------
225 -i
LDGV CO (constant absolute humidity=75grainsflb)
-«-1975
-B-1995
2000
2005
^K-2025
-25 J
100 110
temperature ("F)
Figure 24. The relationship between the percent change in
CO emissions and average daily temperature. The
percentage differences were determined by comparing CO
emissions at an average daily temperature of 82T and the
temperature with emissions at temperatures ranging from
about 10T to HOT. A 24T temperature cycle was used
for each of the different average daily temperatures(see,
e.g., Figure 1).
Fuel RVP (Reid Vapor Pressure)
As mentioned above in the hydrocarbon section fuel RVP is a required input and for exhaust emissions
the RVP dependence is contained with the temperature correction factor5' . And this correction is also
applied to CO emissions. Varying fuel RVP will vary the temperature correction factor at a specific
temperature and the exhaust CO emissions.
Figures 25 and 26 display graphical results for the CO emissions and the percent difference in CO
emissions relative to a standard RVP value of 7.5psi, respectively. The main effects are for RVP values
above 9 pounds per square inch (psi). There is a steep increase in emissions for RVP values above 9psi.
This is again indicative of the exponential dependence of the temperature correction factor on fuel RVP.
However, RVP effects are the same for all RVP values greater than 11.7psi. So, the curves would flatten
out from 11.7psi through 15.2psi (15.2psi is the maximum value of RVP allowed in MOBILE6).
18
-------
All Vehicles CO Emissions and Fuel RVP
D D D D
-4-1995
2005
-^2025
RVP(Mni
Figure 25. Carbon monoxide emissions as a
function of the fuel Reid Vapor Pressure
(RVP).
All Vehicles CO Emissions and Fuel RVP
Figure 26. Percent change in carbon monoxide
emissions relative to the emissions at 7.5psi as a
function of the fuel Reid Vapor Pressure (RVP).
Registration Distribution command
As with HC emissions, CO emissions are affected by changes in the distribution of vehicle ages for a
given year. And again, this reflects the deterioration of emissions with vehicle age which is the main
assumption in MOBILE6 emissions calculations. Figure 27 displays the percent change in CO emissions
versus the percent change in the vehicle age fractions for All Vehicles. The Light-Duty Gasoline Vehicle
relationships are similar.
19
-------
All Vehicle CO Emissions and Vehicle Registrations
All Vehicles CO Emissions and Vehicle Registration
20 25 30
% shift in vehicle fractions
Figure 27.
(a.) All Vehicle CO emissions as a function of
the percent change in the fraction of registered
vehicles with a given age. The percentage is
determined relative to the MOBILE6 default
registration and the emissions determined with
those default vehicle age fractions. (See also
Figure 4 which illustrates the MOBILE6
vehicle age fractions.)
20 25 30
% shift of vehicle fractions
(b.) All Vehicle CO emissions as a function of
the percent change in the fraction of registered
vehicles with a given age. The percentage is
determined relative to the MOBILE6 default
registration and the emissions determined with
those default vehicle age fractions. (See also
Figure 4 which illustrates the MOBILE6 vehicle
age fractions.)
Average Speed Command
The last input parameter in this major affects section for carbon monoxide is the emissions dependence
on vehicle speed through the Average Speed command. Again, the MOBILE6 speed dependence is due
to both an activity factor and a functional vehicle emissions-vehicle speed factor. The Average Speed
command (and the Speed VMT command) set(s) the fraction of vehicles which are operating at a given
speed on the different MOBILE6 roadway types. These fractions in turn apportion the speed correction
factors for different vehicle speeds applied to the CO emissions. Figures 14 through 16 illustrate the
default speed-vehicle fractions used in MOBILE6 for arterial roadways. The freeway fractions are
slightly different and have a higher fraction of vehicles at the speeds above 30mph.
As with HC emissions, variation of the vehicle speed fractions using the Average Speed command has
relatively large effects on CO emissions when compared to the MOBILE6 defaults. This is especially
true when the average speed on a particular roadway type is reduced below 20 mph or increased above
50 mph. Figure 28 shows the MOBILE6 All Vehicle types CO emissions dependence on speed using the
Average Speed command for arterial roadways, freeway, and area wide (or all MOBILE6) roadways.
The variations of the average speeds on arterial roadways and freeways ranged from 10 to 65 mph and
average speeds on all or area wide roadway types ranged from 10 to 35 mph. For the sake of
comparison, Figure 29 shows the percent difference in CO emissions relative to the MOBILE6 defaults
for LDGV freeways, All Vehicles freeways, and All Vehicles area wide roadways. The freeway results
for LDGV and ALL Vehicles show very similar trends. Results for five calendar years, i.e., 1975, 1995,
2000, 2005, and 2025, are displayed in each of the aforementioned figures.
20
-------
Effecl of Average Speed on CO Emissions
All Vehicle Types, Arterial/Collector Roadways
Effect of Average Speed on CO Emissions
All Vehicle Types, Freeways
Elect of Average Speed on CO Emissions
All Vehicle Types, All Roadways Combined
11 111
Figure 28.
(a). All MOBILE6 vehicle (b). All MOBILE6 vehicle (c). All MOBILE6 vehicle
types CO emissions as a types CO emissions as a types CO emissions as a
function of speed on arterial function of speed on freeways function of speed on all
roadways using the Average using the Average Speed MOBILE6 roadway types
Speed command. command. combined or (area wide
roadways) using the Average
Speed command.
21
-------
All Vehicles CO Emissions and Area Wide Average Speed
All Vehicles CO Emissions and Freeway Average Speed
Figure 29.
(a). LDGV CO emissions as
a function of freeway speed
using the Average Speed
command.
(b). All MOBILE6 vehicle
types CO emissions as a
function of freeway speed
using the Average Speed
command.
(c).All MOBILE6 vehicle
types CO emissions as a
function of area wide speed
in the using the Average
Speed command.
A.3 NOx EMISSIONS
The final pollutant considered in this major emission affects section is oxides of nitrogen or NOx. As
with HC and CO the parameters which most impact NOx emissions are the age distribution of the fleet
(Registration Distribution command; see Figures 30 and 31), low vehicle speeds (Average Speed
command; see Figures 32 through 36), and low average daily temperatures (see Figures 37 and 38).
Registration Distribution command
NOx emissions trends relative to changes in the distribution of vehicle ages for a given year are similar
to those exhibited in HC and CO. As with CO and HC, NOx emissions increase with vehicle age. The
dependence is nearly linear as vehicle age shifts from newer to older vehicles. Again, this demonstrates
the basic MOBILE assumption concerning deterioration of emissions along with shifting vehicles to less
restrictive emissions standards and older emissions reduction technologies. Figure 4 above illustrates
how the vehicle ages were changed relative to the MOBILE6 default registration distributions. Figure 30
illustrates the All Vehicle NOx emissions dependence on the percent change in vehicle fractions. Figure
31 displays the percent change in NOx emissions relative to the MOBILE6 default vehicle age
distributions. (As a reminder, the lines are only drawn to guide your eyes.)
22
-------
All Vehicles NOx Emissions and Vehicle Registrations
All Vehicles NOx Emissions and Vehicle Registrations
i i i i i i i i i i i i i i i i i i i i i i i i l i i i i l i i i i i i i i i i i i i i l i i i i i
20 25 30
fa shift in vehicle fractions
20 25 30
% shift in vehicle fractions
Figure 30. All Vehicles NOx emissions as a
function of percent increases in the fraction of
older vehicles relative to MOBILE6 default
vehicle age fractions. (See also Figure 4 which
illustrates the MOBILE6 LDGV age fractions.)
Figure 31. Percent changes in All Vehicle NOx
emissions as a function of increases in the fraction
of older vehicles relative to MOBILE6 default
vehicle age fractions. (See also Figure 4 which
illustrates the MOBILE6 LDGV age fractions.)
Average Speed Command
Next, Figures 32, 33, and 34 show NOx emissions dependence on Light-Duty Gasoline Vehicle, Heavy-
Duty Diesel Vehicle (FtDDV), and All Vehicles freeway speed using the Average Speed command for
five calendar years, i.e., 1975, 1995, 2000, 2005, and 2025. There is a distinguishing characteristic for
the NOx emissions when compared to the results already seen for CO and HC emissions. That is, at
higher speeds (speeds greater than 40mph) the All Vehicle NOx emissions increase considerably at
speeds greater than 40mph due to the inclusion of diesel vehicles. This is apparent when the NOx
emissions for LDGV, heavy duty diesel, and all vehicles are compared (see Figures 32, 33, and 34). The
is only true for NOx emissions when using the Average Speed command on arterial and freeways. The
Area Wide roadway option only allows for average roadway speed inputs below 40mph (see Figures 35
and 36).
23
-------
]'
D D
-MBS
2DD1
2IS
D : a i
2S 35 15
tage Speed (milts pei houi)
» 40
9 a
Effect of Average Speed on NOx Emissions
HDDV, Freeways
2i IS IS
Amage Speed (miles per hour]
Figure 32.
(a). LDGV NOx emissions (b). HDDV NOx emissions
as a function of freeway as a function of freeway
speed using the Average speed using the Average
Speed command. Speed command.
Effect of Average Speed on NOi Emissions
All Vehicle Types, Freeways
IS
3i
Average Speed (miss per ho
(c).All MOBILE6 vehicle
types NOx emissions as a
function of freeway speed in
the using the Average Speed
command.
LDGV NOx Emissions and Arterial Average Speed
All Vehicles NOx Emissions and Arterial Average Speed
Figure 33. Percent change in Light-Duty
Gasoline Vehicle NOx emissions as a function
of the speed on arterial roadways using the
Average Speed command (The percent
differences are relative to emissions
determined with the default vehicle roadway
speed fractions.)
Figure 34. Percent change in All Vehicle NOx
emissions as a function of the speed on arterial
roadways using the Average Speed command.
(The percent differences are relative to
emissions determined with the default vehicle
roadway speed fractions.)
24
-------
LDGV NOx Emissions and Area Wide Average Speed
AH Vehicles NOx Emissions and Area Wide Average Speed
Average Area Wide Vehicle Speed(mph)
I I I I I I I I I I I I I I I I I I I
Figure 35. Percent change in Light-Duty
Gasoline Vehicle NOx emissions as a
function of the vehicle speed on Area Wide
roadways using the Average Speed command.
(The percent differences are relative to
emissions determined with the default vehicle
roadway speed fractions.)
Figure 36. Percent change in All Vehicle NOx
emissions as a function of speed on Area Wide
roadways using the Average Speed command.
(The percent differences are relative to
emissions determined with the default vehicle
roadway speed fractions.)
Min/Max Temperature Command
Although the one-to-one correspondence between input variation and output variation for temperature
and NOx is typically less than one, the last input parameter-emissions relationship considered in this
major parameter section is the relationship between NOx and average daily temperature. This input
parameter is complicated because the corrections to NOx emissions are also dependent on humidity.
High values of humidity which are more likely with higher ambient temperatures tend to decrease the
formation of NOx. However, the temperature (MIN/MAX temperature command) and the humidity
(ABSOLUTE humidity command) values are not inter-related in MOBILE6 calculations. Hence, the
humidity-temperature interaction when using either of those commands does not have a significant
affect on NOx emissions. In the high ambient temperature region for the calendar years relevant to any
current emissions calculations the interplay between humidity and temperature is relatively small.
(Recently, a command and related coding has been added to MOBILE6 allow for the inter-relationship
between humidity and temperature5.)
Figures 37a, 37b, and 37c show the MOBILE6 LDGV, HDDV, and all vehicles NOx emissions as a
function of temperature while holding the absolute humidity constant. Also, Figures 38a and 38b show
the LDGV NOx emissions percent change as a function of temperature and temperature percent
changes, respectively. They show that the MOBILE6 NOx emissions increase most dramatically for
ambient temperatures below 30°F and that these increases decrease with calendar year. The calendar
year dependence is due to the implementation of improved emissions control technologies and emissions
regulations. Especially noticeable are those calendar years greater than 1975 which show a temperature
range between 50*F and 70*F where NOx emissions are relatively constant. Outside of this range NOx
emissions tend to increase. As with HC and CO, the MOBILE6 temperature correction factor9 for NOx
is an exponential function dependent on both temperature and fuel RVP for temperatures above 75*F and
is only temperature dependent for temperatures below 75*F.
25
-------
E >
LDGl'HOi: (constant absolute tai*,=f5piBi;>
[ D I I I I (I ?! I 'II II I'O 12
TtrpitmfF)
Figure 37.
(a). LDGV NOx emissions
as a function of average
daily temperature using the
Min/Max Temperature
command.
HDDVUOi: i constara absolute humidipiSgrains'lbi
[ [ ] D [ [
II I III I
I !] 31 E !I
(b). HDDV NOx emissions
as a function of average
daily temperature using the
Min/Max Temperature
command.
All Vehicles NOx (constant absolute humlditytfgialnsi)
TenpsratefF)
(c). All MOBILE6 vehicle
types NOx emissions as a
function of average daily
temperature using the
Min/Max Temperature
command.
Figure 38.
a. The relationship between the percent change
in NOx emissions and average daily
temperature when the absolute humidity is kept
at a constant value of 75 grains/lb.
b. The relationship between the percent
change in NOx emissions and percent change
average daily temperature when the absolute
humidity is kept at a constant value of 75
grains/lb.
26
-------
As with HC and CO at lower temperatures, NOx start emissions begin to increase between 40*F and
50*F and hence become a larger fraction of the composite (start plus running). And the NOx start
emissions effects due to the average number of vehicle starts per day is listed in the intermediate effects
section. However, at lower temperatures these start emissions will become more important in the
emissions total as will the number of starts per day.
A.4 Major Parameter Summary
Four MOBILE6 input parameters, vehicle age or registration distribution, average daily temperature,
vehicle speed when changed via the Average Speed command, and fuel RVP, can have large affects
(changes in emissions of 20 percent or more relative to the emissions calculated with default input
values) on emissions results calculated by MOBILE6. The above results presented represent only those
inputs which have at least a 1-to-l emissions-to-input percentage rate response and lead to an emissions
increase of at least 20 percent. All pollutant types, CO, HC, and NOx, have a high dependence on the
vehicle registration distribution. This is mainly due to the basic assumptions that older technology
vehicles have higher emissions than newer technology vehicles and that vehicle emissions worsen as
vehicles age. Next, CO emissions increase rapidly with temperature once the average daily temperature
moves below 55°F. Hydrocarbon and oxides of nitrogen emissions also have relatively high emissions at
very low temperatures, i.e., average daily temperatures below 20°F. Increases in emissions due to
temperature changes at higher temperatures (above 75*F) is exponential and at lower temperatures is due
to cold start emissions. Fuel RVP values between 9psi and 1 l.Spsi effect the temperature correction
factor exponentially and is reflected in the large increase in CO, HC, and NOx emissions. Finally, the
Average Speed command changes the default values of speed and the fractions of vehicles travelling on
different MOBILE6 roadways types which produces significant changes in emissions especially at
speeds near lOmph.
B. PARAMETERS WITH INTERMEDIATE EFFECTS ON EMISSIONS (5% TO 20%)
In this section a discussion is given of the parameters which induce intermediate changes in emissions.
Table 2 below lists the inputs which fall into this intermediate level of affects on emissions and the rates
at which they effect emissions for Light-Duty Gasoline Vehicles (LDGV). These parameters have at
about a 1-to-l emissions-to-input percentage rate response and lead to an emissions increase of at least 5
percent but less than 20 percent when the input parameter is changed by 20 percent.
27
-------
Table 2. Summary of LDGV and All Vehicle results with input parameters which have an
"intermediate" effect on emissions
COMMAND
Change in Input
Change in
Hydrocarbon
emissions
Change in CO
emissions
Change in
Oxides of
Nitrogen
emissions
>5% and <20%
Absolute Humidity [Use high and low
humidity values from August morning and
afternoon average relative humidity values
from Atlanta and Tucson (National Weather
Service data).]
Air Conditioning
Altitude
Mileage Accumulation(increase and decrease
mileage accumulation relative to the
MOBILE6 defaults)
Speed VMT (Arterial;
-3% - null low speed vehicle fractions
9% - equal vehicle fractions for all speeds
14% - increase low speed vehicle fraction by
10%
21% - increase low speed vehicle fraction by
20%
29% - increase low speed vehicle fraction by
30%)
Speed VMT (Freeway; reduce fraction of
vehicles from high speeds to lower speeds)
Starts Per Day(change the number of starts
per day from -50% to +50% in increments of
10% for each vehicle type)
-28%
mm. ,- , , ,
(54grams/lb)
100%
max' (149grains/lb)
Emissions Differences with Air
Conditioning Correction
Applied and Not Applied
Emissions Differences Between
High Altitude and Low Altitude
min.
max.
min.
max.
min.
max.
min.
max.
20% decrease
20% increase
-3% (free-flow/
all day non-rush
hour speeds)
29%(congested
traffic flow,i.e.,
30% more
vehicles at the
lower speeds)
-50% (equal
distribution of
speeds)
10%(most
vehicles at the
higher speeds)
-50%
50%
Third Level
Third Level
Low Level
26%(1975)
4%(1995)
<1%(2025)
Third Level
Third Level
Third Level
First Level
(NMHC)
+13%(1975) to
5%(2050)
Third Level
(NMHC)
-17%(2025)
to
-12%(1975)
(NMHC)
17%(2025)
to
12%(1975)
Third Level
Third Level
16%(1975)
20%(2005)
5%(2050)
41%(1975)
8%(1995)
0%(2005)
-2.5%(1985)
to
-11%(2020)
1%(1980)
to
9%(2020)
Third Level
Third Level
Third Level
Third Level
-15%(1975)
to
-11%(2025)
11%(2025)
to
15%(1975)
Idgv running
5%(2025)
to
6%(1975)
Idgv running
-14%(1975)
to
-10%(2025)
5%(1975)
10%(19995)
18%(2025)
-31%(1975)
-4%(1995)
0%(2005)
0%(1990)
to
-24%(2020)
1%(1990)
to
22%(2020)
Third Level
5%(1975) to
8%(2050)
Third Level
Third Level
-13%(1975)
to
-7%(2025)
13%(1975)
to
7%(2025)
28
-------
B.I HC EMISSIONS
Altitude
Internal combustion engines essentially work on the air mass that moves through it and the fuel that
supplies heat. Ambient air conditions such as pressure and temperature effect both the density of air and
hence the supply of air (mass) to the engine. The pressure of the air is of course dependent on altitude. In
mobile6 an altitude correction factor for high altitude regions10 (approximately 4,000 feet above sea
level) is used to account for this ambient condition. In this work, high altitude emissions were compared
with the MOBILE6 default low altitude emissions. The emissions results for Light-Duty Gasoline
Vehicles and All Vehicle types as a function of calendar year are displayed in Figure 39 below. The
percent differences relative to the default low altitude for both Light-Duty Gasoline Vehicles and All
Vehicle types are displayed in Figure 40. Altitude has little effect on Light-Duty Gasoline Vehicle
emissions for calendar years after 1995. However, the All Vehicle emissions percent differences imply
that the MOBILE6 Heavy Duty Vehicles even for calendar years greater than 1995 have emissions
which are about 10 percent higher than the low altitude option.
LDGV NMHC Emissions by Altitude
2000 2010 2020
Calendar Year
Figure 39.
(a). Low and high altitude NMHC emissions for
MOBILE6 Light-Duty Gasoline Vehicles
NMHC Emissions by Altitude for All Vehicles
2000 2010 2020
Calendar Year
(b). Low and high altitude NMHC emissions
for the MOBILE6 All Vehicle types.
29
-------
30 T
LDGV and All Vehicle
Percent Differences Between
NMHC High and Low Altitude Altitude Emissions
1970
1980
1990
2000 2010 2020
Calendar Year
2030
2040
2050
Figure 40. Percent differences between NMHC emissions at low and high altitudes.
Speed VMT Command
MOBILE6 NMHC emissions also have medium level association with the SPEED VMT command for
freeways mainly in earlier calendar years. In a manner similar to what was described in changes in the
SPEED VMT command for arterial roadways for NMHC emissions (see Figures 14, 15, and 16), the
MOBILE6 default fraction of vehicles travelling at speeds of 2.5, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50,
55, 60, and 65 miles/hour on freeways were varied from higher speeds to lower speeds and the resultant
MOBILE6 emissions were compared. Figure 41 displays Light-Duty Gasoline Vehicle emissions results
as a function of the percent change in vehicle fractions relative to MOBILE6 default fractions. Figures
38 and 39 show the percent difference in NMHC emissions relative to emissions produced with default
vehicle fractions.
30
-------
HIGHWAY SPEED and LDGV HC Emissions
e 1975
-B-1995
-A-200D
2005
1^2020
"3T
f 7.
c
8 6
E
01
0
= 0
4
^ o R- n _n 1
- 4 i
XX vx - , ^
1'
0
-* A
% chahVjc in the faction 10
of vehicles at the two
maximum speeds
Figure 41. NMHC emissions from LDGV as a function of changing the fraction
of vehicles travelling at higher speeds. MOBILE6 default vehicle fractions vary
by hour of the day whereas the changed vehicle fractions are constant for each
hour of the day. (See also Figures 14 through 16.)
HIGHWAY SPEED and All Vehicle HC Emissions
Figure 42. NMHC percent changes in LDGV
emissions relative to MOBILE6 defaults as a
function of varying the fraction of vehicles
travelling at higher speeds. The vehicle fractions
were also held constant through each hour of the
day. (See also Figures 14 through 16.)
Figure 43. NMHC percent changes in All
Vehicle emissions as a function of changing the
fraction of vehicles travelling at higher speeds
relative to MOBILE6 defaults. The vehicle
fractions were also held constant for each hour.
(See also Figures 14 through 16.)
31
-------
Starts per Day
A new feature of MOBILE6 is the ability to separate emissions into cold start emissions and hot
stabilized running emissions. Consequently, the number of starts per day that a vehicle experiences can
be changed by the MOBILE6 user. So, the impact of start emissions on total vehicle emissions (start
emissions plus running emissions) can be studied with MOBILE6. In Figures 44 through 46 NMHC
emissions determined using MOBILE6 are depicted as a function of starts per day. The figures include
results for Light-Duty Gasoline Vehicles and for all MOBILE6 vehicle types. The NMHC emissions in
these figures are total emissions from NMHC cold start emissions, NMHC hot stabilized emissions, and
contributions from NMHC evaporative emissions. The relationship for the span of calendar years, 1975
through 2025, is linear. As mentioned in the major affects sections on temperature, there is a sharp
increase in emissions below 45*F which is due to cold start emissions. At these lower temperatures, the
starts per day will contribute significantly to the total emissions.
Although they are not shown, the percent increase/decrease in start emissions alone have a one-to-one
correspondence with the percent increase/decrease in the number of starts per day. That is, a one percent
increase in the number of starts per day will yield a one percent change in emissions. Moreover, this one
percent increase in start emissions is the sole factor for increases in the total (start plus running )
emissions illustrated in Figures 44 through 46 below.
Light Duty Gas Vehicle Starts per Day and HC Emissions
LDGV HC Emissions and Starts Per Day
Figure 44. Percent change in LDGV emissions
as a function of the number of LDGV starts per
day. The MOBILE6 default average number of
LDGV weekday starts per day is 7.28.
Figure 45. Percent change in emissions as a
function of the percent change in the number of
LDGV starts per day relative to the default
number of LDGV starts per day.
32
-------
All Vehicle Emissions and Starts Per Day
20 30 40
% Change in Starts Per Day
Figure 46. Percent change in emissions as a function of the percent
change in All Vehicle starts per day. Most vehicle types have differing
numbers of starts per day. For each vehicle class a percentage of starts
per day was either subtracted (or added). The emissions were then
determined by running MOBILE6 with the starts per day for each
vehicle type changed by a certain given percentage as indicated in the
graph.
B.2 CO Emissions
Air Conditioning
Another new feature of MOBILE6 is the ability to approximate the emissions due to engine air
conditioning load. Part of the correction depends on air conditioning usage which is determined with
what is termed a "heat index". The heat index is dependent on both ambient temperature and humidity.
Hence, the MOBILE6 temperature range and the absolute humidity values impact the air conditioning
correction. However, the temperature and humidity interaction with the air conditioning correction was
not studied here. In this analysis, to determine the impact of the MOBILE6 air conditioning correction
on emissions, a temperature range of 72*F to 92*F with an absolute humidity value of 75grains/lb was
used to compare MOBILE6 CO emissions estimations with and then without the air conditioning
correction. The comparison as a function of calendar year is displayed in Figures 47 through 49. Figures
47 and 48 illustrate the emissions in grams/mile for Light-Duty Gasoline Vehicles and all MOBILE6
vehicle types, respectively, with and without the air conditioning correction. Figure 49 depicts the
percent increase in emissions due to MOBILE6 air conditioning correction as a function of calendar
year.
33
-------
CO Emissions With and Without Air Conditioning
forLDGVs
198!
199! 200!
Calendar Year
2025
2050
Figure 47. A comparison of LDGV CO by
calendar year with MOBILE6 air
conditioning correction on or off.
120
100
s
v
0
'3
ID
1
u
0
o
CO Emissions With and Without AC
for All Vehicles
1985
1995 2005
CalendarYear
2025
2050
Figure 48. A comparison of All Vehicle CO
emissions by calendar year with MOBILE6 air
conditioning correction on or off.
% s.
P
LDGV CO Emissions and Air Conditioning Usage
1970 1980 1990 2000 2010 2020 2030 2040 2050 2060
CalendarYear
Figure 49. Percent difference in CO emissions due to MOBILE6 air
conditioning correction as a function of calendar year for both LDGV and All
Vehicles.
34
-------
Altitude
MOBILE6 includes an altitude correction option. The choices are either high altitude or low
altitude(default). The MOBILE6 CO emission comparisons between low altitude (regions below 4,000
feet10) and high altitude regions are shown in Figures 50, 51, and 52 for both Light-Duty Gasoline
Vehicles and the MOBILE6 All Vehicle types. Figures 50 and 51 illustrate the emissions in grams/mile
for Light-Duty Gasoline Vehicles and All Vehicle types, respectively, at high and low altitude regions.
Figure 52 depicts the percent increase in emissions due to the MOBILE6 high altitude correction as a
function of calendar year.
All Vehicle CO Emissions by Altitude
1995 2005
Calendar Year
Figure 50. MOBILE6 altitude effects on
LDGV CO emissions as a function of
calendar year.
Figure 51. MOBILE6 altitude effects on All
Vehicle types CO emissions as a function of
calendar year.
CO Emissions and Altitude
Figure 52. Percent difference in CO emissions due to MOBILE6 altitude
correction as a function of calendar year for both LDGV's and and All
Vehicles.
35
-------
Mileage Accumulation
Mileage for each of the 28 different vehicle classes is determined by calendar year. In particular, each
vehicle class has a 25-year range of mileage accumulation rates. In other words, in MOBILE6 vehicles
are classified by age, and the age determines how much the vehicle is used in terms of how many miles
it has traveled. Figure 53 displays the default MOBILE6 Light-Duty Gasoline Vehicle mileage as a
function of vehicle age; the dark blue line with open circles. To illustrate the MOBILE6 emissions
dependence on vehicle mileage, the default LDGV mileage was changed by increasing and decreasing
the mileage for each vehicle age. Figure 53 also displays the LDGV mileage curves for each vehicle age
after the changes. In 5 percent increments of the default mileage values, mileage was added to and
subtracted from the default MOBILE6 mileage values. This procedure was duplicated for each of the
different MOBILE6 vehicle categories. That is, the CO emissions were estimated using MOBILE6 with
the Mileage Accumulation command used to increase and decrease all of the different MOBILE6
vehicle types default mileages in increments of 5 percent through a range of 40%.
Figures 54 and 55 display results for Light-Duty Gasoline Vehicles and the All Vehicle types,
respectively, in terms of percent change in CO emissions versus percent change in mileage. Again, the
lines are drawn to guide the reader's eyes. In general, the trends show a nearly linear increase/decrease in
CO emissions with increases/decreases in mileage for each of the calendar years, 1975,1995, 2000,
2005, and 2025. For both the All Vehicles category and the Light-Duty Gasoline Vehicles category CO
emissions show similar functional dependence on mileage.
E
« 0.08
-LDGV default mileage
-20% decrease
15% decrease
-10% decrease
-5% decrease
-5% increase
-15% increase
20% increase
25
vehicle age(yearc)
Figure 53. In MOBILE6 each calendar year is associated with a set of vehicles of
ages 1 through 25. The mileage traveled by a MOBILE6 vehicle type decreases
with age as illustrated in the above graph. The blue line with open circles depicts
the default mileage traveled by LDGV of a particular age. To determine how
changes in this default mileage distribution affects emissions, the default numbers
were increased and decreased in increments of 5 percent as illustrated in this
figure for LDGV's. Figures 54 and 55 illustrate the percent changes in CO
emissions from MOBILE6 default values.
36
-------
LDGV CO Emissions and Mileage Accumulation
All Vehicles CO Emissions and Mileage Accumulation
Figure 54. Percent change in LDGV CO
emissions as the default mileage is changed.
Figure 47 above illustrates how the mileage
changed from the MOBILE6 LDGV default
mileages.
Figure 55. Percent change in All Vehicle CO
emissions as the default mileage is changed
for All Vehicle types. See Figure 47 for an
illustration of how the mileages were varied
relative to the MOBILE6 default values.
Vehicle Starts Per Day
As with NMHC emissions Starts Per Day is a new feature of MOBILE6 and CO emissions can now be
separated into cold start emissions and hot stabilized running emissions. Also, the number of Starts Per
Day that a vehicle experiences can be changed by the MOBILE6 user. So, the impact of start emissions
on the total vehicle CO emissions (start CO emissions plus running CO emissions) can be estimated
using MOBILE6. In Figures 56 through 58, CO emissions determined using MOBILE6 are depicted as a
function of Starts Per Day. The figures include results for Light-Duty Gasoline Vehicles and for all
MOBILE6 vehicle types. The CO emissions in these figures are total emissions and include both start
and running emissions. The relationship for the span of calendar years, from 1975 through 2025 at an
average daily temperature of about 82*F (minimum temperature of 72*F and a maximum temperature of
92*F) is linear. As mentioned in the major affects sections on temperature, there is a sharp increase in
emissions below 45*F which is due to cold start emissions. At these lower temperatures, the starts per
day will contribute significantly to the total emissions.
Although they are not shown, the percent increase/decrease in start emissions alone has a one-to-one
correspondence with the percent increase/decrease in the number of Starts Per Day. That is, a one
percent increase in the number of starts per day will yield a one percent change in emissions. Moreover,
this one percent increase in start emissions is the sole factor for increases in the total (start plus running )
emissions illustrated in Figures 56 through 58.
37
-------
130 T
120
90
80
70 -
60
50
40 -
30 -
20
10
0
LDGV CO Emissions and Starts per Day
CO COMP 2005
-CO COMP 1975
-CO COMP 2000
-CO COMP 2025
A
-Xr
10 11
STARTS PER DAY
Figure 56. LDGV CO emissions as a function of the number of starts per day. These
emissions include both start emissions and running emissions. (The percent change in
start emissions increases by a one-to-one ratio with percent increase in the MOBILE6
deault number for Starts Per Day.)
LDGV CO Emissions and Starts Per Day
20 T
All Vehicle CO Emissions and Starts Per Day
Figure 57. Percent increase in LDGV CO
(running plus start) emissions as a function of
the percent change in default MOBILE6 start
emissions.
Figure 58. Percent increase in All Vehicles CO
(running plus start) emissions as a function of the
percent change in default MOBILE6 start
emissions.
38
-------
B.3 NOx EMISSIONS
This section discusses MOBILE6 commands which effect NOx emissions between 5 percent and 20
percent, i.e., medium or intermediate level commands. They are absolute humidity, air conditioning,
altitude, and mileage accumulation.
Absolute Humidity
High ambient air moisture or humidity levels suppress the creation of NOx emissions by reducing the
available heat needed to create nitrogen oxides during the combustion process. All versions of MOBILE
have contained an algorithm10 to account for this NOX emissions reduction process. Figure 59 displays
the MOBILE6 NOx humidity correction factor as a function of absolute humidity. (In many references
the MOBILE6 absolute humidity is referred to as specific humidity. This quantity has units of grains of
water per pound of air.) Also in Figure 59, the humidity correction affect on Light-Duty Gasoline
Vehicle NOx emissions is displayed as a function of absolute humidity in grains/lb. These LDGV
emissions results are for relative humidity values between about 33%(55 grains/lb. absolute humidity)
and 90% (150grains/lb absolute humidity). A 20 degree Fahrenheit daily temperature cycle defined by
minimum and maximum temperatures of 72 and 92, respectively, was used to compute the emissions.
These values were taken from monthly average temperatures and humidity values in August for Tucson
and Atlanta. The NOx emissions construe to the humidity correction factor. MOBILE6 assumes a
default value for absolute humidity of 75 grains/lb. Figures 60 and 61 display the percent change in
emissions from default values (determined with the default value of absolute humidity) as a function of
the percent change in absolute humidity relative to the default value.
ABSOLUTE HUMIDITY is a new input parameter for MOBILE6 and only allows input of a single
value of absolute humidity. (MOBILE6 has been updated to allow hourly values of humidity; see the
discussion below.) However, as with the ambient temperature, this atmospheric parameter can vary from
hour to hour during the day. Analysis of the temperature and humidity interdependency on MOBILE6
when using the ABSOLUTE HUMIDITY command showed that emissions variations of less than 5
percent (thus, falling into the category of "minor" effects). This is true for all pollutants, hydrocarbons,
carbon monoxide, and oxides of nitrogen. Although details of the temperature-humidity interaction
analysis will not be contained in this discussion, humidity when input through the ABSOLUTE
HUMIDITY command does not effect CO, HC and NOx emissions strongly when considering
variations in the daily average temperature. The ABSOLUTE HUMIDITY parameter only affects NOx
emissions directly though the NOx correction factor which lowers NOx emissions at higher humidity
values. Temperature and humidity do affect CO, HC, and NOx emissions indirectly through the air
conditioning load affect which is discussed elsewhere.
Because relative humidity is the measure of air moisture content which is most readily available to the
public, an additional humidity command, RELATIVE HUMIDITY, was added to MOBILE6. It allows
input of hourly relative humidity values. Internally, MOBILE6 converts the relative humidity values to
absolute humidity using hourly temperature values and an average daily value of barometric pressure
which has a default value of 29.92 inches of mercury, i.e., barometric pressure at sea level. Along with
the relative humidity values, barometric pressure can also be varied with the BAROMETRIC PRES
command.
For a given value of relative humidity, varying barometric pressure and temperature, of course, varies
the absolute humidity. This subject is usually referred to as psychrometry11' 2'13 and the graphical
representation of these relationships is called a psychrometric chart. In Figure 62, a few curves depicting
the relationship between temperature, absolute humidity, and pressure are illustrated. The mathematical
form of the dependencies are derived from the thermodynamics of ideal gases and partial pressure
39
-------
NOx Humidity correction factor
250 300
absolute humidity) grains/lb.)
Figure 59.
(a.) MOBILE6 NOx humidity correction
factor as a function of absolute humidity.
LDGV NOx Emissions and Absolute Humidity
70 80 90 100 110 12Q 130 140 150
(b.) MOBILE6 LDGV NOx emissions as a
function of absolute humidity for calendar
years 1975, 2000, 2005, and 2025. An
absolute humidity value of 75 grains of
water per pound of dry air is the MOBILE6
default value of absolute humidity.
ftt-
All Vehicles NOx emissions 8 absolute humidity
-MS7S
2000
2005
70 90 11]
% change in absolute humidity
Figure 60. Percent change in MOBILE6 All
Vehicle types NOx emissions as a function of the
percent change in absolute humidity from the
default value of 75 grains/pound.
LDGV NOx composite emissions & absolute humidity
-
-------
relationships of mixtures of gases. Extending the curves over the entire range of pressures, temperatures,
and humidity values would produce a psychrometric chart.
350"
300-
I" 250 -
I ;
a
~ 200 -
I
1
I 150-
I
| 10D''
50'
%relative humidity of 50% and 72F
O -relative humidity of 80% and 72F
A -relative humidity of30% and 72F
"A..
A--A--
'A--A--._.
A- -A- - - -A
H 1 1 1 1 1 1I 1 1 1 1 1 1 1 1 1 1 1 1 1 1-
10 15 20 25
barometric pressure (inches of Hg)
H 1 1i 1 1 1
30 35
Figure 62. An Illustration of the relationship between absolute humidity and barometric
pressure for three different values of relative humidity, 30%, 50%, and 80%. The
temperature is held constant at 72*F. When this graphical representation of the
dependence of specific or absolute humidity on temperature and pressure is extended for
all temperatures and pressures, it is called a psychrometric chart.
Air Conditioning
NOx emissions with and without the MOBILE6 air conditioning correction applied are displayed in
Figures 63 through 65 as a function of calendar year. As mentioned above in the section on air
conditioning affects on CO emissions, part of the correction depends on air conditioning usage which is
determined by a heat index. Hence, the MOBILE6 air conditioning correction depends on temperature
range and absolute humidity values. For this analysis, the temperature range used was 72*F to 92*F with
an absolute humidity value of 75grains/lb. Figure 65 depicts the percent increase in emissions due to the
MOBILE6 air conditioning correction as a function of calendar year. Although the NOx emissions
decrease considerably in later calendar years, the proportion of NOx emissions due to air conditioning
engine increases with calendar year for Light-Duty Gasoline Vehicles and for All Vehicle types as
shown in Figure 65.
41
-------
LDGV NOx Emissions With and Without AC
1995 2005
Calendar Year
Figure 63. MOBILE6 air conditioning effects on
LDGV NOx emissions as a function of calendar
year.
NOx Emissions With and Without AC
for All Vehicles
1995 2005
Calendar Year
Figure 64. MOBILE6 air conditioning effects
on All Vehicle NOx emissions as a function of
calendar year.
15
LU
.£
g>
ra
« 10
o
NOx Emissions and MOBILES Air Conditioning Correction
2010 2020
Calendar Year
Figure 65. Percent difference in NOx emissions due to MOBILE6 air conditioning
correction as a function of calendar year for both LDGV and and All Vehicles.
Altitude
MOBILE6 includes a choice for selecting the Altitude parameter. The two choices are, either high
altitude or the default low altitude. The MOBILE6 CO emission comparisons for the low altitude
(regions below 4,000 feet10) and high altitude regions are shown in Figures 66, 67, and 68 for both
Light-Duty Gasoline Vehicles and All Vehicle types.
42
-------
All Vehicle and LDGV NOx Emissions Due to Altitude
Calendar Year
2030 2040
Figure 66. Percent difference in NOx emissions due to MOBILE6 altitude
correction as a function of calendar year for both LDGV and All Vehicle types.
I 3-1
LDGV NOx Emissions by Altitude
1970 1980
1990 2000 2010 2020 2030 2040 2060
Calendar Year
Figure 67. MOBILE6 altitude effects on LDGV
NOx emissions as a function of calendar year.
1,.
All Vehicles NOx Emissions by Altitude
1970 1980 1990
2010 2020 2030 2040 2050 206
Figure 68. MOBILE6 altitude effects on All
Vehicle types NOx emissions as a function of
calendar year.
43
-------
Mileage Accumulation
Mileage for each of the 28 different vehicle classes is stored in MOBILE6 by calendar year. That is,
each vehicle class has a 25-year set of mileage rates. Vehicles are classified by age and the age
determines usage or mile traveled. Figure 53 displays the default MOBILE6 Light-Duty Gasoline
Vehicle mileage as a function of vehicle age; they are displayed with a dark blue line and open circles.
Figure 53 also displays how the mileage for each vehicle age was changed to determine the emissions
dependence on mileage accumulation. In 5 percent increments of the default mileage values, mileage
was added to and subtracted from the default MOBILE6 mileage values. To determine the NOx
emissions dependence this was duplicated for each of the different MOBILE6 vehicle categories and
then emissions were estimated using MOBILE6 with all of the vehicle mileage changed by a given
incremental 5 percent change.
For five specific calendar years, Figure 69 shows the trend in Light-Duty Gasoline Vehicle gram/mile
NOx emissions relative to percent increase/decrease in vehicle mileage as displayed in Figure 53.
Figures 70 and 71 display the results for Light-Duty Gasoline Vehicles and for All Vehicle types in
terms of percent changes in NOx emissions versus percent change in mileage. (Again, the lines are
drawn to guide the reader's eyes.) In general, the trend shows a nearly linear increase/decrease in NOx
emissions with increases/decreases in mileage for each of the calendar years, 1975,1995, 2000, 2005,
and 2025, as shown in the graphs. NOx emissions for both the All Vehicles and the Light-Duty Gasoline
Vehicles categories show similar functional dependence on mileage.
.\
% Change in Vehicle Mileage
Figure 69. Light-Duty Gasoline Vehicle grams/mile emissions as a function of the
percent change in Light-Duty Gasoline Vehicle mileage.
44
-------
Figure 70. Percent change in LDGV NOx emissions
as the default mileage is changed. Figure S
illustrates how the mileage changed from the
MOBILE6 LDGV default mileage.
Figure 71. Percent change in All Vehicle NOx
emissions as the default mileage is changed for
All Vehicle types. See Figure 53 for an
illustration of how the mileage were varied
relative to the MOBILE6 default values.
C. PARAMETERS WITH MINOR EFFECTS ON EMISSIONS ( LESS THAN 5%)
The third and last category of MOBILE6 parameters which have a "minor" (i.e., less than 5%) effect on
emissions are listed in Table 3 below. A complete list of the MOBILE6 commands and a description of
how the inputs were changed is listed in the Appendix, Table A.2. Because of the relatively small
emissions effects the general trends are listed in the table but are not graphically illustrated.
Table 3. List of low level MOBILE6 commands or parameters
HC Emissions :
CO Emissions
NOx Emissions :
Absolute Humidity
Air Conditioning
Facility VMT
Fuel Program/Sulfur Content*
Hourly Temperature
Mileage Accumulation
Oxygenated Fuels
Sulfur Content*
Start Distribution
Temperature Cycles
Temperature and Humidity
Absolute Humidity
Facility VMT
Fuel Program/Sulfur Content*
Hourly Temperature
Oxygenated Fuels
Sulfur Content*
Start Distribution
Temperature Cycles
Temperature and Humidity
Facility VMT
Fuel Program/Sulfur Content*
Fuel RVP
Hourly Temperature
Oxygenated Fuels
Sulfur Content*
Start Distribution
Temperature Cycles
Temperature and Humidity
In MOBILE6 sulfur content of fuel can be changed in two different calendar year ranges, (1)
calendar years less than or equal to 1999 and (2) calendar years greater than 1999. The Fuel
Program/Sulfur Content command is used for post 1999 calendar years and the Sulfur Content is
used for calendar years 1999 and earlier. Sulfur content deteriorates the catalyst. Its effects on
hydrocarbon, carbon monoxide, and nitrogen oxide emissions are small. However, it enables the
production of sulfur oxides and particulate matter which is not within the scope of this report.
45
-------
CONCLUSIONS
A thorough examination of the relationship between MOBILE6 input parameters and the relative
importance each has on MOBILE6 CO, HC, and NOx emissions estimations has been undertaken. Each
parameter evaluated was varied and the resulting MOBILE6 emissions were compared to emissions
determined with default or some base value input. These results were then subdivided into three
categories, major effects, intermediate effects, and minor effects on emissions. There are four MOBILE6
input parameters, Vehicle Age or Registration Distribution, Average Daily Temperature, fuel RVP, and
vehicle speed when changed via the Average Speed command, which fall into the major affects (changes
in emissions of 20% or more relative to the emissions calculated with default input values) category.
The major affects category has the additional caveat that the emissions percent change-to-input percent
change must be greater than or equal to one. Seven Mobile6 input parameters, Absolute Humidity, Air
Conditioning, Altitude, Mileage Accumulation, Speed VMT, and Starts Per Day, have intermediate
affects (changes in emissions between 5% and 20% relative to the emissions calculated with default or a
base input value). Lastly, depending on the pollutant there are about eight to ten input parameters which
effect emissions at the minor level (changes in emissions of less than 5%). These latter parameters are
listed in Table 3 above.
This study was completed to facilitate the use of MOBILE6 and should be used in conjunction with
MOBILE6 technical guidance documentation. It is meant to be a resource for MOBILE6 users so that
they can (a) better evaluate how MOBILE6 input parameters affect the emissions results, (b) formulate
well informed emissions reductions programs through the use of MOBILE6, and (c) efficiently make
accurate emissions inventories by paying attention to how inputs affect emissions and what local data
may be important when using MOBILE6 to make emissions estimations.
46
-------
APPENDIX
Table A.I. Summary of the LDGV results.
COMMAND
Absolute Humidity [Use high and low
humidity values from August morning and
afternoon average relative humidity values
from Atlanta and Tucson (National Weather
Service data).]
Air Conditioning
Altitude
Average Speed ( Arterial roadways)
Average Speed ( Area Wide roadways)
Average Speed (Freeways)
Facility VMT (Add and subtract fraction of
vehicles to/from freeways and arterials:
New freeway + new ramp=(old freeway +
old ramp) + x*old arterial
Newramp= 0.08*(new ramp + new freeway)
new freeway=(0.92/0.08) * new ramp
New arterial=(l-x)*old arterial
Fuel Program/Sulfur Content
(calendar years 2000 and later; for default
conventional eastern program reduce sulfur
content by 10%, 20%, and 30%)
Change in Input
-28%
mm. ,- , , ,
(54grams/lb)
100%
max' (149grains/lb)
Emissions Differences with Air
Conditioning Correction
Applied and Not Applied
Emissions Differences Between
High Altitude and Low Altitude
min.
max.
min.
max.
min.
max.
min.
max.
min.
max.
lOmph
30mph
70mph
lOmph
35mph
lOmph
35mph
70mph
subtract 40%
from arterials
add 40% to
arterials
-10%
-30%
Change in
Hydrocarbon
emissions
(NMHC)
<-!%
Idgv
total:<0.5%
(NMHC)
Idgv
running: 4%
Idgv
total:<0.5%
2%(1975)
2%(2005)
0%(2025)
26%(1975)
4%(1995)
<1%(2025)
(VOC)
68%(1975)
83%(2025)
(VOC)
-24%(2000)
-29%(2025)
(VOC)
73%(1975)
68%(2000)
81%(2025)
(VOC) -12%
(VOC)
74%(1975)
68%(2000)
81%(2025)
(VOC)
-27%(1975)
-22%(2000)
-27%(2025)
(NMHC)
-1%(1975)
0%(2000)
(NMHC)
1%(1975)
0%(2007)
(NMHC)
-0.5% (2000)
to
0%(2025)
(NMHC)
-1.5%(2000)
to
-0.5%(2025)
Change in CO
emissions
Idgv running
-1.9%(2000)
to
-0.6%(2025)
Idgv running
2.3%(2025)
to
8.4%(2000)
16%(1975)
20%(2005)
5%(2050)
41%(1975)
8%(1995)
0%(2005)
39%(1975)
18%(2000)
30%(2025)
-6%(1975)
-12%(2025)
0%(1975)
21%(2000)
15%(2025)
35%(1975)
14%(2000)
26%(2025)
-3%(1975)
1%(2005)
0%(2025)
40%(1975)
28%(2025)
-8%
0%(1975)
17%(2000)
13%(2025)
2%(1975)
4%(2000)
3%(2020)
-1%(1975)
-4%(2005)
-3%(2020)
-1.6%(2000)
to
-0.6%(2025)
-4.7%(2000)
to
-2%(2025)
Change in
Oxides of
Nitrogen
emissions
Idgv running
5%(2025)
to
6%(1975)
Idgv running
-14%(1975)
to
-10%(2025)
5%(1975)
10%(19995)
18%(2025)
-31%(1975)
-4%(1995)
0%(2005)
26%(1975)
51%(2025)
-2%(1975)
-6%(2025)
-2%(1975)
0%(2025)
19%(2025)
38%(2025)
-3%
17%(1975)
32%(2025)
-1%(1975)
-5%(2025)
-2%(1975)
1%(2000)
0%(2025)
1%(1975)
5%(2000)
2%(2020)
-1%(1975)
-5%(2000)
-2%(2020)
-0.7%(2000)
to
0%(2025)
-2.2%(2000)
to
-3.7%(2025)
47
-------
Table A.I. Summary of the LDGV results. (Continued)
COMMAND
Fuel Reid Vapor Pressure(RVP) (The RVP
was increased from 6.51b/in2 to 1 1 .51b/in2 for a
number of calendar years between 1975 and
2050 with minimum and maximum
temperatures 72°F and 92°F, respectively.
Percent differences were determined relative
to 7.51b/in2)
Mileage Accumulation(increase and decrease
mileage accumulation relative to the
MOBILE6 defaults)
Oxygenated Fuels
(ether concentration from 1% to 2.7%; market
share variations from 5% to 50%)
Oxygenated Fuels
(alcohol concentration from 0.7% to 3.5%;
market share variations from 5% to 50%)
Registration Distribution(decrease newer
vehicle fractions and increase older vehicle
fractions)
Speed VMT (Arterial;
-3% - null low speed vehicle fractions
9% - equal vehicle fractions for all speeds
14% - increase low speed vehicle fraction by
10%
21% - increase low speed vehicle fraction by
20%
29% - increase low speed vehicle fraction by
30%)
Speed VMT (Freeway; reduce fraction of
vehicles from high speeds to lower speeds)
Starts Per Day(change the number of starts
per day from -50% to +50% in increments of
10% for each vehicle type)
Change in Input
min.
max.
min.
max.
min.
max.
min.
max.
min.
max.
min.
max.
min.
max.
min.
max.
6.51b/in2
11.51b/in2
20% decrease
20% increase
5% mkt,
l%ether, 0%
alcohol
50% mkt,
0%ether, 2.7%
alcohol
50% mkt,
0%etiier, 0.7%
alcohol
50% mkt,
0%ether, 3.5%
alcohol
5% age shift
20% age shift
-3% (free-flow/
all day non-rush
hour speeds)
29%(congested
traffic flow,i.e.,
30% more
vehicles at the
lower speeds)
-50% (equal
distribution of
speeds)
10%(most
vehicles at the
higher speeds)
-50%
50%
Change in
Hydrocarbon
emissions
approx. -5%
( 1975-2025)
70%(2025)
to
40%(1975)
(NMHC)
3%(1980)
5%(2005)
1%(2015)
-2%(2020)
(NMHC)
1%(1990)
-2%(2000)
-3%(2005)
2%(2020)
(NMHC)
0%(2005&2020
)
(NMHC)
-2% (2000) to
-2%(2020)
(NMHC)
1% (2000) to
2%(2020)
(NMHC)
Approximately
0% (all years)
(NMHC)
4%(1985) to
25%(2015)
(NMHC)
12%(1975)to
80%(2015)
(NMHC)
-3%(all years)
(NMHC)
32%(1985)to
44%(2050)
(NMHC)
+13%(1975) to
5%(2050)
(NMHC)-
3.5%(1975)to-
1%(2010)
(NMHC)
-17%(2025)
to
-12%(1975)
(NMHC)
17%(2025)
to
12%(1975)
Change in CO
emissions
0%
( 1975-2025)
107%(2025)
to
2%(1975)
-2.5%(1985)
to
-11%(2020)
1%(1980)
to
9%(2020)
Approximately
0% (all years)
-5%(2000) to
-3%(2020)
0.3%(2000) to
2%(2020)
-5%(2000) to
-2.5%(2020)
2%(1980)to
16%(2000)
7%(1975)
52%(1995)
24%(2020)
3% (all years)
-2%(2005) to
+3%(1975)
3%(1975)to
-2%(2005)
< 0% and >-2%
-15%(1975)
to
-11%(2025)
11%(2025)
to
15%(1975)
Change in
Oxides of
Nitrogen
emissions
approx. 0%
( 1975-2025)
5%(2025)
to
0%(1985)
0%(1990)
to
-24%(2020)
1%(1990)
to
22%(2020)
0%
0%
0%
0%
0%(1985) to
14%(2020)
-l%(1980)to
50%(2020)
-l%toO%
(all years)
5%(1975) to
8%(2050)
-l.l%(2050)to
-0.5%(1985)
+1.6%(1985)to
2%(2050)
-13%(1975)
to
-7%(2025)
13%(1975)
to
7%(2025)
48
-------
Table A.I. Summary of the LDGV results. (Continued)
COMMAND
Start Distribution
Sulfur Content (calendar years 1999 and
earlier)
Temperature, Average Daily (standard
temperature cycle and vary average daily
temperature 12Fto 107 F)
Temperature Cycles (keep average daily
temperature a constant and vary the standard
temperature cycle)
Temperature, Hourly (hourly temperatures
using temperature cycle variations: The
percent differences here are for a given hour of
the day and model year. They are not results
which have been averaged over an entire day.
The daily averages tend to lessen the effects.)
Temperature, Average Daily and Humidity
[For each of a set of daily average
temperatures (42, 72, 82, 92, 102, and 107 F)
with a 24 F temperature range (the difference
between the minimum and maximum
temperatures is 24 F) variations of absolute
humidity are made. Emission results are
determined and compared for each of these
average daily temperatures with the absolute
humidity set to 53.7, 75, 98.5, 107, and 149.5
grains/lb. for a range of calendar years.]
Change in Input
compare emissions with default
hourly start fractions to a
constant fraction of starts for
each hour of the day
min.
(300ppm)
max.
(30ppm)
min.
max.
min.
max.
min.
max.
min.
max.
0%
-90%
12F
107F
constant
temperature
(-100%)
34F
temperature
range
(+42%)
constant
temperature
(-100%)
34F
temperature
range
(+42%)
-28%
(54grains/lb)
100%
(150grains/lb)
Change in
Hydrocarbon
emissions
(NMHC)
4.5%(1975)
to
0.4%(2025)
(NMHC)
0%(1975)
to
-0.5%(1999)
(NMHC)
0%(1975)
to
-3.5% (1999)
(NMHC)
10%(2025)
37%(1995)
-13%(1975)
(NMHC)
0%(2025)
24%(1995)
-34%(1975)
(NMHC)
-3%(1975,102F)
-2%(1975,42 F)
14%(2025,102F)
-1%(2025,42F)
-8%(2005,82-F)
(NMHC)
3%(1975,102-F)
2%(1 975,42 F)
3%(2025,102F)
2%(2025,42-F)
6%(2005,82F)
(NMHC)
12% to -13%
(102 F)
(NMHC)
-5%(102F)to
3%(72F)
(NMHC)
-l%toO%(all
temperatures
and all years)
(NMHC)
0%tol%(all
temperatures
and all years)
Change in CO
emissions
3%(1975)
to
0%(2025)
0%(1975)
to
-1%(1999)
0%(1975)
to
-1%(1999)
-6%(1975)
to
216%(2025)
63%(1975)
to
2%(2025)
-11%(1975,102-F)
-2%(1975,42-F)
-0.5%(2025, 102 F)
5%(2025,42F)
5%(2005,42F)
4%(1975,102F)
1%(1975,42F)
-0.3%(2025, 102-F)
-2%(2025,42 F)
-2%(2005,42-F)
-35%((102 F) to
27%(92F)
-ll%(92F)to
7%(72F)
-2% to 0% (all
temperatures
and all years)
0% to 6% (all
temperatures
and all years)
Change in
Oxides of
Nitrogen
emissions
3%(1975)
to
1%(2025)
0%(1975)
to
-1%(1999)
0%(1975)
to
-7%(1999)
49%(1975)
to
19%(2025)
-19%(1975)
to
15%(2025)
5%(1975,102F)
1%(1 975,42 F)
-1.4%(2025,102F)
1%(2025,42F)
-8%(2025,75 F)
-1%(1975,102-F)
-1%(1975,42F)
-1%(2025,102F)
-1%(2025,42-F)
8%(2025,75F)
-24%(102F)
to 11%(92F)
-5%(92 F) to
4%(72F)
6%(2025)
7%(2005)
7%(2000)
7%(1975)
-14%(2025)
-15%(2005)
-15%(2000)
-16%(1975)
49
-------
Table A.2. All Vehicle Summary
COMMAND
Absolute Humidity [Use high and low
humidity values from August morning and
afternoon average relative humidity values
from Atlanta and Tucson (National Weather
Service data).]
Air Conditioning
Altitude
Average Speed ( Arterial roadways)
Average Speed ( Area Wide roadways)
Average Speed (Freeways)
Facility VMT (Add and subtract fraction of
vehicles to/from freeways and arterials:
new freeway + new ramp=(old freeway +
old ramp) + x*old arterial
newramp= 0.08*(new ramp + new freeway)
new freeway=(0.92/0.08) *new ramp
new arterial=(l-x)*old arterial
Fuel Program/Sulfur Content
(calendar years 2000 and later; for default
conventional eastern program reduce sulfur
content by 10%, 20%, and 30%)
Fuel Reid Vapor Pressure(RVP) (The RVP
was increased from 6.51b/in2 to 1 1 .51b/in2 for a
number of calendar years between 1975 and
2050 with minimum and maximum
temperatures 72°F and 92°F, respectively.
Percent differences were determined relative to
7.51b/in2)
Change in Input
-28%
mm. ,- . , ,
(54grams/lb)
100%
max- (149grains/lb)
Differences Due to MOBILE6
Air Conditioning Correction
Emission Differences Between
High Altitude and Low Altitude
min.
max.
min.
max.
min.
max.
min.
max.
min.
max.
min.
max.
lOmph
35mph
65mph
lOmph
35mph
lOmph
35mph
65mph
subtract 40%
from arterials
add 40% to
arterials
-10%
-30%
6.51b/in2
11.51b/in2
Change in
Hydrocarbon
emissions
(NMHC)
approx. 0%
(NMHC)
approx. 0%
(NMHC)
1%(1975)
1%(2005)
0%(2050)
(NMHC)
26%(1975)
10%(1995)
7%(2005)
(VOC)
69%(2000)
75%(2025)
-11%
(VOC)
-28%(1975)
-24%(2025)
(VOC) 72%
(VOC) -10%
(VOC)
75%(1975)
68%(2005)
72%(2025)
-9%
(VOC)
-26%(1975)
-22%(2025)
(NMHC)
-1%(1975)
-0.5%(2020)
(NMHC)
1%(1975)
0%(2007)
(NMHC)
0%(2010)
to
-0.5%(2000)
(NMHC)
-0.05%(2010)
to
-1.4%(2000)
-3%(1985)
to
-6%(2005)
77%(2005)
to
38%(1985)
Change in CO
emissions
-1%
3%(1975)
4%(2000)
1%(2025)
11%(1975)
13%(2005)
4%(2050)
41%(1975)
17%(1995)
10%(2005)
43%(1975)
26%(2000)
32%(2025)
-11%
0%(1975)
17%(2000)
15%(2025)
40%(1975)
23%(2000)
28%(2025)
-4%(1975)
0%(2005)
0%(2025)
39%(1975)
26%(2000)
28%(2025)
-8%
0%(1975)
17%(2000)
13%(2025)
1%(1975)
3%(2025)
-2%(1975)
-3%(2025)
-0.2%(2010)
to
-1.3%(2000)
-0.7%(2010)
to
-4%(2000)
0%
( 1975-2050)
101%(2050)
to
2%(1975)
Change in
Oxides of
Nitrogen
emissions
5%(1975)
3%(2005)
-11%(1975)
-7%(2005)
-11%(2025)
3%(1975)
4%(2005)
8%(2050)
-25%(1975)
-3%(1995)
-1%(2005)
22%(1975)
20%(2000)
32%(2025)
-5%(1975)
-12%(2000)
-8%(2025)
13%(1975)
23%(2000)
17%(2025)
17%(1975)
24%(2025)
-2%
16%(1975)
25%(2000)
21%(2025)
-5%(1975)
0%(2000)
-6%(2025)
10%(1975)
29%(2000)
14%(2025)
1%(1975)
5%(2000)
2%(2020)
-1%(1975)
-5%(2000)
-2%(2020)
-0.4%(2000)
to
-0.5%(2025)
-1%(2000)
to
-2%(2025)
approx. 0%
3%(2050)
to
-0.6%(1985)
50
-------
Table A.2. All Vehicle Summary (Continued)
COMMAND
Mileage Accumulation(increase and decrease
mileage accumulation relative to the
MOBILE6 defaults)
Oxygenated Fuels
(ether concentration from 1% to 2.7%; market
share variations from 5% to 50%)
Oxygenated Fuels
(alcohol concentration from 0.7% to 3.5%;
market share variations from 5% to 50%)
Registration Distribution(decrease newer
vehicle fractions and increase older vehicle
fractions)
Speed VMT (Arterial;
-3% - null low speed vehicle fractions
9% - equal vehicle fractions for all speeds
14% - increase low speed vehicle fraction by
10%
21% - increase low speed vehicle fraction by
20%
29% - increase low speed vehicle fraction by
30%)
Speed VMT (Freeway; reduce fraction of
vehicles from high speeds to lower speeds)
Starts Per Day(change the number of starts
per day from -50% to +50% in increments of
10% for each vehicle type)
Start Distribution
Change in Input
min.
max.
min.
max.
min.
max.
min.
max.
min.
max.
min.
max.
min.
max.
20% decrease
20% increase
5%mkt,
l%ether, 0%
alcohol
50%mkt,
0%ether, 2.7%
alcohol
50%mkt,
0%ether, 0.7%
alcohol
50%mkt,
0%ether, 3.5%
alcohol
5% age shift
20% age shift
-3% (free-flow/
all day non-rush
hour speeds)
29%(congested
traffic flow ;i.e.,
30% of rush
hour "free-
flow" vehicles
at the lower
speeds)
-50% (equal
distribution of
speeds)
10%(most
vehicles at the
higher speeds)
-50%
50%
compare emissions with default
hourly start fractions to a
constant fraction of starts for
each hour of the day
Change in
Hydrocarbon
emissions
(NMHC)
3%(1980)
4%(2005)
3%(2015)
0.2%(2020)
(NMHC)
1%(1990)
-1%(2000)
1%(2005)
3%(2020)
(NMHC)
approx. 0%
(NMHC)
-2% (2000)to
-3%(2020)
(NMHC)
approx. 1%
(2000)to (2020)
(NMHC)
-0.5% (2000)to -
1%(2020)
(NMHC)
5%(1985) to
31%(2015)
(NMHC)
13%(1975)to
74%(2015)
(NMHC)
-3%
(NMHC)
35%(1975)
33%(1985)
39%(2050)
(NMHC)
12%(1975)
10%(2020)
11%(2050)
(NMHC)
-4%(1975)
-3%(1985)
-4%(2050)
(NMHC)
-17%(2025)
to
-13%(1975)
(NMHC)
17%(2025)
to
14%(1975)
(NMHC)
0%(1975)
to
3%(2025)
Change in CO
emissions
-1.7%(1985)
to
-7.9%(2020)
3%(1990)
to
11%(2020)
approx. 0%
-5%(2000) to
-3%(2020)
<1%
(2000) to (2020)
-5%(2000) to
-2%(2020)
3%(1980)to
21%(2000)
9%(1975)
47%(1995)
22%(2020)
approx. -1%
21%(1975)
13%(2005)
15%(2020)
+3%(1975)
-1%(2000)
0%(2050)
-3%(1975)
-2%(1995)
-1%(2020)
-16%(1975)
to
-13%(2025)
14%(2025)
to
15%(1975)
1%(1975)
to
3%(2025)
Change in
Oxides of
Nitrogen
emissions
3%(1990)
to
-12%(2020)
-2%(1980)
to
13%(2020)
0%
0%
0%
0%
1%(1985) to
12%(2020)
1%(1980) to
38%(2020)
-3% to -0.5%
5%(1975) to
8%(2050)
0%(1975)
-1%(1995)
-2%(2005)
0%(2050)
approx. -1%
-10%(1975)
to
-7%(2025)
10%(1975)
to
7%(2025)
2%(1975)
to
1%(2025)
51
-------
Table A.2. All Vehicle Summary (Continued)
COMMAND
Sulfur Content (calendar years 1999 and
earlier)
Temperature, Average Daily (standard
temperature cycle and vary average daily
temperature 12 to 1 07' F)
Temperature Cycles (keep average
temperature a constant and vary the standard
temperature cycle)
Temperature, Average Daily and Humidity
[For each of a set of daily average
temperatures (42, 72, 82, 92, 102, and 107' F)
with a 24* F temperature range (the difference
between the minimum and maximum
temperatures is 24' F) variations of absolute
humidity are made. Emissions results are
determined and compared for each of these
average daily temperatures with the absolute
humidity set to 53.7, 75, 98.5, 107, and 149.5
grains/lb.]
Change in Input
min.
max.
min.
max.
min.
max.
min.
max.
10%
-90%
12° F
107° F
constant
temperature
(-100%)
34° F
temperature
range
(+42%)
-28%
(54grains/lb)
100%
(150grains/lb)
Change in
Hydrocarbon
emissions
(NMHC)-0.2%
(1999) to
0%(1975)
(NMHC)-4%
( 1999) to 0%
(1975)
17%(2025);
34%(1995)
-6%(1975)
11%(2025)
26%(1995)
31%(1975
(NMHC)
-3%(1975,42T)
-2%(1975,102T)
-8%(2000,82T)
1%(2025,42T)
3%(2025,102T)
1%(1975,42T)
2%(1 975,102 T)
6%(2005,82T)
1%(2025,42T)
3%(2025,102T)
(NMHC)
<0% and
>-l%(all
temperatures
and all years)
(NMHC)
>0% and <1%
(all
temperatures
and all years)
Change in CO
emissions
-14%(1999)to
0%(1975)
0.8%(1999) to
0% (1975)
0%(1975)to
162%(2025)
56%(1975)to
3%(2025)
-11%(1975,
102T)
-1%(1 975,42 T)
6%(2025,42 T)
-1%(2025,102T)
0%(1975,42T)
5%(1 975,72 T)
3%(1975,102T)
-2%(2025,42T)
0%(2025,102T)
-l%(all
temperatures
and all years)
<4% and
>0%(all
temperatures
and all years)
Change in
Oxides of
Nitrogen
emissions
3%(1999)
toO%(1975
0.3%(1999)to
0%(1975)
41%(1975)to
22%(2025)
-15%(1975)
to7%(2025)
1%(1975,42°F)
4%(1975,102°F)
-1%(2025,102°F)
1%(1975,82°F)
to
-1%(2025,72°F)
5%(2025)
3%(2005)
3%(2000)
5%(1975)
-12%(2025)
-7%(2005)
-6%(2000)
-12%(1975)
52
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Table A.3. Affects of the relative proportion Heavy and Light Duty Trucks (VMT MIX
command) on emissions from Heavy and Light Duty Vehicles
COMMAND
VMT Mix (Effects on Light-Duty Tracks
Emissions Only)
(The vehicle miles traveled fractions for light-
duty tracks 2 were increased and decreased
while holding the total proportion of vehicle
miles traveled by all light-duty tracks constant
and equal to the MOBILE6 default values for
calendar years 1975, 2000, 2005, 2007, and
2020)
VMT Mix (Effects on Heavy-Duty Track
Emissions Only)
(The vehicle miles traveled fractions for
heavy-duty vehicles were increased and
decreased while holding the total proportion of
vehicle miles traveled by all heavy-duty
vehicles constant and equal to the MOBILE6
default values for calendar years 1975, 2000,
2005, 2007, and 2020)
Change in Input
Mill
Max.
Min.
Max.
all LOT vehicle
miles traveled
fractions equal
(approx. a 55%
decrease in LDT2
fractions)
increase vehicle
miles traveled
fractions for
LDT2 by 20%
all HDV vehicle
miles traveled
fractions equal
(approx. a 60%
decrease in HD2B
and HD8B
fractions)
increase vehicle
miles traveled
fractions for
HDV2B and
HDV8Bby20%
Change in
Hydrocarbon
emissions
(NMHC)
LDGT
8%(1975)
13%(2020)
LDDT
0%(1975)
-21%(2000)
0%(2020)
(NMHC)
LDGT
-5%(1975)
-2%(2000)
-3%(2020)
LDDT
0%(1975)
8%(2000)
0%(2020)
(NMHC)
HDGV
15%(1975)
37%(2000)
31%(2020)
HDDV
-10%(1975)
-20%(2000)
-15%(2020)
/XT\ /TTU/~1\
(NJVlrlC)
HDGV
0%(1975)
-6%(2000)
-5%(2020)
HDDV
0%(1975)
4%(2000)
3%(2020)
Change in CO
emissions
LDGT
5%(1975)
12%(2000)
5%(2020)
LDDT
0%(1975)
-19%(2000)
0%(2020)
LDGT
-3%(1975)
-1%(2020)
LDDT
0%(1975)
8%(2000)
0%(2020)
HDGV
19%(1975)
49%(2000)
15%(2020)
HDDV
-8%(1975)
-28%92000)
-17%(2020)
HDGV
0%(1975)
-8%(2000)
-2%(2020)
HDDV
0%(1975)
6%(2000)
4%(2020)
Change in
Oxides of
Nitrogen
emissions
LDGT
4%(1975)
5%(2000)
18%(2020)
LDDT
0%(1975)
4%(2000)
0%(2020)
T nrrr
L-,U^J 1
TO/ f \ Q"7^~\
-J%(19/j)
-1%(2000)
-3%(2020)
LDDT
0%(1975)
40/ fr)f\f\f\\
%(2000)
0%(2020)
HDGV
19%(1975)
11%(2020)
HDDV
-7%(1975)
-26%(2000)
-17%(2020)
HDGV
0%(1975)
-2%(2020)
HDDV
0%(1975)
5%(2000)
4%(2020)
53
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Table A.4. Summary of LDGV results with input parameters which have minor (small)
effects on emissions (changes which are less than 5%).
COMMAND
Absolute Humidity [Use high and low
humidity values from August morning and
afternoon average relative humidity values
from Atlanta and Tucson (National Weather
Service data).]
Air Conditioning
Average Daily Temperature and Humidity
[For each of a set of daily average
temperatures (42, 72, 82, 92, 102, and 107 F)
with a 24 F temperature range (the difference
between the minimum and maximum
temperatures is 24 F) variations of absolute
humidity are made. Emission results are
determined and compared for each of these
average daily temperatures with the absolute
humidity set to 53.7, 75, 98.5, 107, and 149.5
grains/lb. for a range of calendar years.]
Facility VMT [Add and subtract fraction of
vehicles to/from freeways and arterials:
New freeway + new ramp=(old freeway +
old ramp) + x*old arterial
Newramp=0.08*(new ramp + new freeway)
new freeway=(0.92/0.08) * new ramp
New arterial=(l-x)*old arterial ]
Fuel Program/Sulfur Content
(calendar years 2000 and later; for default
conventional eastern program reduce sulfur
content by 10%, 20%, and 30%)
Hourly Temperature (hourly temperatures
using temperature cycle variations: The
percent differences here are for a given hour of
the day and model year. They are not results
which have been averaged over an entire day.
The daily averages tend to lessen the effects.)
Mileage Accumulation(increase and decrease
mileage accumulation relative to the
MOBILE6 defaults)
Change in Input
-28%
mm. /r . ... .
(54grams/lb)
100%
max' (149grains/lb)
Emissions Differences with Air
Conditioning Correction
Applied and Not Applied
min.
max.
min.
max.
min.
max.
min.
max.
min.
max.
-28%
(54grains/lb)
100%
(150grains/lb)
subtract 40%
from arterials
add 40% to
arterials
-10%
-30%
constant
temperature
(-100%)
34F
temperature
range
(+42%)
20% decrease
20% increase
Change in
Hydrocarbon
emissions
(NMHC)
Idgv running
<-!%
Idgv
total:<0.5%
(NMHC)
Idgv
running: 4%
Idgv
total:<0.5%
2%(1975)
2%(2005)
0%(2025)
(NMHC)
-l%toO%(all
temperatures
and all years)
(NMHC)
0%tol%(all
temperatures
and all years)
(NMHC)
-1%(1975)
0%(2000)
(NMHC)
1%(1975)
0%(2007)
(NMHC)
-0.5% (2000)
to
0%(2025)
(NMHC)
-1.5%(2000)
to
-0.5%(2025)
(NMHC)
12% to -13%
(102 F)
(NMHC)
-5%(102F)to
3%(72F)
(NMHC)
3%(1980)
5%(2005)
1%(2015)
-2%(2020)
(NMHC)
1%(1990)
-2%(2000)
-3%(2005)
2%(2020)
Change in CO
emissions
Idgv running
-1.9%(2000)
to
-0.6%(2025)
Idgv running
2.3%(2025)
to
8.4%(2000)
Medium Level
-2% to 0% (all
temperatures
and all years)
0% to 6% (all
temperatures
and all years)
2%(1975)
4%(2000)
3%(2020)
-1%(1975)
-4%(2005)
-3%(2020)
-1.6%(2000)
to
-0.6%(2025)
-4.7%(2000)
to
-2%(2025)
-35%((102 F) to
27%(92F)
-ll%(92F)to
7%(72F)
Medium Level
Medium Level
Change in
Oxides of
Nitrogen
emissions
Medium Level
Medium Level
Medium Level
Medium Level
Medium Level
1%(1975)
5%(2000)
2%(2020)
-1%(1975)
-5%(2000)
-2%(2020)
-0.7%(2000)
to
0%(2025)
-2.2%(2000)
to
-3.7%(2025)
-24%(102F)
toll%(92F)
-5%(92 F) to
4%(72F)
Medium Level
Medium Level
54
-------
Table A.4. Summary of LDGV results with input parameters which have minor (small)
effects on emissions (changes which are less than 5%). (Continued)
COMMAND
Oxygenated Fuels
(ether concentration from 1% to 2.7%; market
share variations from 5% to 50%)
Oxygenated Fuels
(alcohol concentration from 0.7% to 3.5%;
market share variations from 5% to 50%)
Speed VMT (Arterial;
-3% - null low speed vehicle fractions
9% - equal vehicle fractions for all speeds
14% - increase low speed vehicle fraction by
10%
21% - increase low speed vehicle fraction by
20%
29% - increase low speed vehicle fraction by
30%)
Speed VMT (Freeway; reduce fraction of
vehicles from high speeds to lower speeds)
Start Distribution
Sulfur Content (calendar years 1999 and
earlier)
Temperature Cycles (keep average daily
temperature a constant and vary the standard
temperature cycle)
Change in Input
min.
max.
min.
max.
min.
max.
min.
max.
5% mkt,
l%ether, 0%
alcohol
50% mkt,
0%ether, 2.7%
alcohol
50% mkt,
0%ether, 0.7%
alcohol
50% mkt,
0%etiier, 3.5%
alcohol
-3% (free-flow/
all day non-rush
hour speeds)
29%(congested
traffic flow,i.e.,
30% more
vehicles at the
lower speeds)
-50% (equal
distribution of
speeds)
10%(most
vehicles at the
higher speeds)
Compare emissions with default
hourly start fractions to a
constant fraction of starts for
each hour of the day
min.
(300ppm)
max.
(30ppm)
min.
max.
0%
-90%
Constant
temperature
(-100%)
34F
temperature
range
(+42%)
Change in
Hydrocarbon
emissions
(NMHC)
0%(2005&
2020)
(NMHC)
-2% (2000) to
-2%(2020)
(NMHC)
1% (2000) to
2%(2020)
(NMHC)
Approximately
0% (all years)
High Level
High Level
Medium Level
(NMHC)-
3.5%(1975)to-
1%(2010)
(NMHC)
4.5%(1975)
to
0.4%(2025)
(NMHC)
0%(1975)
to
-0.5%(1999)
(NMHC)
0%(1975)
to
-3.5% (1999)
(NMHC)
-3%(1975,102-F)
-2%(1975,42 F)
14%(2025,102F)
-1%(2025,42-F)
-8%(2005,82 F)
(NMHC)
3%(1975,102F)
2%(1975,42-F)
3%(2025,102F)
2%(2025,42F)
6%(2005,82F)
Change in CO
emissions
Approximately
0% (all years)
-5%(2000) to
-3%(2020)
0.3%(2000) to
2%(2020)
-5%(2000) to
-2.5%(2020)
3% (all years)
-2%(2005) to
+3%(1975)
3%(1975)to
-2%(2005)
< 0% and >-2%
3%(1975)
to
0%(2025)
0%(1975)
to
-1%(1999)
0%(1975)
to
-1%(1999)
-11%(1975,102-F)
-2%(1 975,42 F)
-0.5%(2025, 102-F)
5%(2025,42-F)
5%(2005,42-F)
4%(1975,102F)
1%(1975,42F)
-0.3%(2025, 102 F)
-2%(2025,42-F)
-2%(2005,42-F)
Change in
Oxides of
Nitrogen
emissions
0%
0%
0%
0%
-l%toO%
(all years)
5%(1975) to
8%(2050)
-l.l%(2050)to
-0.5%(1985)
+1.6%(1985)to
2%(2050)
3%(1975)
to
1%(2025)
0%(1975)
to
-1%(1999)
0%(1975)
to
-7%(1999)
5%(1975,102F)
1%(1 975,42 F)
-1.4%(2025,102-F)
1%(2025,42-F)
-8%(2025,75-F)
-1%(1975,102-F)
-1%(1975,42F)
-1%(2025,102F)
-1%(2025,42F)
8%(2025,75F)
55
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REFERENCES
1MOBILE6, (http://www.epa.gov/otaq/m6.htm)
r\
Clean Air Act, (http://www.epa.gov/oar/oaq caa.html)
3MOBILE5, (http://www.epa.gov/otaq/m5.htm)
4 Technical Guidance on the Use ofMOBILE6for Inventory Preparation, Jan. 2002,
(http://www.epa.gov/otaq/m6.htm#m60)
5 User's Guide to MOBILE6.0 Mobile Source Emission Factor Model, USEPA Report #EPA420-R-02-
001, (http://www. epa.gov/otaq/m6.htm#m60)
6 Brzezinski, Hart, and Enns, Final Facility Specific Speed Correction Factors, EPA Report #EPA420-
R-01-060, Nov. 2001, (http://www.epa.gov/otaq/models/mobile6/r01060.pdf)
7 Gammariello and Long, Development of Unified Correction Cycles, Sixth CRC On-Road Vehicles
Workshop, March 1996, (http://www.arb.ca.gov/msei/on-road/downloads/pubs/ucc crc5.pdf)
o
Development of Methodology for Estimating VMT Weighting by Facility Type, EPA Report #EPA420-
R-01-009, April 2001, (http://www.epa.gov/otaq/models/mobile6/r01009.pdf)
9Exhaust Emissions Temperature Correction Factors for MOBILE6: Adjustments for Engine Start and
Running LA4 Emissions for Gasoline Vehicles, USEPA Report # EPA420-R-01-029, April 2001,
(http://www.epa.gov/otaq/models/mobile6/r01029.pdf)
10 Code of Federal Regulations (CFR), Title 40, Part 86, U.S. Government Printing Office
uPita, E.G., Air Conditioning Principles and Systems: an Energy Approach, Wiley (1981).
1 9
Heinsohn, R.J., Industrial Ventilation Engineering Principles, Wiley (1991).
13Plint, M. and Matyr, A., Engine Testing : Theory and Practice, 2nd edition, SAE International (1999)
56
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