§ 1066.1005
Symbols, abbreviations, acronyms, and units of measure.
The procedures in this part generally follow either the International System of Units (SI) or the United States customary units, as detailed in NIST Special Publication 811, which we incorporate by reference in § 1066.1010. See 40 CFR 1065.20 for specific provisions related to these conventions. This section summarizes the way we use symbols, units of measure, and other abbreviations.

(a) Symbols for quantities. This part uses the following symbols and units of measure for various quantities:

Symbol
Quantity
Unit
Unit symbol
Unit in terms of SI base units
a
atomic hydrogen to carbon ratio
mole per mole
mol/mol
1

A
area
square meter
m2
m2

A
vehicle frictional load
pound force or newton
lbf or N
kg · s−2

A
m
calculated vehicle frictional load
pound force or newton
lbf or N
kg · s−2

a
0
intercept of least squares regression

a
1
slope of least squares regression

a
acceleration
feet per second squared or meters per second squared
ft/s2 or m/s2
m · s−2

B
vehicle load from drag and rolling resistance
pound force per mile per hour or newton second per meter
lbf/mph or N · s/m
kg · s−1 · m−1

b
ratio of diameters
meter per meter
m/m
1

b
atomic oxygen to carbon ratio
mole per mole
mol/mol
1

c
conversion factor

C
vehicle-specific aerodynamic effects
pound force per mile per hour squared or newton second squared per meter squared
lbf/mph2 or N · s2/m2
kg · m−2

C
#
number of carbon atoms in a molecule
C
#
number of carbon atoms in a molecule
C
#

C
d
discharge coefficient

C
D
A
drag area
meter squared
m2
m2

C
f
flow coefficient

C
p
heat capacity at constant pressure
joule per kelvin
J/K
J · K−1

C
v
heat capacity at constant volume
joule per kelvin
J/K
J · K−1

d
diameter
meters
m
m

D
distance
miles or meters
mi or m
m

D
slope correlation
pound force per mile per hour squared or newton second squared per meter squared
lbf/mph2 or N · s2/m2
kg · m−2

DF
dilution factor
1

e
mass weighted emission result
grams/mile
g/mi

F
force
pound force or newton
lbf or N
kg · s−2

f
frequency
hertz
Hz
s−1

f
n
angular speed (shaft)
revolutions per minute
r/min
2 · π · 60−1 · m · m−1 · s−1

FC
friction compensation error
horsepower or watt
W
kg · m2 · s−3

FR
Road-load force
pound force or newton
lbf or N
kg · s−2

g
gravitational acceleration
meters per second squared
m/s2
m · s−2

g
ratio of specific heats
(joule per kilogram kelvin) per (joule per kilogram kelvin)
(J/(kg · K))/(J/(kg · K))
1

H
ambient humidity
grams water vapor per kilogram dry air
g H2O vapor/kg dry air
g H2O vapor/kg dry air

Δh
change in height
meters
m
m

I
inertia
pound mass or kilogram
lbm or kg
kg

I
current
ampere
A
A

i
indexing variable

IR
inertia work rating

K
correction factor
1

K
v
calibration coefficient
m4 · s · K0.5/kg
m4 · s · K0.5 · kg−1

m
viscosity, dynamic
pascal second
Pa · s
m−1 · kg · s−1

M
molar mass
gram per mole
g/mol
10−3 · kg · mol−1

M
e
effective mass
kilogram
kg
kg

m
mass
pound mass or kilogram
lbm or kg
kg

N
total number in series

n
total number of pulses in a series

p
pressure
pascal
Pa
m−1 · kg · s−2

Δp
differential static pressure
pascal
Pa
m−1 · kg · s−2

p
d
saturated vapor pressure at ambient dry bulb temperature
kilopascal
kPa
m−1 · kg · s−2

PF
penetration fraction

Q
flow
cubic feet or cubic meter
ft3 or m3
m3

Q
flow rate
cubic feet per minute or cubic meter per second
ft3/min or m3/s
m3/s

r
mass density
kilogram per cubic meter
kg/m3
kg · m−3

R
dynamometer roll revolutions
revolutions per minute
rpm
2 · π · 60−1 · m · m−1 · s−1

r
ratio of pressures
pascal per pascal
Pa/Pa
1

r 2
coefficient of determination

Re
#
Reynolds number

RF
response factor

RH
relative humidity

S
Sutherland constant
kelvin
K
K

SEE
standard estimate of error

SG
specific gravity

Δs
distance traveled during measurement interval
meters
m
m

T
absolute temperature
kelvin
K
K

T
Celsius temperature
degree Celsius
°C
K − 273.15

T
torque (moment of force)
newton meter
N · m
m2 · kg · s−2

t
time
second
s
s

Δt
time interval, period, 1/frequency
second
s
s

U
voltage
volt
V
m2 · kg · s−3 · A−1

v
speed
miles per hour or meters per second
mph or m/s
m · s−1

V
volume
cubic meter
m3
m3

VP
volume percent

x
concentration of emission over a test interval
part per million
ppm

y
generic variable

Z
compressibility factor
Z
compressibility factor
Z

(b) Symbols for chemical species. This part uses the following symbols for chemical species and exhaust constituents:

Symbol
Species
CH4
methane.

CH3OH
methanol.

CH2O
formaldehyde.

C2H4O
acetaldehyde.

C2H5OH
ethanol.

C2H6
ethane.

C3H7OH
propanol.

C3H8
propane.

C4H10
butane.

C5H12
pentane.

CO
carbon monoxide.

CO2
carbon dioxide.

H2O
water.

HC
hydrocarbon.

N2
molecular nitrogen.

NMHC
nonmethane hydrocarbon.

NMHCE
nonmethane hydrocarbon equivalent.

NMOG
nonmethane organic gas.

NO
nitric oxide.

NO2
nitrogen dioxide.

NOX
oxides of nitrogen.

N2O
nitrous oxide.

O2
molecular oxygen.

OHC
oxygenated hydrocarbon.

PM
particulate matter.

THC
total hydrocarbon.

THCE
total hydrocarbon equivalent.

(c) Superscripts. This part uses the following superscripts to define a quantity:

Superscript
Quantity
overbar (such as y)
arithmetic mean.

overdot (such as y
)
quantity per unit time.

(d) Subscripts. This part uses the following subscripts to define a quantity:

Subscript
Quantity
0
reference.

abs
absolute quantity.

AC17
air conditioning 2017 test interval.

act
actual or measured condition.

actint
actual or measured condition over the speed interval.

adj
adjusted.

air
air, dry.

atmos
atmospheric.

b
base.

bkgnd
background.

c
cold.

comp
composite.

cor
corrected.

cs
cold stabilized.

ct
cold transient.

cUDDS
cold-start UDDS.

D
driven.

dew
dewpoint.

dexh
dilute exhaust quantity.

dil
dilute.

e
effective.

emission
emission specie.

error
error.

EtOH
ethanol.

exh
raw exhaust quantity.

exp
expected quantity.

fil
filter.

final
final.

flow
flow measurement device type.

gas
gaseous.

h
hot.

HFET
highway fuel economy test.

hs
hot stabilized.

ht
hot transient.

hUDDS
hot-start UDDS.

i
an individual of a series.

ID
driven inertia.

in
inlet.

int
intake.

init
initial quantity, typically before an emission test.

IT
target inertia.

liq
liquid.

max
the maximum (i.e. peak) value expected at the standard over a test interval; not the maximum of an instrument range.

meas
measured quantity.

mix
dilute exhaust gas mixture.

out
outlet.

PM
particulate matter.

record
record.

ref
reference quantity.

rev
revolution.

roll
dynamometer roll.

s
settling.

s
slip.

s
stabilized.

sat
saturated condition.

SC03
air conditioning driving schedule.

span
span quantity.

sda
secondary dilution air.

std
standard conditions.

T
target.

t
throat.

test
test quantity.

uncor
uncorrected quantity.

w
weighted.

zero
zero quantity.

(e) Other acronyms and abbreviations. This part uses the following additional abbreviations and acronyms:

A/C
air conditioning.

AC17
air conditioning 2017 test interval.

ALVW
adjusted loaded vehicle weight.

ASME
American Society of Mechanical Engineers.

CFR
Code of Federal Regulations.

CFV
critical-flow venturi.

CNG
compressed natural gas.

CVS
constant-volume sampler.

EPA
Environmental Protection Agency.

ETW
equivalent test weight.

EV
electric vehicle.

FID
flame-ionization detector.

FTP
Federal test procedure.

GC
gas chromatograph.

GEM
greenhouse gas emissions model.

GHG
greenhouse gas (including CO2, N2O, and CH4).

GPS
global positioning system.

GVWR
gross vehicle weight rating.

HEV
hybrid electric vehicle, including plug-in hybrid electric vehicles.

HFET
highway fuel economy test.

HLDT
heavy light-duty truck.

HPLC
high pressure liquid chromatography.

IBR
incorporated by reference.

LA-92
Los Angeles 1992 driving schedule.

MDPV
medium-duty passenger vehicle.

NIST
National Institute for Standards and Technology.

NMC
nonmethane cutter.

PDP
positive-displacement pump.

PHEV
plug-in hybrid electric vehicle.

PM
particulate matter.

RESS
rechargeable energy storage system.

ppm
parts per million.

SAE
Society of Automotive Engineers.

SC03
air conditioning driving schedule.

SEA
selective enforcement audit.

SFTP
supplemental federal test procedure.

SI
International System of Units.

SSV
subsonic venturi.

UDDS
urban dynamometer driving schedule.

US06
aggressive driving schedule.

U.S.C.
United States Code.

WWV
NIST radio station call sign.

(f) This part uses the following densities of chemical species:

Symbol
Quantity 1 2
g/m3
g/ft3
r
CH4
density of methane
666.905
18.8847

r
CH3OH
density of methanol
1332.02
37.7185

r
C2H5OH
C1-equivalent density of ethanol
957.559
27.1151

r
C2H4O
C1-equivalent density of acetaldehyde
915.658
25.9285

r
C3H8
density of propane
611.035
17.3026

r
C3H7OH
C1-equivalent density of propanol
832.74
23.5806

r
CO
density of carbon monoxide
1164.41
32.9725

r
CO2
density of carbon dioxide
1829.53
51.8064

r
HC-gas
effective density of hydrocarbon—gaseous fuel 3
(see 3)
(see 3)

r
CH2O
density of formaldehyde
1248.21
35.3455

r
HC-liq
effective density of hydrocarbon—liquid fuel 4
576.816
16.3336

r
NMHC-gas
effective density of nonmethane hydrocarbon—gaseous fuel 3
(see 3)
(see 3)

r
NMHC-liq
effective density of nonmethane hydrocarbon—liquid fuel 4
576.816
16.3336

r
NMHCE-gas
effective density of nonmethane equivalent hydrocarbon—gaseous fuel 3
(see 3)
(see 3)

r
NMHCE-liq
effective density of nonmethane equivalent hydrocarbon—liquid fuel 4
576.816
16.3336

r
NOx
effective density of oxides of nitrogen 5
1912.5
54.156

r
N2O
density of nitrous oxide
1829.66
51.8103

r
THC-liq
effective density of total hydrocarbon—liquid fuel 4
576.816
16.3336

r
THCE-liq
effective density of total equivalent hydrocarbon—liquid fuel 4
576.816
16.3336

1 Densities are given at 20 °C and 101.325 kPa.
2 Densities for all hydrocarbon containing quantities are given in g/m3-carbon atom and g/ft3-carbon atom.
3 The effective density for natural gas fuel and liquefied petroleum gas fuel are defined by an atomic hydrogen-to-carbon ratio, a, of the hydrocarbon components of the test fuel. r
HCgas = 41.57 · (12.011 + (a · 1.008)).
4 The effective density for gasoline and diesel fuel are defined by an atomic hydrogen-to-carbon ratio, a, of 1.85.
5 The effective density of NOX is defined by the molar mass of nitrogen dioxide, NO2.
(g) Constants. (1) This part uses the following constants for the composition of dry air:

Symbol
Quantity
mol/mol
x
Arair
amount of argon in dry air
0.00934

x
CO2air
amount of carbon dioxide in dry air
0.000375

x
N2air
amount of nitrogen in dry air
0.78084

x
O2air
amount of oxygen in dry air
0.209445

(2) This part uses the following molar masses or effective molar masses of chemical species:

Symbol
Quantity
g/mol(10−3 · kg · mol−1)
M
air
molar mass of dry air 1
28.96559

M
H2O
molar mass of water
18.01528

1 See paragraph (g)(1) of this section for the composition of dry air.
(3) This part uses the following molar gas constant for ideal gases:

Symbol
Quantity
J/(mol · K)(m2 · kg · s−2 · mol−1 · K−1)
R
molar gas constant
8.314472

(h) Prefixes. This part uses the following prefixes to define a quantity:

Symbol
Quantity
Value
µ
micro
10−6

m
milli
10−3

c
centi
10−2

k
kilo
103

M
mega
106

n
nano
10−9