§1066.1005 Symbols, abbreviations, acronyms, and units of measure.

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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
α	atomic hydrogen to carbon ratio	mole per mole	mol/mol	1.
A	area	square meter	m	m.
A	vehicle frictional load	pound force or newton	lbf or N	m·kg·s⁻ .
a_g	acceleration of Earth's gravity	meters per second squared	m/s	m·s⁻ .
A_m	calculated vehicle frictional load	pound force or newton	lbf or N	m·kg·s⁻ .
a₀	intercept of least squares regression.
a₁	slope of least squares regression.
a	acceleration	feet per second squared or meters per second squared	ft/s or m/s	m·s^- .
B	vehicle load from drag and rolling resistance	pound force per mile per hour or newton second per meter	lbf/(mi/hr) or N·s/m	kg·s^- .
β	ratio of diameters	meter per meter	m/m	1.
β	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/(mi/hr) or N·s/m	m^- ·kg.
C_#	number of carbon atoms in a molecule	C_#	number of carbon atoms in a molecule	C_#.
C_d	discharge coefficient.
C_dA	drag area	meter squared	m	m.
C_f	flow coefficient.
C_p	heat capacity at constant pressure	joule per kelvin	J/K	m·kg·s ·K .
C_v	heat capacity at constant volume	joule per kelvin	J/K	m·kg·s ·K .
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/(mi/hr) or N·s/m	m ·kg.
DF	dilution factor.			1.
e	mass weighted emission result	grams/mile	g/mi.
F	force	pound force or newton	lbf or N	kg·s .
ƒ	frequency	hertz	Hz	s .
ƒn	angular speed (shaft)	revolutions per minute	r/min	π·30·s⁻ .
FC	friction compensation error	horsepower or watt	W	m·kg·s .
FR	road-load force	pound force or newton	lbf or N	kg·s⁻ .
γ	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
K_v	calibration coefficient		m·s·K/kg	m·kg⁻ ·s·K.
μ	viscosity, dynamic	pascal second	Pa·s	m⁻ ·kg·s⁻ .
M	molar mass	gram per mole	g/mol	10-3·kg·mol .
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 ·kg·s .
Δp	differential static pressure	pascal	Pa	m ·kg·s .
p_d	saturated vapor pressure at ambient dry bulb temperature	kilopascal	kPa	m ·kg·s .
PF	penetration fraction.
ρ	mass density	kilogram per cubic meter	kg/m	m ·kg.
R	dynamometer roll revolutions	revolutions per minute	rpm	π·30 ·s .
r	ratio of pressures	pascal per pascal	Pa/Pa	1.
r	coefficient of determination.
Re_#	Reynolds number.
RF	response factor.
RH	relative humidity.
S	Sutherland constant	kelvin	K	K.
SEE	standard error of the estimate.
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	m·kg·s .
t	time	hour or second	hr or s	s.
Δt	time interval, period, 1/frequency	second	s	s.
U	voltage	volt	V	m·kg·s ·A .
v	speed	miles per hour or meters per second	mi/hr or m/s	m·s .
V	volume	cubic meter	m	m.
V	flow volume rate	cubic feet per minute or cubic meter per second	ft/min or m/s	m·/s .
VP	volume percent.
x	concentration of emission over a test interval	part per million	ppm.
y	generic variable.
Z	compressibility factor.

Symbol	Species
CH ₄	methane.
CH ₃ OH	methanol.
CH ₂ O	formaldehyde.
C ₂ H ₄ O	acetaldehyde.
C ₂ H ₅ OH	ethanol.
C ₂ H ₆	ethane.
C ₃ H ₇ OH	propanol.
C ₃ H ₈	propane.
C ₄ H ₁₀	butane.
C ₅ H ₁₂	pentane.
CO	carbon monoxide.
CO ₂	carbon dioxide.
H ₂ O	water.
HC	hydrocarbon.
N ₂	molecular nitrogen.
NMHC	nonmethane hydrocarbon.
NMHCE	nonmethane hydrocarbon equivalent.
NMOG	nonmethane organic gas.
NO	nitric oxide.
NO ₂	nitrogen dioxide.
NO _X	oxides of nitrogen.
N ₂ O	nitrous oxide.
O ₂	molecular oxygen.
OHC	oxygenated hydrocarbon.
PM	particulate matter.
THC	total hydrocarbon.
THCE	total hydrocarbon equivalent.

Superscript	Meaning
overbar (such as y )	arithmetic mean.
overdot (such as y )	quantity per unit time.

Subscript	Meaning
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.

Acronym	Meaning
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.

Symbol	Quantity ^{1 2}	g/m	g/ft
ρ_CH4	density of methane	666.905	18.8847
ρ_CH3OH	density of methanol	1332.02	37.7185
ρ_C2H5OH	C₁-equivalent density of ethanol	957.559	27.1151
ρ_C2H4O	C₁-equivalent density of acetaldehyde	915.658	25.9285
ρ_C3H8	density of propane	611.035	17.3026
ρ_C3H7OH	C₁-equivalent density of propanol	832.74	23.5806
ρ_CO	density of carbon monoxide	1164.41	32.9725
ρ_CO2	density of carbon dioxide	1829.53	51.8064
ρ_HC-gas	effective density of hydrocarbon—gaseous fuel	(see 3)	(see 3)
ρ_CH2O	density of formaldehyde	1248.21	35.3455
ρ_HC-liq	effective density of hydrocarbon—liquid fuel	576.816	16.3336
ρ_NMHC-gas	effective density of nonmethane hydrocarbon—gaseous fuel	(see 3)	(see 3)
ρ_NMHC-liq	effective density of nonmethane hydrocarbon—liquid fuel	576.816	16.3336
ρ_NMHCE-gas	effective density of nonmethane equivalent hydrocarbon—gaseous fuel	(see 3)	(see 3)
ρ_NMHCE-liq	effective density of nonmethane equivalent hydrocarbon—liquid fuel	576.816	16.3336
ρ_NOx	effective density of oxides of nitrogen	1912.5	54.156
ρ_N2O	density of nitrous oxide	1829.66	51.8103
ρ_THC-liq	effective density of total hydrocarbon—liquid fuel	576.816	16.3336
ρ_THCE-liq	effective density of total equivalent hydrocarbon—liquid fuel	576.816	16.3336
Densities are given at 20 °C and 101.325 kPa.
Densities for all hydrocarbon containing quantities are given in g/m-carbon atom and g/ft-carbon atom.
The effective density for natural gas fuel and liquefied petroleum gas fuel are defined by an atomic hydrogen-to-carbon ratio, α, of the hydrocarbon components of the test fuel. ρ_HCgas = 41.57·(12.011 + (α·1.008)).
The effective density for gasoline and diesel fuel are defined by an atomic hydrogen-to-carbon ratio, α, of 1.85.
The effective density of NO_X is defined by the molar mass of nitrogen dioxide, NO₂.

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

Symbol	Quantity	g/mol (10 ⁻³ ·kg·mol ⁻¹ )
¹ See paragraph (g)(1) of this section for the composition of dry air.
M_air	molar mass of dry air ¹	28.96559
M_H2O	molar mass of water	18.01528

Symbol	Quantity	Value
n	nano	10 ⁻⁹
μ	micro	10 ⁻⁶
m	milli	10 ⁻³
c	centi	10 ⁻²
k	kilo	10 ³
M	mega	10 ⁶