40 CFR 1066.1005 - Symbols, abbreviations, acronyms, and units of measure.

View all text of Subpart K [§ 1066.1001 - § 1066.1010]

§ 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:

Table 1 of § 1066.1005—Symbols for 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	m2	m2.	A	vehicle frictional load	pound force or newton	lbf or N	m·kg·s−2.	ag	acceleration of Earth's gravity	meters per second squared	m/s2	m·s−2.	Am	calculated vehicle frictional load	pound force or newton	lbf or N	m·kg·s−2.	a0	intercept of least squares regression.				a1	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/(mi/hr) or N·s/m	kg·s-1.	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)2 or N·s2/m2	m-1·kg.	C#	number of carbon atoms in a molecule	C#	number of carbon atoms in a molecule	C#.	Cd	discharge coefficient.				CdA	drag area	meter squared	m2	m2.	Cf	flow coefficient.				Cp	heat capacity at constant pressure	joule per kelvin	J/K	m2·kg·s-2·K-1.	Cv	heat capacity at constant volume	joule per kelvin	J/K	m2·kg·s-2·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/(mi/hr)2 or N·s2/m2	m−2·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−2.	ƒ	frequency	hertz	Hz	s−1.	ƒn	angular speed (shaft)	revolutions per minute	r/min	π·30·s−1.	FC	friction compensation error	horsepower or watt	W	m2·kg·s−3.	FR	road-load force	pound force or newton	lbf or N	kg·s−2.	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			1.	Kv	calibration coefficient		m4·s·K0.5/kg	m4·kg−1·s·K0.5.	µ	viscosity, dynamic	pascal second	Pa·s	m−1·kg·s−1.	M	molar mass	gram per mole	g/mol	10-3·kg·mol−1.	Me	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.	pd	saturated vapor pressure at ambient dry bulb temperature	kilopascal	kPa	m−1·kg·s−1.	PF	penetration fraction.				ρ	mass density	kilogram per cubic meter	kg/m3	m−3·kg.	R	dynamometer roll revolutions	revolutions per minute	rpm	π·30−1·s−1.	r	ratio of pressures	pascal per pascal	Pa/Pa	1.	r2	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	m2·kg·s-2.	t	time	hour or second	hr or 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	mi/hr or m/s	m·s-1.	V	volume	cubic meter	m3	m3.	V	flow volume rate	cubic feet per minute or cubic meter per second	ft3/min or m3/s	m3·/s−1.	VP	volume percent.				x	concentration of emission over a test interval	part per million	ppm.		y	generic variable.				Z	compressibility factor.

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

Table 2 to Paragraph (b) of § 1066.1005—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.

Table 3 of § 1066.1005—Superscripts

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

(d) Subscripts. This part uses the following subscripts for modifying quantity symbols:

Table 4 of § 1066.1005—Subscripts

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.

(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:

Table 5 of § 1066.1005—Other Acronyms and Abbreviations

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.

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

Table 6 of § 1066.1005—Densities of Chemical Species

Symbol	Quantity a b	g/m3	g/ft3	ρCH4	density of methane	666.905	18.8847	ρCH3OH	density of methanol	1332.02	37.7185	ρC2H5OH	C1-equivalent density of ethanol	957.559	27.1151	ρC2H4O	C1-equivalent density of acetaldehyde	915.658	25.9285	ρC3H8	density of propane	611.035	17.3026	ρC3H7OH	C1-equivalent density of propanol	832.74	23.5806	ρCO	density of carbon monoxide	1164.41	32.9725	ρCO2	density of carbon dioxide	1829.53	51.8064	ρHC-gas	effective density of hydrocarbon—gaseous fuel c	(see 3)	(see 3)	ρCH2O	density of formaldehyde	1248.21	35.3455	ρHC-liq	effective density of hydrocarbon—liquid fueld	576.816	16.3336	ρNMHC-gas	effective density of nonmethane hydrocarbon—gaseous fuel c	(see 3)	(see 3)	ρNMHC-liq	effective density of nonmethane hydrocarbon—liquid fuel d	576.816	16.3336	ρNMHCE-gas	effective density of nonmethane equivalent hydrocarbon—gaseous fuel c	(see 3)	(see 3)	ρNMHCE-liq	effective density of nonmethane equivalent hydrocarbon—liquid fuel d	576.816	16.3336	ρNOx	effective density of oxides of nitrogen e	1912.5	54.156	ρN2O	density of nitrous oxide	1829.66	51.8103	ρTHC-liq	effective density of total hydrocarbon—liquid fuel d	576.816	16.3336	ρTHCE-liq	effective density of total equivalent hydrocarbon—liquid fuel d	576.816	16.3336

a Densities are given at 20 °C and 101.325 kPa.

b Densities for all hydrocarbon containing quantities are given in g/m3-carbon atom and g/ft3-carbon atom.

c 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. ρHCgas = 41.57·(12.011 + (α·1.008)).

d The effective density for gasoline and diesel fuel are defined by an atomic hydrogen-to-carbon ratio, α, of 1.85.

e 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:

Table 7 to Paragraph (g)(1) of § 1066.1005—Constants for the Composition of Dry Air

Symbol	Quantity	mol/mol	xArair	amount of argon in dry air	0.00934	xCO2air	amount of carbon dioxide in dry air	0.000375	xN2air	amount of nitrogen in dry air	0.78084	xO2air	amount of oxygen in dry air	0.209445

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

Table 8 to Paragraph (g)(2) of § 1066.1005—Molar Masses or Effective Molar Masses of Chemical Species

Symbol	Quantity	g/mol (10− 3·kg·mol− 1)	Mair	molar mass of dry air 1	28.96559	MH2O	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:

Table 9 to Paragraph (g)(3) of § 1066.1005—Molar Gas Constant for Ideal Gases

Symbol	Quantity	J/(mol·K) (m 2·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:

Table 10 to Paragraph (h) of § 1066.1005—Prefixes to Define a Quantity

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

[79 FR 23823, Apr. 28, 2014, as amended at 80 FR 9124, Feb. 19, 2015; 81 FR 74215, Oct. 25, 2016; 86 FR 34585, June 29, 2021; 87 FR 64866, Oct. 26, 2022; 88 FR 4710, Jan. 24, 2023]