40 CFR § 1065.1005  Symbols, abbreviations, acronyms, and units of measure.
The procedures in this part generally follow the International System of Units (SI), as detailed in NIST Special Publication 811, which we incorporate by reference in § 1065.1010. See § 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 § 1065.1005  Symbols for Quantities
Symbol  Quantity  Unit  Unit symbol  Units in terms of SI base units 


atomic hydrogentocarbon ratio  mole per mole  mol/mol  1. 

area  square meter  m 
m 

intercept of least squares regression  

slope of least squares regression  

acceleration of Earth's gravity  meter per square second  m/s 
m· s−


ratio of diameters  meter per meter  m/m  1. 

atomic oxygentocarbon ratio  mole per mole  mol/mol  1. 

number of carbon atoms in a molecule  

powerspecific carbon mass error coefficient  gram per kilowatthour  g/(kW·hr)  3.6−


discharge coefficient  

flow coefficient  

atomic nitrogentocarbon ratio  mole per mole  mol/mol  1. 

diameter  meter  m  m. 

powerspecific carbon mass rate absolute error coefficent  gram per kilowatthour  g/(kW·hr)  3.6−


dilution ratio  mole per mole  mol/mol  1. 

error between a quantity and its reference  
∈  difference or error quantity  

brakespecific emission or fuel consumption  gram per kilowatt hour  g/(kW·hr)  3.6−


Ftest statistic  
ƒ  frequency  hertz  Hz  s−

ƒ 
angular speed (shaft)  revolutions per minute  r/min  π · 30−

γ  ratio of specific heats  (joule per kilogram kelvin) per (joule per kilogram kelvin)  (J/(kg·K))/(J/(kg·K))  1. 
γ  atomic sulfurtocarbon ratio  mole per mole  mol/mol  1. 

correction factor  1.  

calibration coefficient  m 
m 


length  meter  m  m. 

limit  

viscosity, dynamic  pascal second  Pa·s  m−


molar mass 
gram per mole  g/mol  10−


mass  kilogram  kg  kg. 

mass rate  kilogram per second  kg/s  kg · s−


viscosity, kinematic  meter squared per second  m 
m 

total number in series  

amount of substance  mole  mol  mol. 

amount of substance rate  mole per second  mol/s  mol · s−


power  kilowatt  kW  10 

penetration fraction  

pressure  pascal  Pa  m−


mass density  kilogram per cubic meter  kg/m 
m−


differential static pressure  pascal  Pa  m−


ratio of pressures  pascal per pascal  Pa/Pa  1. 

coefficient of determination  

average surface roughness  micrometer  µm  10−


Reynolds number  

response factor  

relative humidity  

nonbiased standard deviation  

Sutherland constant  kelvin  K  K. 

standard error of the estimate  

absolute temperature  kelvin  K  K. 

Celsius temperature  degree Celsius  °C  K−273.15. 

torque (moment of force)  newton meter  N·m  m 

plane angle  degrees  °  rad. 

time  second  s  s. 

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

volume  cubic meter  m 
m 

volume rate  cubic meter per second  m 
m 

work  kilowatthour  kW·hr  3.6 · 10 

carbon mass fraction  gram per gram  g/g  1. 

amount of substance mole fraction. 
mole per mole  mol/mol  1. 

flowweighted mean concentration  mole per mole  mol/mol  1. 

generic variable  

compressibility factor 
1 See paragraph (f)(2) of this section for the values to use for molar masses. Note that in the cases of NOX and HC, the regulations specify effective molar masses based on assumed speciation rather than actual speciation.
2 Note that mole fractions for THC, THCE, NMHC, NMHCE, and NOTHC are expressed on a C1equivalent basis.
(b) Symbols for chemical species. This part uses the following symbols for chemical species and exhaust constituents:
Symbol  Species 

Ar  argon. 
C  carbon. 
CH2O  formaldehyde. 
CH2O2  formic acid. 
CH3OH  methanol. 
CH4  methane. 
C2H4O  acetaldehyde. 
C2H5OH  ethanol. 
C2H6  ethane. 
C3H7OH  propanol. 
C3H8  propane. 
C4H10  butane. 
C5H12  pentane. 
CO  carbon monoxide. 
CO2  carbon dioxide. 
H  atomic hydrogen. 
H2  molecular hydrogen. 
H2O  water. 
H2SO4  sulfuric acid. 
HC  hydrocarbon. 
He  helium. 
^{85}Kr  krypton 85. 
N2  molecular nitrogen. 
NH3  ammonia. 
NMHC  nonmethane hydrocarbon. 
NMHCE  nonmethane hydrocarbon equivalent. 
NMNEHC  nonmethanenonethane hydrocarbon. 
NO  nitric oxide. 
NO2  nitrogen dioxide. 
NOX  oxides of nitrogen. 
N2O  nitrous oxide. 
NMOG  nonmethane organic gases. 
NONMHC  nonoxygenated nonmethane hydrocarbon. 
NOTHC  nonoxygenated total hydrocarbon. 
O2  molecular oxygen. 
OHC  oxygenated hydrocarbon. 
^{210}Po  polonium 210. 
PM  particulate matter. 
S  sulfur. 
SVOC  semivolatile organic compound. 
THC  total hydrocarbon. 
THCE  total hydrocarbon equivalent. 
ZrO2  zirconium dioxide. 
(c) Prefixes. This part uses the following prefixes for units and unit symbols:
Table 3 of § 1065.1005  Prefixes
Symbol  Prefix name  Factor 

µ  micro  10−

m  milli  10−

c  centi  10−

k  kilo  10 
M  mega  10 
(d) Superscripts. This part uses the following superscripts for modifying quantity symbols:
Table 4 of § 1065.1005  Superscripts
Superscript  Meaning 

overbar (such as 
arithmetic mean. 
overdot (such as 
quantity per unit time. 
(e) Subscripts. This part uses the following subscripts for modifying quantity symbols:
Table 5 of § 1065.1005  Subscripts
Subscript  Meaning 

a  absolute ( 
abs  absolute quantity. 
act  actual condition. 
air  air, dry. 
amb  ambient. 
atmos  atmospheric. 
bkgnd  background. 
C  carbon mass. 
cal  calibration quantity. 
CFV  critical flow venturi. 
comb  combined. 
comp  composite value. 
cor  corrected quantity. 
dil  dilution air. 
dew  dewpoint. 
dexh  diluted exhaust. 
dry  dry condition. 
dutycycle  duty cycle. 
∈  related to a difference or error quantity. 
exh  raw exhaust. 
exp  expected quantity. 
fluid  fluid stream. 
fn  feedback speed. 
frict  friction. 
fuel  fuel consumption. 
hi,idle  condition at highidle. 
i  an individual of a series. 
idle  condition at idle. 
in  quantity in. 
init  initial quantity, typically before an emission test. 
int  intake air. 
j  an individual of a series. 
mapped  conditions over which an engine can operate. 
max  the maximum ( 
meas  measured quantity. 
media  PM sample media. 
mix  mixture of diluted exhaust and air. 
norm  normalized. 
out  quantity out. 
P  power. 
part  partial quantity. 
PDP  positivedisplacement pump. 
post  after the test interval. 
pre  before the test interval. 
prod  stoichiometric product. 
r  relative ( 
rate  rate (divided by time). 
record  record rate. 
ref  reference quantity. 
rev  revolution. 
sat  saturated condition. 
s  slip. 
span  span quantity. 
SSV  subsonic venturi. 
std  standard condition. 
stroke  engine strokes per power stroke. 
T  torque. 
test  test quantity. 
test,alt  alternate test quantity. 
uncor  uncorrected quantity. 
vac  vacuum side of the sampling system. 
weight  calibration weight. 
zero  zero quantity 
(f) Constants.
(1) This part uses the following constants for the composition of dry air:
Symbol  Quantity  mol/mol 


amount of argon in dry air  0.00934 

amount of carbon dioxide in dry air  0.000375 

amount of nitrogen in dry air  0.78084 

amount of oxygen in dry air  0.209445 
(2) This part uses the following molar masses or effective molar masses of chemical species:
Table 7 of § 1065.1005  Molar Masses
Symbol  Quantity  g/mol
(10 


molar mass of dry air 
28.96559 

molar mass of argon  39.948 

molar mass of carbon  12.0107 

molar mass of methanol  32.04186 

molar mass of ethanol  46.06844 

molar mass of acetaldehyde  44.05256 

molar mass of urea  60.05526 

molar mass of ethane  30.06904 

molar mass of propane  44.09562 

molar mass of propanol  60.09502 

molar mass of carbon monoxide  28.0101 

molar mass of methane  16.0425 

molar mass of carbon dioxide  44.0095 

molar mass of atomic hydrogen  1.00794 

molar mass of molecular hydrogen  2.01588 

molar mass of water  18.01528 

molar mass of formaldehyde  30.02598 

molar mass of helium  4.002602 

molar mass of atomic nitrogen  14.0067 

molar mass of molecular nitrogen  28.0134 

molar mass of ammonia  17.03052 

effective C1 molar mass of nonmethane hydrocarbon 
13.875389 

effective C1 molar mass of nonmethane hydrocarbon equivalent 
13.875389 

effective C1 molar mass of nonmethanenonethane hydrocarbon 
13.875389 

effective molar mass of oxides of nitrogen 
46.0055 

molar mass of nitrous oxide  44.0128 

molar mass of atomic oxygen  15.9994 

molar mass of molecular oxygen  31.9988 

molar mass of sulfur  32.065 

effective C 
13.875389 

effective C 
13.875389 
1 See paragraph (f)(1) of this section for the composition of dry air.
2 The effective molar masses of THC, THCE, NMHC, NMHCE, and NMNEHC are defined on a C1 basis and are based on an atomic hydrogentocarbon ratio, α, of 1.85 (with β, γ, and δ equal to zero).
3 The effective molar mass of NOX is defined by the molar mass of nitrogen dioxide, NO2.
(3) This part uses the following molar gas constant for ideal gases:
Symbol  Quantity  J/(mol · K)
(m ^{2} · kg · s−2 · mol−1 · K−1) 


molar gas constant  8.314472 
(4) This part uses the following ratios of specific heats for dilution air and diluted exhaust:
Symbol  Quantity  [J/(kg · K)]/[J/(kg · K)] 


ratio of specific heats for intake air or dilution air  1.399 

ratio of specific heats for diluted exhaust  1.399 

ratio of specific heats for raw exhaust  1.385 
(g) Other acronyms and abbreviations. This part uses the following additional abbreviations and acronyms:
Table 10 of § 1065.1005  Other Acronyms and Abbreviations
Acronym  Meaning 

ABS  acrylonitrilebutadienestyrene. 
ASTM  ASTM International. 
BMD  bag minidiluter. 
BSFC  brakespecific fuel consumption. 
CARB  California Air Resources Board. 
CFR  Code of Federal Regulations. 
CFV  criticalflow venturi. 
CI  compressionignition. 
CITT  Curb Idle Transmission Torque. 
CLD  chemiluminescent detector. 
CVS  constantvolume sampler. 
DEF  diesel exhaust fluid. 
DF  deterioration factor. 
ECM  electronic control module. 
EFC  electronic flow control. 

exempli gratia, for example. 
EGR  exhaust gas recirculation. 
EPA  Environmental Protection Agency. 
FEL  Family Emission Limit. 
FID  flameionization detector. 
FTIR  Fourier transform infrared. 
GC  gas chromatograph. 
GCECD  gas chromatograph with an electroncapture detector. 
GCFID  gas chromatograph with a flame ionization detector. 
HEPA  highefficiency particulate air. 
IBP  initial boiling point. 
IBR  incorporated by reference. 

id est, in other words. 
ISO  International Organization for Standardization. 
LPG  liquefied petroleum gas. 
MPD  magnetopneumatic detection. 
NDIR  nondispersive infrared. 
NDUV  nondispersive ultraviolet. 
NIST  National Institute for Standards and Technology. 
NMC  nonmethane cutter. 
PDP  positivedisplacement pump. 
PEMS  portable emission measurement system. 
PFD  partialflow dilution. 
PLOT  porous layer open tubular. 
PMD  paramagnetic detection. 
PMP  Polymethylpentene. 
pt.  a single point at the mean value expected at the standard. 
psi  pounds per square inch. 
PTFE  polytetrafluoroethylene (commonly known as TeflonTM). 
RE  rounding error. 
RESS  rechargeable energy storage system. 
RFPF  response factor penetration fraction. 
RMC  rampedmodal cycle. 
rms  rootmean square. 
RTD  resistive temperature detector. 
SAW  surface acoustic wave. 
SEE  standard error of the estimate. 
SSV  subsonic venturi. 
SI  sparkignition. 
THCFID  total hydrocarbon flame ionization detector. 
TINV  inverse student 
UCL  upper confidence limit. 
UFM  ultrasonic flow meter. 
U.S.C.  United States Code 