{"data":{"id":"us/40-cfr-1065.1005","jurisdiction":"us","citation":"40 CFR 1065.1005","heading":"Symbols, abbreviations, acronyms, and units of measure.","body":"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.\n(a) Symbols for quantities. This part uses the following symbols and units of measure for various quantities:\nTable 1 of § 1065.1005—Symbols for Quantities\nSymbol Quantity Unit Unit symbol Units in terms of SI base units\nα atomic hydrogen-to-carbon ratio mole per mole mol/mol 1.\nA area square meter m2 m2.\na0 intercept of least squares regression\na1 slope of least squares regression\nag acceleration of Earth's gravity meter per square second m/s2 m· s− 2.\nβ ratio of diameters meter per meter m/m 1.\nβ atomic oxygen-to-carbon ratio mole per mole mol/mol 1.\nC # number of carbon atoms in a molecule\nc power-specific carbon mass error coefficient gram per kilowatt-hour g/(kW·hr) 3.6− 1 · 10− 9 · m− 2 · s2.\nCd discharge coefficient\nCf flow coefficient\nδ atomic nitrogen-to-carbon ratio mole per mole mol/mol 1.\nd diameter meter m m.\nd power-specific carbon mass rate absolute error coefficent gram per kilowatt-hour g/(kW·hr) 3.6− 1 · 10− 9 · m− 2 · s2.\nDR dilution ratio mole per mole mol/mol 1.\nε error between a quantity and its reference\n∈ difference or error quantity\ne brake-specific emission or fuel consumption gram per kilowatt hour g/(kW·hr) 3.6− 1 · 10− 9 · m− 2 · s2.\nF F-test statistic\nƒ frequency hertz Hz s− 1.\nƒn angular speed (shaft) revolutions per minute r/min π · 30− 1 · s− 1.\nγ ratio of specific heats (joule per kilogram kelvin) per (joule per kilogram kelvin) (J/(kg·K))/(J/(kg·K)) 1.\nγ atomic sulfur-to-carbon ratio mole per mole mol/mol 1.\nκ opacity\nK correction factor 1.\nKv calibration coefficient m4 · s · K0.5/kg m4 · kg− 1 · s · K0.5.\nl length meter m m.\nL limit\nµ viscosity, dynamic pascal second Pa·s m− 1 · kg · s− 1.\nM molar mass 1 gram per mole g/mol 10− 3 · kg · mol− 1.\nm mass kilogram kg kg.\nm mass rate kilogram per second kg/s kg · s− 1.\nv viscosity, kinematic meter squared per second m2/s m2 · s− 1.\nN total number in series\nn amount of substance mole mol mol.\nn amount of substance rate mole per second mol/s mol · s− 1.\nP power kilowatt kW 103 · m2 · kg · s− 3.\nPF penetration fraction\np pressure pascal Pa m− 1 · kg · s− 2.\nρ mass density kilogram per cubic meter kg/m3 m− 3 · kg.\nΔp differential static pressure pascal Pa m− 1 · kg · s− 2.\nr ratio of pressures pascal per pascal Pa/Pa 1.\nr2 coefficient of determination\nRa average surface roughness micrometer µm 10− 6 · m.\nRe# Reynolds number\nRF response factor\nRH relative humidity\nσ non-biased standard deviation\nS Sutherland constant kelvin K K.\nSEE standard error of the estimate\nT absolute temperature kelvin K K.\nT Celsius temperature degree Celsius °C K−273.15.\nT torque (moment of force) newton meter N·m m2 · kg · s− 2.\nθ plane angle degrees ° rad.\nt time second s s.\nΔt time interval, period, 1/frequency second s s.\nV volume cubic meter m3 m3.\nV volume rate cubic meter per second m3/s m3 · s− 1.\nW work kilowatt-hour kW·hr 3.6 · 106 · m2 · kg · s− 2.\nwC carbon mass fraction gram per gram g/g 1.\nx amount of substance mole fraction.2 mole per mole mol/mol 1.\nX flow-weighted mean concentration mole per mole mol/mol 1.\ny generic variable\nZ compressibility factor\n1 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.\n2 Note that mole fractions for THC, THCE, NMHC, NMHCE, and NOTHC are expressed on a C1-equivalent basis.\n(b) Symbols for chemical species. This part uses the following symbols for chemical species and exhaust constituents:\nTable 2 of § 1065.1005—Symbols for Chemical Species and Exhaust Constituents\nSymbol Species\nAr argon.\nC carbon.\nCH2 O formaldehyde.\nCH2 O2 formic acid.\nCH3 OH methanol.\nCH4 methane.\nC2 H4 O acetaldehyde.\nC2 H5 OH ethanol.\nC2 H6 ethane.\nC3 H7 OH propanol.\nC3 H8 propane.\nC4 H10 butane.\nC5 H12 pentane.\nCO carbon monoxide.\nCO2 carbon dioxide.\nH atomic hydrogen.\nH2 molecular hydrogen.\nH2 O water.\nH2 SO4 sulfuric acid.\nHC hydrocarbon.\nHe helium.\n85 Kr krypton 85.\nN2 molecular nitrogen.\nNH3 ammonia.\nNMHC nonmethane hydrocarbon.\nNMHCE nonmethane hydrocarbon equivalent.\nNMNEHC nonmethane-nonethane hydrocarbon.\nNO nitric oxide.\nNO2 nitrogen dioxide.\nNOX oxides of nitrogen.\nN2 O nitrous oxide.\nNMOG nonmethane organic gases.\nNONMHC non-oxygenated nonmethane hydrocarbon.\nNOTHC non-oxygenated total hydrocarbon.\nO2 molecular oxygen.\nOHC oxygenated hydrocarbon.\n210 Po polonium 210.\nPM particulate matter.\nS sulfur.\nSVOC semi-volatile organic compound.\nTHC total hydrocarbon.\nTHCE total hydrocarbon equivalent.\nZrO2 zirconium dioxide.\n(c) Prefixes. This part uses the following prefixes for units and unit symbols:\nTable 3 of § 1065.1005—Prefixes\nSymbol Prefix name Factor\nµ micro 10− 6\nm milli 10− 3\nc centi 10− 2\nk kilo 103\nM mega 106\n(d) Superscripts. This part uses the following superscripts for modifying quantity symbols:\nTable 4 of § 1065.1005—Superscripts\nSuperscript Meaning\noverbar (such as y ) arithmetic mean.\noverdot (such as y ) quantity per unit time.\n(e) Subscripts. This part uses the following subscripts for modifying quantity symbols:\nTable 5 of § 1065.1005—Subscripts\nSubscript Meaning\na absolute (e.g., absolute difference or error).\nabs absolute quantity.\nact actual condition.\nair air, dry.\namb ambient.\natmos atmospheric.\nbkgnd background.\nC carbon mass.\ncal calibration quantity.\nCFV critical flow venturi.\ncomb combined.\ncomp composite value.\ncor corrected quantity.\ndil dilution air.\ndew dewpoint.\ndexh diluted exhaust.\ndry dry condition.\ndutycycle duty cycle.\n∈ related to a difference or error quantity.\nexh raw exhaust.\nexp expected quantity.\nfluid fluid stream.\nfn feedback speed.\nfrict friction.\nfuel fuel consumption.\nhi,idle condition at high-idle.\ni an individual of a series.\nidle condition at idle.\nin quantity in.\ninit initial quantity, typically before an emission test.\nint intake air.\nj an individual of a series.\nmapped conditions over which an engine can operate.\nmax the maximum (i.e., peak) value expected at the standard over a test interval; not the maximum of an instrument range.\nmeas measured quantity.\nmedia PM sample media.\nmix mixture of diluted exhaust and air.\nnorm normalized.\nout quantity out.\nP power.\npart partial quantity.\nPDP positive-displacement pump.\npost after the test interval.\npre before the test interval.\nprod stoichiometric product.\nr relative (e.g., relative difference or error).\nrate rate (divided by time).\nrecord record rate.\nref reference quantity.\nrev revolution.\nsat saturated condition.\ns slip.\nspan span quantity.\nSSV subsonic venturi.\nstd standard condition.\nstroke engine strokes per power stroke.\nT torque.\ntest test quantity.\ntest,alt alternate test quantity.\nuncor uncorrected quantity.\nvac vacuum side of the sampling system.\nweight calibration weight.\nzero zero quantity\n(f) Constants.\n(1) This part uses the following constants for the composition of dry air:\nTable 6 of § 1065.1005—Constants\nSymbol Quantity mol/mol\nγArair amount of argon in dry air 0.00934\nγCO2air amount of carbon dioxide in dry air 0.000375\nγN2air amount of nitrogen in dry air 0.78084\nγO2air amount of oxygen in dry air 0.209445\n(2) This part uses the following molar masses or effective molar masses of chemical species:\nTable 7 of § 1065.1005—Molar Masses\nSymbol Quantity g/mol (10-3·kg·mol-1)\nMair molar mass of dry air 1 28.96559\nMAr molar mass of argon 39.948\nMC molar mass of carbon 12.0107\nMCH3OH molar mass of methanol 32.04186\nMC2H5OH molar mass of ethanol 46.06844\nMC2H4O molar mass of acetaldehyde 44.05256\nMCH4N2O molar mass of urea 60.05526\nMC2H6 molar mass of ethane 30.06904\nMC3H8 molar mass of propane 44.09562\nMC3H7OH molar mass of propanol 60.09502\nMCO molar mass of carbon monoxide 28.0101\nMCH4 molar mass of methane 16.0425\nMCO2 molar mass of carbon dioxide 44.0095\nMH molar mass of atomic hydrogen 1.00794\nMH2 molar mass of molecular hydrogen 2.01588\nMH2O molar mass of water 18.01528\nMCH2O molar mass of formaldehyde 30.02598\nMHe molar mass of helium 4.002602\nMN molar mass of atomic nitrogen 14.0067\nMN2 molar mass of molecular nitrogen 28.0134\nMNH3 molar mass of ammonia 17.03052\nMNMHC effective C1 molar mass of nonmethane hydrocarbon 2 13.875389\nMNMHCE effective C1 molar mass of nonmethane hydrocarbon equivalent 2 13.875389\nMNMNEHC effective C1 molar mass of nonmethane-nonethane hydrocarbon 2 13.875389\nMNOx effective molar mass of oxides of nitrogen 3 46.0055\nMN2O molar mass of nitrous oxide 44.0128\nMO molar mass of atomic oxygen 15.9994\nMO2 molar mass of molecular oxygen 31.9988\nMS molar mass of sulfur 32.065\nMTHC effective C1 molar mass of total hydrocarbon 2 13.875389\nMTHCE effective C1 molar mass of total hydrocarbon equivalent 2 13.875389\n1 See paragraph (f)(1) of this section for the composition of dry air.\n2 The effective molar masses of THC, THCE, NMHC, NMHCE, and NMNEHC are defined on a C1 basis and are based on an atomic hydrogen-to-carbon ratio, α, of 1.85 (with β, γ, and δ equal to zero).\n3 The effective molar mass of NOX is defined by the molar mass of nitrogen dioxide, NO2.\n(3) This part uses the following molar gas constant for ideal gases:\nTable 8 of § 1065.1005—Molar Gas Constant for Ideal Gases\nSymbol Quantity J/(mol·K) (m2·kg·s− 2·mol− 1·K− 1)\nR molar gas constant 8.314472\n(4) This part uses the following ratios of specific heats for dilution air and diluted exhaust:\nTable 9 of § 1065.1005—Ratios of Specific Heats for Dilution Air and Diluted Exhaust\nSymbol Quantity [J/(kg·K)]/[J/(kg·K)]\nγair ratio of specific heats for intake air or dilution air 1.399\nγdil ratio of specific heats for diluted exhaust 1.399\nγexh ratio of specific heats for raw exhaust 1.385\n(g) Other acronyms and abbreviations. This part uses the following additional abbreviations and acronyms:\nTable 10 of § 1065.1005—Other Acronyms and Abbreviations\nAcronym Meaning\nABS acrylonitrile-butadiene-styrene.\nASTM ASTM International.\nBMD bag mini-diluter.\nBSFC brake-specific fuel consumption.\nCARB California Air Resources Board.\nCFR Code of Federal Regulations.\nCFV critical-flow venturi.\nCI compression-ignition.\nCITT Curb Idle Transmission Torque.\nCLD chemiluminescent detector.\nCVS constant-volume sampler.\nDEF diesel exhaust fluid.\nDF deterioration factor.\nECM electronic control module.\nEFC electronic flow control.\ne.g. exempli gratia, for example.\nEGR exhaust gas recirculation.\nEPA Environmental Protection Agency.\nFEL Family Emission Limit.\nFID flame-ionization detector.\nFTIR Fourier transform infrared.\nGC gas chromatograph.\nGC-ECD gas chromatograph with an electron-capture detector.\nGC-FID gas chromatograph with a flame ionization detector.\nHEPA high-efficiency particulate air.\nIBP initial boiling point.\nIBR incorporated by reference.\ni.e. id est, in other words.\nISO International Organization for Standardization.\nLPG liquefied petroleum gas.\nMPD magnetopneumatic detection.\nNDIR nondispersive infrared.\nNDUV nondispersive ultraviolet.\nNIST National Institute for Standards and Technology.\nNMC nonmethane cutter.\nPDP positive-displacement pump.\nPEMS portable emission measurement system.\nPFD partial-flow dilution.\nPLOT porous layer open tubular.\nPMD paramagnetic detection.\nPMP Polymethylpentene.\npt. a single point at the mean value expected at the standard.\npsi pounds per square inch.\nPTFE polytetrafluoroethylene (commonly known as TeflonTM).\nRE rounding error.\nRESS rechargeable energy storage system.\nRFPF response factor penetration fraction.\nRMC ramped-modal cycle.\nrms root-mean square.\nRTD resistive temperature detector.\nSAW surface acoustic wave.\nSEE standard error of the estimate.\nSSV subsonic venturi.\nSI spark-ignition.\nTHC-FID total hydrocarbon flame ionization detector.\nTINV inverse student t-test function in Microsoft Excel.\nUCL upper confidence limit.\nUFM ultrasonic flow meter.\nU.S.C. United States Code","path":["Title 40—Protection of Environment","CHAPTER I—ENVIRONMENTAL PROTECTION AGENCY","SUBCHAPTER U—AIR POLLUTION CONTROLS","PART 1065—ENGINE-TESTING PROCEDURES","Subpart K—Definitions and Other Reference Information"],"source_url":"https://www.ecfr.gov/api/versioner/v1/full/2026-08-25/title-40.xml","current_through":"2026-08-25","vintage":"","retrieved_at":"2026-08-27T02:26:04Z","sha256":"248918ccf3a516cb5db972412058990abbeaf2da4d67110945e19f3a31d692ad","source_id":"us-cfr","stale":true,"prev":"us/40-cfr-1065.1001","next":"us/40-cfr-1065.1010"},"notice":"GroundRules: Original legal text. Not legal advice."}