{"data":{"id":"us/40-cfr-1036.805","jurisdiction":"us","citation":"40 CFR 1036.805","heading":"Symbols, abbreviations, and acronyms.","body":"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 (incorporated by reference, see § 1036.810). 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.\n(a) Symbols for chemical species. This part uses the following symbols for chemical species and exhaust constituents:\nTable 1 to Paragraph (a) of § 1036.805—Symbols for Chemical Species and Exhaust Constituents\nSymbol Species\nC carbon.\nCO carbon monoxide.\nCO2 carbon dioxide.\nH2 O water.\nHC hydrocarbon.\nNMHC nonmethane hydrocarbon.\nNMHCE nonmethane hydrocarbon equivalent.\nNMNEHC nonmethane nonethane hydrocarbon.\nNO nitric oxide.\nNO2 nitrogen dioxide.\nNOX oxides of nitrogen.\nPM particulate matter.\n(b) Symbols for quantities. This part uses the following symbols and units of measure for various quantities:\nTable 2 to Paragraph (b) of § 1036.805—Symbols for Quantities\nSymbol Quantity Unit Unit symbol Unit in terms of SI base units\nα atomic hydrogen-to-carbon ratio mole per mole mol/mol 1\nΑ Area square meter m2 m2\nβ atomic oxygen-to-carbon ratio mole per mole mol/mol 1\nCdΑ drag area meter squared m2 m2\nCrr coefficient of rolling resistance newton per kilonewton N/kN 10− 3\nD distance miles or meters mi or m m\ne efficiency\n∈ Difference or error quantity\nE mass weighted emission result grams/ton-mile g/ton-mi g/kg-km\nEff efficiency\nEm mass-specific net energy content megajoules/kilogram MJ/kg m2·s− 2\nfn angular speed (shaft) revolutions per minute r/min π·30·s− 1\ng gravitational acceleration meters per second squared m/s2 m·s− 2\ni indexing variable\nka drive axle ratio 1\nktopgear highest available transmission gear\nm Mass pound mass or kilogram lbm or kg kg\nM molar mass gram per mole g/mol 10− 3·kg·mol− 1\nM total number in a series\nM vehicle mass kilogram kg kg\nMrotating inertial mass of rotating components kilogram kg kg\nN total number in a series\nQ total number in a series\nP Power kilowatt kW 103·m2·kg·s− 3\nρ mass density kilogram per cubic meter kg/m3 m− 3·kg\nr tire radius meter m m\nSEE standard error of the estimate\nσ standard deviation\nT torque (moment of force) newton meter N·m m2·kg·s− 2\nt Time second s s\nΔt time interval, period, 1/frequency second s s\nUF utility factor\nv Speed miles per hour or meters per second mi/hr or m/s m·s− 1\nW Work kilowatt-hour kW·hr 3.6·m2·kg·s− 1\nwC carbon mass fraction gram/gram g/g 1\nwCH4N2O urea mass fraction gram/gram g/g 1\nx amount of substance mole fraction mole per mole mol/mol 1\nxb brake energy fraction\nxbl brake energy limit\n(c) Superscripts. This part uses the following superscripts for modifying quantity symbols:\nTable 3 to Paragraph (c) of § 1036.805—Superscripts\nSuperscript Meaning\noverbar (such as y ) arithmetic mean.\noverdot (such as y ) quantity per unit time.\n(d) Subscripts. This part uses the following subscripts for modifying quantity symbols:\nTable 4 to Paragraph (d) of § 1036.805—Subscripts\nSubscript Meaning\n65 65 miles per hour.\nA A speed.\na absolute (e.g., absolute difference or error).\nacc accessory.\napp approved.\naxle axle.\nB B speed.\nC C speed.\nC carbon mass.\nCcombdry carbon from fuel per mole of dry exhaust.\nCD charge-depleting.\nCO2 DEF CO2 resulting from diesel exhaust fluid decomposition.\ncomb combustion.\ncomp composite.\ncor corrected.\nCS charge-sustaining.\ncycle cycle.\nD distance.\nD D speed.\nDEF diesel exhaust fluid.\nengine engine.\nexh raw exhaust.\nfront frontal.\nfuel fuel.\nH2 Oexhaustdry H2 O in exhaust per mole of exhaust.\nhi high.\ni an individual of a series.\nidle idle.\nint test interval.\nj an individual of a series.\nk an individual of a series.\nm mass.\nmax maximum.\nmapped mapped.\nmeas measured quantity.\nMY model year.\nneg negative.\npos positive.\nR range.\nr relative (e.g., relative difference or error).\nrate rate (divided by time).\nrated rated.\nrecord record.\nref reference quantity.\nspeed speed.\nstall stall.\ntest test.\ntire tire.\ntransient transient.\nµ vector.\nUF utility factor.\nvehicle vehicle.\n(e) Other acronyms and abbreviations. This part uses the following additional abbreviations and acronyms:\nTable 5 to Paragraph (e) of § 1036.805—Other Acronyms and Abbreviations\nAcronym Meaning\nABT averaging, banking, and trading.\nAECD auxiliary emission control device.\nASTM American Society for Testing and Materials.\nBTU British thermal units.\nCD charge-depleting.\nCFR Code of Federal Regulations.\nCI compression-ignition.\nCOV coefficient of variation.\nCS charge-sustaining.\nDEF diesel exhaust fluid.\nDF deterioration factor.\nDOT Department of Transportation.\nDPF diesel particulate filter.\nE85 gasoline blend including nominally 85 percent denatured ethanol.\nECM Electronic Control Module.\nEGR exhaust gas recirculation.\nEPA Environmental Protection Agency.\nFCL Family Certification Level.\nFEL family emission limit.\nFTP Federal Test Procedure.\nGCWR gross combined weight rating.\nGEM Greenhouse gas Emissions Model.\ng/hp·hr grams per brake horsepower-hour.\nGPS global positioning system.\nGVWR gross vehicle weight rating.\nHeavy HDE heavy heavy-duty engine (see § 1036.140).\nHeavy HDV heavy heavy-duty vehicle (see 40 CFR 1037.140).\nLight HDE light heavy-duty engine (see § 1036.140).\nLight HDV light heavy-duty vehicle (see 40 CFR 1037.140).\nLLC Low Load Cycle.\nLPG liquefied petroleum gas.\nMedium HDE medium heavy-duty engine (see § 1036.140).\nMedium HDV medium heavy-duty vehicle (see 40 CFR 1037.140).\nNARA National Archives and Records Administration.\nNHTSA National Highway Traffic Safety Administration.\nNTE not-to-exceed.\nPEMS portable emission measurement system.\nRESS rechargeable energy storage system.\nSCR selective catalytic reduction.\nSEE standard error of the estimate.\nSET Supplemental Emission Test.\nSpark-ignition HDE spark-ignition heavy-duty engine (see § 1036.140).\nSI spark-ignition.\nUL useful life.\nU.S United States.\nU.S.C United States Code.\n(f) Constants. This part uses the following constants:\nTable 6 to Paragraph (f) of § 1036.805—Constants\nSymbol Quantity Value\ng gravitational constant 9.80665 m·s− 2.\nR molar gas constant 8.314472 J/(mol·K) (m2·kg·s− 2·mol− 1·K− 1).\n(g) Prefixes. This part uses the following prefixes to define a quantity:\nTable 7 to Paragraph (g) of § 1036.805—Prefixes\nSymbol Quantity Value\nµ micro 10− 6\nm milli 10− 3\nc centi 10− 2\nk kilo 103\nM mega 106","path":["Title 40—Protection of Environment","CHAPTER I—ENVIRONMENTAL PROTECTION AGENCY","SUBCHAPTER U—AIR POLLUTION CONTROLS","PART 1036—CONTROL OF EMISSIONS FROM NEW AND IN-USE HEAVY-DUTY HIGHWAY ENGINES","Subpart I—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":"3b5a6eb32a54a646290bc39115e41aa27195a08557ff7fbe1cfcd2e364a3beb4","source_id":"us-cfr","stale":true,"prev":"us/40-cfr-1036.801","next":"us/40-cfr-1036.810"},"notice":"GroundRules: Original legal text. Not legal advice."}