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Glossal)1
Air/fuel (A/F) ratio The ratio, by weight, of air to gasoline entering the
intake in a gasoline engine. The ideal (stoichiometric) ratio for complete com-
bustionis approximately 14.7parts of gasoline to ~ partoffuel, depending on
the composition of the specific filet.
Air-quality mode] A computer-based mathematical model used to predict
air quality based upon emissions and the effects of the transport, dispersion,
and transformation of compounds emitted into the air.
Ambientair- Theairoutsideofs~uctures.Oftenusedinterchangeablywith
"outdoor air."
BAR97 The name for the test and equipment used in the California En-
hanced Smog Check program. The BAR97 test is a steady state, ioaded-
mode emissions test. "Loaded-mode" refers to the fact that the test is run on
a ~eadmill-like device called a dynamometer, which simulates actual Unving
with the engine in gear. "Steady state" refers to the fact that the car denies
under a constant load throughout the test.
iSources: California Air Resources Board at www.arb.ca.gov/html/gloss.htm;
Davis 1997; EPA at www.epa.gov /otaq/epg/keyterm.htm; EPA at www.epa.gov/oar/
oaqps/peg_caa/pegcaalO.html; EPA at www.epa.gov/oms/stds-ld.htm; Harvey and
Deakin 1993; IMRC 2000.
215
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216 Evaluating Vehicle Emissions I/M Programs
California Air Resources Board (CARB) Apart ofthe California Envi-
ronmental Protection Agency whose mission it is to promote and protect public
health, welfare and ecological resources through the effective and efficient
reduction of air pollutants while recognizing and considering the effects on the
economy of the state.
California Inspection and Maintenance Review Committee (IMRC)
- An advisory committee created to evaluate and recommend improvements
for the California Smog Check I/M program.
Carbon monocle (CO - A colorless, odorless poisonous gas resulting from
the incomplete combustion of hydrocarbon fuels.
Clean Air Act (CAA) The original Clean Air Act was passed in ~ 963, but
our rational airpollution control program is actually teased on the ~ 970 version
of the law. The 1990 Clean Air Act Amendments (CAAA90) are the most
recent and far-reaching revisions of the 1970 law.
Clean screening The use of methods such as remote sensing measure-
ments or vehicle profiling by states to excuse cars from a scheduled inspection
and maintenance (I/M) emissions test.
Closed-Ioop fuel control A fuel metering system that uses feedback for
more effective emissions control. The air/fuel ratio of a contemporary vehicle
is "closed-Ioop," using a sensor in the exhaust to evaluate the mixture exiting
the engine, and adjusting the air/fuel ratio through the use of an on-board com-
puter to optimize emissions performance.
Cold-start emissions—Tailpipe emissions that occur before a vehicle is fully
warmed up. Vehicle emissions are higher during the first few minutes of
operation, because the engine and the catalytic converter must come to operat-
ing temperature before they can become effective.
Conformity (transportation conformity) A process to demonstrate
whether a federally supported activity is consistent with the air quality goals
in State implementation Plans (Sips). Transportation conformity demonstrates
thatplans, programs, and projects approved or funded by the Federal Highway
Administration, or the Federal Transit Administration for reg~onally-sign~ficant
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Glossary 21 7
projects do not create new violations, increase the frequency or severity of
existing violations, or delay timely attainment of NAAQS. General conformity
refers to projects approved or funded by other federal agencies.
Criteria air pollutants A group of six common air pollutants (CO, lead,
nitrogen dioxide, ozone, particulate matter, and sulfur dioxide) regulated by the
Federal Government since the passage of the Clean Air Act in 1970 on the
basis of information on health and/or environmental effects of each pollutant.
Cutpoint—For each pollutant, the emissions level above which a car is con-
sidered to have failed the emissions test for that pollutant.
Data link connector The connector where the scan tool interfaces with a
vehicle's OBD system. Also know as the diagnostic link connector.
Diagnostic trouble codes—Codes stored in the engine's computer that
identify emission control systems and/or components that are malfunctioning
and can be retrieved using a scan tool..
Dynamometer—A treadmill-like machine that allows cars to be tested under
the loads typical of on-road driving.
Emissions budget Allowable emissions levels identified as part of a state
implementation plan for pollutants emitted from mobile, industnal, stationary,
and area sources. These emissions levels are used for meeting emission re-
duction milestones, attainment, or maintenance demonstrations.
Emissions factor The predicted ratio ofthe amount of pollution produced
to the amount of raw material processed or burned, or ofthe amount of pollu-
lion produced to the activity level. By using the emission factor of a pollutant
and data regarding quantities of materials used by a given source or the activity
{ever of a given source, it is possible to compute emissions for the source. in
the case of mobile source emissions, estimated emissions are the product of an
emission factor inmass of pollutant per unit distance (e.g., grams per mire) and
an activity estimate in distance (e.g., average miles traveled). In the case of
stationary source emissions, estimated emissions are the product of an emis-
sion factor in mass of pollutant per unit energy (e.g., pounds per million Btu)
and the amount of energy consumed.
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218 Evaluating Vehicle Emissions I/M Programs
Emissions inventory Estimates ofthe amount of pollutants emitted into the
atmosphere frommajormobile, stationary, area-wide, end natural source cate-
gories over a specific period of time such as a day or a year.
Environmental Protection Agency (EPA) The federal government agen-
cy that establishes regulations and oversees the enforcement of laws related
to the environment.
Exceedancc An air pollution event in which the ambient concentration of
a pollutant exceeds a National Ambient Air Quality Standard (NAAQS).
Evaporative emissions Hydrocarbon emissions that do not come from the
tailpipe of a car. Evaporative emissions can come from evaporation, perme-
ation, seepage, andleaks ina car's fueling system. Often usedinterchangeably
with non-tai~pipe emissions.
Fast pass Fast pass is aprocess that recognizes very clean cars earlyin the
IM240 test cycle and passes them without the need to complete the full test.
Federal Test Procedure (FTP) A certification test for measuring the
tailpipe and evaporative emissions from new vehicles over the Urban Dyna-
mometer Driving Schedule, which attempts to simulate an urban driving cycle.
Gross vehicle weight rating (GVWR) The value specified by the manu-
facturer as the maximum design loaded weight of a vehicle (i.e., vehicle weight
plus rated cargo capacity).
Heavy-duty vehicle (HDV) Any motor vehicle rated at more than 8,500
pounds gross vehicle weight (GVWR) or that has a vehicle curb weight of
more than 6,000 pounds or that has a basic vehicle frontal area in excess of 45
square feet. This excludes vehicles that will be classified as medium-duty
passenger vehicles for the purposes of the Tier 2 emissions standards.
Heavy-duty diesel vehicle (H 'JDV) An HDV using diesel fuel.
Hydrocarbon (HC)~rganic compounds containing various combinations
of hydrogen and carbon. See Appendix B for details of how HC relates to
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Glossary 219
other terms, such as volatile organic compounds (VOC), used to describe
organic compounds.
IM240 The name for the emissions test used in some I/M programs includ-
ing those in Arizona and Colorado. The IM240 is a transient, ioade<~-mode
emissions test. "Loaded-mode" refers to the fact that the test is run on a
trea~nill-like device called a dynamometer, which simulates driving with the
engine in gear. "Transient" refers to the fact that the car drives under a Toad
that varies from second to second during the test. The "240" in IM240 indi-
cates that the test lasts for 240 seconds. The IM240 is intended by EPA to be
a shortened version of part of the FTP and to correlate well with the FTP.
Light-duty vehicle (LDV)—A passenger car or passenger car derivative
capable of seating 12 or fewer passengers. All vehicles and trucks under
8,500 GVWR are included (this limit previously was 6,000 pounds). Small
pick-up trucks, vans, and sport utility vehicles may be included.
Loaded-mode emissions test—An emissions test performed with the en-
. .
gme In gear.
Malfunction indicator light—~—The instrument pane} light used by the
on-board diagnostic (OBD) system to notify the vehicle operator of an emis-
sions related fault. The MIL is also known as the "service engine soon" or
"check engine" lamp.
Medium-duty passenger vehicle (MDPV)—A new class of vehicles intro-
duced with the Tier 2 emissions standards that includes sport utility vehicles
and passenger vans rated at 8,5000 to 10,000 GVWR.
Metropolitan Planning Organization (MPO - The organized entity desig-
nated by law with lead responsibilities for developing transportation plans and
programs for urbanized areas with populations of 50,000 or more people.
MPOs are established by agreement of the governor and units of general
purpose local government, which together represent 75°/O of the affected
population of an urbanized area.
Mode] year Vehicles are certified for sate, marketed, and later registered
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220 Evaluating Vehicle Emissions I/M Programs
as a certain model year that indicates the year a vehicle was produced and
offered for sale. Model years typically began in September or October ofthe
prior year and ran for roughly 12 months. In the last decade, certain vehicles
have been introduced as a "pull-ahead" vehicle, appearing as early as January
of the year.
National low-emissions vehicle (NLEV)—A vehicle that meets voluntary
Tow-emissions tailpipe standards that are more stringent then canbe mandated
by EPA prior to model-year 2004. The NLEV program introduces Tow-emis-
sions cars and light-duty trucks into the Northeast beginning in model-year
1999 and the rest of the country in model-year 2001.
National Ambient Air Quality Standar(ls (NAAQS) Standards set by
EPA for the maximum levels of criteria air pollutants that can exist in the
outdoor air without unacceptable effects on human health or the public wel-
fare.
Nonattainment area—A geographic area in which the level of a criteria air
pollutant is higher than the level allowed by the federal standards. A single
geographic area may have acceptable levels of one criteria air pollutant but
unacceptable levels of one or more other criteria; thus, an area can be both an
attainment area and a nonattainment area at the same time.
Nitrogen oxides (oxides of nitrogen, NO,] A general term referring to
nitric oxide (NO), and nitrogen dioxide (Nets. Nitrogen oxides are formed
when air is raised to high temperatures, such as during combustion or lightning,
and are major contributors to ozone formation and acid deposition.
On-board diagnostic (OBD) systems Devices incorporated into the com-
puters of new motor vehicles to monitor the performance of the emission
controls. The computer triggers a dashboard indicator light, referred to as a
malfunction indicator light, when the controls malfunction, alerting the driver
to seek maintenance forthe vehicle. The system also communicates its find-
ings to repair technicians by means of diagnostic trouble codes, which can be
downloaded from the vehicle's computer. OBD systems do not measure
. .
emlsslons.
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Glossary 221
On-board diagnostic generation one (OBDI) systems- An on-board
automotive diagnostic system required by the California AirResources Board
since ~ 988. The OBDI uses the microprocessor and sensors to monitor and
control various engine system functions.
On-board diagnostic generation two (OBDIl) systems OBDIT expands
upon OBDI to include emissions system and sensor deterioration monitoring.
Open-Ioop fuel control A system in which the air/fuel mixture is preset by
design and contains no feedback correction signal to optimize fuel metering for
emissions control (see also "Closed-Ioop fuel controls.
Oxygen Sensor A sensor placed in the exhaust that measures exhaust
oxygen content. Typically, there are oxygen sensors before and after the
catalytic converter.
Oxygenated gasoline (oxyfuel) Gasoline containing oxygenates, typically
methyl tertiary-butyl ether (MTBE) or ethanol, intended to reduce production
of CO, a criteria air pollutant. in some parts ofthe country, CO emissions from
cars makes a major contribution to pollution. In some ofthese areas, gasoline
refiners must market oxygenated fuels, which typically contain 2-3% oxygen
by weight.
Oxygenates—Compounds containing oxygen (alcohols and ethers) that are
added to gasoline to increase its oxygen content. MTBE and ethanol are the
most common oxygenates currently used, although a number of others are
available.
Ozone A reactive gas whose molecules contain three oxygen atoms. It is a
product of photochemical processes involving sunlight and ozone precursors,
such as HC and NOx. Ozone exists in the upper atmosphere Stratospheric
ozone) where it helps shield the earth from excessive ultraviolet rays, as well
as in the lower atmosphere near the earth's surface (tropospheric ozone).
Tropospheric ozone causes plant damage and adverse health effects and is a
criteria air pollutant. Troposphenc ozone is a major component of smog.
Particulate matter (PM) Any material, except uncombined water, that
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222 Evaluating Vehicle Emissions I/M Programs
exists in the solid or liquid states in the atmosphere. The size of particulate
matter can vary from coarse, wind-blown dust particles to fine particles di-
rectly emitted as combustion products or formed through secondary reactions
in the atmosphere.
Photochemical reaction—A term referring to a chemical reaction brought
about by the light ofthe sun. The formation ofozone from NOx end HC in the
presence of sunlight involves photochemical reactions.
Ping-pong—Colloquial term to describe the case where a car fails its emis-
sions test at a testing facility, is repaired at a repair facility, goes back to the
testing facility for retesting, and fails again.
PM-2.5 A subset of particulate matter that includes fine particles with an
aerodynamic diameter less than or equal to a nominal 2.5 micrometers. This
fraction of particulate master penetrates most deeply into the lungs and causes
the majority of visibility reduction.
PM-IO A major air pollutant consisting of small particles with an aerody-
namic diameter less than or equal to a nominal 10 micrometers (about one-
seventh the diameter of a single human hair). Their small size allows them to
make their way to the air sacs deep within the lungs where they may be de-
posited and result in adverse health effects. PM- ~ O also causes visibility reduc-
tion.
Preconditioning Preconditioning refers to a set of steps followed to warm
up a vehicle prior to the emission test. Cutpoints, which determine passing or
failing for such a vehicle, are based on testing a fully warmed-up vehicle in
which the emissions control equipment, including the catalytic converter, are
hot and fully functional. If an owner drives a short distance to the test station
orifthe vehicle has to waitin the test station for a longtime, the vehicle may
not be fully warmed up. This may result in a false reading: a car that would
have passed if fully warmed (i.e., fully preconditioned) would fail.
Primary standard—A NAAQS for criteria air pollutants based on health
effects.
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Glossary 223
Reformulated gasoline (RFG) Specifically formulated fuel blended such
that, on average, the exhaust and evaporative emissions of VOCs and hazard-
ous air pollutants (chiefly benzene, I,3-butadiene, polycyclic aromatic HC,
formaldehyde, and acetaldehyde) resulting from RFG use in motor vehicles
might tee significantly and consistently Tower Man such emissions resulting from
use of conventional gasolines. The ~ 990 Clean Air Act Amendments requires
sale of reformulated gasoline in the nine areas with the most severe ozone
pollution problems. RFG contains, on average, a minimum of 2.0 weightper-
cent oxygen.
Remote sensing—A method for measunug pollution levels in a vehicle's
exhaust while the vehicle is traveling on the road. Remote-sensing systems
use infrared absorption to measure HC and CO emissions relative to carbon
dioxide. These systems typically operate by continuously projecting a beam
of infrared radiation across a roadway and measuring the exhaust plume after
a vehicle passes through the beam.
Scan too] A hand-held computer that is plugged into a vehicle's data link
connector allowing a technician to read diagnostic trouble codes, readiness
status, and other information collected by the OBD system.
Secondary parffcIc Particulate matter that is formed in the atmosphere and
generally composed of such species as ammonium ions or the products of
atmospheric chemical reactions, such as nitrates, sulfates, and organic mate-
rial. Secondary particles are distinguished from primary particles, which are
emitted directly into the atmosphere.
Secondary standard ANAAQS for criteria air pollutants based on environ-
mental effects, such as damage to proper~, plants, and visibility.
Speed-correction factor (SCF)- Factors used in the MOBILE model to
adjust emissions factors from the average speed used in the Federal Test
Procedure (used to obtain emissions data) to other average speeds driven by
vehicles in the geographical area being modeled.
Supplemental Federal Test Procedure (SFTP) The SFTP is a certiiFica-
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224 Evaluating Vehicle Emissions I/M Programs
lion test for measuring the tailpipe and evaporative emissions from new vehi-
cles. Two driving cycles not represented in the FTP are a test cycle that
simulates high-speed and high-acceleration driving (US06 cycle) and a test
cycle that evaluates the effects of air-conditioner operation (SC03 cycle).
State implementation plan (SIP) A detailed description ofthe programs
a state will use to carry out its responsibilities under the Clean Air Act for
complying with the NAAQS. SIPs are a collection ofthe programs used by a
state to reduce air pollution. The Clean Air Act requires that EPA approve
each SIP. The public is given opportunities to participate in the review and
approval of SIPs.
Steady-state emission test- An emissions test performed under one stable
operating condition, such as testing when a vehicle is at idle or under a con-
stant engine load.
Tampering The malfunctioning of one or more emissions-control devices
due to either deliberate disablement or mechanical failure.
Three-way catalytic converter A catalytic converter designed to both
oxidize CO and HC and reduce NOX emissions from gasoline-fueled vehicles
Tier O vehicles- Vehicles that meet Tier O tailpipe standards. For light-duty
vehicles, these tailpipe standards began with model-year 1981 and were
phased out in model-year ~ 995 forpassenger cars and most light-duty trucks.
Tier ~ vehicles—Vehicles that meet Tier ~ tailpipe standards. Forlight-duty
vehicles, these tailpipe standards began with model-year ~ 994.
Tier 2 vehicles Vehicles that will meet Tier 2 tailpipe standards. For light-
duty vehicles, these standards would not begin until model-year 2004.
Transient emission test—An emissions test performed under a load that
varies from moment to moment during the test.
Two-way catalytic converter—A first-generation catalytic converter de-
signed to oxidize CO and HC emissions from gasoline-fueled vehicles.
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Glossary 225
Vehicle miles traveled (VMT) The number of miles driven by a fleet of
vehicles over a set period of time, such as a day, month, or year.
Zero emissions vehicle (ZEV) A vehicle that produces no emissions from
the on-board source of power, e.g., an electric vehicle.
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Representative terms from entire chapter:
criteria air
