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Glossary ADEC. See Alaska Department of Environmental Conservation. AFV. See alternative fuel vehicle. Air-fuel ratio. The ratio, by weight, of air to gasoline entering the intake in a gasoline-powered engine. The ideal (stoichiometric) ratio for complete combustion is approximately 14.7 parts of air to ~ part of fuel, depending on the composition of the specific fuel. Air quality model. A computer-based mathematical model used to predict air quality on the basis of emissions and the effects ofthe transport, disper- sion, and transformation of compounds emitted into the air. Air tonics. Air tonics refers to a host of carcinogens, respiratory toxicants, neurotoxicants, and other harmful atmospheric pollutants not included as criteria air pollutants. The Clean Air Act Amendments of ~ 990 listed 189 of these air toxic s as hazardous air pollutants (HAPs) for future regulation. (One of the HAPS was removed in 1996, leaving 188 tonics on the HAP list.) Alaska Department of Environmental Conservation (ADEC). The Sepal lenient that deals with clean air, land, and water issues in the state of Alaska Albedo. The fraction of incoming sunlight that is reflected from the sur- face of the earth. Albedo is higher over whiter surfaces, such as snow cover, and Tower over darker surfaces, such as oceans and forests. 178

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Glossary 1 79 Alternative fuel vehicle (AFV). Any dedicated, flexible-fuel, or dual-fuel vehicle designed to operate on at least one alternative fuel, such as com- pressed natural gas. Ambient air. The air outside of structures. Often used interchangeably with "outdoor air." Box model. A model that simulates how pollutant concentrations vary with time within a designated volume of air. The effects of emissions, chemical reactions, and exchange with the surrounding atmosphere are usually con- sidered. The air is assumed to be well-mixed within the box. CAA. See Clean Air Act. CAAA90. See Clean Air Act. California Air Resources Board (CARB). A part of the 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, recognizing and considering the effects on the economy of the state. CARB. See California Air Resources Board. Carbon monoxide (CO). A colorless, odorless, tasteless, and toxic gas that results from the incomplete combustion of fuels containing carbon. Carboxyhemoglobin (COHb). A molecule formed when CO reacts with hemoglobin, the intracellular protein that transports oxygen in the blood. The presence of carboxyhemogIobin increases hemogIobin's affinity for oxygen, thereby reducing the transport of oxygen from the blood to the body's tissues. Clean Air Act (CAA). The original Clean Air Act was passed in ~ 963, but our national air pollution control program is actually based on the 1970 version of the law. The Clean Air Act Amendments of ~ 990 (CAAA90) are the most recent revisions of the law. COHb. See carboxyhemoglobin. 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 operating temperature before they can become effective. Conformity. See transportation conformity. Criteria air pollutants. A group of six common air pollutants (carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide) regulated by the federal government since the passage ofthe Clean AirAct in 1970, on the basis of information on health and/or environmental effects of each pollutant.

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180 Managing CO in Meteorological and Topographical Problem Areas Diagnostic trouble codes. Codes that identify emissions control systems and/or components that are malfunctioning and are stored in the engine's computer. They can be retrieved using a scan tool. Dose. The amount of a contaminant that is absorbed or deposited in the body of an exposed person for an interval of time usually from a single medium. Total dose is the sum of doses received by interactions with all environmental media that contain the contaminant. Units (mass) of dose and total dose are often converted to units of mass or contaminant per vol- ume of physiological fluid or mass of tissue. Dynamometer. A treadmill-like machine that allows cars to be tested under the loads typical of on-road driving. Emissions factor. See emission rate. Emissions inventory. An estimate of the amount of a pollutant emitted into the atmosphere from major mobile, stationary, area-wide, and natural sources over a specific period of time, such as a day or a year. Emissions rate. The amount of pollutant emissions produced by an activ- ity per unit of activity. By using the emissions rate of a pollutant and data regarding quantities of materials used by a given source grits activity level, it is possible to compute emissions for the source. In the case of mobile- source emissions, estimated emissions are the product of an emissions rate in mass of pollutant per unit distance (e.g., grams per mile) 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 emissions rate in mass of pollutant per unit energy (e.g., pounds per million Btus) and the amount of energy consumed. Ethanol. EthyI-aTcohol is a volatile alcohol containing two carbon atoms (CH3CH2OH). For fuel use, ethanol is produced by fermentation of corn or other plant products. Evaporative emissions. Hydrocarbon emissions that do not come from the tailpipe of a car but come from evaporation, permeation, seepage, and leaks in a car's fueling system. The term is sometimes used interchangeably with "nontailpipe emissions." Exceedance. An air pollution event in which the ambient concentration of a pollutant exceeds a National Ambient Air Quality Standard (NAAQS9. Exceedance day. A day during which one or more exceedances takes place. Exposure. An event that occurs when there is contact at a boundary be- tween a human and an environmental contaminant of a specific concentra- tion for an interval of time; the units of exposure are concentration multi- plied by time.

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Glossary 181 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. FTP. See federal test procedure. Gaussian dispersion model. A microscaTe model that simulates the dis- persion of pollution from a source such as an intersection or a factory. The spatial dispersion is assumed to be Gaussian in nature, and the ambient concentrations are assumed to be proportional to emissions. Geostrophic winds. Large-scale winds controlled by pressure differences in the atmosphere. Geostrophic winds are not influenced much by the surface of the earth. Gross vehicle weight rating (GVWR). The value specified by the manu- facturer as the maximum design loaded weight of a single vehicle (i.e., vehicle weight plus rated cargo capacity). GVWR. See gross vehicle weight rating. HC. See hydrocarbons. HDV. See heavy-duty vehicles. HDDV. See heavy-duty diesel vehicles. Heavy-duty diesel vehicles (H ODV). A heavy-duty vehicle using diesel fuel. Heavy-duty vehicles (HDV). Any motor vehicle rated at more than 8,500 pounds GV~ or that has a vehicle curb weight of more than 6,000 pounds or a 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. Hydrocarbons (HC). Organic compounds containing hydrogen and car- bon. I/1\~. See inspection and maintenance. IM240. The name for the emissions test used in some I/M programs, in- cluding those in Arizona and Colorado. The ~M240 is a transient, Toaded- mode emissions test. "Loaded-mode" refers to the fact that the test is run on a treadmill-like device called a dynamometer, which simulates driving with the engine in gear. "Transient" refers to the fact that the car drives under a load that varies from second to second during the test. The "240" in IM240 indicates that the test lasts for 240 seconds. The shorter IM240 test is composed of pieces offederal test procedure (FTP) test activity and tends to correlate well with FTP results.

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182 Managing CO in Meteorological and Topographical Problem Areas Inspection and maintenance (I/M). State emissions testing programs that attempt to identify vehicles with higher than allowable emissions and en- sure that such vehicles are repaired or removed from the fleet. Inversion. See temperature inversion. Lapse rate. The rate at which temperature in the atmosphere changes with altitude. The average lapse rate is about-6.5C/km. Under temperature inversion conditions, the lapse rate can be positive. LDV. See light-duty vehicle. LEV. See low emission vehicle. 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 (SWs) may also be in- cluded. Low-emission vehicle (LEV). A vehicle that meets EPA's Clean Fuel Vehicle or LEV standards or CARB's California LEV standards. Malfunction indicator light (MIL). The instrument panel light used by the onboard diagnostic (OBD) system to notify the vehicle operator of an emissions related fault. The MIL is also known as the "service engine soon" or "check engine" lamp. MIL. See malfunction indicator light. Model year. Vehicles are certified for sale, marketed, and later registered as a certain "mode] year" indicating the year a vehicle was produced and offered for sale. Mode] years typically begin in September or October of the prior year, and run 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 preceding year. NAAQS. See National Ambient Air Quality Standards. National Ambient Air Quality Standards (NAAQS). Standards set by EPA for the maximum levels of criteria air pollutants that can exist in the ambient air without unacceptable effects on human health or the public welfare. Nitrogen oxides (NOX). A general term referring to nitric oxide (NO) and nitrogen dioxide (Next. Nitrogen oxides are formed when air is raised to high temperatures, such as during combustion or lightning, and are major contributors to smog fo~ation and acid deposition. NOX. See nitrogen oxide.

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Glossary 183 Nonattainment area. A geographic area in which the time-averaged con- centrations of a criteria air pollutant have exceeded at some recent time a level allowed by the federal standards. A single geographic area may have acceptable levels of some criteria air pollutants but unacceptable levels of others; thus, an area can be both in attainment for one pollutant and in nonattainment for another. Numerical predictive model. A mesoscale or large-scale mode] used to predict chemical concentrations in the atmosphere based on observed mete- orological variables, emissions, and chemistry. Numerical predictive mod- els represent the atmosphere as a three-dimensional grid of air parcels. Chemical transformations take place within the air parcels and air is trans- ported between them. O3. See ozone. OBD. See onboard diagnostic system. OBDI. See onboard diagnostics generation one. OBDII. See onboard diagnostics generation two. Onboard 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 (MIL9, when the controls malfunction, alerting the driver to seek maintenance for the vehicle. The system also communi- cates its findings to repair technicians by means of diagnostics trouble codes, which can be downloaded from the vehicle's computer. Current OBD systems do not directly measure emissions. Onboard diagnostics generation one (OBDT). An onboard automotive diagnostic system required by the California Air Resources Board since 1988 that uses a microprocessor and sensors to monitor and control various engine system functions. A malfunction indicator light (MIL) illuminates when a malfunction is noted, but engine technicians cannot connect to the system and download diagnostic trouble codes. (M~ flash patterns com- municate the problem.) Onboard diagnostics generation two (OBDII). OBDU expands upon OBDI to include monitoring of both the emissions system and sensor dete- rioration and to standardize the interface and code systems. Oxides of nitrogen. See nitrogen oxide. Oxyfuel. See oxygenatedtfuelt. Oxygen sensor. A sensor placed in the exhaust manifold to measure oxy- gen content. On some vehicles, oxygen sensors are located both before and after the catalytic converter.

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184 Managing CO in Meteorological and Topographical Problem Areas Oxygenated fuel. Gasoline containing an oxygenate, typically methyl tertiary-busy! ether (MTBE) or ethanol, intended to reduce production of CO, a criteria air pollutant. in some parts of the country, CO emissions from cars make a major contribution to pollution. In some of these 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. Methyl tertiary-busy! ether (MTBE) and ethanol are the most common oxygenates currently used, although there are a number of others. Ozone (03~. A reactive gas whose molecules contain three oxygen atoms. it is a product of photochemical processes involving sunlight and ozone precursors, such as hydrocarbons and nitrogen oxides. Ozone exists in the upper atmosphere (stratospheric ozone), where it helps shield the earth from excessive ultraviolet rays, as well as in the Tower atmosphere (tropo- spheric ozone) near the earth's surface. Tropospheric ozone causes plant damage and adverse health effects and is a criteria air pollutant; it is a major component of smog. Particulate matter (PM). Any material, except uncombined water, that exists in the solid or liquid droplet states in the atmosphere. Particulate matter includes wind-blown dust particles, particles directly emitted as combustion products, and particles formed through secondary reactions in the atmosphere. Photochemical reaction. A term referring to a chemical reaction brought about by sunlight, such as the formation of ozone from the interaction of nitrogen oxides and hydrocarbons in the presence of sunlight. Plug-in. An electrical device used to heat the engine under extreme cold conditions in order to facilitate engine starting and reduce the time for emissions control devices to be activated. PM. See particulate matter. PM2 s. A subset of particulate matter that includes those particles with an aerodynamic equivalent diameter less than or equal to a nominal 2.5 mi- crometers (~m). This fraction of PM penetrates most deeply into the lungs, and causes the majority of visibility reduction. PM,o. A subset of particulate matter that includes those particles with an aerodynamic equivalent diameter less than or equal to a nominal 10 Em (about 1/7 the diameter of a single human hair). This fraction of PM causes visibility reduction and can penetrate into the lungs. Preconditioning. A set of steps followed to warm-up a vehicle prior to an I/M emissions test so that it can give valid results. Cut points, which deter-

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Glossary 185 mine passing or failing for a vehicle, are based on testing a fully warmed- up vehicle in which the emissions control equipment, including the cata- lytic converter, are hot and fully functional. If an owner drives a short distance to the test station or if the vehicle has to wait in the test station for a Tong time, it may not be fully warmed up. This may result in a false read- ing; a car that would have passed if fully warmed (i.e., fully precondi- tioned) might fail. Process numerical model. A mesoscaTe or large-scale model used to ana- lyze atmospheric processes and their impacts on air quality, typically for research purposes. Like numerical predictive models, process numerical models represent the atmosphere as a three-dimensional grid of air parcels. Process numerical models better resolve the coupling between meteorology and chemistry than numerical predictive models and are not necessarily constrained by observations. Reformulated gasoline (RFG). Specifically formulated fuels blended such that, on average, the exhaust and evaporative emissions of VOCs and hazardous air pollutants (chiefly benzene, I,3-butadiene, polycyclic aro- matic hydrocarbons, formaldehyde, and acetaldehyde) are significantly and consistently Tower than such emissions resulting from use of conventional gasolines. The 1990 Clean Air Act amendments required sale of reformu- lated gasoline in the nine areas with the most severe ozone pollution prob- lems. RFG contains, on average, a minimum of 2.0 weight percent oxygen. Remote sensing. A method for measuring pollutant concentrations from a vehicle's exhaust while the vehicle is traveling down the road. Remote- sensing systems employ infrared absorption to measure VOC and CO con- centrations relative to carbon dioxide. These systems typically operate by continuously projecting a beam of infrared radiation across a roadway and making measurements on the exhaust plume after a vehicle passes through the beam. RFG. See reformulated gasoline. Scan tool. A hand-held computer that is plugged into a vehicle's OBD data link connector to allow a technician to read diagnostic trouble codes, readi- ness status, and monitor other information collected by the OBD system. Secondary particulate matter. Particulate matter that is formed in the atmosphere, and is generally composed of species such as ammonia or the products of atmospheric chemical reactions, such as nitrates, sulfates and organic material, in addition to some water. Secondary particles are distin- guished from primary particles, which are emitted directly into the atmo- sphere. SIP. See state implementation plan.

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186 Managing CO in Meteorological and Topographical Problem Areas State implementation plan (SIP). A detailed description of the scientific methods and programs a state will use to carry out its responsibilities under the Clean AirAct for complying with the NAAQS. SIPs are a collection of the programs used by a state to reduce air pollution. The Clean Air Act requires that EPA approve each SIP, after the public has had an opportunity to participate in its review and approval. Statistical roll-back model. A mode! that estimates the emission reduc- tions needed for a desired improvement in air quality. The emission reduc- tions are assumed to be linearly related to ambient concentrations of pollut- ants. Subsidence. Slow descent of air cooled by radiative cooling. Super ultra-low emission vehicle (SULEV). A vehicle that produces fewer exhaust emissions than ultra-iow emission vehicles (ULE V). Supplemental federal test procedure (SFTP). The SFTP is a certif~ca- tion test for measuring the tailpipe and evaporative emissions from new vehicles that includes two driving cycles not represented in the FTP. The SFTP includes a test cycle simulating high speed and high acceleration driving (US06 cycle) and a test cycle that evaluates the effects of simulat- ing air conditioner operation (SC03 cycle). Synoptic. Used to describe meteorological processes that occur over re- gional spatial scales over several days. TCM. See transportation control measure. TDM. See transportation-demand management strategies. Temperature inversion. An atmospheric condition in which temperature in the Tower part of the atmosphere increases with altitude, rather than decreasing with altitude, as is more typical. Inversion conditions can trap pollution near the surface because warmer, less dense air is resting above colder, more dense air. Three-way catalytic converter. A catalytic converter designed to both oxidize CO and VOCs and reduce NOX emitted from gasoline-fueled vehi- cles. Tier O vehicles. Vehicles that meet Tier O tailpipe standards. For light- duty vehicles, these standards began with model year 1981 vehicles and were phased out in mode] year ~ 995 for passenger cars and most light-duty trucks. Tier 1 vehicles. Vehicles that meet Tier ~ tailpipe standards. Forlight- duty vehicles, these standards began with model year 1994 vehicles. Tier 2 vehicles. Vehicles that will meet Tier 2 tailpipe standards. For light-a~uty vehicles, these standards would not begin until modelyear 2004 vehicles.

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Glossary 187 Transitional low emission vehicle (TLEV). A vehicle meeting either EPA's Clean Fuel Vehicle TLEV standards or CARB's California Low- Emission Vehicle Program TLEV standards. TLEVs produce fewer emis- sions than federal Tier 1 vehicles. Transportation conformity. Aprocess to demonstrate whether a federally supported activity is consistent with the air quality goals in state implemen- tation plans (SIPs9. Transportation conformity demonstrates that plans, programs, and projects approved or funded by the Federal Highway Admin- istration or the Federal Transit Administration for regionally significant projects do not create new violations, increase the frequency or severity of existing violations, or delay timely attainment ofthe National AmbientAir Quality Standards (NAAQSJ. Transportation control measure (TCM). Any control measure to reduce vehicle trips, vehicle use, vehicle-miles traveled, vehicle idling, or traffic congestion for the purpose of reducing motor-vehicle emissions. TCMs can include encouraging the use of carpools and mass transit. Transportation-demand management (TDM) strategies. Strategies which use regulatory mandates, economic incentives, or educational cam- paigns to change driver behavior. TDM strategies attempt to reduce the frequency or length of automobile trips or to shift the timing of automobile trips. Transportation plan. A long-range plan that identifies facilities that should function as an integrated transportation system. Under the ~ter- modal Surface Transportation Efficiency Act of 1991, metropolitan plan- ning organizations (MPOs) must have transportation plans in place that present a 20-year perspective on transportation investments for their region. The transportation plan gives emphasis to those facilities that serve impor- tant national and regional transportation functions, and includes a financial plan that demonstrates how the long-range plan can be implemented. Transportation-supply improvement (TSI) strategies. TSI strategies attempt to reduce emissions by changing the physical infrastructure of road system to improve traffic flow and reduce stop-and-go movements. Travel-demand model. An analysis procedure using heuristics or formal systems of equations to estimate the number, distribution, mode choice, anchor route choice of trips made by a household or individual that can be aggregated to estimate the number of trips starting and/or ending in a spe- cific geographical area. The model determines the amount of transportation activity occurring in a region based on an understanding ofthe daily activi- ties of individuals and employers, as well as the resources and transporta-

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188 Managing CO in Meteorological and Topographical Problem Areas lion infrastructure available to households and individuals when making their daily activity and travel decisions. TSI. See transportation-supply improvement strategies. Two-way catalytic converter. A first generation catalytic converter de- signed to oxidize CO and VOC emissions from gasoline-fueled vehicles. UAM. See urban airshed model. ULEV. See u/(tra-iow emission vehicle. Ultra-low emission vehicle (ULEV). A vehicle meeting either EPA's Clean Fuel Vehicle ULEV standards or CARB's California Low-Emission Vehicle Program ULEV standards. ULEVs produce fewer emissions than LEVs. Urban airshed model ~JAM). A three-dimensional photochemical air quality grid model for calculating the concentrations of both inert and chemically reactive pollutants in the atmosphere. It simulates the physical and chemical processes that affect concentrations of pollutants. The UAM was a specific model developed by Systems Application International, Inc., but the term is now often used generically to describe a variety of models used in this field. 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. One vehi- cle traveling one mile is one vehicle-mile. VMT. See vehicle-miles traveled. VOC. See volatile organic compounds. Volatile organic compounds (VOCs). Organic compounds that can in- clude oxygen-, nitrogen-, and sulfur-containing compounds. Alkanes, alkenes and aromatic hydrocarbons are all VOCs (as well as being HCs). The simple carbon-containing compounds CO and carbon dioxide are usu- ally classified as inorganic compounds. A volatile organic compound is one that can exist as a gas at ambient temperatures. Many volatile organic chemicals are hazardous air pollutants; for example, benzene causes cancer. Zero emission vehicle. A vehicle that emits no tailpipe exhaust emissions.