This document is a result of my research for those of us new to learning about vehicles that produce less 'bad' emissions and get 'better' mileage. Please help out by commenting on errors and omissions. You have my permission to reproduce all or portions.

Most Information Obtained From:
http://epa.gov/greenvehicles

Mike
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Fuel Economy Guide:
The fuel economy values are the same ones seen on window stickers of new cars, and in the Fuel Economy Guide published annually by EPA and DOE (available at dealers, public libraries, and online at www.fueleconomy.gov.) You compare these fuel economy values to any other vehicle. There is a direct relationship between fuel economy and global warming. Regardless of how cleanly a vehicle runs, it can still emit large amounts of carbon dioxide (CO2), a greenhouse gas. Carbon dioxide is a natural byproduct of fossil fuel combustion, and will always be present in a vehicle's emissions; every gallon of gasoline your vehicle burns puts 20 pounds of CO2 into the atmosphere. The only way to reduce CO2 is to reduce fuel consumption. Better fuel economy means lower CO2 production. In fact, a 5 mpg difference equates to about 2,800 pounds of CO2 a year. Fuel economy should be an important environmental consideration when buying a vehicle. More information on this important environmental topic can be found at

Greenhouse Gas Guide:
The Greenhouse Gas Score reflects the exhaust emissions of carbon dioxide. The score is from 0 to 10, where 10 is best. Carbon dioxide is a greenhouse gas that is released into the atmosphere when solid waste, fossil fuels (oil, natural gas, and coal), and wood and wood products are burned. It's well accepted by scientists that greenhouse gases trap heat in the Earth's atmosphere and tend to warm the planet. The Greenhouse Gas Score is determined from the vehicle's estimated fuel economy and its fuel type. The lower the fuel economy, the more carbon dioxide is emitted as a by-product of combustion. The amount of carbon dioxide emitted per gallon burned varies by fuel type, since each type of fuel contains a different amount of carbon per gallon. A higher score means a vehicle is designed to emit less carbon dioxide. This chart shows the expected amounts of carbon dioxide emissions at each score for each fuel type.

Air Pollution Guide:
The Air Pollution Score reflects pollutants that cause health problems and smog. The score is from 0 to 10, where 10 is best. The air pollutants coming out of a vehicle's tailpipe are tightly controlled by EPA's emissions regulations. Thanks to efforts from both EPA (on the regulation side) and the automotive industry (on the compliance side), today's vehicles are significantly cleaner than in the past. Technology advances such as catalytic converters, exhaust gas recirculation and electronic fuel controls have made tighter pollution control from vehicles possible. However, emission levels will still vary between vehicles due to differences in emissions standards. Emissions performance should be an important environmental consideration when buying a vehicle. This chart shows the expected amounts of emissions per mile at each score.
NOx=Oxides of Nitrogen: Compounds containing nitrogen and oxygen; they combine with hydrocarbons in the sunlight to form smog
NMOG=Non-Methane Organic Compounds: Compounds containing carbon; they combine with NOx in the sunlight to form smog
CO=Carbon Monoxide: A colorless, odorless, poisonous gas
PM=Particulate Matter: Tiny particles of solid matter that lodge in the lungs and deposit on buildings
HCHO=Formaldehyde: A lung irritant and carcinogen

Emission Level Guide
The emission level of a vehicle tells how clean a vehicle is designed to operate. All new vehicles sold in the United States are certified by the EPA to meet a set of emissions standards. This set of standards limits the amount of several types of air pollutants emitted from the vehicle as a result of fuel combustion and evaporation. Some states set stricter standards, including the Northeast states, under EPA's National Low Emission Vehicle (NLEV) Program and California.

The levels of emissions standards, listed from the least clean to the cleanest are:
T1: Tier 1 Current EPA (Federal) standards
TLEV: Transitional Low Emission Vehicle
Least strict NLEV and California standards and are phased out in 2004; more stringent on hydrocarbons than Tier 1 standards
LEV: Low Emission Vehicle
Intermediate NLEV and California standards, allowing about half as many emissions of hydrocarbons and oxides of nitrogen as Tier 1. All new cars sold in California starting in 2004 will have at least a LEV or better rating.
ULEV: Ultra Low Emission Vehicle
Even more stringent hydrocarbon standards than LEV. ULEVs are 50% cleaner than the average 2003 model year car.
SULEV: Super Ultra Low Emission Vehicle
A stricter set of standards for the larger light trucks and medium trucks. SULEVs are 90% cleaner than the average 2003 model year car.
PZEV: Partial Zero Emission Vehicle
PZEVs meet SULEV tailpipe emission standards, have zero evaporative emissions and a 15 year / 150,000 mile warranty. No evaporative emissions means that they have fewer emissions while being driven than a typical gasoline car has while just sitting.
AT-PZEV: Advanced Technology PZEVs
AT-PZEVs meet the PZEV requirements and have additional "ZEV-like" characteristics. A dedicated compressed natural gas vehicle, or a hybrid vehicle with engine emissions that meet the PZEV standards would be an AT-PZEV.
ZEV: Zero Emission Vehicle
The strictest vehicle standard, allowing no emissions at all. ZEVs have zero tailpipe emissions are 98% cleaner than the average 2003 model year vehicle. These include battery electric vehicles and hydrogen fuel cell vehicles.
T2 (Bin 1-Bin 11)
EPA's Tier 2 Bin standards, where Bin 1 is the most stringent and Bin 11 is the least stringent.

In 1998, the California Air Resources Board extended the passenger car emissions standards to heavier sport utility vehicles and pickup trucks (with gross vehicle weight up to 8,500 pounds), which formerly had been regulated under less stringent emission standards (LEV I). The new regulations (LEV II) provide a transition period between 2004 and 2007 for manufacturers to meet the new standards for trucks, vans and SUVs. Consequently, a portion of the large vehicle fleet will meet less stringent emission standards (LEV I) until 2008. For the consumer this means that until 2008, larger vehicles with, for example, a SULEV emissions rating could pollute up to ten times more than a passenger vehicle with that same rating.

EPA Air Pollution Ratings 0-10 are at:
http://www.epa.gov/greenvehicles/0-10chart.htm
They include CO, PM, NOx, NMOG, NOx+NMOG, and NOx+NMOG in Lbs.

*One important point to remember is that the emission levels are not the same for all vehicle classes. For instance, a LEV for a car vehicle class is cleaner than a LEV for a truck vehicle class.

PZEV - Partial Zero Emission Vehicle. A PZEV-rated vehicle is 90% cleaner than the average new car and also has zero evaporative emissions.

AT-PEZ - Advanced Technology Partial Zero Emissions Vehicle. AT-PZEV-rated vehicles meets PZEV ratings and incorporates alternate fuel, gas electric, or other technology.