Emission standards limit the amount of pollution that can be released into the atmosphere. Emissions come from many places including industry, power plants, vehicles (from trains to automobiles to mopeds), and small equipment such as lawn mowers. Many emissions standards focus on regulating the amount of material that can be released by automobiles, which use the largest portion of energy in most places around the world. Regulations limit mandate the types of fuels that can be used and the amount of smog-forming material that can be released, but they generally do not directly limit fuel economy—the amount of fuel that can be consumed.
Standards generally regulate the amount of carbon monoxide (CO), oxides of nitrogen (NOx), sulfur, hydrocarbons, and particulate matter (PM) or soot that can be released. The main components of automobile exhaust, carbon dioxide (CO2) and water vapor (H2O), are not considered to be emissions in most cases. Carbon monoxide and other chemicals can generally be reduced by modifying engines to more completely burn fuel, and by using catalytic converters to convert the chemicals into less noxious compounds. Hydrocarbons sometimes leak out of the fuel system, so redesigning that to prevent fuel vapors from escaping can reduce emissions. Reducing carbon dioxide emissions can be accomplished by reformulating fuels and by reducing overall fuel consumption.
EPA standards in the United States
In the United States, emissions standards are managed by the Environmental Protection Agency as well as some state governments. Some of the strictest standards in the world are enforced in California by the California Air Resources Board (CARB). Currently, vehicles sold in the United States must meet "Tier 1" standards that went into effect in 1994. Additional "Tier 2" standards have been optional from 2001 to 2003, and are currently being phased in—a process that should be complete by 2009. The current Tier 1 standards are different between automobiles and light trucks (SUVs, pickup trucks, and minivans), but Tier 2 standards will be the same for both types. A common measurement system for American standards is the somewhat confusing mixed-standard unit of gram per mile.
There are several ratings that can be given to vehicles. A certain percentage of the cars produced by major manufacturers must meet these different levels in order for the company to sell their products in affected regions. Tier 1 has been the baseline used. Beyond Tier 1, in increasing stringency, there are
- TLEV – Transitional Low Emission Vehicle
- LEV – Low Emission Vehicle
- ULEV – Ultra-Low Emission Vehicle
- SULEV – Super-Ultra Low Emission Vehicle
- ZEV – Zero Emission Vehicle
The last category is largely restricted to electric vehicles and hydrogen cars, although such vehicles are usually not entirely non-polluting. In those cases, the other emissions are transferred to another site, such as a power plant or hydrogen reforming center, unless such sites run on renewable energy. However, a battery-powered electric vehicle charged from the California power grid will still be up to ten times cleaner than even the cleanest gasoline vehicles over their respective lifetimes.
The above standards are being made even more stringent. Tier 2 variations are appended with "II", such as LEV II or SULEV II. There are other categories that have also been created.
- ILEV – Inherently Low-Emission Vehicle
- PZEV – Partial Zero Emission Vehicle
- AT-PZEV – Advanced Technology Partial Zero Emission Vehicle
- NLEV – National Low Emission Vehicle
PZEVs meet SULEV emission standards, but in addition have zero evaporative emissions and an extended (15-year/150,000 mile) warranty on their emission-control equipment. Several ordinary gasoline vehicles from the 2001 and later model years qualify as PZEVs; in addition, if a PZEV has technology that can also be used in ZEVs like an electric motor or high-pressure gaseous fuel tanks for compressed natural gas, it qualifies as an AT-PZEV. Hybrid electric vehicles like the Toyota Prius can qualify, as can internal combustion engine vehicles that run on natural gas like the Honda Civic GX. These vehicles are called "partial" ZEVs because they receive partial credit in place of ZEVs that automakers would otherwise be required to sell in California.
The European Union has its own set of standards that vehicles must meet. The tiers are:
- Euro I (1992-1995) limits car emissions 8 g/kWh of NOX and 0.36 g/kWh of PM (Particle Matter)
- Euro II (1995-1999) limits car emissions to 7 g/kWh of NOX and 0.15 g/kWh of PM (Particle Matter)
- Euro III (1999-2005) limits car emissions to 5 g/kWh of NOx and 0.10 g/kWh of PM (Particle Matter)
- Euro IV (2005-2008) limits car emissions to 3.5 g/kWh of NOX and 0.02 g/kWh of PM (Particle Matter)
- Euro V (2008-2012) limits car emissions to 2 g/kWh of NOx and 0.02 g/kWh of PM (Particle Matter)
In addition, all car advertisements in the EU mandate the display of car's value of CO2 emissions in gram/kilometer format (usually 120-160 gr/km for a small compact).
Although most cars in Europe are significantly smaller and lighter than US vehicles, with compact cars predominant, in recent years there has been a marked trend of increasing engine power made available in the same sized chassis. Most EU-made cars that used to sell with some 75hp six years ago are now frequently sporting 100 horsepower or more. Thus CO2 emission sums are rising and a fine print at the bottom of car ads is apparently not enough to stop this trend. The EU must act on vehicular CO2 emissions if it intends to maintain an international lead role in the fight against Global Warming.