In the United States, emissions standards are managed nationally by the Environmental Protection Agency (EPA). State and local governments may apply for waivers to enact stricter regulations.
Contents
Motor vehicles
Due to its preexisting standards and particularly severe motor vehicle air pollution problems in the Los Angeles metropolitan area, the U.S. state of California has special dispensation from the federal government to promulgate its own automobile emissions standards. Other states may choose to follow either the national standard or the stricter California standards. States adopting the California standards include Arizona (2012 model year), Connecticut, Maine, Maryland, Massachusetts, New Jersey, New Mexico (2011 model year), New York, Oregon, Pennsylvania, Rhode Island, Vermont, and Washington, as well as the District of Columbia. Such states are frequently referred to as "CARB states" in automotive discussions because the regulations are defined by the California Air Resources Board.
The EPA has adopted the California emissions standards as a national standard by the 2016 model year and is collaborating with California regulators on stricter national emissions standards for model years 2017–2025.
Light-duty vehicles
Light-duty vehicles are certified for compliance with emission standards by measuring their tailpipe emissions during rigorously-defined driving cycles that simulate a typical driving pattern. The FTP-75 city driving test (averaging about 21 MPH) and the HWFET highway driving test (averaging about 48 MPH) are used for measuring both emissions and fuel economy.
Two sets, or tiers, of emission standards for light-duty vehicles in the United States were defined as a result of the Clean Air Act Amendments of 1990. The Tier I standard was adopted in 1991 and was phased in from 1994 to 1997. Tier II standards are being phased in from 2004 to 2009.
Within the Tier II ranking, there is a subranking ranging from BIN 1–10, with 1 being the cleanest (Zero Emission vehicle) and 10 being the dirtiest. The former Tier 1 standards that were effective from 1994 until 2003 were different between automobiles and light trucks (SUVs, pickup trucks, and minivans), but Tier II standards are the same for both types.
These standards specifically restrict emissions of carbon monoxide (CO), oxides of nitrogen (NOx), particulate matter (PM), formaldehyde (HCHO), and non-methane organic gases (NMOG) or non-methane hydrocarbons (NMHC). The limits are defined in grams per mile (g/mi).
Phase 1: 1994–1999
Were phased in from 1994 to 1997, and were phased out in favor of the national Tier 2 standard, from 2004 to 2009.
Tier I standards cover vehicles with a gross vehicular weight rating (GVWR) below 8,500 pounds (3,856 kg) and are divided into five categories: one for passenger cars, and four for light-duty trucks (which include SUVs and minivans) divided up based on the vehicle weight and cargo capacity.
California's Low-emission vehicle (LEV) program defines six automotive emission standards which are stricter than the United States' national Tier regulations. Each standard has several targets depending on vehicle weight and cargo capacity; the regulations cover vehicles with test weights up to 14,000 pounds (6,350 kg). Listed in order of increasing stringency, the standards are:
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.
Transitional NLEV: 1999–2003
A set of transitional and initially voluntary "national low emission vehicle" (NLEV) standards were in effect starting in 1999 for northeastern states and 2001 in the rest of the country until Tier II, adopted in 1999, began to be phased in from 2004 onwards. The National Low Emission Vehicle program covered vehicles below 6,000 pounds GVWR and adapted the national standards to accommodate California's stricter regulations.
Phase 2: 2004–2009
Instead of basing emissions on vehicle weight, Tier II standards are divided into several numbered "bins". Eleven bins were initially defined, with bin 1 being the cleanest (zero-emission vehicle) and 11 the dirtiest. However, bins 9, 10, and 11 are temporary. Only the first ten bins were used for light-duty vehicles below 8,500 pounds GVWR, but medium-duty passenger vehicles up to 10,000 pounds (4,536 kg) GVWR and to all 11 bins. Manufacturers can make vehicles which fit into any of the available bins, but still must meet average targets for their entire fleets.
The two least-restrictive bins for passenger cars, 9 and 10, were phased out at the end of 2006. However, bins 9 and 10 were available for classifying a restricted number of light-duty trucks until the end of 2008, when they were removed along with bin 11 for medium-duty vehicles. As of 2009, light-duty trucks must meet the same emissions standards as passenger cars.
Tier II regulations also defined restrictions for the amount of sulfur allowed in gasoline and diesel fuel, since sulfur can interfere with the operation of advanced exhaust treatment systems such as selective catalytic converters and particulate filters. Sulfur content in gasoline was limited to an average of 120 parts-per-million (maximum 300 ppm) in 2004, and this was reduced to an average 30 ppm (maximum 80 ppm) for 2006. Ultra-low sulfur diesel began to be restricted to a maximum 15 ppm in 2006 and refiners are to be 100% compliant with that level by 2010.
Phase 3A: 2010–2016
In 2009, President Obama announced a new national fuel economy and emissions policy that incorporated California's contested plan to curb greenhouse gas emissions on its own, apart from federal government regulations.
The combined fleet fuel economy for an auto manufacturer of cars and trucks with a GVWR of 10,000 lbs or less will have to average 35.5 mpg. The average for its cars will have to be 42 mpg, and for its trucks will be 26 mpg by 2016, all based upon CAFE Standards. If the average fuel economy of a manufacturer's annual fleet of vehicle production falls below the defined standard, the manufacturer must pay a penalty, currently $5.50 USD per 0.1 mpg under the standard, multiplied by the manufacturer's total production for the U.S. domestic market. This is in addition to any Gas Guzzler Tax, if applicable.
A second round of California standards, known as Low Emission Vehicle II, is timed to coordinate with the Tier 2 rollout.
The PZEV and AT-PZEV ratings are for vehicles which achieve a SULEV II rating and also have systems to eliminate evaporative emissions from the fuel system and which have 150,000-mile/15-year warranties on emission-control components. Several ordinary gasoline vehicles from the 2001 and later model years qualify as PZEVs.
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 (CNG) or liquified petroleum gas (LPG), it qualifies as an AT-PZEV.
Heavy-duty vehicles
Heavy-duty vehicles must comply with more stringent exhaust emission standards and requires ultra-low sulfur diesel (ULSD) fuel (15 ppm maximum) beginning in 2007. Since 2007 only diesel models are allowed in the heavy duty class; the EPA banned gasoline models in 2007.
Greenhouse gases
Federal emissions regulations do not cover the primary component of vehicle exhaust, carbon dioxide (CO2). Since CO2 emissions are proportional to the amount of fuel used, the national Corporate Average Fuel Economy regulations are the primary way in which automotive CO2 emissions are regulated in the U.S. However, the EPA is facing a lawsuit seeking to compel it to regulate greenhouse gases as a pollutant.
As of 2007, the California Air Resources Board passed strict greenhouse gas emission standards which are being challenged in the courts.
On September 12, 2007, a judge in Vermont ruled in favor of allowing states to conditionally regulate greenhouse gas (GHG) emissions from new cars and trucks, defeating an attempt by automakers to block state emissions standards. A group of automakers including General Motors, DaimlerChrysler, and the Alliance of Automobile Manufacturers had sued the state of Vermont in order to block rules calling for a 30 percent reduction in GHG emissions by 2016. Members of the auto industry argued that complying with these regulations would require major technological advances and raise the prices of vehicles as much as $6,000 per automobile. U.S. District Judge William K. Sessions III dismissed these claims in his ruling. "The court remains unconvinced automakers cannot meet the challenge of Vermont and California's (greenhouse gas) regulations," he wrote.
Meanwhile, environmentalists continue to press the Administration to grant California a waiver from the EPA in order for its emissions standards to take effect. Doing so would allow Vermont and other states to adopt these same standards under the Clean Air Act. Without such a waiver, Judge Sessions wrote, the Vermont rules will be invalid.
Air pollution score
EPA's air pollution score represents the amount of health-damaging and smog-forming airborne pollutants the vehicle emits. Scoring ranges from 0 (worst) to 10 (best). The pollutants considered are nitrogen oxides (NOx), particulate matter (PM), carbon monoxide (CO), formaldehyde (HCHO), and various hydrocarbon measures – non-methane organic gases (NMOG), and non-methane hydrocarbons (NMHC), and total hydrocarbons (THC). This score does not include emissions of greenhouse gases (but see Greenhouse gas score, below).
Greenhouse gas score
EPA's greenhouse gas score reflects the amount of greenhouse gases a vehicle will produce over its lifetime, based on typical consumer usage. The scoring is from 0 to 10, where 10 represents the lowest amount of greenhouse gases.
The Greenhouse gas score is determined from the vehicle's estimated fuel economy and its fuel type. The lower the fuel economy, the more greenhouse gas is emitted as a by-product of combustion. The amount of carbon dioxide emitted per liter or gallon burned varies by fuel type, since each type of fuel contains a different amount of carbon per gallon or liter.
The ratings reflect carbon dioxide (CO2), nitrous oxide (N20) and methane (CH4) emissions, weighted to reflect each gas' relative contribution to the greenhouse effect.
Non-road engines
Non-road engines, including equipment and vehicles that are not operated on the public roadways, are used in an extremely wide range of applications, each involving great differences in operating characteristics and engine technology. Emissions from all non-road engines are regulated by categories.
In the United States, the emission standards for non-road diesel engines are published in the US Code of Federal Regulations, Title 40, Part 89 (40 CFR Part 89). Tier 1-3 Standards were adopted in 1994 and was phased in between 1996 and 2000 for engines over 37 kW (50 hp). In 1998 the regulation included engines under 37 kW and introduced more stringent Tier 2 and Tier 3 standards which was scheduled to be phased in between 2000 and 2008. In 2004, US EPA introduced the more stringent Tier 4 standards which was scheduled to be phased in between 2008 and 2015. The testing cycles used for certification follow the ISO 8178 standards.
Small engines
Pollution from small engines, such as those used in gas-powered groundskeeping equipment reduces air quality. Emissions from small offroad engines are regulated by the EPA. Specific pollutants subject to limits include hydrocarbons, carbon monoxide, and nitrogen oxides.
Electricity generation
Performance-based regulation of greenhouse gases from electricity generation has been initiated on the state level. California was the first to implement this standard in January 2007 by adopting Senate Bill 1368, which set a limit of 1,100 lbs. CO2 per megawatt-hour on "new long-term commitments" for baseload power generation. This legislation was intended to apply to new plant investments (new construction), new or renewal contracts with a term of five years or more, or major investments by the electrical utility in its existing baseload power plants. The number of 1,100 lbs. CO2/MWhr corresponds to the emissions per electrical output of a combined cycle gas turbine plant. By comparison, coal-fired steam turbine plants produce 2,200 lbs. CO2/MWhr or more. Other western states followed suit soon after California, with Oregon, Washington, and Montana passing similar bills into law later that year.
Composite wood products
In 2009, the California Air Resources Board (CARB) has established rules for allowable emissions of formaldehyde from wood products made of pieces, chips, particles, or fibers of wood bonded together with a resin. In 2016, the United States the Environmental Protection Agency also issued regulations to limit formaldehyde emissions.
Air quality standards
Individual states with areas that do not attain the targets set by the EPA in the National Ambient Air Quality Standards must promulgate specific regulations which reduce the corresponding emissions from local sources.