Emission standards are the legal requirements governing air pollutants released into the atmosphere. Emission standards set quantitative limits on the permissible amount of specific air pollutants that may be released from specific sources over specific timeframes. They are generally designed to achieve air quality standards and to protect human life. Different regions and countries have different standards for vehicle emissions.

Regulated sources Many emissions standards focus on regulating pollutants released by automobiles (motor cars) and other powered vehicles. Others regulate emissions from industry, power plants, small equipment such as lawn mowers and diesel generators, and other sources of air pollution.

The first automobile emissions standards were enacted in 1963 in the United States, mainly as a response to Los Angeles' smog problems. Three years later Japan enacted their first emissions rules, followed between 1970 and 1972 by Canada, Australia, and several European nations. The early standards mainly concerned carbon monoxide (CO) and hydrocarbons (HC). Regulations on nitrogen oxide emissions (NOx) were introduced in the United States, Japan, and Canada in 1973 and 1974, with Sweden following in 1976 and the European Economic Community in 1977. These standards gradually grew more and more stringent but have never been unified.Dicorato, p. 152

There are largely three main sets of standards: United States, Japanese, and European, with various markets mostly using these as their base. Sweden, Switzerland, and Australia had separate emissions standards for many years but have since adopted the European standards. India, China, and other newer markets have also begun enforcing vehicle emissions standards (derived from the European requirements) in the twenty-first century, as growing vehicle fleets have given rise to severe air quality problems there, too.

Vehicle emission performance standard

An emission performance standard is a limit that sets thresholds above which a different type of vehicle emissions control technology might be needed. While emission performance standards have been used to dictate limits for conventional pollutants such as oxides of nitrogen and oxides of sulphur (NOx and SOx), this regulatory technique may be used to regulate greenhouse gases, particularly carbon dioxide (). In the US, this is given in pounds of carbon dioxide per megawatt-hour (lbs. /MWhr), and kilograms /MWhr elsewhere.

Africa ECOWAS Since 1 January 2021, all new vehicles in ECOWAS must comply with Euro 4.

Morocco From 1 January 2024, all new vehicles in Morocco must comply with Euro 6b.

South Africa South Africa's first clean fuels programme was implemented in 2006 with the banning of lead from petrol and the reduction of sulphur levels in diesel from 3,000 parts per million (ppm) to 500 ppm, along with a niche grade of 50 ppm.

The Clean Fuels 2 standard, expected to begin in 2017, includes the reduction of sulphur to 10 ppm; the lowering of benzene from 5 percent to 1 percent of volume; the reduction of aromatics from 50 percent to 35 percent of volume; and the specification of olefins at 18 percent of volume.

North America

Canada In Canada, the Canadian Environmental Protection Act, 1999 (CEPA 1999) transfers the legislative authority for regulating emissions from on-road vehicles and engines to Environment Canada from Transport Canada's Motor Vehicle Safety Act. The Regulations align emission standards with the U.S. federal standards and apply to light-duty vehicles (e.g., passenger cars), light-duty trucks (e.g., vans, pickup trucks, sport utility vehicles), heavy-duty vehicles (e.g., trucks and buses), heavy-duty engines and motorcycles.

Mexico From 1 July 2019, all new heavy vehicles must comply with EPA 07 and Euro 5. From 1 January 2025, all new heavy vehicles must comply with EPA 10 and Euro 6.

United States

The United States has its own set of emissions standards that all new vehicles must meet. In the United States, emissions standards are managed by the Environmental Protection Agency (EPA). It uses tiers to identify emission standards for cars, trucks and other motor vehicles. In 2014, the EPA published its "Tier 3" standards for these vehicles, which tightened air pollution emission requirements and lowered the sulfur content in gasoline.U.S. Environmental Protection Agency (EPA), Washington, D.C. (2014-04-18). "Control of Air Pollution From Motor Vehicles: Tier 3 Motor Vehicle Emission and Fuel Standards." Final rule. Federal Register,

EPA has separate regulations for small engines, such as groundskeeping equipment. The states must also promulgate miscellaneous emissions regulations in order to comply with the National Ambient Air Quality Standards.

In December 2021 EPA issued new greenhouse gas standards for passenger cars and light trucks, effective for the 2023 vehicle model year.

State-level standards

Under federal law, the state of California is allowed to promulgate more stringent vehicle emissions standards (subject to EPA approval), and other states may choose to follow either the national or California standards. California had produced air quality standards prior to EPA, with severe air quality problems in the Los Angeles metropolitan area. LA is the country's second-largest city, by population, and relies much more heavily on automobiles and has less favorable meteorological conditions than the largest and third-largest cities (New York and Chicago).

Some states have areas within the state that require emissions testing while other cities within the state do not require emission testing. Arizona emissions testing locations are located primarily in the two largest metropolitan areas (Phoenix and Tucson). People outside of these areas are not required to submit their vehicle for testing as these areas are the only ones that have failed the air quality tests by the state.

California's emissions standards are set by the California Air Resources Board (CARB). By mid-2009, 16 other states had adopted CARB rules; given the size of the California market plus these other states, many manufacturers choose to build to the CARB standard when selling in all 50 states. CARB's policies have also influenced EU emissions standards.

California is attempting to regulate greenhouse gas emissions from automobiles, but faces a court challenge from the federal government. The states are also attempting to compel the federal EPA to regulate greenhouse gas emissions, which as of 2007 it has declined to do. On 19 May 2009, news reports indicate that the Federal EPA will largely adopt California's standards on greenhouse gas emissions.

California and several other western states have passed bills requiring performance-based regulation of greenhouse gases from electricity generation.

In an effort to decrease emissions from heavy-duty diesel engines faster, CARB's Carl Moyer Program funds upgrades that are in advance of regulations.

The California ARB standard for light vehicle emissions is a regulation of equipment first, with verification of emissions second. The property owner of the vehicle is not permitted to modify, improve, or innovate solutions in order to pass a true emissions-only standard set for their vehicle driven on public highways. Therefore, California's attempt at regulation of emissions is a regulation of equipment, not of air quality. Vehicle owners are excluded from modifying their property in any way that has not been extensively researched and approved by CARB and still operate them on public highways.

South America

Argentina From 1 January 2016, all new heavy vehicles in Argentina must comply with Euro 5. From 1 January 2018, all new light and heavy vehicles in Argentina must comply with Euro 5.

Brazil

From 1 January 2012, all new heavy vehicles in Brazil must comply with Proconve P7 (similar to Euro 5) From 1 January 2015, all new light vehicles in Brazil must comply with Proconve L6 (similar to Euro 5). From 1 January 2022, all new light vehicles in Brazil must comply with Proconve L7 (similar to Euro 6). From 1 January 2023, all new heavy vehicles in Brazil must comply with Proconve P8 (similar to Euro 6). From 1 January 2025, the new light vehicle fleets in Brazil must comply with the first stage of Proconve L8 (automaker average).

Chile From September 2014, all new cars in Chile must comply with Euro 5. From September 2022, all new light and medium vehicle models in Chile must comply with Euro 6b. From 30 September 2025, all new light and medium vehicle models in Chile must comply with Euro 6c.

Colombia From 1 January 2023, all new vehicles in Colombia must comply with Euro 6b.

Peru From 1 April 2018, Euro 4, Tier 2, and EPA 2007 are mandated. From 1 October 2024, Euro 6b, Tier 3, and EPA 2010 are mandated.

Asia Cambodia Since 1 January 2022, all new vehicles in Cambodia must comply with Euro 4.

From 1 January 2027, all new vehicles in Cambodia must comply with Euro 5.

China

Due to rapidly expanding wealth and prosperity, the number of coal power plants and cars on China's roads is rapidly growing, creating an ongoing pollution problem. China enacted its first emissions controls on automobiles in 2000, equivalent to Euro I standards. China's State Environmental Protection Administration (SEPA) upgraded emission controls again on 1 July 2004 to the Euro II standard. More stringent emission standard, National Standard III, equivalent to Euro III standards, went into effect on 1 July 2007. Plans were for Euro IV standards to take effect in 2010. Beijing introduced the Euro IV standard in advance on 1 January 2008, becoming the first city in mainland China to adopt this standard. Since 1 January 2018, all new vehicles must comply with China 5 (similar to Euro 5). Since 1 January 2021, all new vehicles in China must comply with China 6a (similar to Euro 6). Since 1 July 2023, all new vehicles in China must comply with China 6b (stricter than Euro 6).

Hong Kong

From 1 January 2006, all new passenger cars with spark-ignition engines in Hong Kong must meet either Euro IV petrol standard, Japanese Heisei 17 standard or US EPA Tier 2 Bin 5 standard. For new passenger cars with compression-ignition engines, they must meet US EPA Tier 2 Bin 5 standard.

The current standard is Euro 6C, it has been phased in since 2019.

India

Bharat stage emission standards are emission standards instituted by the Government of India to regulate the output of air pollutants from internal combustion engine equipment, including motor vehicles. The standards and the timeline for implementation are set by the Central Pollution Control Board under the Ministry of Environment & Forests.

The standards, based on European regulations were first introduced in 2000. Progressively stringent norms have been rolled out since then. All new vehicles manufactured after the implementation of the norms have to be compliant with the regulations. By 2014, the country was under a combination of Euro 3 and Euro 4-based norms, with Euro 4 standards partly implemented in 13 major cities. Till April 2017, the entire country was under BS IV norms, which is based on Euro 4.

As of now manufacturing and registration of BS VI vehicles has started, from April 2020 all BS VI manufacturing is mandatory, respectively.

Japan Background