Emissions standards are requirements for specific limits on the amount of pollutants that can be released into the environment. Many emissions standards focus on regulating pollutants released by automobiles and other motor vehicles, but they can also regulate emissions from industry, power plants, and small equipment such as lawnmowers and fuel-powered generators. Common policy alternatives to emissions standards are technology standards (which mandate the use of a specific technology) and emissions market standards.

Standards generally regulate emissions of nitrous oxides (NO), sulfur oxides (Sulfur oxide (IV)), suspended particulate matter (PS) or soot, carbon monoxide (CO), or volatile hydrocarbons (see carbon dioxide equivalence).

An emissions performance standard is the limit that establishes the limits above which a different type of emissions control technology may be necessary. While emissions performance standards have been used to impose limits on conventional pollutants such as nitrous oxides and sulfur oxides (NOx & SOx), these regulations can be used to regulate greenhouse gases, particularly carbon dioxide (CO). In the US, that is given in pounds of carbon dioxide per megawatt-hour (lbs. CO/MWh), and kg of CO/MWh worldwide.

In the last five years, several countries have joined the adoption of vehicle emissions performance standards, bringing the number of countries in the world to 71 that now adhere to the Euro 4/IV regime. However, by 2020, there were still more than 80 countries that did not have this type of standard, which complicates the measurement of fuel quality. [1]​.

India

On 6 October 2003, a national fuel policy was announced, which envisaged a phased program to introduce Euro 2 - 4 emissions regulations by 2010. The implementation program of the European Union emissions standards in India is summarized in Table 1.[2]​.