Emission standards are standards set by governments which specify limits on the amount of pollutants that can be released into the atmosphere from mobile sources such as vehicles and stationary sources such as industry and power plants. The alternative is to set technology standards which designate specific technologies to reduce emissions. Emission standards are preferred since it encourages development of the best technology to meet standards at the least cost.
The World Health Organization (WHO) has established air quality guidelines which can be applied in all regions of the world. They provide uniform standards or targets for ambient air quality. Many countries have set their own national air quality standards that regulate the extent of pollutants in the ambient air. These national standards may be stricter than the WHO guidelines.
Typical examples of vehicle emission standards are the European, Japanese and American emission systems. All of these set emission standards for criteria pollutants such as lead, SO2, NOx, HC, CO and PM on the basis of vehicle type.
The European emission standards (Euro Standards) are followed by all European Union member countries and many other automobile manufacturing countries in Asia and Africa such as China, India, South Africa and Nigeria. Several non-manufacturing countries have also adopted Euro Standards.
Euro Standards are set on the basis of vehicles of different weight categories and engine capacity. Separate standards are set for 2-wheelers and 4-wheelers. In countries like Vietnam, China and India where the number of 2- wheelers (e.g. motocycles) is large the emission standards are more stringent than those in Europe where 2- wheelers are a small proportion of the vehicle fleet and generally have 4-stroke engines. There is a marked discrepancy in the level of standards followed by different countries. For instance, while all countries in Europe have progressed through increasingly strict standards from Euro I to Euro IV, and are moving to Euro V (also see link below) China will introduce Euro IV standards in Beijing and will only introduce them nationwide in 2010. In India Euro III equivalent standards are in force only in the 11 most polluted cities and will apply to the rest of the country only in 2010. No date has yet been set for introducing Euro IV equivalent norms for the rest of the country.
Most countries in Asia have developed vehicle emissions roadmaps based on Euro II standards but very few countries have developed roadmaps to reach Euro IV standards according to the Asian Development Bank (2006). Also, countries that do not manufacture vehicles but allow imports can at best only ensure that vehicles imported conformed to the prevailing standards at the time and in the place of their manufacture. As many imported vehicles are not new, this results in a time lag in introducing improved standards.