What is the difference between National III and National IV vehicles?

[SanKeegan]

The difference between National III and National IV vehicles lies in their emission standards: The National III emission standard requires HC emissions to be below 0.2g per kilometer, CO emissions below 2.3g per kilometer, and NOx emissions below 0.15g per kilometer. The National IV emission standard requires HC emissions to be below 0.1g per kilometer, CO emissions below 1.0g per kilometer, and NOx emissions below 0.08g per kilometer. The main pollutants emitted from vehicle exhaust include hydrocarbons, nitrogen oxides, carbon monoxide, and particulate matter, which are primarily discharged through the vehicle's exhaust pipe. Due to the increasing environmental harm caused by vehicle emissions, countries and regions worldwide have successively established limits on vehicle exhaust emissions.