EMISSION TEST PROCEDURES
The vehicle emission limits are specified based on a standard test procedure, which includes;

• A specified vehicle driving or engine operation schedule of varying speeds and loads which represents real life driving/usage pattern of the vehicles and engines. The test schedule of vehicle or engine operation is known as ‘driving cycle’.
• Use of emission sampling systems and analyzers that operate on the working principles specified in the emission regulations.

The new production vehicles and engines are tested for compliance with the emission standards in a government approved laboratory.
The USA and particularly the state of California have led the world in developing vehicle emission test methods and in   setting the vehicle emission limits. The test cycles used in the USA, Europe and Japan for emission measurement and certification of vehicles/engines for compliance with the standards differ and so also the numerical values of the emission limits. Therefore, direct comparison between standards in different countries is generally not possible.

Units of Emission Limits

 Two types of emission limits are specified in the standards

• For the light and medium duty vehicles, passenger cars and, two and three wheelers are in terms of mass of pollutant emitted per unit distance travelled i.e., g/km ( g/mile in the USA , 1 g/km = 1.61 g/mile).
• For heavy duty vehicles and engines  test is carried on the engine itself and the limits are specified in terms of mass of pollutant per unit of work done, i.e., g/kW-h or g/bhp-h (1 g/kW-h = 1.34 g/bhp-h) .

The test cycle and measurement procedures have been accordingly developed whether test is to be done on a vehicle or on the engine.