Diesel engine emission standard

Look here for EU Stage V explanation,

Tier4 info here,

DieselNet is a good source of info for these type questions.

Aftertreatment requirements vary based on where the engine is being applied, its rating, certification level and application.

A DOC (Diesel Oxidation Catalyst) is usually required to reduce CO emissions, a DPF (Diesel Particulate Filter) is used to reduce particulate emissions, in some cases only one is required, in others both.

Local, state and regional regulations may also apply.

Hope that helps, MikeL.

Thanks for responding, @catserveng.
The site you suggested, cleared my doubts.