What is a diesel emissions system, anyway?
All engines have an intake system to breathe air in and an exhaust system that expels the dirty air after it is used and mixed with particulates from the fuel combustion process. As a part of the exhaust system, filters trap these particulates and dramatically reduce the output of harmful little nasties like nitrous oxides (NOx). For larger clean diesel engines, VW takes the additional step of urea injection, which further reduces NOx. Check out how diesels work.
