Ask Shorty: What is AdBlue?

I recently brought a second-hand diesel vehicle. When the salesman told me this vehicle uses AdBlue I said "yeah, no worries" as if I knew what he was talking about but I honestly had no idea. Can you tell me why some diesel vehicles require AdBlue and why it's used?

Cheers, Ian

AdBlue, sometimes referred to as Diesel Emission Fluid (DEF), is an additive that helps to reduce harmful emissions from diesel vehicles, in particular oxides of nitrogen (NOx). It's a mixture of roughly one-third pure urea and two-thirds demineralised water. The AdBlue is housed in a special tank and injected into the exhaust gases before they pass through a Selective Catalytic Reduction (SCR) converter. In the converter, the NOx is turned into harmless nitrogen gas and water vapour. It is already widely used in the trucking industry in Europe and Australia and is common in diesel cars in Europe. The technology was developed in response to increasingly strict emissions laws being adopted in Europe.