Before developing their own NOx reduction technology, Volkswagen considered using urea-based selective catalytic reduction (SCR) systems. This technology is widely used in the automotive industry to reduce nitrogen oxides (NOx) emissions from diesel engines. Urea SCR systems inject a urea solution (commonly known as diesel exhaust fluid or DEF) into the exhaust stream, where it reacts with NOx in the presence of a catalyst to convert it into harmless nitrogen and water.

However, Volkswagen ultimately decided to pursue a different approach, which led to the infamous emissions scandal. They developed a software solution that could detect when vehicles were being tested for emissions and alter the engine performance to meet regulatory standards, while in normal driving conditions, the vehicles emitted far more NOx than allowed.

This decision has had significant legal and reputational repercussions for the company, highlighting the importance of adhering to environmental regulations and the potential consequences of circumventing them.