What AdBlue Is, Why “Deletes” Are Marketed, and What Gets Overlooked AdBlue is a high-purity urea-and-water solution used by Selective Catalytic Reduction (SCR) systems to neutralize nitrogen oxides (NOx) in diesel exhaust. When injected upstream of the catalyst, AdBlue transforms harmful NOx into harmless nitrogen and water vapor, allowing modern diesels to deliver torque…