What is Adblue diesel exhaust fluid?

Adblue is an additive used in many newer diesel cars and has lately made news for being in short supply. So what is it and what does it do?

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What is diesel exhaust fluid and why is it more important than

AdBlue/DEF 101 – FAQ & What You Need To KnoW – IDParts Blog

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Genuine BMW # 83190440158

Genuine BMW Diesel Exhaust Fluid Adblue - 2.5 gallon - 83190440158

26L Adblue Diesel Exhaust Fluid, For Automotive at Rs 1299/bucket

Diesel Exhaust Fluid (DEF) LR072258, AdBlue, Half Gallon (1.89