Question: what is the difference between euro 4 and euro 6?
Answer: By 2006, Euro 4 emissions were in place reducing the maximum NOx in diesels to 250mg/km and Euro 5 reduced it further to 180mg/km in 2011. ... Under Euro 6 standards, however, the maximum level for NOx in diesel models is 80mg/km, compared to 60mg/km in petrol cars.