Are EURO4 emissions better than EURO5 emissions?

No, in every cathegory the EURO5 emission levels are more stringent then EURO4.

For example, at Diesel Passanger Cars, PM level is 0.025 g/km (EURO4) and 0.005 g/km (EURO5)

Emission measurement methods might have been modified as well.

More details can be found eg. here:

http://www.dieselnet.com/standards/#eu

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