Audi Models

Audi A4

Cars need to meet minimum emission standards when travelling in the Ultra Low Emission Zone (ULEZ) or the daily charge must be paid.

Petrol: Euro 4
Diesel: Euro 6

The ULEZ will be enforced based on the declared emissions of the vehicle rather than the age. However:

Petrol cars that meet the ULEZ standards are generally those registered with the DVLA after 2005, although cars that meet the standards have been available since 2001
Diesel cars that meet the standards are generally those registered with the DVLA after September 2015

Information from Transport For London

Check this car on the TFL website before purchasing: https://tfl.gov.uk/modes/driving/check-your-vehicle/