I think you are over complicating this. The standards are set out here:
https://tfl.gov.uk/modes/driving/ultra-low-emission-zone/ways-to-meet-the-standard#:~:text=The%20ULEZ%20standards%20are%3A,minibuses%20and%20other%20specialist%20vehicles
Euro 4 for petrol on Nox. That's it.
If your car...