Its actually not too bad to work out. For a 2011 F20 120d Nox is rated at 146 mg/km
http://www.emissionsfinder.com/bmw-1...ront-rear-20cc
(I dont know how accurate this is so take it with a grain of salt)
So Nox charge is as follows:
https://www.myvehicle.ie/car-news/vrt-nox-emissions
0-60mg/km = 300
60- 80 mg/km = 300
80 - 146 mg/km = 1650
Total 2,250
The actual nox rate for that car might be much lower so double check it, but gives you an idea how to calculate it. The Nox rate for my F10 530d is 40mg/km so I'd be surprised if the one series is as high.