The Green amendment is a good result as far as I'm concerned. The LEZ as it stood wouldn't have reduced emissions significantly lower than what would have happened organically anyway. This is because most of the non-compliant vehicles would be scrapped before enforcement.
Honestly, the best way to reduce emissions (of all gases) in the city is to remove 90% of on-street parking and implement bus gates and modal filters. Add on top a surcharge for permit parking of oversized vehicles and Bob is your uncle.