I'm surprised how little time Rick spends on these low-emission zones in his guides. I've not paid much attention in the past as I don't rent a car in Europe but my son-in-law just did and got a surprise! He rented in Switzerland and was driving to and returning in Germany. The car met the right standards but had a Swiss permit, not a German one! They were unaware that their hotel was in a green zone and on the road there was no (easy) way to get a German permit. From the states I found a parking lot for them outside of the green zone and they taxied to their hotel.
Granted, he should have done a bit more research (and the Swiss said, "It will be fine!") But like I said, I'm surprised that so little ink is devoted to this. I just read the Belgium guide cover to cover in advance of my upcoming trip and there is nothing.