Encourage the poorer people you mean. The rich can and will carry on polluting as either their vehicles are compliant (but often still polluting) or they can afford to pay the tax!
It's *****, but it was ever thus. People at the bottom are always disproportionately affected by these sorts of taxes (beer, wine, petrol, you name it). The likelihood is that most people with a bit of money in their pocket will already have compliant cars.
That's why the support part of it is important.