@Mor - While you're right that they have taken steps to reduce sulfur in pollution and thus acid rain, it isn't really a "success story" yet.
The international community has definitely set goals in reducing that kind of pollution and met them, actually quite easily.
But, acid rain is still a huge problem because it is difficult to get businesses to agree to reduce their pollution entirely. And acid rain can come from livestock emissions as well, which is almost impossible to desulfurize.
Many famous statues are actually wrapped up to prevent them from being harmed by acid rain now. And it still damages buildings all over the world, but particularly in countries like China and Russia where there is less regulation.
It is a good example of how pollution can be reduced, but it needs more communal effort to be a complete success.