I think this is something that we really need to try, to be sure. I think that any speculation about what would happen (or not happen) as a result of nuclear war is just pure spitballing. No way to know. For example, if billions of people die and countries are destroyed as a part of a nuclear war, you could predict that industrial and manufacturing industries would cease to exist, too. And the people would be dead, meaning less consumption. So on that basis you could assume that pollution would decrease as well. Of course, civilization would be pretty much decimated. So billions of people would be dead but the environment would be much improved. The Sierra Club’s wet dream.