Every usage of Ballistic missiles in wars adds to the epicenter pollution.
Every epicenter extends its pollution to the other regions, that are located in 1.500 km radius. You can see the summ of epicenter and extended (acquired from another epicenters) pollutions on the region page.
Every 120 points of damage, dealt by using Ballistic missiles add 1 point of pollution to the epicenter.
Every point of pollution adds 0.5% to the time, needed for Energy to restore in natural way.
You can see all active epicenters here.