It's important to note that the chemical properties of coal vary significantly from region to region. It is a geological mineral influenced by the conditions of its formation.

In eastern Canada (and I assume the broad area of the USA that is geologically contiguous) the coal is very high in sulphur, making it pretty nasty stuff when burned in volume. The treaties dealing with the acid rain that affected lakes on both sides of the border were, to a substantial degree, related to coal burning. (The granite underpinning, already naturally acidic, did nothing to temper the effects.)

In western Canada, in my general area at least, the coal is low in sulphur. The underlying rock of the basin is limestone, tending toward basic, providing some buffering of acidic effects. (The concerns over super-fine particulate matter and other emissions are leading to a slow phase-out in the power generation industry; it's become an air quality issue. But this does not affect modest use in non-urban areas.)

As for Alaska? I'm curious as to the general chemistry.