Just the wind patterns. And where the bulk of the fires are. They're mostly in Northern Quebec, so fairly far east, and the smoke seems to be pushing south from there down over Ottawa and then the eastern half of New York and kind of pooling further south.

Just got home to southern Ontario from a work trip (in South Dakota, where there was no smoke at all) and I was expecting it to be pretty bad, but it really isn't (though I won't be exerting myself outside or anything). It's sitting mostly east of here, so far.

Rain coming next week, that should relieve things.