Pea soup this morning. These were common in my youth. They are caused by the lack of any warm air plumes pushing the stuff away. They were always so bad in the 60's and 70's that the airport and anything north was totally cut off. I was going on a car trip to cut a Christmas tree, but now that is not on the table.
I really can't remember all the other weather conditions of those by-gone years, but I'm sure we'll be seeing them soon.
ps. I just went for a walk with the dog. OMG, the stuff just goes through you. This was all thrown out of my memory a long time ago. Now, the solar and wind people will get to know the real Ontario.