keep them inside w fans blowing on them. dont ride or stress their lungs any
I'm in NorCal and we got some pretty bad smoke too. I have fans in my barn I don't know if that helps but it definitely keeps my horses comfortable. I have barely worked my horses for the past week or so just light riding and long walk brakes.
I live in the west coast of Canada and we have bad smoke too there's nothing I can do but don't work them hard or else they inhale the smoke from the fires