It could also be that outdoor AQ is worse around you in the winter because everyone is running their boilers, and then that outdoor air ends up inside. I can't

It could also be that outdoor AQ is worse around you in the winter because everyone is running their boilers, and then that outdoor air ends up inside. I can't test it because I have a heat pump, but I would be curious to know what happens to your VOCs if you turn off your boiler at a time when your neighbors are still running theirs.