The atmosphere above Christchurch, NZ tends to form layers in winter that trap the smoke and make this worse, and new fireplaces have been restricted to clean-burning log burners and dry wood by law.

It seemed like the biggest change in air quality in recent years came from the tragic earthquakes in 2010 and 2011 knocking down all the unreinforced-masonry chimneys, though.

Why would anyone burn anything but dry wood in their indoor fireplace...