If you want to travel in my city at at the winter time, there is a tip about about the air quality in my city.
If you want to travel in my city at the Dec, the air quality is ok because of the most of the important sites are all indoors. But from 11/15, the central heating system start to burn more coal to provide the heat to the local people, so that the pullation get more and more worse from that time. Better bring a mask with you just in case you will use it at the uncertain situation.
hope this can help you all