Care to share more about trash burning? I'd be surprised if people living in Krakow or Warsaw commonly burn trash.
A common sight in my area at this time of the year is a senior person driving up to a community dumpster in an equally old car with plates indicating not being from around here and looking for loose pieces of wood - typically furniture.
The sale of furnaces that would even fit something like this for burning was banned in IIRC 2018, but there's a backlog of still functioning ones that are used.
Anyone trying this in a city would have the authorities called on them, but deep in rural areas few care.
It's coming from the surrounding areas, not the city itself.
But people around the city and, frankly, in most of Poland still burn solid fuels and if you drive around these places the smell can be really terrible and the smoke color and density coming from some chimneys definitely doesn't look like a dry wood smoke. Such smoke is often a product of burning very low quality, super fine-grained coal or rather coal dust, which is the cheapest fuel available.