From this source: https://www.iqair.com/mx-en/newsroom/krakow-among-top-10-mos...

"Krakow’s pollution stems from a mix of local and regional sources. A primary culprit is domestic heating, the burning of coal and wood in older, inefficient household boilers and stoves remains widespread in the Małopolska region (1).

Car traffic also adds nitrogen oxides and fine particulates, exacerbated by an ageing vehicle fleet. Topography and meteorology worsen the problem, Krakow sits in a basin-like region prone to temperature inversions and limited ventilation, allowing pollutants to accumulate.

Additionally, emissions drift in from surrounding municipalities and industrial zones, making regional coordination crucial to air quality. Despite a solid-fuel ban in the city since 2019 and the replacement of many coal boilers, compliance is uneven and some residents still use banned fuel."