Free Public Transport in Krakow when PM10 over 150

Krakow Post: "Due to the improving quality of air in Krakow, starting midnight free public transport was called off. Public transport is free when PM10 is over 150 µg/m3, and last night it was recorded at 83 µg/m3. Public transport was free this weekend after the average air pollution at all stations was recorded being over 150 µg/m3. Public transit was free for those with valid vehicle registrations and their passengers.  [lovekrakow.pl]"