It's a sad state of affairs in major Polish cities. Out of the 4 major tech hubs: Warsaw, Krakow, Wroclaw, 3-city (Gdansk/Sopot/Gdynia which form one long city) air is terrible in all with the exception of 3-city. Even there it's not so rosy (depends on the area, some are very clean, some not so much but air pollution stations are too sparse to show it). I moved out because of it and I wouldn't advise anyone to live in Poland (outside 3-city) if they have other options. It's not worth it to risk your health.

The situation is terrible for many reasons but major 2 are ancient coal/junk heating (people won't upgrade to eco-friendly heating because most of them are dirty poor and their main problem is to find a cheaper coal substitute for next winter) and Germans flooding us with used diesel cars with particulate filters long not working (or removed). There is a lot of talk about CO2 but this is long term danger while used diesel cars are poisoning us right now at massive scale.

How the Germans flood you with these diesels? Do they drop their used car right across the border or is it organized at state level? And why they take out particle filters before that?

It is literally the worst in Europe at the moment. It's a huge issue over there.

In Krakow? Has it changed a lot in the past years? I was there in 2014 and the air was great.

I spent some time in Krakow and it has horrible air quality. Summer feels normal like any other city, but certain times during the winter it's difficult to see due to the smog. See the below video for reference.

https://www.youtube.com/watch?v=x7nxugvTmJo

Wow darn I'm never throwing the stone at China again, seeing this in Europe, so close to home !

Were you in summer? The problem with air pollution is rather seasonal and while in warmer months it's not an issue, winters are terrible.

Source: I lived in Kraków for 4 years.

Yeah I was, so that was probably it.

It's so bad that Dynatrace, who is hiring in Gdańsk (another Polish city), is trying to convince devs from Kraków to move there with this: http://zmiensrodowisko.pl/

In the whole area. Where I spent time people still use coal heating and you had garbage pick up once a week (and you had to tip), so even tho burning garbage in the stove is illegal you surely knew when a neighbor was doing it. Part of my coming back home culture shock was not seeing cars covered in sooth.

Smarter neighbors segregate their garbage. For burning during the day, and for burning during the night.