10 most polluted cities in the world

After morning tea we watched a small clip about the 10 most polluted cities in the world and they were all in the middle east.  The most polluted city was in Iran!!  Some people had to drive with their lights on and some of the air looked like fog but it was all gas!  Some animals ate rubbish, on the land was just all rubbish and some people had to wear masks because of all the gas in the air.  All of us had to do two facts and one wondering, my wondering was is it cold or hot in the polluted cities and my friend (Jacob) wondered how did the city get polluted in the first place.