Which cities face most, least air pollution according to new WHO data

By Jen Christensen, CNN

Updated 2203 GMT (0603 HKT) May 1, 2018

Chat with us in Facebook Messenger. Find out what's happening in the world as it unfolds.

The Nigerian city of Port Harcourt used to be known as "The Garden City." Black soot is now everywhere.
Photos: The Nigerian city covered in soot
Port Harcourt, Nigeria – The Nigerian city of Port Harcourt used to be known as "The Garden City." Black soot is now everywhere.
Hide Caption
1 of 9
The city is in the oil-producing Niger Delta region.
Photos: The Nigerian city covered in soot
Port Harcourt, Nigeria – The city is in the oil-producing Niger Delta region.
Hide Caption
2 of 9
A social media campaign has been launched by radio host Sandra Ezekwesili, #StopTheSoot.
Photos: The Nigerian city covered in soot
Port Harcourt, Nigeria – A social media campaign has been launched by radio host Sandra Ezekwesili, #StopTheSoot.
Hide Caption
3 of 9
The cause of the soot is has been a mysterious to residents, but many think it's related to the destruction of illegal oil refineries.
Photos: The Nigerian city