Air pollution has caused nearly four million deaths, where the deaths are mostly related to respiratory diseases including lung cancer.

How can air pollution affects the lungs and causes cancer?

In much the same way that cigarettes do, just at lower concentrations.

Is this a homework question? What do YOU think and can you ask a more specific question? 

13 minutes ago, FrancoK said:

Air pollution has caused nearly four million deaths, where the deaths are mostly related to respiratory diseases

Apart from cancer, pollution of air can cause pneumoconiosis.

https://en.wikipedia.org/wiki/Pneumoconiosis

Dust obviously has the highest concentration in coalmines, silica mines, factories processing ores and surrounding them areas. Therefor industry workers are the most affected by it.

"In 2013, it resulted in 260,000 deaths globally, up from 251,000 deaths in 1990.[4] Of these deaths, 46,000 were due to silicosis, 24,000 due to asbestosis and 25,000 due to coal workers pneumoconiosis.[4]"

 

Read pathogenesis section in the above article.