Question

what are the causes of air pollution?

Answer 1

the causes of air pollution are following:-
BY fuel combustion in cars,bikes,xuves & trucks (it makes carbon monioxide CO,hydrocarbon HC & nitrogen-oxide NC these are harm full for us and make air pollute) 
BY burning of fossil fuels like coal, wood, dry grass, and construction activity
BY cutting down of trees
BY smoke from factories & cigarette
BY more vehicles  
and BY Climate Change Pollution (CO2) 
Ozone-Causing Pollution (NOx) 
Acid Rain Causing Pollution (SO2) 
Small Particulate Pollution 
Toxic Lead Pollution (Pb) 
Toxic Mercury Pollution (Hg)

Answer 2

Cars, factory's, other vehicles are the main things that cause air pollution.