What are two sources of air pollution?

Answer 1

There are many sources of air pollution.

Two sources could be:
Car exhausts
Coal fired power stations

This web site has the main air pollutants and their sources:

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Answer 2

Automobiles, power plants, chimneys, forest burning (and other agricultural burning), garbage dumps and landfills (methane). Tobacco in indoor situations, especially in North Carolina shopping malls (I almost choked in that Mall).

Answer 3

Some lesser sources are windblown dust (especially in northern China), volcanic eruptions and radioactive radon from the ground that gets trapped inside buildings. The photolysis of organic matter released by trees and spilled gasoline also creates a haze.