What causes air pollution?

What causes air pollution?
How much pollution we breathe in is dependent on many factors, such as access to clean energy for cooking and heating, the time of day and the weather. Rush hour is an obvious source of local pollution, but air pollution can travel long distances, sometimes across continents on international weather patterns.
Nobody is safe from this pollution, which comes from five main human sources. These sources spew out a range of substances including carbon monoxide, carbon dioxide, nitrogen dioxide, nitrogen oxide, ground-level ozone, particulate matter, sulfur dioxide, hydrocarbons, and lead–all of which are harmful to human health.