What are some of the major sources or causes of ambient air pollution?

Industries, households, cars, and trucks emit complex mixtures of air pollutants, many of which are harmful to health. Of all of these pollutants, fine particulate matter has the greatest effect on human health. Most fine particulate matter comes from fuel combustion, both from mobile sources such as vehicles and from stationary sources such as power plants, industry, households, agriculture or biomass burning.[1]

[1] https://www.who.int/gho/phe/outdoor_air_pollution/en/