What is the cause of smog?

What is needed for smog to be formed are appropriate weather conditions (low temperature, small wind, low humidity) and land topography, as well as the presence of polluting substance emissions. In large cities with developed district heating, the main emitters of pollutants are cars and busses, while in suburban and rural areas emissions are also caused by farming and combustion of inappropriate substances (waste, wood that is not dry enough).

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Coal