Smoke and fog.
Smog is a kind of air pollution that is produced by the photochemical reaction of sunlight with nitrogen oxides and hydrocarbons which have been released into the atmosphere, specifically by automotive emissions.
Smog is created out of nitrogen, ozone, oxides of sulfur, smoke and other particles. It can be caused due to agricultural fibres and natural forest fires as well. The reaction of these chemicals can lead to smog. It can lead to health hazards such as cancer, bronchitis, asthma, emphysema and many more.