Smog has been a problem in coal-burning areas for several centuries. Smog finally decreased when coal combustion was replaced by oil and gas combustion. Air pollution is caused by a number of different types of pollutants. The first type, particulate matter, consists of solid and liquid aerosols suspended in the atmosphere. These arise from the burning of coal and from industrial processes.
Atmospheric particles can scatter and absorb sunlight which reduces visibility.
Particles also reduce visibility by attenuating the light from objects and illuminating the air causing the contrast between the objects and their backgrounds to reduce. Not only does it effect visibility, but it hastens the erosion of building materials and the corrosion of metals, interferes with the human respiratory system, and brings toxic materials into the body. The second type is sulfur oxides which come from the burning of coal and industrial processes. Damage to materials, to vegetation, and to the human respiratory system are caused by the acid nature of oxides. The third type of pollutant is carbon monoxide.