Industrial pollution is caused primarily by industrial processes, the burning of coal, oil and natural gas, which in turn produces smoke and fumes. Because the burning fuels contain significant amounts of sulfur, the principal ingredients of smoke and fumes are sulfur dioxide (SO 2 ) and particulate matter. This type of pollution occurs most severely during still, damp and cool weather, such as at night. Even in its less severe form, this pollutant is not confined to just cities. Because of air movements, the pollutants move for miles over the surrounding countryside, leaving in their path a barren and unhealthy environment for all living things.
Working with Federal, State and local mandated rules/regulations and by carefully monitoring emissions, industries have greatly reduced the amount of pollution which they emit, while striving to obtain an acceptable level. Because of the mandated industrial emission clean-up, many land areas and streams in and around the cities that were formerly barren of vegetation and life, have now begun to move back in the direction of nature's intended balance.