Sulfur dioxide (SO2) is a colorless gas with a strong, irritating odor that comes from many sources, including:

 

Fossil fuel combustion

The largest source of sulfur dioxide is burning coal and oil in power plants and other industrial facilities. 

Smelting mineral ores

Extracting metals like aluminum, copper, zinc, lead, and iron from ores produces sulfur dioxide. 

Volcanic eruptions

Natural sources of sulfur dioxide include erupting volcanoes. 

Vehicles and equipment

Locomotives, ships, and other vehicles and equipment that burn fuel that contains sulfur produce sulfur dioxide. 

Other industrial processes

Petroleum refineries, cement manufacturing, and paper pulp manufacturing also produce sulfur dioxide. 

Sulfur dioxide is somewhat toxic to humans when inhaled in relatively large quantities for a period of several minutes or more. It can cause respiratory problems such as bronchitis, coughing, wheezing, phlegm, and asthma attacks. The effects of sulfur dioxide are worse when exercising. 

Reducing sulfur dioxide emissions can be done by shifting from fossil fuels to cleaner energy sources, such as renewable energy. Increased use of natural gas, which emits lower levels of sulfur dioxide compared to coal and oil, can also help reduce emissions