Question: What are the primary environmental sources for the chemical sulfur dioxide?
Answer: Sulfur dioxide in the air comes mainly from activities such as the burning of coal and oil at power plants or from copper smelting. In nature, sulfur dioxide can be released to the air from volcanic eruptions. (https://www.atsdr.cdc.gov/substances/toxsubstance.asp?toxid=46; accessed December 2016)
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