Vog is a portmanteau (blened word) from the words "volcanic" and "smog," and is a volcanic smog formed when sulfur dioxide and other pollutants emitted by an erupting volcano mix with oxygen and moisture in the presence of sunlight. The term is most often applied to the island of Hawaii, where the Kīlauea volcano has been erupting continuously since 1983. Kilauea emits an estimated 2,000 tons of vog every day.