Volcanoes are a major source of sulfur dioxide (SO₂) gas in the atmosphere. This gas is poisonous and is an irritant to the mucous membranes found in your throat, eyes, and nose. Sulfur dioxide also reacts with oxygen, sunlight, dust, and water to create SO₄^2- droplets and sulfuric acid (H₂SO₄), which leads to a type of smog referred to as volcanic smog, or “vog.” Vog can cause asthma attacks and damage the upper respiratory tract. The sulfuric acid produced can also cause acid rain.