Air quality monitors measure concentrations of SO₂ throughout the country. EPA, state, tribal and local agencies use that data to ensure that SO₂ in the air is at levels that protect public health and the environment. Nationally, average SO₂ concentrations have decreased substantially over the years. The charts below show national and regional trends in SO₂ concentrations. For information on SO₂ standards, sources, health effects, and programs to reduce SO₂, please see our Sulfur Dioxide Pollution page.