Sulfur Dioxide (SO2) Pollution

What is sulfur dioxide?

Sulfur dioxide (SO₂) is a toxic, colorless gas that has a pungent odor, much like that of a just-struck match. Chemically, it is a compound made up of one sulfur atom and two oxygen atoms. SO₂ is also part of a larger group of compounds found in the atmosphere called “sulfur oxides” (SOx). Since SO₂ is the predominant sulfur oxide in the atmosphere, and therefore of greatest concern, the Environmental Protection Agency (EPA) has established a National Ambient Air Quality Standard (NAAQS) for SO₂. In general, the regulation of SO₂ is assumed to cover all other sulfur oxides as well.

For more information about SO₂, NAAQS and areas in Arizona that do not meet standards, visit:
EPA SO₂ NAAQS | View Page >
Hayden SO₂ Nonattainment Area | View Page >
Miami SO₂ Nonattainment Area | View Page >

Where does SO2 come from?

The majority of SO₂ in the atmosphere comes from the burning of fossil fuels (for example, coal and oil) by power plants and other industrial facilities. Other sources include: industrial processes, such as metal extraction (smelting); non-road vehicles, such as large ships, locomotives, etc.; and natural sources, such as volcanoes.

How does SO2 affect my health?

Breathing SO₂can irritate the nose, throat and airways within 10 to 15 minutes of exposure. Coughing, wheezing, shortness of breath or a tight feeling around the chest may be experienced. Children, elderly and those who suffer from asthma or other lung diseases are particularly sensitive to the effects of SO₂. Chronic exposure can increase the susceptibility of the effects of SO₂.

Moreover, SO₂ and other sulfur oxides can react with other compounds in the air and form small particles, or fine particulate matter (PM_2.5). Fine particulates are small enough to penetrate into the lungs and even the bloodstream, which may cause additional health problems.

For more information visit:
EPA Sulfur Dioxide (SO₂) Pollution| View Page >
Air Quality Guide for Particle Pollution | View Page >

How can I protect myself?

The EPA has recommendations for 1-hour SO₂ average concentrations | Learn More >

Current and historical monitored SO2 levels in Arizona

Hayden SO₂ Data (2018) | View >
Miami SO₂ Data (2018) | View >

Air Arizona App | SO2 Monitoring

Air Arizona is a free smartphone app. Within the app, Miami/Globe and Hayden/Winkelman area residents, workers and visitors can access local SO₂ air quality conditions.

Available from the Apple Store and Google Play in English and Spanish, the Air Arizona smartphone mobile app provides users with:

Alerts when the 10-minute average SO₂ concentration reaches 200 parts per billion (ppb)
Notifications when the previous 1-hour average SO₂ concentration exceeds the National Ambient Air Quality Standard (75 ppb)
Health suggestions for protecting yourself and your family
Information on pollution controls
Historical pollution data
Links to additional ADEQ resources

Get the FREE Air Arizona smartphone app today:
Apple iOS | Download >
Android | Download >

Sulfur Dioxide Plans

Currently, Arizona has several nonattainment and maintenance areas for the 1971 and 2010 SO₂ standards. See our e-Map for the Sulfur Dioxide (SO₂ ) nonattainment and maintenance areas | View >

Gila and Pinal Counties

2002 Hayden SO₂ Nonattainment Maintenance Plan | Download >
2017 Hayden SO₂ State Implementation Plan (SIP) | Download >

Gila County

2002 Miami SO₂ Nonattainment and Maintenance Plan | Download >
2017 Miami SO₂ State Implementation Plan (SIP) | Download >