Sulfur Dioxide


What is Sulfur Dioxide (SO2)?

SO2  is a gas that is chiefly released into the environment by several common industrial processes and by active volcanoes. Sulfur is a trace component in many raw materials, and when those materials are processed or burned for fuel, Sulfur bonds with oxygen and produces SO2. According to the Environmental Protection Agency (EPA) 65 % of the SO2 in the air comes from utilities especially those burning coal (U.S. Environmental Protection Agency, 2007). SO2 in the air poses several health concerns and is the leading cause of acid rain.
What are the allowable levels of SO2?

  • According to the EPA, the following are important levels of SO2  to note
    • 0.03 parts per million (ppm) of SO2 for long term atmospheric levels
    • 0.14 ppm for a period of 24 hours, this type of exposure should occur no more than once a year
    • 100 ppm is considered to be immediately life threatening
    • 2 ppm is the recommendation set for the workplace by the Occupational Safety and Health Administration (OSHA)

*** All of these figures are from the Agency for Toxic Substances and Disease Registry ToxFAQs on Sulfur Dioxide (1999)

  • How do you know if it’s a problem in your area?
    • SO2  is an issue in many areas, however as a result of the EPA’s acid rain reduction initiatives, emissions of SO2 have been improving.
    • Heavily industrial areas have higher levels of SO2 and people who live in those areas should limit their activities outside and pay attention to daily air quality reports particularly in the summer time.
    • To determine what pollutants are a problem in your area go to and enter the zip code you are inquiring about.


  • What are the health effects if exposed?
    • General Symptoms:
      • Irritated, itchy eyes, nose, or throat
      • Coughing
      • Chest tightness


    • Respiratory:
      • long-term exposure to SO2 increases your risk of developing chronic bronchitis
      • SO2 can trigger an asthma attack
      • Irritation of nasal passages, if concentrations are high enough SO2 can cause a chemical burn of the nasal passages can happen


    • Cancer: There has been no conclusive research to show that typical environmental exposure to SO2 increases a person’s risk of developing cancer. If a person works where SO2 is a common material they are exposed to, there is an increased risk of cancer of the respiratory tract.


    • Children who live in areas where air pollution is a problem, have higher rates of bronchitis, and more frequent ear infections


  • How to know when it is unsafe to be active outside:
    • The Air Quality Index (AQI) is a scale used to identify potential problems occurring in a given area.


AQI Value
Level of Health Concern
0-50 Low Green Air quality is considered satisfactory, and air pollution poses little or no risk.
51-100 Moderate Yellow Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.
101-150 Unhealthy for Sensitive Groups Orange Members of sensitive groups may experience health effects. The general public is not likely to be affected.
151-200 Unhealthy Red Everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects.
201-300 Very Unhealthy Purple Health alert: everyone may experience more serious health effects.
301-500 Hazardous Maroon Health warnings of emergency conditions. The entire population is more likely to be affected.

**This chart was taken from AirNow’s website Understanding of the AQI at

  • To determine the AQI for your area, go to and click on your state.


Developed by:  Cindy Riehn, Radford University School of Nursing

Comments are closed.