FAQ for SO2 and Asthma

Frequently Asked Questions (FAQ) Regarding Asthma and Sulfur Dioxide (SO2) Exposure (Information obtained directly from the American Lung Association website)

What Is Sulfur Dioxide?

Sulfur dioxide (SO2) is a gaseous air pollutant composed of sulfur and oxygen. SO2 forms when sulfur-containing fuel such as coal, oil, or diesel is burned. Sulfur dioxide also converts in the atmosphere to sulfates, a major part of fine particle pollution in the eastern U.S.

What Are the Sources of SO2 Emissions?

Manmade sources in the U.S. emitted more than 6.4 million tons of sulfur dioxide in the most recent reports.1 The largest sources of sulfur dioxide emissions are electricity generation, industrial boilers, and other industrial processes such as petroleum refining and metal processing. Diesel engines are another major source, including old buses and trucks, locomotives, ships, and off-road diesel equipment.

What Causes High Concentrations of SO2?

Coal-fired power plants remain one of the biggest sources of sulfur dioxide in the U.S., particularly in the eastern states. The plume from a coal-fired power plant touches down at ground level during high wind conditions or gets trapped by inversions in the atmosphere. High levels can happen during start-up, shutdown, upsets, and malfunctions of pollution control equipment. Ports, smelters, and other sources of sulfur dioxide also cause high concentrations of emissions nearby. People who live and work nearby these large sources get the highest exposure to SO2. After SO2 gets into the air, it changes chemically into sulfate particles, which can blow hundreds of miles away.

What are the Health Effects of Sulfur Dioxide Air Pollution?

Sulfur dioxide causes a range of harmful effects on the lungs, as the EPA’s most recent review of the science concluded:

  • Wheezing, shortness of breath and chest tightness and other problems, especially during exercise or physical activity.
  • Continued exposure at high levels increases respiratory symptoms and reduces the ability of the lungs to function.
  • Short exposures to peak levels of SO2 in the air can make it difficult for people with asthma to breathe when they are active outdoors.
  • Rapid breathing during exercise helps SO2 reach the lower respiratory tract, as does breathing through the mouth.
  • Increased risk of hospital admissions or emergency room visits, especially among children, older adults and people with asthma.2

For more information on indoor and outdoor air quality, please visit the following link to the American Lung Association https://www.lung.org/our-initiatives/healthy-air/outdoor/air-pollution/sulfur-dioxide.html


U.S. Environmental Protection Agency. Data from the National Emissions Inventory, 2011. Accessed August 23, 2016.

U.S. EPA. Integrated Science Assessment for Sulfur Oxides – Health Criteria. EPA/600/R-08/047F, September 2008.

Allegheny County Resources for Questions Related to Asthma and Sulfur Dioxide

  • Allegheny Alerts: Provides notifications about community news sign up for the Community Notification System.
  •  Follow this link
  • Signup for account
  • Select how you would like to be alerted (Text, email, phone, etc)
  • Provide your home address so the alerts you receive are relevant to your community
  • Select however many topics you want to be alerted about. We suggest at minimum to subscribe to the following
    • County Announcements: Emergency Notification Information
    • Allegheny County Health Department: Air-Air Quality Action Day, Air Quality Burn Ban Day, Today‚Äôs Air Quality
  • Purple Air Quality Citizen Science Monitor Network: This provides you with local air quality data in Allegheny County. Note these air monitors are not managed by Allegheny County and is not considered official data. They are a network of monitors managed by community residents and businesses. Anyone with asthma could potentially have symptoms when air quality is not good. See link below as well as a key to help understand the air data.


Color Key



Orange= Unhealthy for Sensitive Groups

Red= Poor

  • Smell Pittsburgh: This is an app you can download on your phone to record smells related to air pollution in your community. The information from the app is shared with the Allegheny County Health Department. The Smell app is easy to use. All you have to do is
    • Download the app here https://smellpgh.org/
    • Enter the smell
    • Add any symptoms you may experience you feel may be associated with the smell
    • Option to add a personal note to the Allegheny County Health Department