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’s 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

FAQ for Clairton Coke Works Fire

Q: What happened?

A: A fire at Clairton Coke Works (in Clairton, PA) broke equipment that controls how much air pollution (in particular, sulfur dioxide) is released into the air on Monday 6/17/19.

Q: When/how will this issue be fixed?

A: U.S. Steel said the systems were working again at approximately 8:15 p.m. Monday. Be on alert for community alerts from the Allegheny County Health Department, the news, or social media to follow the story.

Q: Why does this sound familiar?

A: You may remember the fire from December 24, 2018 at the Clairton Coke Works. This fire shut down the same pollution controls. The good news is, this time they were able to take quicker action to restore the pollution control systems and alert the public.

Q: How does this affect the health of my community?

A: Anyone with asthma and/or other respiratory conditions, children, pregnant women, and the elderly may be at risk to health effects from the increased pollution/poor air quality.

Q: How may increased air pollution/poor air quality in my community potentially affect my asthma?

A: Could experience wheezing, shortness of breath and chest tightness and other problems, especially during exercise or physical activity. There could also be an increased risk for the need to visit your doctor, urgent care, or the emergency room related to your asthma symptoms.

Q: How can long term periods of increased air pollution affect my asthma?

A: Longer periods of increased air pollution/poor air quality could increase your asthma symptoms and affect how well your lungs are able to function.

Q: How can short term periods of increased air pollution affect my asthma?

A: Short-term effects of increased air pollution/poor air quality may make it hard to breathe when you are active outdoors.

Q: How can I help keep myself healthy during periods of increased air pollution/poor air quality?

A: Be on alert for community news related to poor air quality. Check the status of your local air quality. Limit your outdoor activity if air quality is poor. You could also sign up for Allegheny Alerts, check your local Purple Air Sensor network online for up to date air quality information (see Asthma Institute website for instructions on how to access the Allegheny Alerts or Purple Air Monitor information online). In addition, you could click the following link for daily air quality conditions in your community https://www.alleghenycounty.us/Health-Department/Programs/Air-Quality/Air-Quality.aspx

Q: What should I do if I feel my asthma symptoms are worsening?

A: If your symptoms are worse than normal for you but not an emergency, you should use your doctor prescribed medications, including a rescue inhaler if needed, and schedule an appointment with your doctor. If your symptoms are much worse than normal for you and you feel it is an emergency, you should go to your local urgent care or hospital emergency room.

Q: How can I report increased air pollution I notice in my community?

A: If you wish to report any air, pollution related smells in your community you can download the PGH Smell app (instructions found on Asthma Institute website). You could also call the Allegheny County Health Department directly to file a complaint at (412) 578-8103. You may also wish to discuss with your doctor, they may be able to provide you with additional information.

Q: Will Clairton Coke Works continue to have more fires that could affect the air quality in my community?

A: There is no way to know for sure. People who live near factories, airports, major highways and other similar places have an increased risk of higher air pollution/poor air quality. It is important for all people to be aware of events (air quality in particular) in their community that could affect your health. It is especially important for people with asthma to be alert since poor air quality can worsen your asthma symptoms.

Q: What’s being done in my community to protect residents from poor air quality?

A: The Allegheny County Health Department monitors the air pollution coming from Clairton Coke Works (and other factories), it is the law. When any factory process/event worsens air quality, they are required to correct the problem. Many community groups/researchers/government leaders are helping support efforts in the Mon Valley to help advocate protecting your community.

Clairton Coke Works Fire

From the team at the University of Pittsburgh Asthma Institute at UPMC, we would like to give you this information about a recent environmental event in your area that may have affected your air quality and your asthma.

Allegheny County released this statement on 6/17/19:

Health Department Advised of Clairton Coke Works Electrical Equipment Fire PITTSBURGH – The Allegheny County Health Department (ACHD) was notified by U.S Steel at approximately 4:43 a.m. of an electrical equipment fire that occurred at its Clairton Coke Works facility. The fire has been put out. Control rooms 1, 2 and 5 were shut down because of the fire. Control 1 is now back to normal operations. Currently, control rooms 2 and 5, which hold the equipment and controls necessary to clean the coke oven gases, remain shut down. These are the same two control rooms that were immediately shut down following the December 24, 2018 fire. As these control rooms remain offline, this means there is no desulfurization of coke oven gas. Multiple mitigation measures are underway, like those used after the December 24 fire. Health Department inspectors on-site have been instructed to observe the damage and will be providing additional information to the department. Sensitive populations, including those with respiratory conditions, children and the elderly, should be aware of the potential for elevated levels of SO2; however, there is no need for residents to take specific precautions at this time. ACHD will continue to gather additional details to determine the next course of action and will keep the public updated as further information becomes available.

Allegheny County released this statement later in the day on 6/17/19:

Health Department Issues Emergency Order Against U.S. Steel PITTSBURGH – The Allegheny County Health Department (ACHD) has issued an emergency order requiring U.S. Steel to come into compliance with its hydrogen sulfide (H2S) standard and sulfur dioxide (SO2) limits. U.S. Steel must submit a plan within 24 hours to ACHD as to how this will be achieved. The company will then have up to 20 days to achieve compliance. If these requirements are not met, the company will have to cease all coking operations. The complete order can be viewed here. At approximately 4:20 a.m., an electrical equipment fire forced a shutdown of control rooms 2 and 5 at the Clairton Coke Works. These control rooms hold the equipment and controls necessary to clean the coke oven gases, and they are the same two control rooms that were immediately shut down following the December 24, 2018 fire. As these control rooms remain offline, there is no means for desulfurization of the coke oven gas. ACHD staff have notified local and state elected officials and have contacted school nurses and pediatricians in the Mon Valley. Additionally, staff will be monitoring emergency room visits in the Mon Valley. As of 12 p.m. today, there have been no elevated SO2 levels at any of the monitors in the Mon Valley. It’s important to understand that there is no need for individuals to take specific precautions at this time. Residents should be aware of the potential for elevated SO2 levels. ACHD continues to gather and review information. Additional public notifications will occur as more information becomes available.

U.S. Steel said the systems were working again at approximately 8:15 p.m. Monday.

So what does this all mean? We have attached a quick FAQ for what you need to know.

Has this event impacted you and your family? We want to know! Please email us at asthmainstitute@upmc.edu with your thoughts and you may be featured in an article from the Asthma Institute.

For more information and further resources to stay more connected with your local air quality, check out our website at www.asthmainstitute.edu .


The Asthma Institute Team