What is Sulfur Dioxide (SO2)?
Sulfur dioxide (SO2) is a colorless gas with a sharp, irritating odor. It's produced primarily from burning fossil fuels containing sulfur, particularly coal and oil. At high concentrations, it can be detected by smell, but at lower levels it's invisible and odorless.
Why SO2 is Harmful
SO2 is a respiratory irritant that can affect breathing and worsen existing conditions:
- Irritates and inflames respiratory passages
- Makes breathing difficult, especially during physical activity
- Worsens asthma and other lung diseases
- Contributes to acid rain formation
- Can combine with other pollutants to form harmful particles
Major Sources of SO2
SO2 emissions come primarily from:
- Fossil fuel combustion at power plants: The largest source, especially coal-fired plants
- Industrial facilities: Petroleum refineries, metal processing
- Metal smelting and processing: Extracting metal from ore
- Locomotives and large ships: Using high-sulfur fuel
- Volcanic eruptions: Natural but significant source
Health Effects of SO2 Exposure
Short-term Effects:
- Difficulty breathing and shortness of breath
- Throat irritation and coughing
- Worsening asthma symptoms
- Increased emergency room visits
- Bronchospasm (narrowing of airways)
Long-term Effects:
- Decreased lung function
- Increased respiratory infections
- Chronic bronchitis
- Cardiovascular effects
Who Is Most at Risk?
Certain groups are more vulnerable to SO2:
- People with asthma: SO2 can trigger attacks even at low levels
- Children: Higher breathing rates and developing lungs
- Older adults: More likely to have pre-existing conditions
- Active outdoor workers: Higher exposure during physical exertion
SO2 Levels and the AQI
The EPA sets Air Quality Index standards for SO2:
- Good (0-50): Air quality is satisfactory
- Moderate (51-100): Acceptable, sensitive people should watch for symptoms
- Unhealthy for Sensitive Groups (101-150): Asthmatics should reduce outdoor exertion
- Unhealthy (151-200): Everyone may experience effects
- Very Unhealthy (201+): Health alert, limit outdoor activity
Protection Strategies
- Check daily SO2 levels in your area
- Limit outdoor activities when levels are elevated
- People with asthma should follow their action plan
- Stay indoors with windows closed during high SO2 days
- Use air purifiers with activated carbon filters
- Avoid exercising near industrial areas or busy roadways
Reducing SO2 Pollution
Community and individual actions can help:
- Support cleaner energy sources (renewable, natural gas)
- Advocate for stricter industrial emission standards
- Use low-sulfur fuels when available
- Support policies requiring SO2 scrubbers at power plants
- Reduce electricity consumption to lower power plant emissions
Regulatory Standards
The EPA's National Ambient Air Quality Standards (NAAQS) for SO2 are:
- 1-hour standard: 75 parts per billion (ppb)
- Measured at the 99th percentile of daily maximum 1-hour average
- Averaged over 3 years