Sulfur Dioxide Effects on Health

Visitors viewing the plume coming off lava lake Halema'uma'u
The Halema'uma'u plume in Kilauea Crater at Hawai'i Volcanoes NP contains extremely high levels of sulfur dioxide, about 500-1,000 tones/day. The NPS sulfur dioxide advisory program alerts the public and park staff if air quality conditions reach unhealthy levels.

What is sulfur dioxide?

Sulfur dioxide (SO2) is a colorless, reactive air pollutant with a strong odor. This gas can be a threat to human health, animal health, and plant life.

The main sources of sulfur dioxide emissions are from fossil fuel combustion and natural volcanic activity. Hawai'i Volcanoes National Park (NP) is unique in the national park system because it sometimes has extremely high concentrations of sulfur dioxide — far higher than any other national park, or even most urban areas.

How can sulfur dioxide affect your health?

Sulfur dioxide irritates the skin and mucous membranes of the eyes, nose, throat, and lungs. High concentrations of SO2 can cause inflammation and irritation of the respiratory system, especially during heavy physical activity. The resulting symptoms can include pain when taking a deep breath, coughing, throat irritation, and breathing difficulties. High concentrations of SO2 can affect lung function, worsen asthma attacks, and worsen existing heart disease in sensitive groups. This gas can also react with other chemicals in the air and change to a small particle that can get into the lungs and cause similar health effects.

Who is at risk?

People sensitive to sulfur dioxide include:

  • People with lung diseases, such as asthma, chronic bronchitis, and emphysema will generally have more serious health effects at higher SO2 levels.
  • Children are at higher risk from SO2 exposure because their lungs are still developing. They are also more likely to have asthma, which can get worse with SO2 exposure.
  • Older adults may be more affected by SO2 exposure, possibly because they are more likely to have pre-existing lung or cardiovascular disease.
  • Active people of all ages who exercise or work outdoors have higher exposure to sulfur dioxide than people who are less active.
Hawai'i Volcanoes NP visitors, residents, and park staff downwind of the volcanic SO2 emissions can be exposed to unhealthy levels of pollution. Since it is not possible to control volcanic activity, the National Park Service participates in a sulfur dioxide advisory program, which gives out warnings to let people know when unhealthy levels of this pollutant are present. Advisories encourage people to limit their exposure when necessary.

How can I avoid unhealthy exposure?

You can take simple steps to reduce your exposure to unhealthy air. First, visit the Current Conditions Website to find out about current sulfur dioxide conditions and the health advisory level.

When possibly unhealthy sulfur dioxide pollution happens, your chances of being affected increase with high levels of activity and the length of time you are active outdoors. If your planned activity has long or heavy physical exertion and the sulfur dioxide levels are high, you may want to limit or stop your activity. For recommended ways to protect yourself at high levels of sulfur dioxide, consult the Health Advisory Table.

What are the NPS sulfur dioxide health advisories?

A SO2 air pollution advisory program was created at Hawai'i Volcanoes NP to deliver timely information about possible unhealthy air pollution conditions that could affect the health of visitors, island residents, and park personnel. Using the Environmental Protection Agency (EPA) air quality index, the NPS SO2 health advisories for Hawai'i Volcanoes NP help you understand what local air quality means to your health. The air quality index is divided into six levels of health concern:

Scale describing the health advisory levels for sulfur dioxide (SO2), ranging from good (green) to hazardous (maroon)

Understanding Sulfur Dioxide Health Advisory Levels

  • Sulfur dioxide air quality index good condition icon (green) Good (0–0.1 ppm)
    No cautionary statement.
  • Sulfur dioxide air quality index moderate condition icon (yellow) Moderate (0.1–0.2 ppm)
    Unusually sensitive people should consider reducing prolonged or heavy exertion outdoors.
  • Sulfur dioxide air quality index unhealthy-for-sensitive-groups condition icon (orange) Unhealthy for Sensitive Groups (0.2–1.0 ppm)
    Active children and adults, and people with lung disease, such as asthma, should reduce prolonged or heavy exertion outdoors.
  • Sulfur dioxide air quality index unhealthy condition icon (red) Unhealthy (1.0–3.0 ppm)
    Active children and adults, and people with lung disease, such as asthma, should avoid prolonged or heavy exertion outdoors. Everyone else, especially children, should reduce prolonged or heavy exertion outdoors.
  • Sulfur dioxide air quality index very-unhealthy condition icon (purple) Very Unhealthy (3.0–5.0 ppm)
    Active children and adults, and people with lung disease, such as asthma, should avoid all outdoor exertion. Everyone else, especially children, should avoid prolonged or heavy exertion outdoors.
  • Sulfur dioxide air quality index hazardous condition icon (maroon) Hazardous ( > 5.0 ppm)
    Triggers health warnings of emergency conditions. Entire population is more likely to be affected. Avoid outdoor activities & remain indoors. Leave the area if directed by Civil Defense.
The SO2 and weather data used in this program are collected by the National Park Service at the Jaggar Museum and Kilauea Visitor Center monitoring sites. The SO2 concentrations measured at the monitoring sites are reviewed every 15 minutes and one of six advisory levels of health concern are assigned for that 15-minute period for each site.

How does sulfur dioxide affect national parks?

Hawai'i Volcanoes NP is significantly impacted by sulfur dioxide because the high levels create a human health concern. Sulfate particles can also create haze and reduce visibility at Hawai'i Volcanoes NP and other national parks. Sulfur dioxide can convert to acids in the atmosphere and come down from the atmosphere in rain, snow, or fog, or as dry particles. This atmospheric deposition can damage vegetation, affect soils, acidify lakes and streams, and ruin memorials, buildings, and statues at our national cultural monuments.

Last updated: February 27, 2023


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