If volcanic gas or vog is causing breathing difficulty where you are in Hawaiʻi, reduce your exposure immediately and seek medical advice. Go to a cleaner indoor location when safe, close windows and exterior doors when doing so will not cause dangerous overheating, and reduce strenuous activity. Keep prescribed asthma or other respiratory medication available and follow the person’s medical action plan. Call 911 for severe breathing difficulty, chest pain, collapse or another life-threatening emergency. Do not approach a volcanic vent or enter closed park roads or trails to assess the smell.
Check current measurements instead of judging by the colour of the sky. The Hawaiʻi Department of Health (DOH) short-term sulfur dioxide advisory, Hawaiʻi ambient air quality data, USGS Hawaiian Volcano Observatory and Hawaiʻi County Civil Defense answer different questions. Air concentrations vary with emissions, wind and location. Data from one monitoring station do not guarantee conditions at a different house or trail.
Quick answer: *Vog* is volcanic air pollution, often containing sulfur dioxide (SO₂) gas near a source and fine sulfate particles (PM2.5) downwind. Volcanic emissions may increase, winds carry the plume across communities, and sensitive people may develop irritation or respiratory symptoms. Air quality can improve or worsen when winds change, including when volcanic activity looks quiet. People generally reduce exposure, use appropriate cleaner indoor environments, follow DOH guidance and relocate temporarily when necessary. Ordinary dust masks or N95 particle respirators do not protect against sulfur dioxide gas. This is crucial to understand before going near a volcanic plume.
First 10 actions for people exposed to vog
- For serious breathing trouble or collapse, call 911 and follow emergency dispatcher instructions.
- Move away from visibly or measurably polluted air toward a safer, cleaner location when possible; follow Civil Defense evacuation and park restrictions.
- Reduce outdoor exercise and heavy work while concentrations are elevated, especially for people with respiratory disease.
- Close exterior doors and windows when vog is a problem, while maintaining safe ventilation and indoor temperature.
- Use appropriate air filtration where available. A purifier designed for particles can reduce PM2.5; removal of SO₂ requires different capabilities and should not be assumed.
- Keep prescription respiratory medicines available and act on a clinician-provided treatment plan.
- Check both SO₂ and PM2.5 information, not just an overall haze image or one pollutant reading.
- Do not rely on an N95, bandana or surgical mask to block volcanic gases. A fitted particle respirator may help with particles during specific tasks but is not a gas-protection plan.
- Keep infants, older adults and people with heart or lung conditions in mind; arrange a cleaner place to stay if symptoms or conditions require it.
- Stay away from closed volcanic vents, craters and trails. USGS, the National Park Service and Civil Defense issue separate hazard and access instructions.
Stage 1 — Emissions begin or change at the volcano
Hawaiʻi’s active volcanoes emit gases through vents and during eruptions. The composition and amount of gas can change with volcanic activity. Kīlauea on Hawaiʻi Island is a major source of sulfur dioxide emissions when erupting. The USGS Hawaiian Volcano Observatory (HVO) monitors the volcano using seismic, deformation, visual and other scientific observations.
In an HVO update dated 4 November 2026, the observatory described intermittent summit lava flows and elevated SO₂ emissions. This is a dated example, not a live measurement for the day you are reading the article. Check the newest HVO update before making travel or exposure decisions.
Volcanic gas exposure depends on more than whether red lava is visible. Vents can emit gas when a fountain is not especially impressive from a tourist viewpoint. At a crater or directly downwind, concentrations may rise quickly, and access restrictions may be necessary.
For residents and visitors, the appropriate early question is: Is volcanic emission active, and is wind carrying the plume toward the area where I live, work or plan to hike? A livestream image showing a quiet-looking crater cannot answer the second question reliably.
Stage 2 — Sulfur dioxide leaves the vent and the plume moves
Sulfur dioxide (SO₂) is an irritating gas emitted by volcanic systems. Near the vent, the air may contain relatively high concentrations of the gas along with volcanic particles and other substances. Winds can transport emissions away from the source and across populated areas.
A person may notice an acrid odour or eye and throat irritation. Smell is not a reliable safety meter: the relationship between smell, concentration and individual symptoms is complex, and some dangerous gases can affect people’s ability to detect their odour. Do not move closer to investigate.
The USGS guide to vog explains that near-vent vog can contain SO₂ and fine particles, while farther downwind the material has had more time to react and particle pollution may dominate. That difference affects which air-quality readings are important.
Trade winds often carry Kīlauea gas toward Kaʻū and the western side of Hawaiʻi Island; during light or shifting winds, communities elsewhere may be affected. The actual direction changes from day to day. Do not assume one side of the island is permanently safe or exposed.
Stage 3 — Vog forms: why a hazy horizon is not a complete warning
Volcanic SO₂ reacts with moisture, oxygen and other atmospheric constituents to form tiny sulfate aerosols over time. The haze that people call vog may therefore be a mixture of gas and fine particles in proportions that vary with distance from the vent and time in the atmosphere.
Particles around 2.5 micrometres and smaller (PM2.5) can penetrate into the respiratory system. Both particles and SO₂ can affect health, but a filter that helps with particles is not automatically able to remove gases. That is why treating every kind of vog as simple dust creates false reassurance.
Visible haze can be affected by moisture and sunlight. A clear-looking sky does not prove SO₂ is absent, and a grey photograph alone cannot quantify what a person is breathing. Monitor actual readings where available, the time of measurement and the wind.
Hawaiʻi’s Interagency Vog Information Dashboard combines explanations, monitoring links, forecasts and health resources. It is useful for learning what each data source means, while the latest DOH station information is more directly relevant to current observations.
Stage 4 — Reading air-quality monitors without confusing the numbers
The Hawaiʻi Department of Health reports SO₂ concentrations and ambient air quality information through official monitoring networks. Its short-term SO₂ advisory page is oriented to volcanic sulfur dioxide, while ambient air monitoring information explains other pollutants and station data.
Read the station name, reading time, pollutant, units and advisory category. A value near Pāhala, Kona or Hilo is a measurement at that station for the reported period. It cannot fully describe personal exposure at a distant valley, school or hiking trail. Monitoring data may also be preliminary or revised.
SO₂ is a gas measurement and PM2.5 is a particle measurement. Do not compare their raw numerical values as though they have the same units. The Air Quality Index interprets concentrations into categories for public health, but it also depends on which pollutants are measured and how categories are calculated.
Some monitoring stations do not measure every pollutant. Missing data, a disconnected monitor or a “good” reading at an unsuitable station is not proof that another exposure site is safe. Follow current DOH and Civil Defense guidance, especially if people are experiencing symptoms.
Stage 5 — Who is most vulnerable when concentrations rise?
People vary in their sensitivity to vog. The USGS and Hawaiʻi DOH guidance identifies people with asthma or other lung diseases, people with heart conditions, infants and children, older adults, and pregnant people among groups who warrant extra care.
A person with asthma may experience coughing, wheezing, shortness of breath or chest tightness during elevated SO₂ exposure. Someone without diagnosed lung disease may still experience eye, nose or throat irritation. Symptoms alone do not tell you exactly which pollutant is responsible.
If symptoms start, get to cleaner air when safe, avoid exercise and contact a health professional. Follow the person’s prescribed inhaler or other treatment plan. Do not prescribe another person’s medication or decide that every breathing symptom is “just vog”. Infection, heart conditions and other illnesses can have overlapping signs.
Severe breathlessness, collapse, chest pain or a person unable to speak comfortably because of breathing difficulty warrants emergency attention. Call 911. Do not wait for the next air-quality graph to refresh before helping someone who is struggling.
Stage 6 — Indoors: improving the air without making the room dangerously hot
The usual first protective measure during troublesome vog is to reduce outdoor air entering a suitable indoor space. Close doors and windows where practical, limit outdoor activity and use an air-conditioned or otherwise cleaner indoor environment if one is available.
The USGS vog FAQ recommends considering suitably filtered air and avoiding additional indoor pollutants such as smoking, incense, candles and poorly vented fuel-burning appliances. However, an unventilated room can become too hot, especially if air conditioning is unavailable. Reducing vog exposure must not create dangerous heat exposure.
A portable purifier with a suitable particle filter may reduce PM2.5 inside a closed room. That does not mean it removes SO₂. Removing gases requires equipment and media designed and maintained for the relevant contaminant, and the effectiveness depends on many factors. Never assume a generic “HEPA” label is protection from volcanic gas.
If the home remains irritating or unhealthy indoors, consider moving temporarily to an area with better air quality, following official advice and taking account of the person’s medical and mobility needs. An outdoor trip may itself increase exposure; plan the route and destination rather than moving impulsively toward the plume.
Stage 7 — Masks and respirators: one of the most important safety distinctions
A common mistake is to put on an N95 mask and then assume volcanic gas can be approached safely. N95 is a particulate-filter designation. It does not protect against SO₂ gas. Cloth face coverings, bandanas and basic surgical masks also offer no reliable sulfur dioxide protection.
The Hawaiʻi Department of Health does not recommend respirators for the general public as the routine response to vog exposure. Proper occupational respiratory protection for particular gases involves appropriate cartridges and equipment, correct fit, training and medical assessment.
A correctly fitted particle respirator may reduce exposure to ash or airborne particulates during some specific activities, but that is a different hazard. Do not let the mask make you stay outdoors longer in unhealthy air or enter a closed volcanic area.
Children may not achieve an adequate respirator fit, and people with breathing problems may find some respirators difficult to tolerate. Seek appropriate medical and public-health advice instead of forcing a poorly fitting device onto a child.
Stage 8 — Driving and travel: the plume does not follow a tourist itinerary
A visitor may see an erupting volcano promoted in travel materials and assume that viewing areas are accessible. In reality, Hawaiʻi Volcanoes National Park may close roads, overlooks and trails because of volcanic gas, hot material, rockfall or other hazards. Check the National Park Service park page and current closure information on the same day you plan to visit.
Near the plume, avoid unnecessary travel. If travelling through a temporarily affected area by vehicle when authorities allow it, keep windows closed and use recirculation in accordance with vehicle and health guidance. Do not stop at a roadside overlook to investigate a strong gas smell.
The safety of the route depends on current Civil Defense directions, volcanic activity and changing winds. A road may have acceptable air quality at one end and much worse exposure nearby. Do not treat a single county-wide air-quality screenshot as a permit to enter a closed park site.
If you are visiting from another island or country with respiratory or heart disease, speak with your healthcare professional before making travel decisions about expected exposure. A visitor who experiences symptoms should seek local medical advice rather than trying to complete a booked activity at any cost.
Stage 9 — Schools, outdoor work and exercise: reduce inhaled dose
Exercise and hard physical work make people breathe more rapidly, increasing the amount of polluted air they inhale. An area where someone sitting briefly feels little irritation may still be unsuitable for vigorous outdoor training during elevated vog.
Schools and sports organisers should monitor appropriate local air information and public-health guidance, adjust exposed activities and make clean indoor options available. Children with asthma need access to their prescribed care plan and authorised school support.
Outdoor workers, farmers, park rangers, delivery workers and contractors may need to change duties or move away from an affected zone. Employers should consider the actual pollutant and work intensity, not just whether a generic mask is available.
People exercising should not try to “build tolerance” to volcanic gas by continuing a run while wheezing. Reduce or stop exertion, move to cleaner air and seek medical advice when symptoms occur.
Stage 10 — Rainwater catchment, food and agriculture: less visible consequences
Vog can contribute to acidic precipitation and corrosion of some exposed materials. On Hawaiʻi Island, people may rely on rooftop rainwater catchment systems for domestic supply. The USGS vog FAQ explains that acidic deposition can leach certain metals, including lead or copper, from roof and plumbing materials.
Do not assume that boiling water removes dissolved metals or chemical contaminants. If you rely on catchment water, follow Hawaiʻi Department of Health guidance about system maintenance, suitable materials and water testing. Use an approved drinking-water source when testing or authorities identify a concern.
Plants can also suffer leaf injury under some volcanic-gas and acidic-particle conditions. Damage depends on exposure and plant species. A farmer should seek local agricultural extension advice rather than applying an unverified neutralising spray to crops.
Pets and livestock may be exposed outdoors as well. Move them to a safer environment when practical and seek veterinary advice for concerning symptoms. Do not assume animals are unaffected because people in the household appear comfortable.
Stage 11 — When the wind changes: a temporary improvement is not a permanent all-clear
Air concentrations can rise and fall rapidly when the wind shifts or emissions change. A neighbourhood that felt polluted in the morning may feel much better later, or the reverse. Several days of low readings at one station do not guarantee the volcano will stop producing emissions.
Continue checking data and official guidance during active periods. Do not rely solely on the absence of a visible plume from your window. Fine particles and gases can move beyond a person’s view, and not every location has a monitor.
If the health department or County Civil Defense advises residents to reduce exposure, relocate or avoid a specified area, follow that instruction. A scientific volcano status bulletin does not replace a local public-health recommendation.
When resuming outdoor exercise or school activities, consider the current pollutant readings, medical needs and local advisory rather than using an arbitrary fixed number of hours.
Stage 12 — The difference between vog, ashfall and other volcanic hazards
Vog: a mixture of volcanic gases and fine sulfate particles carried in the air. Main decisions concern exposure, medical symptoms, indoor air and wind.
Ashfall or tephra: solid volcanic rock fragments that can affect breathing, eyes, roads, roofs and machinery. Particle protection and cleanup rules may be appropriate, but the hazards are not identical to gas.
Lava and vent hazards: hot molten rock, dangerous gas concentrations, unstable ground and other restrictions near active volcanic areas. Distance and official access boundaries are essential.
Other volcanic processes: ground cracks, rockfall and earthquakes can also affect the summit or rift zones. An ordinary air filter does not protect a person standing on unstable hot ground.
The correct action depends on which hazard actually threatens your location. Shelter indoors may be useful for vog; an official evacuation for lava or another destructive flow takes priority over a suggestion to remain in the house.
Where Hawaiʻi’s information comes from
USGS Hawaiian Volcano Observatory: publishes scientific volcano status, eruptions, gas-emission observations and hazard notices. Its Kīlauea updates page is the primary source for a dated volcanic-activity report.
Hawaiʻi Department of Health: monitors pollutants, publishes SO₂ advisories and provides health-related guidance. Station values may be preliminary, so check the time.
Hawaiʻi County Civil Defense: publishes hazard notices and coordinates county-level emergency protection measures. The Civil Defense Agency information portal provides community and contact information. For urgent emergencies, call 911.
National Park Service: determines visitor access, closures and safety guidance inside Hawaiʻi Volcanoes National Park.
Interagency Vog Dashboard: collects explanatory resources, monitoring links and forecasts. A model forecast should not be confused with measured concentrations or a local emergency instruction.
Use each authority for its proper job. Scientific observation, health advice and an evacuation instruction are related but different products.
Example: a family in a downwind community
A family on Hawaiʻi Island notices stronger vog and a family member with asthma develops coughing after outdoor chores. They check the DOH pollutant dashboard and its timestamps, then reduce exposed activity and move the person into a cooler, cleaner indoor room. The person uses prescribed treatment according to their clinician’s plan. When symptoms persist, they contact medical services rather than waiting for the plume to disappear.
The family does not attempt a long drive to a volcano viewpoint. Later, a wind change brings improvement, but they continue to check advisories before outdoor sports. This is an illustrative scenario, not a measurement or active warning for Kaʻū, Kona, Hilo or any neighbourhood.
Example: a visitor who bought an N95 mask
A visitor planning to see Kīlauea reads that gas can be elevated near the vent. They assume an N95 mask makes the plume safe. After reading the DOH and USGS guidance, they recognise that the mask is for particles and does not filter SO₂ gas. They check National Park Service restrictions and change plans rather than entering a closed trail.
This is the kind of small decision that prevents a scientific misunderstanding from becoming a real exposure problem. The correct alternative is not buying a thicker ordinary mask; it is avoiding hazardous air and respecting the park’s restrictions.
Eight myths about Hawaiian volcanic smog
- “Vog is just harmless fog.” It may contain irritating SO₂ and fine acidic particles.
- “If I cannot smell it, it cannot affect me.” Odour is not a reliable measure of safety.
- “An N95 blocks sulfur dioxide gas.” It is a particle filter, not a gas respirator.
- “A purifier that filters PM2.5 must remove SO₂ too.” Gas removal requires separate appropriate technology.
- “Every part of Hawaiʻi Island has the same exposure.” Wind, terrain, emissions and distance matter.
- “The volcano looks quiet, so vog cannot be present.” Gas emissions and atmospheric transport can continue.
- “Children and adults have identical risk.” Vulnerability differs; underlying conditions and age matter.
- “A scientific WATCH level is an evacuation order.” HVO’s volcano status and Civil Defense protective instructions serve different purposes.
Household and visitor safety checklist
- Save the DOH SO₂ advisory and DOH ambient air data.
- Read HVO current volcano updates and County Civil Defense.
- Learn which station and pollutant measurements are most relevant to your location.
- Keep prescribed asthma and other necessary medicines accessible.
- Identify a cleaner indoor location that also remains at a safe temperature.
- Avoid smoking, incense and other unnecessary indoor particle sources during vog.
- Do not use N95 or basic masks as supposed protection from volcanic gas.
- Check NPS trail and park closures before visiting volcano areas.
- Use safe practices for rainwater catchment and seek appropriate testing advice where needed.
- Call 911 for severe breathing difficulty or other life-threatening symptoms.
Frequently asked questions
What is vog in Hawaiʻi?
Vog is volcanic smog produced when gases such as sulfur dioxide and their reaction products create a mixture of gas and fine aerosol particles. Composition varies with distance and atmospheric conditions.
Will an N95 mask protect me from SO₂?
No. N95 respirators filter particles but are not designed to remove sulfur dioxide gas. Avoid the hazardous air and follow public-health guidance.
Can vog affect people with asthma?
Yes. SO₂ can trigger respiratory symptoms, particularly during exertion. Keep prescribed treatment available and seek urgent medical assistance for severe symptoms.
Does a good air-quality reading at one location make my hiking trail safe?
No. Station coverage, pollutant types, wind and time differ. Follow park restrictions and official alerts for the actual trail.
Can a HEPA purifier remove volcanic gases?
A typical HEPA filter is intended for particles, not SO₂. Do not assume gas removal without verified equipment designed for that purpose.
What should I do if a child develops breathing difficulty during vog?
Move the child to cleaner air if safe, follow their prescribed medical plan and seek medical assessment. For severe distress, call 911.
Is a Kīlauea volcanic alert the same as a Hawaiʻi County evacuation order?
No. USGS scientific status reports and county public-safety instructions have different purposes. A specific protective order from an authorised agency must be followed.
Official sources and further reading
- USGS — Frequently Asked Questions About Vog: gas/particle differences, wind, health effects, masks and rainwater concerns.
- Hawaiʻi DOH — Short-Term SO₂ Advisory: station readings and advisory categories.
- Hawaiʻi DOH — Ambient Air Quality Data Explanation: readings, time delays and data limitations.
- Hawaiʻi DOH — Elevated Volcanic Gas Health Recommendations: reducing exposure and vulnerable populations.
- USGS HVO — Kīlauea Official Updates: current dated reports, not a forecast frozen into this article.
- Hawaiʻi Interagency Vog Dashboard: monitoring, forecasts, effects and school resources.
- Hawaiʻi County Civil Defense Agency: local alerts, agency contacts and 911 emergency guidance.
- Hawaiʻi Volcanoes National Park — Official Access and Conditions: permitted park activity and closures.
- eduKateSG — Volcanic Ashfall in Ecuador: the different protection needed for solid volcanic particles.
- eduKateSG — Volcanic Eruption in Iceland: local evacuations, gases and fissure hazards at another volcanic system.
Reader note — updated 6 November 2026: This is a public-health and preparedness guide, not a live air-quality reading or personal medical diagnosis. Always check station times and current DOH, HVO, National Park Service and County Civil Defense notices.