Vog is a hazy mixture of SO2 gas and aerosols (tiny particles or droplets) which are primarily sulfuric acid and other sulfate (SO4) compounds. Aerosols are created when SO2 and other volcanic gases combine in the atmosphere and interact chemically with oxygen, moisture, dust, and sunlight over minutes to days.
The exact composition of vog depends on how much time the volcanic plume has had to react in the atmosphere. In areas such as the Kona coast, far from Kīlauea Volcano's active vents, aerosols are the main component of vog. Closer to the volcano, vog contains both aerosols and unreacted SO2 gas.
Vog concentrations are primarily dependent on the amount of SO2 emitted from Kīlauea, the distance downwind, and the wind direction and speed on a given day. The main wind direction in the Hawaiian Islands is from the northeast (trade winds). From May through September, the trade winds blow 80–95 percent of the time. Consequently, the areas southwest of Kīlauea are most frequently affected by vog. Under trade wind conditions, vog travels around the southern part of the island, and along the Kona coast, where it becomes trapped by daytime onshore and nighttime offshore sea breezes. Most vog stays below 6,000–8,000 feet above sea level, the usual height of the trade wind inversion. This layer of the atmosphere increases in temperature with altitude, inhibiting the rise of cooler, vog-laden air. When trade winds are absent, most often during winter months, East Hawai‘i Island, the entire Island of Hawai‘i, or the even the entire State of Hawaii can be affected by vog.
Communities in the path of summit SO2 emissions, particularly those nearest the source vent, can be subjected to a very acrid haze that contains both SO2 gas and acidic particles. The near-vent volcanic plume has had little time to disperse and dilute before reaching downwind communities within about 40 miles downwind of the summit vent.
Volcanic activity at Kīlauea Volcano creates the potential for airborne health hazards to residents and visitors. At current emission levels, individuals with pre-existing respiratory conditions are the primary group at risk of experiencing health effects from vog exposures, but healthy people may also experience symptoms.
It is very important to take measures to protect yourself if you feel your health is being affected by vog. "Sensitive groups" most likely to experience health impacts include:
An indirect health effect of vog is associated with the leaching of metals from building and plumbing materials. Sulfuric acid in vog creates acid rain, which can leach lead and copper from roofing and plumbing materials, such as nails, paint, solder, and metal flashings. Leached lead and copper can pose a health hazard when they contaminate drinking water in rooftop rainwater-catchment systems.
Find a detailed list of scientific articles from the Hawaii Interagency Vog Information Dashboard.
Sulfuric acid droplets in vog have the corrosive properties of dilute battery acid. When vog mixes directly with moisture on the leaves of plants, it can cause chemical burns, which can damage or kill the plants. Sulfur dioxide (SO2) gas can also diffuse through leaves and dissolve to form acidic conditions within plant tissue. Farmers on Hawai‘i Island, particularly in the Ka‘ū District, have reported losses to agricultural crops and flowers as a result of the recent high SO2 emissions from the gas vent at Kīlauea's summit.
The agency primarily in charge of monitoring Hawai‘i's air quality, including vog and its effects on people, is the Hawai‘i State Department of Health (HDOH). Air Quality is monitored by measuring the concentration of SO2 gas and inhalable particulate matter smaller than 2.5 microns in diameter (PM2.5). Stationary air quality monitors that measure particulate levels are located in Hilo, Mountain View, Pahala, Ocean View, and Kona on Hawai‘i Island, and on Maui, O`ahu, and Kauai. DOH also has air monitoring stations for SO2 on the islands of Hawai‘i, O‘ahu, and Kauai.
The National Park Service (NPS) monitors air quality within Hawai‘i Volcanoes National Park. You can find air quality monitoring data and links to additional resources Hawai‘i Interagency Vog Information Dashboard.
Hawai‘i Volcanoes National Park monitors SO2 within park boundaries to inform the public of hazardous conditions and to mandate closures if necessary. Roads and trails downwind of and leading to Halema‘uma‘u Crater were closed by park officials in February 2008, when SO2 emissions and ambient air concentrations reached levels that were potentially hazardous to human health. These areas remain closed because SO2 emissions and downwind concentrations remain elevated, and the threat of sudden eruption from the Overlook vent can produce hazardous conditions downwind of the vent. You can find updated information about closed areas on the National Park's website.
Vog is a hazy mixture of sulfur dioxide gas (SO2) and particles (PM2.5) originating from Kīlauea Volcano. Sensitivity to vog varies among people, so all people need to take responsibility to protect themselves and dependent family members, as necessary. Individuals in 'sensitive groups,' such as people with pre-existing respiratory or other medical conditions, are expected to be at highest risk for potential health effects, depending on the amount of emissions, distance away from the vent, and wind direction from day to day.Below are suggested actions for limiting impacts of vog:
Predicting vog concentrations for a short stay in Hawai‘i is as difficult as predicting the weather. Once volcanic gas is in the atmosphere, they cloud is distributed by prevailing winds. Trade, or northeasterly, winds are dominant 80-95% of the time from May through September and can produce poor air quality on the southern and western sides of the island. The east or windward side is more likely to experience poor air quality during trade wind interruptions, which occur more frequently during the winter months. Where and how bad the vog is ultimately depends on wind direction, wind speed, air temperature, humidity, and rainfall as well as the location of the source and amount of SO2 being emitted from Kīlauea Volcano.
At the levels of volcanic emissions occurring from Kīlauea over recent years, individuals with pre-existing respiratory conditions are the primary group at risk of experiencing health effects from vog exposures, but healthy people may also experience symptoms. If you have existing heart and/or respiratory ailments or other conditions that compromise your physical health, or if you are pregnant, check with your personal physician for advice about traveling to any location with poor air quality. While vog does contain acidic particles (as well as elevated levels of SO2 gas at near-vent locations) it lacks other contaminants typically present in urban or industrial smog, such as ozone, hydrocarbons, nitrogen oxides, and heavy metals.
Because of the proximity of the erupting vents, SO2 and other acid gas concentrations can reach unhealthy levels quickly in some areas within Hawai‘i Volcanoes National Park. Elevated vog levels, and poor air quality at the coast, are most common when trade winds are absent. Current air quality and wind conditions can be checked online prior to visiting the park, and people with preexisting respiratory conditions should have their medications available. All visitors should pay attention to park warnings and follow park advisories.
In general, to protect your health, take heed of all advisories released by Civil Defense and other relevant emergency management agencies.
Whether or not you should cancel your trip to Hawai‘i Island is a personal decision that only you can make. To help you make an informed decision, information about vog and air quality in Hawai‘i is provided in the Frequently Asked Questions above, as well as on the IVHHN vog dashboard at ivhhn.org/vog. You can also monitor the volcanic gas plumes and real-time air quality conditions for yourself on local Webcams and air quality advisory websites.
In any given year, there are 50-70 volcanic eruptions around the world, during which water vapor (H2O), carbon dioxide (CO2), sulfur dioxide (SO2), and other gases are released. Many volcanoes also emit gases between eruptions. The impact of these gases depends on the vigor and duration of the eruption, the proximity of the volcano to populated areas, and wind speed and direction.
Examples of volcanoes that have adversely affected people due to persistent SO2 emissions include Nyiragongo (DR Congo); Masaya (Nicaragua); Poas (Costa Rica); and Miyakejima, Aso, and Sakurajima (Japan).