Hawaiian Volcano Observatory

Frequently Asked Questions about Air Quality in Hawaiʻi

1. What gases are emitted by Kīlauea and other active volcanoes?
Ninety-nine percent of the gas molecules emitted during a volcanic eruption are water vapor (H2O), carbon dioxide (CO2), and sulfur dioxide (SO2). The remaining one percent is comprised of small amounts of hydrogen sulfide, carbon monoxide, hydrogen chloride, hydrogen fluoride, and other minor gas species.
Halemaʻumaʻu    Crater gas plume.
2. Who monitors volcanic gases emitted by Kīlauea?
As part of its mission to monitor eruptions and assess volcanic hazards, the U.S. Geological Survey's Hawaiian Volcano Observatory (HVO) determines the amount and composition of gases emitted by Kīlauea Volcano. Changes in gas emissions can reveal important clues about the inner workings of a volcano, so they are measured on a regular basis. How these measurements are made is addressed below.

HVO scientists collect gas samples from a fumarole on the rim of Halemaʻumaʻu    Crater. HVO scientists share scientific data and work closely with officials from other government agencies responsible for making decisions regarding public safety, including Hawaiʻi County Civil Defense and Hawaiʻi State Department of Health.

3. How do HVO scientists measure volcanic gas emissions?
USGS Hawaiian Volcano Observatory geochemists use both remote and direct sampling techniques to measure compositions and emission rates of gas from Kīlauea Volcano. Because of the technical challenges posed by Kīlauea's unique eruptive style, gas emissions are measured "campaign style," that is, scientists must go to the field to collect the data.

The Flyspec, pictured here strapped to an HVO vehicle, has replaced the larger, heavier, and more expensive optical correlation spectrometer (COSPEC), which was used to measure SO2 emissions at Kīlauea for over two decades.  A scientific comparison of Flyspec and COSPEC showed no loss in accuracy or precision of data collected with the mini-spectrometer. To determine the rate at which sulfur dioxide (SO2) is emitted, HVO scientists measure the amount of ultraviolet (UV) radiation energy absorbed by the volcanic gas plume as sunlight passes through it. They do this by attaching a mini-UV spectrometer—called "Flyspec" because of its small size—to a field vehicle and driving the upward-facing instrument beneath the plume. Using data collected in this way, scientists can then compute the SO2 emission rate, typically reported in units of metric tonnes per day (one tonne equals 2,200 pounds).

During periods of elevated SO2 emissions, HVO strives to measure emission rates daily. Flyspec measurements, however, can be taken only when certain weather conditions exist. Generally, steady trade winds and little or no rain enable the highest quality gas data to be collected.

The amount of carbon dioxide (CO2) emitted by Kīlauea is measured using a small infrared analyzer (LI-COR). Scientists drive this instrument through a gas plume, along with the Flyspec, while it continuously and directly samples the ground-level cross-section of the plume.

Another tool used to measure the relative abundance of some gases, including SO2, CO2, hydrogen chloride (HCl), hydrogen fluoride (HF), carbon monoxide (CO) and water vapor (H20), is the Fourier Transform infrared spectrometer (FTIR), which can continuously sample gas in a volcanic plume. The FTIR measures the amount of light absorbed by gases along an open path between the spectrometer and an infrared source, such as an eruptive vent or lamp.

4. How much sulfur dioxide (SO2) gas does Kīlauea emit?
Based on recent (June 2008) measurements of gas emissions from the two currently active vents on Kīlauea—Puʻu ʻŌʻō (east rift) and Halemaʻumaʻu (summit)—the combined total ranges from 2,000 to 4,000 tonnes (on average) of SO2 emitted from the volcano each day. These gas emission rates are often affected by changes in magma supply, seismicity, and surface deformation of the volcano.

Kīlauea has been erupting nearly continuously along its east rift zone since 1983. For most of those years, Puʻu ʻŌʻō, the active east rift vent, has been emitting around 1,500-2,000 tonnes of SO2 daily. As seen in the graph below, occasional spikes in SO2 emissions from Puʻu ʻŌʻō have exceeded 5,000 tonnes/day.

Data for road-based COSPEC and Flyspec measurements of SO2 emissions from Puʻu ʻŌʻō.  Puʻu ʻŌʻō gas emission rates were measured by other methods  prior to 1992 and the data are not directly comparable.

Data for road-based COSPEC and Flyspec measurements of SO2 emissions from Puʻu ʻŌʻō. Puʻu ʻŌʻō gas emission rates were measured by other methods prior to 1992 and the data are not directly comparable. emissions from Puʻu ʻŌʻō.

Sulfur dioxide is also released at Kīlauea's summit. The amount was small—150-200 tonnes each day—until mid-2007, when SO2 emission rates at Kīlauea's summit began to increase. By the time the new gas vent opened in Halemaʻumaʻu Crater on March 12, 2008, summit SO2 emissions had reached 2,000 tonnes/day—the highest recorded at Kīlauea's summit since measurements began in 1979. As of June 2008, summit SO2 emissions have been fluctuating between 500 and 1,500 tonnes/day.

Data for road-based COSPEC and Flyspec measurements of SO2 emissions from Kīlauea's summit.

Data for road-based COSPEC and Flyspec measurements of SO2 emissions from Kīlauea's summit.

5. How long will the Halemaʻumaʻu vent emit high levels of SO2?
Kīlauea is one of the best-studied volcanoes on Earth, but there's still much about it that is not known. The current eruptive activity at Kīlauea's summit is a prime example. One HVO scientist described efforts to unravel the mystery of the summit vent as being "perched on Pele's roof, trying to understand what is going on inside the house by watching smoke rise from the chimney and listening very carefully to the sounds coming from within."

Halemaʻumaʻu    Eruptions since 1924 table While scientists are trying to determine the specific volcanic processes causing the copious release of gases from Halemaʻumaʻu Crater's new vent, Hawaiʻi Island residents and visitors are asking, "How long will it last?"

To predict future behavior of active volcanoes, we often look to the past. The first written accounts of Halemaʻumaʻu were recorded by William Ellis when he trekked to Kīlauea's summit in 1823. Since that time, records show that Halemaʻumaʻu eruptions have ranged in duration from over a century to less than day. Thus, the current summit activity is not out of the ordinary. It could end tomorrow or go on for decades.

When Puʻu ʻŌʻō burst to life in 1983, no one had a clue that it would still be erupting 25 years later—and now, no one knows how long Halemaʻumaʻu will remain active. As of June 2008, HVO scientists are monitoring the new summit vent around the clock and looking at all geologic, geophysical, geochemical, and seismic clues that might help forecast its future.

6. What is "vog"? How is it related to SO2 emissions?
Left: Area without vog. Right: Same area with vog. Vog (volcanic smog) is a visible haze comprised of gas and an aerosol of tiny particles and acidic droplets, created when sulfur dioxide (SO2) and other gases emitted from Kīlauea Volcano chemically interact with sunlight and atmospheric oxygen, moisture, and dust. Near Kīlauea's active vents, vog consists mostly of SO2 gas. Along the Kona coast on the west side of Hawaiʻi Island and in other areas far from the volcano, vog is dominated by an aerosol of sulfuric acid and other sulfate compounds.

7. Where and how do SO2 and vog affect air quality in Hawaiʻi?
The most critical factors that determines how much vog impacts any area are wind direction and speed. Where and how bad the vog is ultimately depends on several additional factors including air temperature, humidity, and rainfall as well as the location of the source and amount of SO2being emitted from Kīlauea Volcano.

There are currently two main sources of SO2 emissions on Kīlauea—Puʻu ʻŌʻō (east rift) and the active vent in Halemaʻumaʻu Crater (summit). The amount of SO2 emitted by Kīlauea began to increase in mid-2007 and has been particularly high since the new gas vent in Halemaʻumaʻu opened in March 2008.

During prevailing northeasterly tradewinds, emissions from Kīlauea are blown to the leeward side of the island, creating a chronic pollution problem along the Kona coast.  During wind reversals, shown by the red arrows, emissions are blown to the east side of the island impacting windward population centers. During prevailing trade (from northeast) wind conditions, much of the SO2 from Puʻu ʻŌʻō is blown out to sea, while SO2 from the summit vent often creates vog in Ka`u communities from Pahala to Ocean View. Unfortunately, both plumes eventually reach the west side of Hawaiʻi Island in a "double-whammy" of combined effects, resulting in an especially dense and nearly constant haze of vog along the Kona coast.

When the winds become light and variable or blow from the south, communities in East Hawaiʻi and along the entire Hawaiian Island chain can also suffer the effects of vog. Under these conditions, people living in the path of Puʻu ʻŌʻō gas emissions continue to experience vog levels similar to those that have beset them for two decades. Communities in the path of summit SO2 emissions, particularly those nearest the source vent, can be subjected to an unusually acrid haze that contains both gas and acidic particles because the emissions have had little time to disperse and dilute before reaching them.

8. What health hazards are posed by vog?
Vog poses a health hazard by aggravating preexisting respiratory ailments. SO2 gas, which can irritate skin and the tissues and mucous membranes of the eyes, nose, and throat, can penetrate airways, producing respiratory distress in some individuals. Aerosol particles in vog can also penetrate deep into human lungs and, at elevated levels, can induce symptoms of asthma.

Physical complaints associated with vog exposure include headaches, breathing difficulties, increased susceptibility to respiratory ailments, watery eyes, sore throat, flu-like symptoms, and a general lack of energy.

Tiny droplets of sulfuric acid in vog creates acid rain, which can leach lead from roofing and plumbing materials, such as nails, paint, solder, and metal flashings. Leached lead poses a health hazard when it contaminates drinking water in rooftop rainwater-catchment systems.

The presence of vog reduces visibility, creating a potential hazard for drivers. Vog can also limit visibility for air and ocean traffic.

9. Where can I find results from scientific research or technical data about the effects of vog on human health?
A number of scientific studies on the health effects of vog have been conducted or are in progress. Data from these studies have been presented at professional conferences or published in scientific journals, some of which are available through the links listed below.
10. Does vog impact plants and animals?
The 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 severe 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 Hawaiʻi Island, particularly in the Ka`u District, have reported losses to agricultural crops and flowers as a result of the recent high SO2 emissions from the new gas vent at Kīlauea's summit.

11. Where can I find results from scientific research or technical data about the effects of vog on Hawaiʻi plants?
12. Who monitors air quality—including vog—in Hawaiʻi?
The agency primarily in charge of monitoring Hawaiʻi's air quality, including vog and its effects on people, is the Hawaiʻi State Department of Health (DOH). Air Quality is monitored by measuring the concentration of SO2 and inhalable particulate matter smaller than 2.5 microns (PM2.5). Stationary ambient air quality monitors that measure particulate levels are located in Hilo, Mountain View, Puna, Pahala, Ocean View, and Kona on Hawaiʻi Island, and on Maui, O`ahu, and Kauai. DOH also has air monitoring stations for SO2 on the islands of Hawaiʻi and O`ahu.
    DOH logo DOH Clean Air Branch The Department of Health, Clean Air Branch, provides public notifications of air pollutant exceedences on Hawaiʻi Island, a 15-minute short-term SO2 advisory, and one-hour average SO2 and particle data.

    The National Park Service (NPS) has nine SO2 monitoring sites within Hawaiʻi Volcanoes National Park.

    NPS logo Current Sulfur Dioxide SO2 Conditions, Hawaiʻi Volcanoes National Park NPS illustration shows SO2 concentrations (ppm) at the Kīlauea Visitor Center, Jaggar Museum, and other locations in Hawaiʻi Volcanoes National Park and approximate location of gas plumes based on wind direction. Display is updated every 15 minutes.

    Hawaiʻi County Civil Defense is responsible for emergency preparedness and response to natural or man-caused disasters. As such, it proactively organized a group of County, State, and Federal agencies in a collaborative effort to mitigate the risks of sulfur dioxide emissions, vog, and other volcanic air quality hazards to people in Hawaiʻi. If/when vog poses a threat to human health, Civil Defense posts advisories on its Web site and through local radio broadcasts.

    CD logo

    Emissions from Kīlauea Volcano Brochure produced through a partnership of Federal, State, and County agencies to address SO2, vog, ash fall, and protective health measures.

13. Why are some roads and trails in Hawaiʻi Volcanoes National Park closed?
A section of Crater Rim Drive in Hawaiʻi Volcanoes National Park is closed because gases from Halemaʻumaʻu    Crater are blown across it by prevailing trade winds. Hawaiʻi Volcanoes National Park monitors SO2 and vog within park boundaries and issues air quality advisories or mandates closures if necessary. Roads and trails downwind of and leading to Halemaʻumaʻu Crater were closed by park officials in February 2008, when SO2 emissions reached levels that became potentially hazardous to human health. These areas are still closed as of June 2008 because SO2 emission levels remain elevated.

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Updated: 23 November 2015 (pnf)