Vog: Volcanic Air Pollution on the Island of Hawai‘i

By Tamar Elias and A. Jeff Sutton, USGS Hawaiian Volcano Observatory

The vent that opened in Halemaʻumaʻu in 2008, at the summit of Kīlauea. The new eruption raised the volcano's output of sulfur dioxide (SO₂) and other gases — and the vog over the island. Photo: J. Babb, USGS.

When the air turned dangerous

On January 28, 2008, rangers at Hawaiʻi Volcanoes National Park answered a call from a visitor struggling to breathe at Kīlauea's summit. Gas from the summit caldera had been rising for weeks, and toxic levels downwind of Halemaʻumaʻu were enough to cause respiratory distress in sensitive people. Within weeks, the Park Service closed much of the caldera floor. When a new vent opened in Halemaʻumaʻu in March 2008, summit gas emissions reached never-before-measured levels.

Where vog comes from

Besides lava, Kīlauea emits 500 to 10,000 metric tons of SO₂ a day during sustained eruptions. Deep in the volcano, under high pressure, SO₂ is dissolved in magma. As magma rises and pressure drops, it forms bubbles that escape as a gas plume.

• 1983: the East Rift Zone eruption begins, with brief lava fountains about every 3 weeks — the wind cleared the air in between.
• Mid-1986: the eruption becomes a constant outpouring of lava and gas. People downwind report haze, health problems and crop damage. The word "vog" — volcanic + smog — is coined.
• 2008: a second eruption begins at the summit, and SO₂ output rises several times over.

What's in a plume: mostly water vapor, carbon dioxide and SO₂, with entrained air, smaller amounts of hydrogen chloride and hydrogen fluoride, traces of toxic metals — selenium, mercury, lead — and aerosols, tiny particles and droplets that make the plume visible.

What vog is: a haze of SO₂ gas and aerosols, mostly sulfuric acid droplets and other sulfate compounds, formed as volcanic gases react with oxygen, moisture, dust and sunlight over minutes to days.

• The particles are PM2.5 — under 2.5 micrometers, less than 1/20th the width of a human hair — small enough to reach deep into the lungs. They grow in moist air, as in the nose and throat.
• Far from the vents, as on the Kona coast, vog is mostly aerosols; nearer, it also carries unreacted SO₂.
• SO₂ is invisible; the haze comes from particles scattering sunlight.

Where vog goes

Vog depends on how much SO₂ Kīlauea emits, distance from the vents, and the wind.

• Trade winds blow from the northeast 80–95 percent of the time from May through September, so areas southwest of Kīlauea get the most vog. It wraps around the island's south end and along the Kona coast, trapped by daytime onshore and nighttime offshore sea breezes.
• Most vog stays below 6,000–8,000 feet, under the trade wind inversion — a warm layer that keeps cooler, vog-laden air from rising.
• Without trade winds — most often in winter — vog can cover east Hawaiʻi, the whole island, or even the whole State.

Trade winds (blue) carry the plumes southwest, where sea breezes (green) trap them; kona winds (red) push vog to the east side. The 2009 view from Space Shuttle Atlantis shows the summit plume hugging Mauna Loa's flank toward downwind towns, while the Puʻu ʻŌʻō and ocean entry plumes travel lower, along the coast. USGS; NASA.

Measuring it

The USGS Hawaiian Volcano Observatory (HVO) measures SO₂ and other gases to track eruptions, assess air quality hazards, and feed vog forecasts and climate models — usually with an ultraviolet spectrometer, which measures sunlight absorbed by SO₂ in the plume. The Hawaii State Department of Health and Hawaiʻi Volcanoes National Park measure SO₂ and PM2.5 in the air to report hazards to the public.

Paired ultraviolet cameras image the plume rising from the lava lake; in the analyzed image of October 17, 2016, warmer colors mean more SO₂. Photo: T. Elias, USGS.

How much: SO₂ output roughly follows how much magma sits at shallow depth, and the lava lake's activity — more when it spatters.

SO₂ from the summit (black) and Puʻu ʻŌʻō on the East Rift Zone (red) since 1979 — rising in 1983 when the rift eruption began, and again in 2008 with the summit eruption. Photo: M. Patrick, USGS.

Effects

On people: sensitivity varies, but many residents and visitors report sore eyes and throat, runny nose, headaches, cough, phlegm, breathing difficulty, more respiratory illness and low energy. Research on children found vog does not cause asthma, but can worsen existing asthma and other respiratory conditions. Vog lacks the ozone and hydrocarbons of urban and industrial smog. More research is needed on how it interacts with cigarette smoke, mold, traffic exhaust and pollen, and on its short- and long-term effects.

On farms: damage to vegetable, orchard and flower crops rose sharply in 2008 — sulfuric acid droplets fall as acid rain. Some farmers went out of business, moved, or switched crops. Ranchers report corroding fences and effects on livestock, and the U.S. Department of Agriculture has provided disaster assistance since 2008.

On rain: in dry west Hawaiʻi, acid aerosols can actually suppress raindrops, as industrial pollution does in the northeastern United States — reducing summer rain for crops, forests and water supplies.

Native plants cope: the dominant forest tree, ʻōhiʻa lehua, can close its stomata (breathing pores) when SO₂ is high.

On drinking water: many homes rely on rooftop rainwater catchment. In 1988, water from 40 percent of catchment systems in the Kona districts had lead leached by acid rain from nails, paint, solder and flashing; some residents had elevated blood lead, prompting an island-wide effort to remove lead-bearing materials. Such materials were rarely installed after 1986, but older homes may still see lead, copper and zinc. Hydrogen fluoride can also contaminate water and soil, though household and municipal supplies tested so far meet EPA standards.

Where lava reaches the sea, it makes "laze" — steam plumes laden with hydrochloric acid and volcanic glass — a local hazard near the ocean entry. Photo: J. Babb, USGS.

On climate: Kīlauea is a natural experiment in how aerosols affect Earth's energy balance. Aerosols absorb and scatter sunlight and make clouds more extensive and brighter, reflecting more sunlight to space — which can cool the climate. Kīlauea's emissions affect trade-wind clouds and cut rainfall thousands of miles downwind; research suggests continuous eruptions may matter more for climate than once thought.

Living with vog

Emissions have fallen substantially since 2008, but sensitive people, plants, animals and infrastructure still face vog downwind. Kīlauea's activity could stop abruptly, but there's no sign it will soon — and visitors in the 1800s noted the smell of volcanic gas far downwind.

• Forecasts: the Vog Measurement and Prediction Project (VMAP) gives a two-day forecast of SO₂ and sulfate, colored by the Department of Health's advisory levels (weather.hawaii.edu/vmap).
• Information: real-time vog levels, health and environmental effects, and how to protect yourself: ivhhn.org/vog.
• More: USGS Hawaiian Volcano Observatory · USGS Volcano Hazards Program.

Sources

Based on Volcanic Air Pollution Hazards in Hawaii, by Tamar Elias and A. Jeff Sutton, USGS Fact Sheet 2017–3017, U.S. Geological Survey; a work of the United States government in the public domain. The photographs, diagrams and the climate section are taken from the fact sheet's PDF, which the import had left out.