U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2017–3017

April 2017

Volcanic Air Pollution Hazards in Hawaii

Noxious sulfur dioxide gas 

and other air pollutants 

emitted from Kīlauea 

Volcano on the Island of 

Hawai‘i react with oxygen, 

atmospheric moisture, 

and sunlight to produce 

volcanic smog (vog) and 

acid rain. Vog can negatively 

affect human health and 

agriculture, and acid rain 

can contaminate household 

water supplies by leaching 

metals from building and 

plumbing materials in 

rooftop rainwater-catchment 

systems. U.S. Geological 

Survey scientists, along with 

health professionals and 

local government officials 

are working together to 

better understand volcanic 

air pollution and to enhance 

public awareness of this 

hazard.

On the afternoon of January 28, 

2008, Hawai‘i Volcanoes National Park 

rangers responded to a distress call from 

a park visitor who was having trouble 

breathing while touring the summit of 

Kīlauea Volcano. Gas emissions from 

the summit caldera had been increasing 

for weeks, and concentrations of toxic 

gas downwind of Halemaʻumaʻu were 

sufficient to cause respiratory distress 

for this visitor, as well as other sensitive individuals. Within a few weeks, the 

National Park Service had closed visitor 

access to much of the caldera floor due 

to the gas hazards. When a new eruptive vent appeared in Halemaʻumaʻu in 

March 2008, summit gas emissions rose 

to never-before-measured levels, abruptly 

increasing the damaging effects of volcanic air pollution in Hawaii.

Kīlauea, best known for its spectacular lava fountains and flows, also emits 

between 500 and 10,000 metric tons of 

noxious sulfur dioxide gas (SO2

) daily, 

during periods of sustained eruption. 

Deep inside the volcano, where pressure is high, SO2

 is dissolved in magma 

(molten rock below the Earth’s surface). 

When the magma rises toward the 

surface, where pressure is lower, the 

dissolved SO2 forms gas bubbles, which 

can travel through the magma and escape, 

generating a gas plume. 

Air pollution, caused mainly by SO2

emitted from Kīlauea, became a frequent 

problem on the Island of Hawai‘i in 

1986. Until that time, the volcano’s 

ongoing East Rift Zone eruption, which 

began in 1983, consisted of brief episodes 

of high lava fountains about once every 

3 weeks. This intermittent timing allowed 

the wind to clear the air between eruptive episodes. In mid-1986, the style 

of the eruption changed from episodic 

fountains to a constant effusion of lava 

and gas. People downwind of the volcano 

began reporting a wide range of problems, including reduced visibility, health 

issues, and damage to crops. The word 

“vog,” a blend of the words volcanic and 

smog, was coined to identify this form of 

air pollution. 

In 2008, a second eruption began at 

the summit of Kīlauea, and the amount 

of SO2 released from the volcano became 

several times higher. While vog had been 

a part of everyday life for people on the 

Island of Hawai‘i for many years, the 

summit eruption increased the scope of 

the problem substantially.

In 2008, a new vent opened in Halema‘uma‘u, pictured here, 

at the summit of Kīlauea Volcano on the Island of Hawai‘i. 

The new eruption increased the amount of SO2

 and other 

gases released from the volcano, as well as the amount of 

vog affecting the island. Photograph by J. Babb, USGS.
Eruption Plumes and the Creation 

of Vog

Presently, large eruption plumes 

are released from a lava lake within 

Halemaʻumaʻu at Kīlauea Volcano’s 

summit, and from Puʻu ʻŌʻō and other 

vents along the East Rift Zone. The 

plumes are composed primarily of water 

vapor, carbon dioxide, sulfur dioxide, and 

entrained air, along with smaller amounts 

of other gases, including hydrogen chloride and hydrogen fluoride. In addition, 

small amounts of toxic metals, including 

selenium, mercury, and lead have been 

found in the volcanic gas plumes emitted 

from Kīlauea’s vents. Kīlauea Volcano’s 

eruption plumes also contain a suspended 

mixture of tiny solid particles and liquid 

droplets known as aerosols. Aerosols are 

one of the components that make an eruption plume visible. 

Vog is a hazy mixture of SO2 gas and 

aerosols, which are primarily composed 

of sulfuric acid droplets 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 periods of minutes 

to days. The particles, or particulate 

matter (PM), in vog, are characterized as 

PM2.5 because the particles are less than 

2.5 micrometers in diameter—or less than 

1/20th the width of a human hair. These 

‘fine’ particles can travel deep into human 

lungs. Vog particles grow by absorbing 

water vapor and other gases, so they can 

increase in size in a moist environment, 

such as the human upper respiratory tract 

(nose, mouth, and throat). 

The composition of vog depends on 

how much time the volcanic plume has 

had to react in the atmosphere. In areas 

such as the Kona Districts, far from 

Kīlauea Volcano’s active vents, aerosols 

are the main component of vog; however, 

closer to the volcano, vog contains both 

aerosols and unreacted SO2 gas. Like 

smog, the presence of vog reduces visibility. SO2

 gas is colorless and invisible, but 

the tiny particles in vog create a visible 

light-colored haze by scattering sunlight.

What Controls Vog on the Island of 

Hawai‘i?

Vog concentrations on Hawai‘i Island 

are primarily dependent on the amount of 

SO2 emitted from Kīlauea, the distance 

from the source vents, 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 

of the vog stays beneath an altitude of 

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, which occurs most often 

during winter months, east Hawai‘i, the 

entire Island of Hawai‘i, or even the entire 

State of Hawaii can be affected by vog.

Measuring Volcanic SO2 and its 

Impact on Air Quality

Scientists at the U.S. Geological 

Survey’s Hawaiian Volcano Observatory 

(HVO) measure the amount of SO2 and 

other gases emitted from Kīlauea to track 

the eruptions, assess air quality hazards, 

and provide data for vog forecasts and 

climate models. The most common 

instrument for measuring volcanic SO2

worldwide is an ultraviolet spectrometer, 

which measures the amount of incoming 

sunlight absorbed by SO2 in the plume. 

These data are then used to calculate how 

much SO2 is emitted from the volcano. 

The Hawaii State Department of 

Health (HDOH), the agency responsible 

for monitoring air pollution for the State, 

measures SO2 and PM2.5 concentrations in 

vog, as does Hawai‘i Volcanoes National 

Where Does Vog Go?

TRADE 

 WINDS

Kailua-Kona

South

Kona

South Point

Hilo

KONA WINDS

N

Mauna Loa

Kohala

Mauna

Kea Hualālai

Kīlauea

100 MILES

NI‘IHAU

KAUA‘I

O‘AHU

MOLOKA‘I

MAUI

HAWAI‘I LĀNA‘I

KAHO‘OLAWE

Honolulu

Hilo

PACIFIC OCEAN

N

Vog

Vog Halema‘uma‘u

Pu‘u ‘Ō‘ō

Ocean entry

On the Island of Hawai‘i (left), prevailing northeasterly trade winds (blue arrows) blow volcanic emissions (white plumes) to the southwest, 

where they wrap around the southern part of the island, and are trapped by daytime onshore and nighttime offshore sea breezes (green 

arrows). When “kona” winds (red arrows) blow, much of the vog is concentrated on the eastern side of the island. The 2009 view from the 

Space Shuttle Atlantis (right) reveals how during trade wind conditions, the summit plume from Halema‘uma‘u hugs the flank of Mauna Loa as 

it travels overland directly toward downwind communities. The Pu‘u ‘Ō‘ō (East Rift Zone) and ocean entry plumes are emitted at lower elevations and mainly travel along the coast as they wrap around the island.
Measuring Volcanic SO2

Two paired of cameras sensitive to ultraviolet light (left) image the eruption plume as it rises 

from the lava lake. The analyzed image from October 17, 2016 (right) displays warmer colors 

for higher SO2

 concentrations in the plume. Photograph by T. Elias, USGS.

How Much SO2 is There?

1978 1982 1990 1994 1986 1998 2002 2006 2010 2014

Year

2

1

0.5

1.5

2.5

0

Sulfur dioxide gas, in million

metric tons per year

Summit (Halema‘uma‘u)

Rift (Pu‘u ‘Ō‘ō)

EXPLANATION

In general, the amount of SO2 released from Kīlauea is proportional to how much magma resides at shallow depths within the volcano. Changes 

in the lava lake surface activity at the summit of Kīlauea (left), also regulate the release of SO2

. When the lake is spattering, more SO2 is released 

compared to nonspattering episodes. Graph (right) shows SO2

 released from Halema‘uma‘u at the Kīlauea summit (black bars) and Pu‘u ‘Ō‘ō on 

the volcano’s East Rift Zone (red bars) since 1979. Emissions increased in 1983 with the onset of the East Rift Zone eruption (blue arrow) and in 

2008, when the summit eruption began (green arrow). Photograph by M. Patrick, USGS.

Park for areas within the national park. 

These measurements are used to report air 

quality hazard information to the public.

How Vog Affects Humans

Individuals vary in their sensitivity to 

vog, but many Hawaii residents and visitors report physical complaints associated 

with vog exposure. These include sore 

eyes and throat, runny nose, headaches, 

cough, phlegm, breathing difficulties, 

increased susceptibility to respiratory 

ailments, and a general lack of energy. 

Research on children has shown that 

vog exposure is not associated with the 

development of asthma, although it can 

aggravate pre-existing asthma, and other 

respiratory conditions.

Though vog is rich in SO2 and acidic 

aerosols, it does not contain additional 

toxic contaminants, such as ozone and 

hydrocarbons, present in urban and 

industrial pollution, which also cause 

health issues. Further investigations by 

health and physical science researchers 

on how volcanic air pollution interacts 

with common environmental factors 

such as cigarette smoke, mold, traffic 

exhaust, and pollen are important to 

help people identify the triggers for their 

health symptoms and to understand the 

short- and long-term impacts of vog on 

human health. 

How Vog Affects Agriculture and 

the Natural Environment

Agricultural impacts from vog, including significant damage to vegetable, 

orchard, and commercial flower crops, 

increased dramatically in 2008 as a result 

of the increased gas emissions that began 

with Kīlauea Volcano’s summit eruption. 

When atmospheric moisture is abundant, 

the tiny sulfuric acid droplets in vog 

combine with the water in clouds and fall 

as acid rain, damaging plants. Although 

SO2

 emissions and agricultural damage 

have declined in recent years, the impacts 

from the ongoing 2008 summit eruption 

have resulted in some farmers going out 

of business, relocating, or switching to 

more vog-tolerant crops.

Ranchers on the Island of Hawai‘i 

report rapid deterioration of metal fencing 

and infrastructure, as well as negative 

health effects on livestock. Owing to the 

agricultural impacts and financial losses, 

the U.S. Department of Agriculture has 

provided farmers and ranchers with 

Federal disaster assistance since 2008.

In drier conditions, such as those that 

prevail in west Hawai‘i (Kona coast), the 

acid aerosols in vog can actually impede 

the formation of raindrops, much like 

industrial pollution does in the northeastern United States. The resulting decrease 

in summer rainfall for west Hawai‘i 

affects crops, forests, and water supplies. 

In contrast to agricultural and other 

nonnative plants, native plants in Hawaii 
have evolved to live with frequent volcanic eruptions. The dominant forest tree, 

the ʻōhiʻa lehua, can close its stomata, or 

breathing pores, during periods of high 

SO2 exposure to protect itself from vog 

damage. 

How the Volcanic Plume Affects 

Water Quality

Many homes on the Island of Hawai‘i 

rely on rooftop rainwater-catchment 

systems for their household water 

supply. In 1988, the drinking water from 

40 percent of home catchment systems 

in the Kona Districts was found to be 

contaminated with lead leached from 

roofing and plumbing materials, such 

as nails, paint, solder, and metal flashings, by acid rain. Blood tests confirmed 

that some residents of these homes had 

elevated lead levels, which prompted an 

island-wide effort to remove lead-bearing 

materials from rainwater-catchment 

systems. Although lead-rich plumbing and building materials were rarely 

installed after 1986, water systems in 

older homes affected by vog may still 

be susceptible to lead, copper, and zinc 

contamination.

Hydrogen fluoride gas, a minor 

component of Kīlauea Volcano’s eruption 

plumes, can also contaminate water and 

soils. To date, tests of Hawai‘i household 

Molten lava from Kīlauea Volcano can flow through lava tubes to reach the Pacific Ocean, where it 

reacts with seawater to create large steam plumes laden with hydrochloric acid and volcanic glass 

particles. These acidic ‘laze’ plumes mainly create a local hazard for people visiting the ocean entry. 

Photograph by J. Babb, USGS.

catchment and municipal water supplies 

have shown that they are within U.S. 

Environmental Protection Agency 

(EPA) safe drinking-water standards 

for fluoride and other common volcanic 

contaminants.

Adapting to Life with Vog

Gas emissions from Kīlauea have 

decreased substantially since 2008, 

resulting in less vog for the Island and 

State of Hawaii. However, sensitive 

people, plants, animals, and infrastructure 

continue to be challenged by elevated 

concentrations of SO2 gas and acid aerosols downwind of the volcano. 

Although the decades-long activity at Kīlauea could end abruptly, there 

are no signs that gas emissions from 

Kīlauea will cease in the near future. 

Visitors in the 1800s mentioned the 

smell of volcanic gas far downwind of 

the volcano, suggesting that vog has also 

been noteworthy in the past. 

HVO scientists have helped develop 

resources to enable people to understand the hazard and minimize their 

exposure to vog. The Volcano Measurement and Prediction Project (VMAP) 

provides a two-day forecast of SO2

gas and sulfate particle concentrations 

(weather.hawaii.edu/vmap/). A centralized online website provides links to 

comprehensive vog information, including real-time vog concentrations, information on health, environmental impacts, 

and protecting yourself from vog (www.

ivhhn.org/vog). Climate and Weather: 

Regional and Global 

Impacts of Vog

Kīlauea Volcano’s eruptions currently 

serve as a natural experiment for exploring the impact of aerosols on the Earth’s 

energy balance and climate. Aerosols, 

like those associated with vog, absorb 

and scatter solar radiation. They also 

affect the amount of incoming sunlight 

reflected back into space (known as the 

planetary albedo) by increasing cloud 

coverage and brightness (a cloud’s 

ability to reflect radiation). These effects 

can potentially cause net cooling of the 

climate. Emissions from Kīlauea have a 

regional impact, influencing trade-wind 

cloud amounts and properties, and reducing rainfall thousands of miles downwind 

of Hawai‘i. Research by atmospheric 

scientists shows that continuous eruptions, like those at Kīlauea, may have a 

greater effect on climate than previously 

estimated, and are important to consider 

for climate models.

ADVISORY LEVELS

GOOD

MODERATE

UNHEALTHY FOR

SENSITIVE GROUPS

UNHEALTHY

VERY UNHEALTHY

HAZARDOUS

UH MANOA VMAP VOG MODEL

The Vog Measurement and Prediction Project (VMAP) uses estimates 

of volcanic emissions along with 

wind forecasts to predict concentrations of sulfur dioxide gas (SO2

) and 

sulfate (SO4

) aerosols. The colors 

on the map are correlated with the 

Hawaii State Department of Health 

advisory levels (weather.hawaii.edu/

vmap).

By Tamar Elias and A. Jeff Sutton

Edited by Katherine Jacques

Layout by Suzanne Roberts

For more information, contact:

U.S. Geological Survey Hawaiian Volcano Observatory

http://hvo.wr.usgs.gov/

U.S. Geological Survey Volcano Hazards Program 

http://volcanoes.usgs.gov/

ISSN 2327-6916 (print) 

ISSN 2327-6932 (online)

https://doi.org/10.3133/fs20173017