air pollution
Air pollution is the contamination of air due to the presence of substances in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or to materials. There are many different typ ...
that results when sulfur dioxide and other gases and particles emitted by an erupting
volcano
A volcano is a rupture in the Crust (geology), crust of a Planet#Planetary-mass objects, planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and volcanic gas, gases to escape from a magma chamber below the surface.
On Ear ...
react with
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
and moisture in the presence of sunlight. The word is a
portmanteau
A portmanteau word, or portmanteau (, ) is a blend of wordssmog". The term is in common use in the Hawaiian islands, where the Kīlauea volcano, on the
Island of Hawaii
Hawaii ( ; haw, Hawaii ) is the largest island in the United States, located in the state of Hawaii. It is the southeasternmost of the Hawaiian Islands, a chain of volcanic islands in the North Pacific Ocean. With an area of , it has 63% of th ...
(the "Big Island"), erupted continuously between 1983 and 2018. Based in June 2008 measurements, Kīlauea emits 2,000–4,000 tons of sulfur dioxide (SO2) every day.
Description
Vog is created when
volcanic gas
Volcanic gases are gases given off by active (or, at times, by dormant) volcanoes. These include gases trapped in cavities (vesicles) in volcanic rocks, dissolved or dissociated gases in magma and lava, or gases emanating from lava, from volcani ...
es (primarily oxides of sulfur) react with sunlight,
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
and
moisture
Moisture is the presence of a liquid, especially water, often in trace amounts. Small amounts of water may be found, for example, in the air (humidity), in foods, and in some commercial products. Moisture also refers to the amount of water vapo ...
. The result includes sulfuric acid and other sulfates. Vog is made up of a mixture of gases and aerosols which makes it hard to study and potentially more dangerous than either on their own.
Vog, which originates from volcanic vents, differs from laze, created when lava enters the ocean.
Vog in Hawaii
In
Hawaii
Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only state ...
, the gas plumes of Kīlauea rise up from three locations:
Halemaʻumaʻu
Halemaumau (''six syllables: HAH-lay-MAH-oo-MAH-oo'') is a pit crater within the much larger Kīlauea Caldera at the summit of Kīlauea volcano on island of Hawaiʻi. The roughly circular crater was x before collapses that roughly doubled ...
, Puʻu ʻŌʻō, and from along the coastline where lava flows from the East
Rift zone
A rift zone is a feature of some volcanoes, especially shield volcanoes, in which a set of linear cracks (or rifts) develops in a volcanic edifice, typically forming into two or three well-defined regions along the flanks of the vent. Believed t ...
enter the ocean. The plumes create a blanket of vog that can envelop the island. Vog mostly affects the Kona coast on the west side of the Island of
Hawaii
Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only state ...
, where the prevailing
trade wind
The trade winds or easterlies are the permanent east-to-west prevailing winds that flow in the Earth's equatorial region. The trade winds blow mainly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisph ...
s blow the vog to the southwest and southern winds then blow it north up the Kohala coast.
Prolonged periods of southerly Kona winds, however, can cause vog to affect the eastern side of the Island on rare occasions, and affect islands across the entire state as well."Vog: A Volcanic Hazard" on USGS web site By the time the vog reaches other islands, the sulfur dioxide has largely dissipated, leaving behind ash, smoke, sulfates, and ammonia.
Comparing vog and smog
Vog and smog are different. Vog is formed when sulfur oxides emitted by a volcano react with moisture to form an aerosol. The aerosol scatters light, thus making the vog visible. Smog is formed largely from the incomplete
combustion
Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combus ...
of fuel, reacting with
nitrogen oxides Nitrogen oxide may refer to a binary compound of oxygen and nitrogen, or a mixture of such compounds:
Charge-neutral
*Nitric oxide (NO), nitrogen(II) oxide, or nitrogen monoxide
*Nitrogen dioxide (), nitrogen(IV) oxide
* Nitrogen trioxide (), or ...
and
ozone
Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...
produced from
carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
by reactions with sunlight. The result is also a visible aerosol.
When smog levels are high, the sky appears yellowish-grey because nitrogen oxides are yellow. In contrast,
sulfur oxides
Sulfur oxide refers to many types of sulfur and oxygen containing compounds such as SO, SO2, SO3, S7O2, S6O2, S2O2, etc.
Sulfur oxide (SO''x'') refers to one or more of the following:
* Lower sulfur oxides (S''n''O, S7O2 and S6O2)
* Sulfur mono ...
are colorless and vog looks grey. Once the vog layer dissipates, grey spots of vog in the sky may, for a time, remain trapped in the inversion layer.
Several chemicals emitted from cars are not emitted from volcanoes. Similarly, some chemicals emitted from volcanoes, such as hydrogen sulfide, hydrogen chloride, and hydrogen fluoride, are not created by
exhaust gas
Exhaust gas or flue gas is emitted as a result of the combustion of fuels such as natural gas, gasoline (petrol), diesel fuel, fuel oil, biodiesel blends, or coal. According to the type of engine, it is discharged into the atmosphere through an ...
. Moreover, smog generated by factories has its own unique mix of contaminants.
Health hazards
Most studies of vog have been in areas where vog is naturally present and not in controlled conditions. Vog contains chemicals that can damage the environment and the health of plants, humans and other animals. Most of the aerosols are acidic and of a size where they can remain in the lungs to damage the lungs and impair function. Headaches, watery eyes, sore throat, breathing difficulties (including inducing
asthma
Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, co ...
attacks), flu-like symptoms and general
lethargy
Lethargy is a state of tiredness, sleepiness, weariness, fatigue, sluggishness or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to inadequate sleep, overexertion, overwo ...
are commonly reported. These effects are especially pronounced in children and in people with respiratory conditions. Vog generally reduces visibility, creating a hazard for road, air and ocean traffic.
The long-term health effects of vog are unknown.
Recent events
Several studies are underway to measure the air quality near volcanoes more carefully.
Sulfur dioxide emissions increased on March 12, 2008, when a new vent opened. The increased vog level has caused evacuations and damaged crops. In the summer of 2008 and in 2012, the County of Hawaii received a disaster designation due to the agricultural damage."Vog: Important Information and Facts" on State of Hawaii Office of the Governor web site
A recent multi-year computer-modeling feasibility study, known as VMAP, designed to predict the location and concentrations of vog from Kīlauea was conducted by the University of Hawaii.