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Volcano Watch — Volcanoes affect atmospheric ozone, our friend and foe

July 28, 2005

Summer in Hawaiʻi - a season for school vacations, shave ice, and Japanese bon dances. Trade winds blow most of the time, which is good news for east Hawaiʻi residents, as the noxious emissions from Kīlauea volcano, the island's largest pollution source, are blown to the west side of the island.

Photo of Ozone pollution over a city.
Ozone pollution, the main ingredient in urban smog. (Public domain.)

On the mainland, and other regions in the northern latitudes, the warm sunny summer months can be a time of very poor air quality. In addition to the SO2 gas and aerosol pollution that we experience on the big island from Kīlauea, metropolitan and even some rural areas are besieged with ozone pollution, the main ingredient in urban smog.

Ground-level ozone is formed by the interaction of sunlight with hydrocarbons and nitrogen oxides, which are emitted by automobiles, power plants, and other industries. It is damaging to vegetation, materials such as nylon and rubber, respiratory health, and other living tissue.

On the other hand, ozone in the stratosphere, the layer of the earth's atmosphere between about 10 km and 50 km above the surface, shields us from ultraviolet (UV) radiation and is essential to life as we know it. Overexposure to UV rays can lead to skin cancer, cataracts, weakened immune systems, reduced crop yields, and disruptions in the marine food chain.

The protective stratospheric ozone layer is gradually being destroyed by chemicals, particularly man-made halogenated hydrocarbons, which contain one or more atoms of chlorine, bromine, or fluorine. In the past, these substances were used extensively in coolants, fire extinguishers, solvents, pesticides, and aerosol propellants.

Once released into the air, these ozone-depleting substances degrade very slowly. They can remain intact for years as they drift up into the stratosphere, where they are broken down by the intensity of the sun's UV rays. The ozone-depleting substances release chlorine and bromine molecules, which destroy the "good" ozone through chemical reactions. Estimates suggest that one chlorine atom can destroy as many as 100,000 ozone molecules before it is removed from the atmosphere.

Volcanoes play an interesting role in the destruction of ozone. For instance, hydrogen chloride, a common volcanic gas, efficiently destroys ozone; however, it dissolves readily in water. So most volcanic hydrogen chloride is washed out by rain before it has the opportunity to reach and react with the protective stratospheric ozone layer.

On the other hand, significant ozone loss was observed in the stratosphere after the devastating 1991 eruption of Mt. Pinatubo (Philippines), which produced a plume that rose to 34 km, well into the stratosphere. Although measurements found no increase in stratospheric chlorine, the eruption played an indirect role in reducing ozone levels.

Particles formed from the eruption provided surfaces upon which chemical reactions took place. The particles themselves do not contribute to ozone destruction, but they interact with chlorine- and bromine-bearing compounds from human-made chemicals, allowing increased ozone depletion. Fortunately, volcanic particles take only two or three years to settle out of the stratosphere, so their effects on ozone depletion are short-lived.

A recent discovery suggests that volcanoes may contribute to ozone depletion in an additional way. The reactive chemical bromine oxide (BrO) has been measured in a number of volcanic plumes around the globe. The BrO is likely formed in the plume downwind of a volcano by reactions that occur between bromine species, which are present in high-temperature volcanic gases, and ozone.

While bromine is nearly 100 times less abundant than chlorine, it is about 10 times more effective in depleting ozone. Volcanoes are potentially a very important source of atmospheric bromine. Other natural sources include certain brine wells, the Dead Sea, and ocean waters. The bromine emitted from volcanoes is likely large enough to cause local ozone depletion and affect stratospheric chemistry.

Estimates suggest that volcanoes account for 1 to 5 percent of ozone damage, with 15 to 20 percent from other natural sources, and a whopping 75 to 85 percent due to human activity. As the ozone layer recovers due to restrictions on human-made ozone-depleting chemicals, future volcanic eruptions will cause fluctuations in the recovery process through direct and indirect contributions. Although BrO has yet to be detected in the Kīlauea plume, it is likely that the volcano in our backyard plays a role in atmospheric ozone chemistry.

Volcano Activity Update

Eruptive activity at Pu`u `O`o continues. On clear nights, glow is visible from several vents within the crater and on the southwest side of the cone.

Lava continues to flow through the PKK lava tube from its source near Pu`u `O`o to the ocean, with very few surface flows breaking out of the tube. Small flows are visible intermittently from the top of Pulama pali to the ocean. Two ocean entries, at East Lae`apuki and East Kamoamoa, were active as of July 28. Several partial collapses of the East Lae`apuki bench have occurred during the last month. Access to the ocean entries and the surrounding area has been closed due to significant hazards. No easily accessible surface flows are currently present. If you visit the eruption site, check with the rangers for current updates, and remember to carry lots of water when venturing out onto the flow field.

During the week ending July 27, only one earthquake was felt on Hawai`i Island. At 10:08 p.m. on July 15, a magnitude-4.5 light earthquake located 9 km (6 miles) southwest of Kīlauea summit occurred at a depth of 30 km (19 miles); this earthquake was felt throughout Hawai`i island and parts of Maui, Moloka`i, and O`ahu.

Mauna Loa is not erupting. During the week ending July 27, only three earthquakes were recorded beneath the summit area. All were deep and long-period in nature. Inflation has resumed after a several week-long pause.