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Hydroxyl Radicals - Nature's "Scrubbing Bubbles" for Air Pollution

written by: Tony Smejek•edited by: Lamar Stonecypher•updated: 1/31/2011

Nature has its own solution to air pollution -- hydroxyl radicals. When the sun's UV rays cause oxygen and hydrogen atoms to bond, the result is a natural hydroxyl radical air purifier substance that combats pollution in the air.

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    Hydroxyl Radicals and Air Pollution

    Scientists have determined that something beneficial going on with the world’s air pollution, and it’s the earth’s atmosphere itself that is making the contribution. When the sun’s ultraviolet rays make contact with atmospheric gases, it causes some of the oxygen atoms to bind with hydrogen atoms, but not in the familiar form that constitutes water. Instead, this process forms hydroxyl radicals.

    Despite its short life, this substance is so chemically reactive that after combining with air pollutants, it is able to break the pollutants down into a less toxic chemical before it disappears from the atmosphere. In this way, the hydroxyl radical is sort of nature’s atmospheric "scrubbing bubbles."

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    Measurement of Hydroxyl Radicals

    Hydroxyl radicals are so short-lived, it is difficult for scientists to get a good grasp of the amount in the atmosphere on a global level. Computer analyses were thought to have given non-representative results stating that the levels of hydroxyl radicals are steady when measurements in the field say otherwise. Further investigation determined that the computers were right after all. The resulting data now shows less variability of hydroxyl levels than was found in the prior research.

    Regulatory agencies like the EPA now have a better baseline to be confident about when predicting the amount of hydroxyl radicals produced, thereby forecasting the future extent of air pollution. Will this have an effect on regulations for fossil fuels like coal and oil that are expected to be beneficial to alternative energy? It may be too early to tell.

    The primary concern of greenhouse gases still remains problematic because GHGs are in a class upon which hydroxyl radicals seem to have no effect.

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    Indoor Use of Hydroxyl Radicals

    Air purifying devices called hydroxyl radical air purifiers are capable of killing germs or other contaminants in indoor environments. Although hydroxyl radicals, or reactive oxygen species and their ions, can outperform ozone itself, they cannot travel to any extent throughout a building. Such devices are only good for small, localized areas or rooms.

    The only air that these systems can purify is the air that actually passes through the purifier's filter where the hydroxyl radicals are located. Though they can operate in the same manner as regular ozone producing devices, they are only minimally effective in large spaces.

    Air Purifier Image Source: 

    Air Purifier (Inside) Image Source: 

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    Chemical Signature for Hydroxyl Radicals

    In chemical terms the symbol for hydroxyl radicals is OH, but it is the neutral version of a hydroxide ion (OH-). Even though it is short lived, it is highly reactive and falls into a sub-category of radical chemistry.

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    Free Radical Formation

    Any atom capable of existing independently with one electron in its outermost shell is a free radical. This existence of unpaired bonds makes them highly reactive; this occurs when a covalent bond between entities break apart forming new atoms with unpaired electrons. As an example, any oxygen atom that exists in this state results in a highly reactive oxygen atom or a reactive oxygen species.

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    Reactive Oxygen Species

    During its brief existence, a free radical oxygen atom with an unpaired atom is highly reactive, and can steal an electron from another molecule or compound with a corresponding unpaired electron outer shell. This can result in a new free radical. This free radical seeks to return to its ground state, the state at which an atom is most stable.