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Advanced Oxidation Processes (AOP)

Hydroxyls Radicals - Nature's Detergent - the Basis of Advanced Oxidation Processes

Nobel Laureate Dr. Paul Crutzen, coined the phrase "detergent of the atmosphere" to describe the air-cleaning function of the Hydroxyl Radical (OH). 

What happens to the millions of tonnes of gases that nature and humankind lob into the atmosphere every year?  Fortunately,  their rate of accumulation is countered by the atmosphere’s ability to cleanse itself of most of these so-called trace gases,  especially those in chemically reduced form. Through chemical changes initiated by sunlight  (photo-oxidation or photolysis),  such trace gases are transformed into products that are more easily removed by rain and snow, or that deposit directly onto the earth’s surface.

Reidel, K. & Lassey, K. (2008). Atmospheric chemistry: Detergent of the atmosphere. Water & Atmosphere 16(1), p.22.

How does it Work?

Thousands of megatons of natural and anthropogenic gases are released into the Earth's atmosphere annually. Photochemical-based chemical reactions, initiated by Hydroxyl (OH) radicals, oxidize the majority of these gases into products that are more easily removed through the precipitation cycle and dry deposition at the Earth's surface. 


Mother Natures Key Oxidant

The hydroxyl radical (OH) is the most important oxidant in the troposphere and lower stratosphere. It initiates removal from the atmosphere of toxic gases such as carbon monoxide (CO), radiatively active gases such as methane (CH4), tropospheric ozone precursors such as volatile organic compounds (VOCs), and NOx (NO + NO2), and stratospheric ozone-depleting compounds such as hydrochlorofluorocarbons (HCFCs). Therefore, it plays a key role in the atmospheric oxidation capacity, air quality, and climate.

Li, M., Karu, E., Brenninkmeijer, C., Fischer, H., Lelieveld, J., & Williams, J. (2018). Tropospheric OH and stratospheric OH and Cl concentrations determined from CH4, CH3Cl, and SF6 measurements. Npj Climate and Atmospheric Science1(1).

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