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Volcanoes and the ozone layer

There has been a debate on whether volcanic eruptions and oceans have any effect on the ozone layer. The main causes or events that pump excess Chlorine and ODS in the stratosphere are those that are human caused. Volcanoes and oceans contribute to some extent, but these are natural causes and they are taken care of by the natural production of Ozone in the stratosphere.

“First, the vast majority of volcanic eruptions are too weak to reach the stratosphere, around 10 km above the surface. Thus, any HCl emitted in the eruption begins in the troposphere. Sea salt from the oceans is also released very low in the atmosphere. These compounds would have to remain airborne for 2-5 years to be carried to the stratosphere. However, both sea salt and HCl are extremely soluble in water, as opposed to CFCs which do not dissolve in water.” Source: EPA, Myth: Volcanoes and the Oceans are Causing Ozone Depletion, Ozone Layer Protection Science.

There are no records that large amounts of volcanic eruptions contributed to ozone depletion. Data that showed that El Chichon’s eruption in 1982 increased concentrations of HCL in the stratosphere by 10%, was updated by the fact that the HCL disappeared in about a year.

However it is true that volcanic ash and other gases emitted into the atmosphere contain high concentrations of bromine and chlorine. Ashes can stay in the stratosphere for about two to five years, and within this period, there are chemical reactions that destroy the stratospheric ozone molecules. In these volcanic ashes are some chemicals including bromine and chlorine belonging to a group of highly reactive elements called halogens, that need electrons to become stable. They get these electrons from the Ozone gas. Ozone destroying gases like hydrogen chloride, can also be found in volcanic ashes, but they dissolve readily in water. In many cases rain can wash down these chemicals before they get high up into the stratosphere, but some do escape into it.

“Researchers have also examined the potential impacts of other chlorine sources, such as swimming pools, industrial plants, sea salt, and volcanoes. However, chlorine compounds from these sources readily combine with water and repeated measurements show that they rain out of the troposphere very quickly before they have a chance to reach the stratosphere. In contrast, CFCs are very stable and do not dissolve in rain. There are no natural processes that remove the CFCs from the lower atmosphere. Over time, winds drive the CFCs into the stratosphere.’

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