Context:
A new ozone hole has been detected over the tropics, at latitudes of 30 degrees South to 30 degrees North, a recent study claimed. But some experts are divided over this.
Relevance:
GS I- Geography
Dimensions of the Article:
- What is Ozone Layer and what are Ozone Holes?
- Ozone creation and destruction
- Tropical Ozone Hole
- What caused an ozone hole in the tropics?
- Significance of the finding
What is Ozone Layer and what are Ozone Holes?
- Ozone layer, also called ozonosphere, is a region of the upper atmosphere, between roughly 15 and 35 km (9 and 22 miles) above Earth’s surface which contains relatively high concentrations of ozone molecules (O3).
- Approximately 90 percent of the atmosphere’s ozone occurs in the stratosphere, the region extending from 10–18 km (6–11 miles) to approximately 50 km (about 30 miles) above Earth’s surface.
- The ozone layer effectively blocks almost all solar radiation of wavelengths less than 290 nanometres from reaching Earth’s surface, including certain types of ultraviolet (UV) and other forms of radiation that could injure or kill most living things.
What are Ozone Holes?
- The ‘ozone hole’ is not really a hole — it refers to a region in the stratosphere where the concentration of ozone becomes extremely low in certain months.
- The ‘ozone holes’ most commonly talked about are the depletions over Antarctica, forming each year in the months of September, October and November, due to a set of special meteorological and chemical conditions that arise at the South Pole, and can reach sizes of around 20 to 25 million sq km.
- Such holes are also spotted over the North Pole, but owing to warmer temperatures than the South Pole, the depletions here are much smaller in size.
Ozone creation and destruction
- The production of ozone in the stratosphere results primarily from the breaking of the chemical bonds within oxygen molecules (O2) by high-energy solar photons. This process, called photodissociation, results in the release of single oxygen atoms, which later join with intact oxygen molecules to form ozone.
- The amount of ozone in the stratosphere varies naturally throughout the year as a result of chemical processes that create and destroy ozone molecules and as a result of winds and other transport processes that move ozone molecules around the planet.
- Over the course of several decades, however, human activities substantially altered the ozone layer.
- Ozone depletion, the global decrease in stratospheric ozone observed since the 1970s, is most pronounced in polar regions, and it is well correlated with the increase of chlorine and bromine in the stratosphere.
- Those chemicals, once freed by UV radiation from the chlorofluorocarbons (CFCs) and other halocarbons (carbon-halogen compounds) that contain them, destroy ozone by stripping away single oxygen atoms from ozone molecules.
- As the amount of stratospheric ozone declines, more UV radiation reaches Earth’s surface, and scientists worry that such increases could have significant effects on ecosystems and human health.
Tropical Ozone Hole
- According to the study, the ozone hole is located at altitudes of 10-25 km over the tropics.
- This hole is about seven times larger than Antarctica, the study suggested.
- It also appears across all seasons, unlike that of Antarctica, which is visible only in the spring.
- The hole has become significant since the 1980s. But it was not discovered until this study.
What caused an ozone hole in the tropics?
- Studies suggested another mechanism of ozone depletion: Cosmic rays.
- Chlorofluorocarbon’s (CFC) role in depleting the ozone layer is well-documented.
- The tropical stratosphere recorded a low temperature of 190-200 Kelvin (K).
- This can explain why the tropical ozone hole is constantly formed over the seasons.
Significance of the finding
- The tropical ozone hole, which makes up 50 percent of Earth’s surface, could cause a global concern due to the risks associated with it.
- It is likely to cause skin cancer, cataracts and other negative effects on the health and ecosystems in tropical regions.
-Source: Down to Earth
