Laboratory and epidemiological studies demonstrate that UVB causes non-melanoma skin cancer and plays a major role in malignant melanoma development. EPA uses the Atmospheric and Health Effects Framework model to estimate the health benefits of stronger ozone layer protection under the Montreal Protocol.
Ozone is formed in the stratosphere when oxygen molecules photodissociate after intaking ultraviolet photons. This converts a single O 2 into two atomic oxygen radicals. The atomic oxygen radicals then combine with separate O 2 molecules to create two O 3 molecules.
These ozone molecules absorb ultraviolet UV light, following which ozone splits into a molecule of O 2 and an oxygen atom. The oxygen atom then joins up with an oxygen molecule to regenerate ozone. This is a continuing process that terminates when an oxygen atom recombines with an ozone molecule to make two O 2 molecules.
The dot is a notation to indicate that each species has an unpaired electron and is thus extremely reactive. These elements are found in stable organic compounds, especially chlorofluorocarbonswhich can travel to the stratosphere without being destroyed in the troposphere due to their low reactivity.
Once in the stratosphere, the Cl and Br atoms are released from the parent compounds by the action Ozone layer deplection ultraviolet light, e. Cl and Br atoms destroy ozone molecules through a variety of catalytic cycles. In the simplest example of such a cycle,  a chlorine atom reacts with an ozone molecule O Ozone layer deplectiontaking an oxygen atom to form chlorine monoxide ClO and leaving an oxygen molecule O 2.
The ClO can react with a second molecule of ozone, releasing the chlorine atom and yielding two molecules of oxygen. The chemical shorthand for these gas-phase reactions is: More complicated mechanisms have also been discovered that lead to ozone destruction in the lower stratosphere. The ozone cycle Global monthly average total ozone amount Lowest value of ozone measured by TOMS each year in the ozone hole A single chlorine atom would continuously destroy ozone thus a catalyst for up to two years the time scale for transport back down to the troposphere were it not for reactions that remove them from this cycle by forming reservoir species such as hydrogen chloride HCl and chlorine nitrate ClONO 2.
Bromine is even more efficient than chlorine at destroying ozone on a per atom basis, but there is much less bromine in the atmosphere at present.
Both chlorine and bromine contribute significantly to overall ozone depletion. Laboratory studies have also shown that fluorine and iodine atoms participate in analogous catalytic cycles.
A single chlorine atom is able to react with an average ofozone molecules before it is removed from the catalytic cycle. This is normally expressed in Dobson units ; abbreviated as "DU". The most prominent decrease in ozone has been in the lower stratosphere.
Marked decreases in column ozone in the Antarctic spring and early summer compared to the early s and before have been observed using instruments such as the Total Ozone Mapping Spectrometer TOMS. Antarctic total column ozone in September and October have continued to be 40—50 percent lower than pre-ozone-hole values since the s.
It is expected to recover around The greatest Arctic declines are in the winter and spring, reaching up to 30 percent when the stratosphere is coldest.
Reactions that take place on polar stratospheric clouds PSCs play an important role in enhancing ozone depletion. This is why ozone holes first formed, and are deeper, over Antarctica. Early models failed to take PSCs into account and predicted a gradual global depletion, which is why the sudden Antarctic ozone hole was such a surprise to many scientists.
Total column ozone declined below pre values between and for mid-latitudes. In the northern mid-latitudes, it then increased from the minimum value by about two percent from to as regulations took effect and the amount of chlorine in the stratosphere decreased.
There are no significant trends in the tropics, largely because halogen-containing compounds have not had time to break down and release chlorine and bromine atoms at tropical latitudes.
Pinotubo in the Philippines. Some stratospheric cooling is also predicted from increases in greenhouse gases such as CO 2 and CFCs themselves; however, the ozone-induced cooling appears to be dominant.
The total amount of effective halogens chlorine and bromine in the stratosphere can be calculated and are known as the equivalent effective stratospheric chlorine EESC.
They were used in air conditioning and cooling units, as aerosol spray propellants prior to the s, and in the cleaning processes of delicate electronic equipment. They also occur as by-products of some chemical processes.
No significant natural sources have ever been identified for these compounds—their presence in the atmosphere is due almost entirely to human manufacture.Ozone layer depletion is one of the most serious problems faced by our planet earth.
It is also one of the prime reasons which are leading to global warming. Ozone is a colourless gas which is found in the stratosphere of our upper atmosphere.
Ozone depletion describes two related events observed since the late s: a steady lowering of about four percent in the total amount of ozone in Earth's atmosphere (the ozone layer), and a much larger springtime decrease in stratospheric ozone around Earth's polar regions.
The ozone layer is responsible for absorbing harmful ultraviolet rays, and preventing them from entering the Earth's atmosphere. However, various factors have led to the depletion and damage of this protective layer.
Learn more about the process, causes, and effects of ozone layer depletion. The ozone layer above the Antarctic has been particularly impacted by pollution since the mids.
This region’s low temperatures speed up the conversion of CFCs to chlorine. The ozone layer protects the Earth against most UVB coming from the sun. It is always important to protect oneself against UVB, even in the absence of ozone depletion, by wearing hats, sunglasses, and sunscreen.
However, these precautions will become more important as ozone depletion worsens. What is Ozone Layer? To understand ozone layer, it would be helpful to know the different layers of the atmosphere.
The earth’s atmosphere is composed of many layers, each playing a significant role. The first layer stretching approximately 10 kilometers upwards from the earth’s surface is known as the troposphere.