Case Study Depletion of ozone in the atmosphere







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Case Study

Depletion of ozone in the atmosphere

The work of G.M.B Dobson and other scientists in measuring concentrations of chloride and ozone in the atmosphere

G.M.B Dobson inferred correctly that the cause of the warm stratosphere was heating by the absorption of ultraviolet solar radiation by ozone, and he set out to make measurements of the amounts and their variability. (6)

During the 1920s, G.M.B. Dobson developed a spectrometer that could measure small concentrations of the ozone.

Dobson's first spectrograph employed a Fabry prism, an optical wedge consisting of gelatine and carbon black between quartz plates designed by T. Merton of the Clarendon Laboratory, and a filter consisting of a mixture of chlorine and bromine vapour to cut out unwanted solar radiation at longer wavelengths. A special tank was built to ensure consistent development of the photographic plates. (6) The Dobson Spectrometer measures the total ozone by measuring the relative intensity of the dangerous UVB radiation that reaches the Earth and comparing it to that of UVA radiation at ground level. (8) As ozone does exist in the

atmosphere, the Dobson Spectrometer can use the ratio between UVA and UVB radiation on the ground to determine how much ozone is present in the upper atmosphere to absorb the UVC radiation.(8)

Dobson spectrophotometers can be used to measure both total column ozone and profiles of ozone in the atmosphere. (8)

Dobson improved on his spectrometer, he even invented the photoelectric spectrophotometer, and theses spectrometers were such a useful invention that many scientists today use them, to measure the concentration of the ozone. To measure the line intensities Dobson built a photoelectric microphotometer using a potassium photocell, the current from which was measured by an electrometer. (6) The photoelectric spectrophotometer is shown in the diagram below.


The development of the photoelectric spectrophotometer diagram

Techniques used when using a spectrometer

However, using a spectrometer is a skilful technique, for example, the photometer shown in the diagram, is suitable for the purpose of measuring extinction

coefficients of substances in a solution more particularly in the ultraviolet region. The method employed is a purely electrical one, and does not involve the use of any mechanical devices (e.g. sectors or wedges.) for the quantitative variation of light intensity. (7)

The sun direction is part of the photoelectric spectrophotometer, and is shown in the diagram above, it enters light and a fraction of this light is reflected at the plate and enters one of the photoelectric cells, which we will call the comparison cell. (7) A fraction of the light is transmitted by the plate and passes onto the other

photoelectric cell, which we will call the measuring cell. (7) The ethical issues involved in using the photometer

Using a spectrometer may arise some ethical questions, such as, is using an intense, homogeneous and stable magnetic field, safe? Isn’t using a spectrometer a useful tool in measuring the concentration of the ozone? Is it okay for scientists to use a spectrometer to intervene with natural occurrences of the earth? Theses are ethical questions, for the use of spectrometers. (7)


Exposure of ultraviolet radiation

Some scientists measure the ozone in the atmosphere by observing the exposure of ultraviolet radiation. Stratospheric ozone is a naturally-occurring gas that filters the sun's ultraviolet radiation. (1) The weaker the ozone layer, the more ultraviolet radiation that reaches the Earth's surface. (1) Overexposure to certain ultraviolet rays can lead to skin cancer, cataracts, and weakened immune systems. (1)

(Fig 8.2)

The diagram (Fig8.3) above shows the levels of ozone decreasing when more ultraviolet radiation is increased in the atmosphere. This supports the idea of some scientist’s measure in the ozone of the atmosphere by observing the exposure of ultraviolet radiation actually changes the ozone causing it to decline.

Techniques used in absorbing ultraviolet radiation

When theses scientists absorb ultraviolet radiation to measure the ozone they measure it using a UV spectrometer, as a spectrometer is an instrument which measures the amount of light of a specified wavelength which passes through a medium. (19)

According to Beer's law, the amount of light absorbed by a medium is proportional to the concentration of the absorbing material or solute present. Thus, the

concentration of a coloured solute in a solution was determined in their laboratory by measuring the absorbency of light at a given wavelength. Wavelength (often abbreviated as lambda) is measured in nm. The scientist’s spectrophotometer then


allowed a selection of a wavelength pass through the solution. Finally, the scientists were then able to measure UV radiation. (19)

The ethical issues involved in using ultraviolet radiation

There are some ethical considerations in absorbing UV radiation, as UV radiation has a high-frequency light invisible to humans. Therefore, excessive exposure to UV light can destroy the bonds between molecules in skin cells and damage DNA tremendously; thus, this damage and can cause skin cancer and eye cataracts. (20). Therefore, some ethical questions may occur such as, how much time do us

humans have before UV radiation completely damages human health? Are human activities (such as using CFCs) worth using if it decreases the ozone, and causes humans to be exposed to UV radiation? (20)

Thus, certain industrial chemical pollutants in the atmosphere are gradually eroding earth's protective shield (ozone layer) which stops the sun's UV radiation from reaching the earth. In recent years, there has been growing concern about increasing levels of UV radiation in the sunlight, especially during the summer months. It may be beneficial for health reasons to measure the amounts of UV light present in living and work spaces. (19)

Therefore, scientists who measure the amount of UV radiation in the atmosphere, to measure ozone concentration, helps other scientists to detect how much UV radiation is being exposed in the atmosphere and this can lead to procedures that citizens are to carry out in order to reduce the amount of UV radiation being exposed in the earth. Alternatively, some industrial applications depend on a consistently high UV level that must be checked regularly. (19)

The ozone layer by NOAA research

Some scientist from the NOAA Research has, for many years, played a vital role in studying the ozone layer. For instance, at the Chemical Sciences Division of ESRL, researchers are conducting laboratory and field experiments and designing

computer models to study this issue. One of the primary missions of ESRL's Global Monitoring Division is to observe and understand the ozone layer through accurate, long-term measurements of ozone, chlorofluorocarbons, greenhouse gases, and solar radiation. (4)

NOAA scientists have travelled to Antarctica to study the ozone hole that has been occurring there since the late 1970s. In 1986, soon after the reported discovery of the ozone hole, Aeronomy Lab (now ESRL) scientist Dr. Susan Solomon led a team of 16 scientists, the National Ozone Expedition (NOZE I), to Antarctica. (4)


The scientists took measurements of various trace gases and physical properties of the atmosphere. The data, along with additional findings from the NOZE II mission the following year, showed conclusively that human-produced trace gases that contain chlorine and bromine were causing the ozone hole. The Global

Monitoring Division of ESRL has monitored the yearly Antarctic ozone hole since 1986 by launching balloon-borne Ozonesondes, from the South Pole station and measuring total column ozone from a ground based Dobson spectrophotometer since 1963. (4)

(Fig 1.1)

According to (fig 1.1), the amount of aerosol used in Europe, which contain

chloride and bromine gases have lead to high aerosol emissions from 2.0 – 3.5; this suggest that Europe is causing an ozone hole due to the amount of aerosol that is used there.

Techniques used in balloon-borne Ozonesondes

There are techniques used in measuring balloon-borne Ozonesondes. Firstly, local measurements of atmospheric zone abundance are those that require air to be drawn directly into an instrument. Once inside this instrument, ozone can be measured by its absorption of ultraviolet (UV) light or by the electrical current produced in an ozone chemical reaction. (18)


Ambient air is continuously forced into the sensing cell by a battery driven sampling pump. An electrical current is generated proportional to the mass flow rate of ozone through the cell. By knowing the volume flow rate and temperature, the electrical current can be converted to an ozone concentration under the

assumption that the ozone reaction with potassium iodide is quantitatively known. (18)

Next, the latter approach is used in the construction of Ozonesondes, which is light weight; theses are ozone-measuring modules suitable for launching on small balloons. Then the balloons ascend far enough in the atmosphere to measure ozone in the stratospheric ozone layer. Therefore, Ozonesondes are launched regularly at many locations around the world. (18)

Ethical issues of using balloon-borne Ozonesondes

There are some ethical issues that are involved with using Ozonesondes. Te procedure of using Ozonesondes involves ambient air being continuously forced into the sensing cell by a battery driven sampling pump. Therefore, ethical

questions occur such as, is using so much electricity worth measuring ozone concentrations?

However, it is often argued that Ozonesondes use mainly normally measured are the ozone concentration, ambient air pressure, temperature, humidity, and, in some cases, the wind direction and speed. Therefore, there are some natural resources used in this method. Some questions could arise such as, should scientists be prevented from using balloon-borne Ozonesondes, if Ozonesondes help to measure ozone concentrations?

Measuring ozone changes

Other scientists measure the concentrations of ozone in the atmosphere by observing the weather changes of the atmosphere. As they claim that CFCs alone could not have the profound impact on the ozone that is being observed. (1) Observing the changes in weather patterns, eruptions of volcanoes, changes in the ultraviolet radiation from the sun which changes through a ten year cycle, and other phenomena can, like CFCs, inhibit the production of ozone. (1)

Techniques used in measuring weather changes in the ozone

Weather is the daily condition of the air around us over a short period of time. Some scientists carry out weather techniques, in order to measure ozone levels. Weather can


be measured by using temperature. Furthermore, temperature it is usually measured with a thermometer in degrees centigrade. (ºC) (20)

Although, measuring the pressure on the weather is another way to detect the ozone levels, pressure is a measure of the mass of air the atmosphere. Therefore, pressure is measured with a barometer in milliards. (Mb) (20)

However, Wind can be used to detect ozone levels. An anemometer measures wind speed in mph. The most common type is a windmill. Three cups are fixed to a central shaft and the stronger the wind blows the faster the windmill rotates. (20)

Also, measuring sunlight is another way of measuring ozone levels, as sunshine is Campbell Stokes Recorder measures sunlight. This type of recorder is made up of a glass ball which concentrates sunshine on to a thick piece of card. (20)

Therefore, these weather changes in the atmosphere help to measure ozone concentration. (20)

Ethical issues involved in measuring weather changes

There are ethical issues in measuring weather changes, such as is it right for scientists to test the weather? Can measuring the weather cause for an increase in earthquakes and floods? If scientists measure weather conditions won’t it help benefit the earth keep tract of the ozone concentration? (20)

Atmospheric effects of the Mt Pinatubo eruption

Some scientists did research at the British Research Station at Halley Bay in Antarctica to measure the concentrations of chloride by looking at the meteorological

conditions that ozone holes form. (2) High levels of molecular chlorine (Cl2) can be

produced in the stratosphere at the poles during the winter. In the spring, the Sun reappears and levels of solar ultra-violet radiation increase.

This ultra-violet radiation breaks down the Cl2 into chlorine radicals, these then destroy ozone and then an ozone hole will form. (2)

However, the ozone seems to not be fully affected by chloride levels, according the diagram (fig 1.2) chloride is not fully affecting the ozone hole in atmosphere as chlorine levels in 2007 were higher, than the chloride levels in 2008.


(Fig 1.2)

‘Chloride suppress for inland US’ created by the Environmental research website

To measure the concentration of chloride, a spectrometer was used by the scientist Thornton. Thornton and his fellow colleagues used a chemical ionization mass spectrometer. (9)

Techniques used for measuring the concentrations of chloride

By using a chemical ionization mass spectrometer, Thornton and colleagues from the University of Washington; the US National Oceanic and Atmospheric

Administration; and the Cooperative Institute for Research in Environmental Studies, Boulder, US, found that the concentration of nitryl chloride at Boulder, Colorado, roughly one mile above sea level, was 500 parts per trillion.(9)

This is about the same as the concentration that was measured above the ocean during a subsequent research cruise between Long Island Sound, US, Norway and Iceland. (9)


Once, Thornton and his colleagues were, back from the research cruise, the team carried out more measurements, this time from a park 150 feet above the city, a location removed from any obvious sources of chloride. Information from air-quality monitoring in national parks around the US indicated that nitryl chloride is present there too. (9)

Thornton concluded from his work that most chlorine in the first kilometre or two of the atmosphere is emitted by sea spray. (9)

The concentration of chloride by using Inhaled chlorine gas forms hypochlorous acid and hydrochloric acid, by different scientists

The scientist’s Vetrano (2001) and Winder (2001) measured the concentrations of chloride by using Inhaled chlorine gas forms hypochlorous acid and hydrochloric acid upon contact with the moist mucous membranes of the upper respiratory tract. (10)

Winder found that once chloride concentrations have been absorbed into the body, hypochlorous and hydrochloric acid are expected to react with proteins and nucleotides to produce a wide variety of chlorinated organic compounds (EPA 1999; Winder 2001). (10)

Abdel-Rahman et al. 1982, 1983; EPA 1999; Suh and Abdel-Rahman 198, are scientists that measured the concentration of chloride through biological factors based on a study that traced radiolabel chlorine (as hypochlorite) through

metabolism inside rats. Moreover it is expected that chlorine is ultimately converted to chloride in the blood and eliminated in the urine and faeces of humans and animals primarily as the chloride ion. (10)

Chloroform has also been detected in the blood of rats exposed to hypochlorous acid (Abdel-Rahman et al. 1984). Since chloride is a natural component of blood, urine, and faeces, monitoring chloride concentrations in these materials would not be helpful for assessing exposure to chlorine. (10)

Techniques used in finding chloride concentrations in the atmosphere

Scientists of the APHA used a spectrometer to find the concentrations of chloride in the atmosphere. Also, the scientists such as, Abdel-Rahman et al. 1982, 1983; EPA 1999; Suh and Abdel-Rahman 198 used chloride through biological factors based on a study that traced radiolabel chlorine (as hypochlorite) through

metabolism inside rats, to measure ozone concentrations. Whereas, scientists such as, Vetrano and Winder (2001) measured the concentrations of chloride by using


Inhaled chlorine gas. Moreover, when chlorine is released into the environment, it reacts very quickly with both organic and inorganic matter forming chloride ion and chlorinated compounds. (10) The total chlorine is measured

spectrophotometrically at 515 nm (APHA 1998a, 1998b). (10) Ethical issues in using chloride concentrations in the atmosphere

The main ethical issue for measuring chloride concentrations in the atmosphere is the fact that a spectrometer is used. Ethics include questions, such as, is using a spectrometer a secure device? Will using a spectrometer cause any long-term health risks?

The total column ozone, annual average at south pole in DU

This table below is also on the information of TOMS. This table from TOMS is based on the total column ozone of annual average at the South Pole in DU.

(Table 1)

Year Total column ozone, annual

averages at south pole in DU

1965 287.3 P 1970 303.0 p 1975 289.0 p 1980 287.7 p 1985 244.5 p 1990 203.5 p 1995 234.5 p 2005 250.2 p

The table above (table 1) shows that the ozone from TOMS decreases from the years of 1965 to 2005.

The graph of the annual average of ozone in South Pole


Total column ozone, annual averages at south pole in DU

0 50 100 150 200 250 300 350 1960 1970 1980 1990 2000 2010

Total column ozone, annual averages at south pole in DU

The graph above shows that the total column ozone annual averages at South Pole in DU, has decreased between the years of 1960 - 2010. The annual ozone

averages, had started to increase as in 1990 the annual average ozone in the South Pole was 234.5 and in 2010 the annual average ozone in the South Pole was 250.2 DU

Why the total annual average ozone decreases in the South Pole

The oxygen we breathe has 2 atoms of oxygen in it (O2). Ozone is constantly

produced and destroyed by chemical reactions in the upper atmosphere that

involve the breaking of O2 into two O atoms that then react with more O2 to make

O3. Oxygen atoms are a type of "free radical", which is an atom or molecule with a

very reactive electron on it. (17)

Light of ultra-violet wavelengths (around 300 nm) exits O2 and O3 molecules to the proper energy to allow both production and destruction reactions of O2 and O3

to proceed. Furthermore, these reactions normally absorb much of the UV radiation the sun directs towards us, protecting the Earth's surface from its harmful effects. (17)

The ozone reaction is actually more complex as it requires mediator molecules that help the reactions along by transferring some of the energy between the reacting molecules. Also, other chemicals can get involved, including other "free radicals" such as Cl and NO. (17)

There is a natural production and destruction of ozone in the stratosphere, as the ozone in the stratosphere makes available all the materials involved in the chemical reactions and keeping their concentrations relatively constant with time. One


natural phenomenon that can disrupt this balance is a volcanic eruption that sends gasses and volcanic ash into the stratosphere. Not all eruptions do this but

particularly violent ones (such as Mt. Pinatubo) can add particles to the upper atmosphere that will affect the ozone budget for some period of time. (17) Under normal conditions, the amount of stratospheric ozone depends on the amount of sunlight reaching a certain geographic area of the atmosphere. The seasonal variation is low in low latitudes because sunlight is fairly constant year-round. In high latitudes, sunlight decreases more within the winter months. Ozone typically "builds up" to higher values over the poles during the winter and early spring in each hemisphere. (17)

The air masses above the poles become isolated from the rest of the atmosphere during their winter and early spring seasons due to a phenomenon known as the "polar vortex". In simplest terms, this vortex is a spinning, funnel shaped region of the atmosphere that forms in late fall and early winter over a pole, allowing

chemical reactions in the enclosed air mass to be enhanced due to the lack of mixing with other, lower latitude, air masses. (17)

The effect of the pollutants added the atmosphere e.g. CFCs, are enhanced in these isolated regions of the atmosphere. The Antarctic vortex over the South Pole is more effective at isolating this region of the atmosphere during the austral winter than is the corresponding arctic vortex. (17)

A second feature of the polar stratosphere is that it aids the polar ozone depletion by its polar stratospheric clouds. These very high altitude clouds are composed of ice crystals, sometimes greatly enriched in nitrogen oxide ("NOx") that can enhance

the ozone degradation reactions discussed above. These ice particles can react with various forms of Chlorine in the atmosphere and accumulate the molecule

ClONO2, which is a source of ozone depleting Cl radicals. Once spring time comes, this ClONO2 decomposes and allows ozone degradation reactions to

occur. (17)

The "ozone hole" is an area over the South Pole where lower than normal levels of ozone have been detected. As discussed above, the amount of ozone in the layer varies naturally throughout the year because it is formed and destroyed by chemical reactions that require light. So the ozone hole is more intense when there is

sunlight over the South Pole then where then is darkness (i.e., the austral winter). The size of the hole also changes (in some years it stretches to lower latitudes as the whole size increases). (17)


The diagram above (fig3.7) shows that the suns UV radiation causes a removal of the chlorine atom from the CFC molecule. The chloride radical breaks bonds in ozone molecules and creates chloride monoxide and diatomic oxygen and oxygen atom in atmosphere. The oxygen breaks bonds in chloride monoxide molecule, and this produces diatomic oxygen and free chloride radical. (15)

In conclusion, human activities have made the hole much more intense. Although, there was always a lower amount of ozone over the south pole (and to a lesser extent over the north pole too) before human activities altered the composition of the atmosphere. Also, the reason for the South Pole decreasing is due to the fact that ozone depletion decreases at lower latitudes and the South Pole has low latitude.


Most reliable and valid (source)

The most reliable and valid website, out of all the referenced websites is ‘Measured ozone depletion’ by the TOMS website.

The reason why the TOMS website is the most reliable is because has launched a probe on July 2nd 1996 to provide supplemental measurements. A space probe is a

scientific space exploration mission in which a robotic spacecraft leaves the gravity well of Earth and approaches the Moon or enters interplanetary or interstellar space. This suggests that Toms uses its own scientific interpretations that are based on the findings and evidence from using probe space missions to make sure that the facts and information on this site are regularly updated and true; this adds accuracy to the data, making the data reliable.

Furthermore, the TOMS website is very reliable as although it was updated five years ago, it is regularly updated by satellites provided by the ‘Ozone Monitoring Instrument (OMI) aboard the Aura satellite.’ Also, TOMS is so consistent that they launched another probe to a higher orbit and replace a failed ADEOS. This

suggests that they are on schedule with their work, and this indicates that the work

Reference number Referenced websites

(1) pdf (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14)

(15) TOMS monitoring ozone concentrations in the atmosphere in Arosa

(16) TOMS monitoring ozone concentrations in the south pole





on the TOMS website is dependable, and information is kept up-to-date regularly, as it’s the spectrometer brings, ‘measurements of total column ozone on a daily basis.’

The TOMS website is also valid as the information is related to the website title ‘Measured ozone depletion’, and also the information is correct as the scientific ideas of ozone depletion is used today by other scientists. Also, information is in a logical order with diagrams, and also links to NASA (NASA is an official government website, which shows real-life mission profiles and events, and top professors and scientists latest work and recent projects.

The TOMS website explains how methods of ozone depletion are used, and why these methods were used. For example, the TOMS website explains that ‘Balloons have been used almost as long as ground devices to measure ozone.’ And they continue to explain that balloons ‘can measure the change in ozone concentration with altitude as high as 25 miles (40 km) and provide several days of continuous coverage.’ Also, TOMS uses a range of instruments to measure the ozone concentrations in the atmosphere, ‘Many devices are used to measure ozone from balloons often called

“Ozonesondes”. The TOMS instruments could include, Electrochemical Concentration Cells (ECCs), which measure current produced by chemical reactions with ozone. This method is most common. This shows high levels of explanation of the website, and this makes the website valid.

Also, the TOMS website explains each method of ozone depletion with a diagram, with clear reference to text. This suggests that the TOMs website is user- friendly, as the user of the website can understand perfectly what methods are used, and the information of how and why the methods are used are most likely to stay in the users mind with illustrations as they are visual, and this includes interest within the text.

In conclusion, the TOMs website has good reference to text, the context has highly knowledgeable and understandable ideas and explanation to Ozone depletion and how it has been measured in the past by other scientists and the website also includes why theses measurements were used.

Also, the structure and context was legible, and there were diagrams in this website, that were referenced and were used to give the user an understanding of the text.


Least reliable and valid website (source)

The least reliable and valid website is the (7) referenced was A photoelectric spectrometer using Duels electrostatic compensation by Leonard A. Woodward, B.A PhD; Massey scientific research Fellow of university college Nottingham. The reason why this website was the least reliable was because this website does not clearly state when it was published, also there is no indication of when or if this website has been updated. Therefore, it is uncertain of when the information was produced, and if it was made years ago the information would not be relevant today. Also, as the information has not been updated, it implies that the

information is not checked regularly, and it is not fully accurate. This website lacks reliability.

The information on this site does have lots of detailed information, yet the

information is limited and it only explains two paragraphs of the photometer. This means the data lacks validity as there is not a complete range of scientific


Moreover, having two – three detailed paragraphs makes this website lack validity, as the information does not include theories of other scientists or full scientific interpretation form a range of scientists. Also, the website will not show other scientists interpretations, unless the user signs up to the website. Therefore, information is very limited.

Also, the website text is illegible, as the context and witting is very small, making the context information difficult to interpret. Therefore, this website lacks validity. This article lacks validity, as it indicates that there is a diagram to refer to within the website; although, there is no diagram to refer to at all. Thus, this website has false information as well as limited context and interpretation.

To conclude, this website has no publication or updates, so the website lacks reliability. Also, the website does not illustrate text, or use ideas from other scientific interpretations, and the actual information within the site is limited and illegible, this makes the site lack validity.





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