Dobson was a scientist that devoted most of his life to the observation of the atmospheric ozone. The results of his devotion to the study of the atmospheric led to a great understanding of the structure and circulation of the stratosphere. He went to Oxford in 1920 to become a lecturer of Meteorology, having previously been a Captain in the Royal Flying Corps and Director of the Experimental Department at the royal Aircraft Establishment, Farnborough, during World War 1. He built a machine; it was the first spectrograph that he built in 1924 in his laboratory and workshop in a gut. His home was in Robin Wood, Boars Hill, near Oxford where he built the machine. The machine allowed relative intensity at two wavelengths to be measured directly. It was completed in 1927 0r 1928, the design being remarkably advanced for its day. (1) (Figure 1) Scientists have been looking at the concentration of ozone in the atmosphere since the 1920 s. Instruments have become more advanced since then by using: balloons, aircraft, rockets and satellites. Figure two shows satellites observe the ozone concentration. (2) (Figure 2) There are six ways of measuring ozone, the very first machine that was built was by Dobson, it was a ground based measurement it was called the Dobson spectrometer and provided long term data of both column ozone and ozone distribution. But the problem with this is that it was only a small area. Instruments that are commonly used overhead ozone from the ground are Dobson s spectrometer and light Detection and Raging (LIDAR). In figure 3 there is a clearer image of Dobson s spectrometer. There are 71 Dobson stations worldwide. Another
disadvantage about Dobson s method is that it is strongly affected by aerosols and pollutants in the atmosphere. These measurements are often used to compare with data obtained by satellites. The vertical distribution is measured using Umkehr method. This method relies on the intensities of things reflected, rather than direct UV light. An Umkehr takes about three hours and provides data up to an altitude of 48Km, with the most accurate information for altitude above 30 Km. The problem with ground based measurements is that they are on the ground so there is more stratosphere to look through. (2) (Figure 3) Another method of measuring ozone is by using, Light detective and ranging (LIDER). This technique relies on the absorption of laser light ozone. A telescope is used to collect ultraviolet light that is scattered by two laser beams, one that is absorbed by ozone and the other not. By comparing light intensity scattered from each laser the concentration of ozone is measured against altitude measurements. Figure four shows the instrument. (2) (Figure 4) This is another ground based way of measuring the ozone concentration. Scientists then decided to send things up in the air to get a more accurate reading, because this would mean there are fewer stratospheres to look through so you can take a measurement from a bigger area then a small area off the ground. Figure 5 shows pictures of what the balloons looked like. Balloons have been used almost just as long as ground based devices have been used. They can measure Ozone concentration with latitudes as high as 25 miles.
(40km) and it can still provide reactions with ozone, for example chorine. Many devices are often used to measure ozone from balloons often called Ozonesondes. (2) (Figure 5) I have also found some the earliest measurements of total column ozone dated to 1925. These were made at Arosa in Switzerland. The results include some results made at Arosa ground station. Ozone concentration is measured in Dobson Unites, (DU). One Dobson Unit represents the amount of ozone in a column that would be 0.01 millimetres thick if it was compressed into a layer at a standard temperature and pressure of the earth s surface. From what the graph shows the global chlorine emissions has increased from 1926 to 1990, however it decreased rapidly in 1990 to 2000. From 1960 to 1990 there was a rapid increase in global chlorine emissions. The reason for this may have been due to the excessive use of chlorine in 1960 to 1990.
From what the graph shows the total ozone increased rapidly from 1930 to 1940 and then dropped in 1950. This up and down ward pattern increase continues up until 1960 where it drops then stays almost constant. After 1970 there isn t much of a change up until 200 when rises again. This may be due to the increase in the use of chlorine emissions as it shows in the graph above. From looking at graph one the global chlorine emissions have increased throughout 1935 to 2000. This might be due to the release of CFC s in the atmosphere. This can explain why there is ozone depletion in the atmosphere because CFC s are very stable molecules which do not break down in the troposphere. Instead, they diffuse into the stratosphere where they are exposed to ultraviolet radiation. This breaks the bonds between carbon atoms and chlorine atoms in the molecules. When this happens chlorine atoms then act like NO molecules, and break ozone down in a catalytic cycle. Step 1: O₃+ Cl ClO + O₂ Step 2: ClO + O Cl+ O₂ Overall: O₃ + O O₂ + O₂
Reference: web address Figure Text http://www.atm.ox.ac.uk/user/barnett/ozoneconference/dobson.htm (1) (1) http://www.albany.edu/faculty/rgk/atm101/ozmeas.htm (2) (3) (4) (5) (2)