Lesson 1: Ozone and UV radiation The objectives of this lesson is to introduce material on ozone and UV radiation, concepts important to the later understanding of ozone depletion. Some students may have already studied part of this material, but a review will likely not be a waste of time. It also could be the case that some of this material may be too advanced for younger students, or require further explanation. Some overheads are labeled in the notes section with (optional) to alert teachers that material may be too detailed for all students. In general, the idea of this lecture is to answer the questions, what is the ozone layer, where is it, and why it is important. Ozone module prepared by Eugene C. Cordero

Learning Objectives To understand the role ozone plays in the Earth’s system. To understand how surface Ultraviolet (UV) radiation varies. Ozone module prepared by Eugene C. Cordero

What is ozone? The ozone molecule contains three oxygen atoms, hence O3 is ozone. How is ozone produced? It is formed when oxygen absorbs solar radiation O2 +h(<240nm)  O+O O+ O2  O3 Ozone reacts with various other chemicals, and thus is highly reactive. Ozone also absorbs incoming UV radiation O3 + h( <320nm)  O2+O (advanced; more advanced students with some chemistry knowledge) Ozone is a gas, made of three oxygen atoms. It is produced and destroyed naturally by sunlight. Ozone is produced when molecular oxygen (O2) absorbs solar radiation with a wavelength less than 240 nanometers (2.40 x 10 –11 meters), producing two oxygen atoms (O). A free oxygen atom may then react with an O2 molecule to form O3, ozone. Ozone is very reactive and reacts with various other chemical families including Chlorine, Bromine, Hydrogen. Ozone absorbs incoming solar radiation with a wavelength less than 320 nm, namely UV radiation. Ozone module prepared by Eugene C. Cordero

Ozone formation (advanced; this is a graphical description of previous overhead) Ozone exists in the upper atmosphere: Is formed by sunlight (one way) and destroyed by sunlight (another way), as explained in the previous viewgraph. Ozone module prepared by Eugene C. Cordero

Key Learning Figure: The ozone bucket analogy (useful to explain the natural production and destruction of ozone) a)Ozone is formed naturally by the sun, hence, the sun is filling up our bucket of ozone Chemicals naturally destroy ozone (Noy, Hox, Clx; chemical families of Nitrogen, Hydrogen and Chlorine) These natural destruction methods are like holes in the bucket, thereby reducing the amount of ozone in the bucket. The result is that the ozone layer or sometimes called, the ozone column (which means total column of ozone from the ground to the top of the atmosphere), is in some balance. Water comes in, water leaks out, or in our case, ozone is produced (by the sun) and ozone in destroyed (by natural chemicals). The result is an equilibrium is reached. However, if we add Man-made chemicals (e.g. CFC’s) to the atmosphere, then this adds an extra hole to our bucket because these chemicals also destroy ozone. The result is that the ozone column (or ozone layer) will get thinner. The neat part is: If we plug up the man-made holes, by reducing the amount of these ozone-destroying chemicals, then eventually, the ozone column (or layer) will come back to the same equilibrium as it did before. This is a good summary figure that can be referred to later after discussions of ozone depletion.

Good ozone/bad ozone Key Learning Figure: Good ozone/Bad ozone concept Note: Students (and the public) often get confused about ozone in the stratosphere (upper atmosphere), and ozone in the lower atmosphere, which is simply photochemical smog. They are the same chemical, just are produced in different ways. Ozone exists from the ground up to more than 35 km in the altitude (e.g. planes fly up to 30,000 ft or 10km). Most of the Earth’s ozone exists around 25 km in altitude, which is what we call the ozone layer. However, near the ground where we live, ozone is also produces from automobile pollution. Because ozone is harmful to human health if breathed in, this is what we call ‘smog’ or ‘air pollution’. Thus, we have the good ozone, in the upper atmosphere, and bad ozone in the lower atmosphere. They are the same gas, but one is produced naturally and the other by automobile pollution. Unfortunately, ‘bad ozone’ doesn’t help much with absorbing UV radiation since the abundances are relatively small. Ozone module prepared by Eugene C. Cordero

Why is the ozone layer important Ozone acts as the Earth’s protective shield against the Sun’s harmful Ultraviolet radiation (UV radiation). Without the ozone layer, life would not exist on Earth! The natural development of the ozone layer permitted life to evolve above water. Why is the ozone layer important? The ozone layer absorbs most of the Sun’s harmful radiation (UV radiation). Without the ozone layer, life would not exist due to the presence of very strong and harmful radiation from the sun. Ozone module prepared by Eugene C. Cordero

Ozone in the Atmosphere Ozone is mainly produced in the tropics because of the higher amounts of solar radiation. Ozone is mainly destroyed at middle and higher latitudes by chemical processes. Ozone is also largely affected by atmospheric winds. Thus, ozone naturally has large variations in space and time. (advanced) The evolution of ozone is determined both by chemistry and dynamics (weather). Ozone is produced naturally in the tropics (by the large amount of sunlight) and large scale weather transports the ozone to higher latitudes, especially during winter. Ozone module prepared by Eugene C. Cordero

Satellite Ozone Observations The Total Ozone Mapping Spectrophotometer (TOMS) is a satellite measuring total ozone. Total ozone is the column of ozone from the surface of the earth through the entire atmosphere. Total ozone is the normal unit of ozone measurement, and ranges from 80 Dobson Units (DU) to 500+ DU, where the higher the number, the more ozone there is. This overhead explains how to understand the TOMS pictures. Ozone module prepared by Eugene C. Cordero

The ozone layer for one day Ozone observations for one particular day From the overhead, we see that there is less ozone in the tropics than the higher latitudes. This is due to the prevailing winds in the atmosphere, which push out more ozone from the tropics to the higher latitudes, especially in the winter hemisphere. (note: ozone is a gas that can be blown around by the winds) Notice the ozone levels over Australia which get smaller as you go north: Notice the low ozone values over Antarctica (100-150 DU). This is the ozone hole (more on this in next lesson) The important part of this overhead is that ozone changes a lot from one location to another. Just like clouds move around, ozone also moves around, producing regions where more ozone exists, and less ozone exists. However, normally there is always a minimum amount of ozone in the atmosphere, which protects the Earth. Ozone module prepared by Eugene C. Cordero

Dobson Units (DU) as a measure of total ozone definition of ozone hole: < 220 DU Melbourne Avg. 280-380DU Darwin Avg. 260DU (advanced) This is a description of what a Dobson Unit is. As mentioned earlier, a Dobson Unit is a measurement of total ozone, or the amount of ozone from the ground up through the atmosphere. The idea of this viewgraph is this: Although the ozone layer is fairly thick (from 15-45 km in altitude), if you brought all those ozone molecules to the Earth’s surface, where the pressure is much greater, the entire ozone layer(i.e. 300 DU) would compress to be about 300 mm thick, or the thickness of a 2 dollar coin. Average amounts of ozone for Darwin and Melbourne are given. Ozone module prepared by Eugene C. Cordero

UV radiation UV radiation is emitted from the sun with wavelength from 200-400 nm (nanometers) UV radiation is divided into three ranges UV-A, 320 - 400 nm UV-B, 290 - 320 nm UV-C, 200 - 290 nm The shorter wavelength are more harmful to biological life. advanced Main idea is that UV radiation (ultraviolet radiation) is harmful to biological life (humans, animals, plants etc.) UV radiation is divided into three classes, UV-A, UV-B and UV-C. The ozone layer absorbs virtually all of the UV-A, and most of UV-B, and only a small amount of UV-C. Fortunately, UV-C is not harmful to life on the planet, while UV-A is extremely harmful to biological life. The major concern with ozone depletion concerns UV-B, which is harmful to humans, and it only partially absorbed by the ozone layer. Ozone module prepared by Eugene C. Cordero

Ozone profile with height and UV Key Learning Figure: This is a graphical description of how UV radiation is absorbed by the ozone layer. The yellow line illustrates the ozone concentration from 0-80 km. Notice how the maximum ozone concentrations is near 25 km in altitude, about three times the altitude of Mt. Everest. The amount of UV radiation that reaches the surface is indicated by the pink, green and blue colors. The shorter wavelengths (UVC and some of UVB, get strongly absorbed by the ozone layer), while UVA is only weaker absorbed, but does little biological harm. Ozone module prepared by Eugene C. Cordero

Typical UV forecast This is the UV forecast for a particular day. You may omit the word forecast, and just simply say this is the range of UV values that may occur for a day in October over Australia. UV Index, which is what this graph is given in, goes from 0-15, where 0 means no UV radiation and 15 means very high UV radiation. Notice how UV Index is higher in N. Australia compared to S. Australia. You could look at today’s current UV forecast at the Australian Bureau of Meteorology www.bom.gov.au Question: The point of this overhead is to raise the question. Why does UV radiation increase as you go towards the tropics? Ozone module prepared by Eugene C. Cordero

UV radiation What affects the amount of UV radiation hitting the Earth? -Location (latitude) -Time of day -Time of the year -cloud cover Thus, UV radiation naturally has large variations in space and time!!! UV radiation is absorbed by ozone, and scattered by clouds. Thus, determining the amount of UV radiation at the surface depends on your latitude, the time of day, the time of year, and how many clouds are above. Ozone module prepared by Eugene C. Cordero

UV changes during the day Key Learning Figure: This figure illustrates how the amount of surface UV radiation changes during the day. In early morning and late afternoon, UV levels are relatively low. This is because the sun has to pass through more of the ozone layer, thereby being absorbed more. However, at midday, say around 12:00 noon, the sun rays only have to pass through a smaller path of ozone, and thus do not get absorbed as much. Thus, UV values depend on time of day. Other causes of UV radiation changes? Time of the year, as suggested in the following graphic. Note: Many students associate UV radiation with temperature, thinking that the warmer it is, the more UV radiation there is. This is not strictly true. This idea of path length of the radiation also explains why there is more UV radiation in the summer than in the winter. The sun is higher in the sky during summer, thus the amount of ozone the radiation must pass is less then during winter. Ozone module prepared by Eugene C. Cordero

Satellite UV measurements These are satellite measurements of UV radiation for the globe (notice outline of continents in white lines). Units are in Energy per square meter, or basically how much UV radiation is striking the earth. Notice how in July, 2000 the higher amounts of UV radiation are over the N. Hemisphere, while in Jan, the higher amounts of UV radiation are over the S. Hem. This is due to the seasonal change in the sun angle (in July, the sun is more directly overhead the N. Hemisphere, thus they have higher UV values. In Jan, the Southern Hemisphere has the sun directly overhead, so Australia has higher levels of UV. Note: This concept ties in well with the concept of seasons July 1, 2000 January 14, 2000 Ozone module prepared by Eugene C. Cordero

Summary Ozone is produced and destroyed naturally in the atmosphere (ozone bucket picture). Ozone is responsible for absorbing much of the sun’s harmful UV radiation. UV radiation varies due to time of day, season, cloud amount, and ozone amount. Ozone module prepared by Eugene C. Cordero