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1: How do scientists know that chlorine is responsible for stratospheric ozone depletion? Answer: In 1987, NASA and a group of scientists flew a modified U-2 spy plane (now called the ER-2) into the ozone hole over Antarctica. During this flight they found that as they entered the hole chlorine compounds went up at exactly the same time that ozone decreased. This measurement was proof that chlorine really was responsible for the ozone hole. (For more read: , Anderson, J.G., W.H. Brune, M.H. Proffett, 1989, Journal of Geophysical Research, vol 94, PP 11465-11479. and Anderson, J.G. D.W. Toohey, W.H. Brune, 1991, Science, vol 251, pp39-46. Question 2: I've heard that the amount of chlorine put into the atmosphere is by natural sources like volcanoes and sea spray is many times larger that from CFC's? Answer: This statement is actually true in one respect but false in another. The amount of chlorine put into the atmosphere by sea spray is very large. Of course, the chlorine is in the form of dissolved salt or sodium chloride. This chlorine is in big droplets or particles that do not stay in the atmosphere very long because they fall back to earth or are swept out of the air by rain. Therefore, this chlorine does not stay in the atmosphere long enough to get mixed up into the stratosphere. Only chemicals that stay in the atmosphere for many years can be mixed into the stratosphere, and for this reason CFC's are the chemicals that carry most of the chlorine into the stratosphere. Question 3: Some say that chlorine from the rockets used to launch the space shuttle is a major contributor to ozone depletion? Answer: The amount of chlorine put into the stratosphere by rocket is, in fact, very small compared to the amount put there by CFC's. Question 4: How much does the ozone in the stratosphere vary from day to day? Answer: Stratospheric ozone can vary by 10 to 20% from day-to-day. Just like we have changes in the wind and air temperature down in our part of the atmosphere, the "weather" in the stratosphere changes from day-to-day. These changes affect how much ozone is in the atmosphere. Question 5: Scientists actually discovered the ozone hole over Antarctica before CFC's were produced. Is this true? Answer: This common idea is not true. In 1956, before CFC's were widely used, the now famous scientist, Dobson, measured ozone over Antarctica and found about 20% less than he had expected. The levels he saw back then were 4-5 times more than what is measured in the ozone hole today. Question 6: CFC's are heavier than air, so how can they get all the way up to the stratosphere? Answer: CFC molecules are, in fact, heavier than most air molecules, but in the atmosphere this does not matter. As the wind blows, the molecules are mixed together and are not allowed to "settle out" by gravity. This is a very good thing for us because if the heavier molecules actually dropped to the bottom of the atmosphere we would all die from a lack of oxygen. Gases like carbon dioxide would be at the bottom of the atmosphere where we are and that is simply not what happens in nature. Question 7: Ozone in the air of some polluted areas is considered bad for people's health. How can some ozone be bad for our health and some be good for our health? Answer: Ozone is a very aggressive chemical that eats away at (chemically reacts with) many other chemicals. Unfortunately, if we breathe ozone, it eats away at the protective mucous in our nose, eyes, and throat. This can give us head aches, make it hard to breathe, and be very irritating. For this reason ozone in the air we breathe is bad for our health. On the other hand, ozone way above our head in the stratosphere is good because it provides a shield from harmful radiation from the sun, by absorbing that radiation before it reaches the ground. Question 8: If ozone is made from oxygen and sunlight, two ingredients that are plentiful, why do we care if some ozone is destroyed? Won't the sunlight and oxygen simply make more to replace it? Answer: The problem with this idea is that although sunlight and oxygen in the air seem plentiful, in fact the sunlight is limited. As sunlight travels through the atmosphere, the harmful high energy light, that we cannot see with our eyes, gets absorbed. It is this high energy light that causes ozone to be formed and once it is used up no more ozone can be made. Question
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