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Lecture 16

CHEM H90 Lecture 16: The Ozone Hole and the Man Who Saved the Planet, pt.2 (05/10/17)

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LECTURE 16 Wednesday, May 10, 2017 Atmospheric Chemistry: Ozone Hole The Ozone Hole and the Man Who Saved the Planet (pt.2) Ozone and Cl• • Data from Susan Soloman’s 1987 flight into the Antarctic ozone hole o This would have been flying over the ocean, very little chlorine in the air o As you approach a certain degrees latitude, the stratospheric chlorine goes up and stratospheric ozone goes down ▪ Shows very clearly that when there’s more chlorine, there’s less ozone Why Antarctica? • Coldest spot on the planet (-90 C) • Good stratospheric circulation due to land mass • Get polar stratospheric clouds with tiny ice crystals in winter o Makes all sorts of chemistry happen o Once you have these little, little particles, you can catalyze a reaction • Reactions on ice surfaces make reactive species for ozone depletion • Chlorine is released in Antarctic spring Antarctic ozone readings • This is the full curve of the British Antarctic readings, from 1980 o A sudden drop, from about 200 to below 100 since 1990 • Is there a misleading impression created by the choice of scale on the y-axis? o Yes, because it doesn’t start from 0. ▪ They want to emphasize their point, this huge drop • Antarctica didn’t have that much ozone to begin with, and half of that vanished o Human processes can affect the planet Largest ever Antarctic O3hole • Ozone depletion, the ozone hole, is the area on the surface of the earth where ozone is seriously missing Changing size of O3hole • A function of month • As you go from August to December, you see the ozone hole appear and disappear Global Response • We have the scientific paper in 1974… how did the world respond? Industry’s response • Let’s find a way to not worry about the problem • They don’t really want to know because it’s not good for business CFC production • Thirteen years later, 1987, the Montreal Protocol was signed • In the mid 1970s, energy crisis occurred o Lots of our chemicals come from cracking oil o CFC production leveled off • In 1987, the whole world signs a treaty saying they’ll stop producing CFC o CFC production goes way down Halons • Replace CFC with halons • Which element might be substituted in CFC’s to try to make them less harmful, but still have the same unreactive chemistry (so can be used for the same purposes)? o Cl replaced by Br ▪ Logic: it’s heavier, so it won’t get to the stratosphere Other replacements • Halons (using Br) are heavier, so go less high, but even more destructive to 3 • Hydro-CFCs (HCFCs) at first, such as CHClF2and C 2 3l 2 o Replace one Cl with a H or replace with a metal group (CH )3 • Much less destructive, but now being phased out • Now we have HFC’s (no chlorine – chlorine is the thing that eats up ozone), such as C 2F 5nd CH F 2 2.e., no Cl. • A lot more reactive, so they don’t make it to the stratosphere o The reason those CFCs were getting up there was because they don’t react to anything. If you’re more reactive, you don’t get up there Modern dust-off can • “No CFCs” o No more CFCs in these aerosol products • Difluoroethane – two flourines, no chlorines Melanoma incidence in US • Rates of melanoma in the US, from 1974 to 2002 • Among the white population, the rates are going up and up and up o Is this because of ozone depletion? o The answer is no o Things can be correlated without being causally related to each other Correlation versus causation • Two things can be correlated without one causing the other • Many possible explanations for melanoma increase in US o (e.g.) folks are living longer o Get increased UV just by being higher up or living further south • Maybe increase UV awareness leads to more use of sunblock leads to more time outdoors (exposure to UV rays) leads to more melanoma Projected Cl• in atmosphere • The projection is 2100 • Not even at 2100 is at the level of 1950 • It takes a long time This looks like cause and eff
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