Ozone Layer Solid Research Essays - Ozone Depletion,

Ozone Layer Solid Research Subject: TABLE OF CONTENTS How to get this FAQ Copyright Statement General remarks Caveats, Disclaimers, and Contact Information TABLE OF CONTENTS 1. THE STRATOSPHERE 1.1) What is the stratosphere? 1.2) How is the composition of air described? 1.3) How does the composition of the atmosphere change with 2. THE OZONE LAYER 2.1) How is ozone created? 2.2) How much ozone is in the layer, and what is a 2.3) How is ozone distributed in the stratosphere? 2.4) How does the ozone layer work? 2.5) What sorts of natural variations does the ozone layer show? 2.5.a) Regional and Seasonal Variation 2.5.b) Year-to-year variations. 2.6) What are CFC's? 2.7) How do CFC's destroy ozone? 2.8) What is an Ozone Depletion Potential? 2.9) What about HCFC's and HFC's? Do they destroy ozone? 2.10) *IS* the ozone layer getting thinner? 2.11) Is the middle-latitude ozone loss due to CFC emissions? 2.12) If the ozone is lost, won't the UV light just penetrate 2.13) Do Space Shuttle launches damage the ozone layer? 2.14) Will commercial supersonic aircraft damage the ozone layer? 2.15) What is being done about ozone depletion? 3. REFERENCES FOR PART I Introductory Reading Books and Review Articles More Specialized References Internet Resources ----------------------------- Subject: 1. THE STRATOSPHERE ----------------------------- Subject: 1.1) What is the stratosphere? The stratosphere extends from about 15 km to 50 km. In the stratosphere temperature _increases_ with altitude, due to the absorption of UV light by oxygen and ozone. This creates a global inversion layer which impedes vertical motion into and within the stratosphere - since warmer air lies above colder air, convection is inhibited. The word stratosphere is related to the word stratification or layering. The stratosphere is often compared to the troposphere, which is the atmosphere below about 15 km. The boundary - called the tropopause - between these regions is quite sharp, but its precise location varies between ~9 and ~18 km, depending upon latitude and season. The prefix tropo refers to change: the troposphere is the part of the atmosphere in which weather occurs. This results in rapid mixing of tropospheric air. [Wayne] [Wallace and Hobbs] Above the stratosphere lie the mesosphere, ranging from ~50 to ~100 km, in which temperature decreases with altitude; the thermosphere, ~100-400 km, in which temperature increases with altitude again, and the exosphere, beyond ~400 km, which fades into the background of interplanetary space. In the upper mesosphere and thermosphere electrons and ions are abundant, so these regions are also referred to as the ionosphere. In technical literature the term lower atmosphere is synonymous with the troposphere, middle atmosphere refers to the stratosphere and mesosphere, while upper atmosphere is usually reserved for the thermosphere and exosphere. This usage is not universal, however, and one occasionally sees the term upper atmosphere used to describe everything above the troposphere (for example, in NASA's Upper Atmosphere Research Satellite, UARS.) ----------------------------- Subject: 1.2) How is the composition of air described? (Or, what is a 'mixing ratio'?) The density of the air in the atmosphere depends upon altitude, and in a complicated way because the temperature also varies with altitude. It is therefore awkward to report concentrations of atmospheric species in units like g/cc or molecules/cc. Instead, it is convenient to report the mole fraction, the relative number of molecules of a given type in an air sample. Atmospheric scientists usually call a mole fraction a mixing ratio. Typical units for mixing ratios are parts-per-million, billion, or trillion by volume, designated as ppmv, ppbv, and pptv respectively. (The expression by volume reflects Avogadro's Law - for an ideal gas mixture, equal volumes contain equal numbers of molecules - and serves to distinguish mixing ratios from mass fractions which are given as parts-per-million by weight.) Thus when someone says the mixing ratio of hydrogen chloride at 3 km is 0.1 ppbv, he means that 1 out of every 10 billion molecules in an air sample collected at that altitude will be an HCl molecule. [Wayne] [Graedel and Crutzen] ----------------------------- Subject: 1.3) How does the composition of the atmosphere change with altitude? (Or, how can CFC's get up to the stratosphere when they are heavier than air?) In the earth's troposphere and stratosphere, most _stable_ chemical species are well-mixed - their mixing ratios are independent of altitude. If a species' mixing ratio changes with altitude, some kind of physical or chemical transformation is taking place. That last statement may seem surprising - one might expect the heavier molecules to dominate at lower altitudes. The mixing ratio of Krypton (mass 84), then, would decrease with altitude, while that of Helium (mass 4) would increase. In reality, however, molecules do not segregate by weight in