The Atmosphere The thin layer of gases that envelops the Earth Chemical reactions Atmospheric circulation produces weather and climates

The Atmosphere by weight thickest layer weather Very little water

Levels of the Atmosphere Troposphere—we live here!! --extends up to around 17 km (11 miles) above sea level --contains the Earth’s weather --made of mostly nitrogen (78%) and oxygen (21%), along with water vapor, argon, dust and soot particles, methane (CH 4 ), ozone (O 3 ), and nitrous oxide (N 2 O) --heated by infrared radiation from the Earth (Infrared radiation emitted from the sun and reaches Earth’s surface; bounced off infrared radiation from the surface is trapped in this level of the atmosphere by clouds and other greenhouse gases) ***This movement of heat is done by convection: The transfer of heat from one place to another by the movement of fluids (air/wind, etc.) ***convection moves air parcels with their content water vapor components/moisture (explains the formation of clouds)

Stratosphere—extends from about km above sea level --our “global sunscreen”—contains the ozone layer --UV radiation + 3 O 2  2 O 3 (about 95% of sun’s UV rays are absorbed here in the ozone layer) Mesosphere---extends about 50 km to 80 km above sea level Thermosphere—the highest layer of the atmosphere (above 80 km) Levels of the Atmosphere

Processes That Remove Materials from the Atmosphere Sedimentation: –Particles that are heavier than air settle out as a result of gravity. –Ex: Coal /volcanic particles will settle out over time Rain out: –Precipitation will physically and chemically flush materials from the atmosphere. –Ex: CO 2 + H 2 O  H 2 CO 3 carbon dioxide is removed Oxidation: –Where oxygen is chemically combined with other subtances. –Ex: atmospheric sulfur dioxide oxidizes to form sulfur trioxide which produces sulfuric acid Photodissociation: –Solar radiation can break down bonds in this chemical process. For example ozone may break down due to this process from O 3 to O 2.

Vocabulary Used to Characterize Air Pressure: force per unit area Atmospheric pressure: is the weight of overlying atmosphere per unit area Question: Does the atmospheric pressure increase as altitude increases or does it decrease? Temperature: a measure of thermal energy, ie the kinetic energy of the motion of atoms in a substance. Question: as temperature increases does kinetic energy increase or decrease? Water vapor: The amount of water vapor present in a particular place depends on several things including air temperature, air pressure and available water vapor (from various processes – remember the water cycle?)

Ozone

Ozone Loss Central Questions & Key Concepts 1.Ozone depletion and global warming are two very different things! 2.How are human activities affecting the ozone layer? 3.What can humans do about changes in the ozone layer?

Ozone A form of oxygen in which three atoms of oxygen occur together: O 3 Produced in photochemical reactions involving sunlight, nitrogen oxides, hydrocarbons, and diatomic oxygen. Chemically active and has a short average lifetime in the atmosphere. Forms a natural layer high in the atmosphere (in the stratosphere) that protects us from harmful ultraviolet radiation from the sun. A pollutant when present in the lower atmosphere (the troposphere)

Ultraviolet Radiation and Ozone Ozone Shield: Stratospheric ozone layer that absorbs ultraviolet radiation Movie - Take notes!

Measurement of Stratospheric Ozone Dobson Unit (DU) –Commonly used to measure the concentration of ozone.

Production of Ozone in the Stratosphere A.photo dissociation of diatomic oxygen B. Two single oxygen atoms C. single oxygen atom combines with O 2 D. Ozone is produced

Average Antarctic Minimum Ozone Concentration ( )

What are CFCs?! Chlorofluorocarbons (made of carbon, chloride, and fluorine atoms) Developed in the 1930s—developed industrially –Solvents in cleaners, Coolants in refrigeration and air conditioning, Blowing agents in the production of foam, Propellants in aerosols, flame retardant Man-made CFCs are the main cause of ozone depletion in the atmosphere Low reactivity  Lifespan is 100+ years—they make their way into the stratosphere—the sun’s UV rays break off a chlorine atom (highly reactive free radical) Chlorine catalyzes the break up of ozone into oxygen (Cl + O 3  ClO + O 2 ) Cl regenerated in the reaction, therefore one Cl atom can destroy many thousands of ozone molecules (ClO + O 3  Cl + 2 O 2 )

Polar Stratospheric Clouds Polar Stratospheric Clouds (PSCs) –Ozone destroying clouds that form in the stratosphere during the polar winter –Nitric acid (HNO 3 ) in clouds reacts with CFCs to form chlorine, which catalyzes the photochemical destruction of the ozone –Cl builds up in the winter, then the ozone destruction is the greatest when the sunlight returns in the spring (seasonal variations with sunlight and temp)

Why is There Seasonal Thinning of Ozone over the Antarctic? researchers discovered 40-50% of ozone in upper stratosphere over Antarctica was being destroyed “smoking gun” expedition- found that: –CFCs are primarily cause of ozone thinning –Polar vortex- huge swirling mass of very cold air that is isolated from the rest of the atmosphere until the sun returns a month later (contains lots of Cl) –Showed a negative correlation between ClO (chlorine monoxide) and the concentration or ozone (more ClO, less ozone—due to Cl reacting with and breaking down O 3, forming ClO) Cl + O 3  ClO + O 2

So why is ozone depletion greatest at the poles!? Recap… The presence of the polar stratospheric clouds (PSCs) along with the presence of CFCs (CFCs accumulate on ice crystals from the cold temps)  PSCs react with CFCs to produce Cl radicals The cold temperatures of winter and the polar vortex traps and chills the air (containing lots of Cl) Cl builds up for the spring, when the sunlight comes and brings about (provides energy for) the photochemical reaction of Cl with ozone molecules (therefore higher destruction of ozone in the spring)

Average Change in Concentration of Stratospheric Ozone ( ) by Latitude Ozone reduction varies most in the Antarctic –Highest concentrations of O 3 are found here naturally Concentrations at the equator are nearly constant. –Lowest concentrations are found at the equator

Size of the Antarctic Ozone Hole This graph above shows the minimum Ozone (measured in Dobson units) detected over the Antarctic. It shows that stratospheric ozone levels have been decreasing over the last two decades. The Ozone hole has, in general, been increasing in size over the last two decades. At times the Ozone hole has extended over 25 million square kilometers, an area one hundred times larger than the United Kingdom and equivalent to one sixth of the total world land mass.

Ozone Depleting Chemicals Chlorofluorocarbons (CFCs) Halons (compounds containing Br, F, Cl, or C) Methyl bromide (CH 3 Br) Carbon tetrachloride (CCl 4 ) Methyl chloroform (CH 3 CCl 3 ) Hydrogen chloride (HCl) “...use of CFCs increases rapidly...” (generally contain chlorine, fluorine, bromine, carbon, and hydrogen in varying proportions)

Recap: Ozone Depletion and CFCs Ozone depleted due to emission of CFCs CFCs are stable and have a long residence time in the atmosphere In stratosphere, release chlorine and enter into catalytic chain reaction- depletes ozone So what?  More UV radiation reaches the lower atmosphere! “Scientists discover a link between CFCs and ozone layer depletion.”

Why Should We Be Worried about Ozone Depletion? Reasons for Concern Less Ozone Causes: –Immune system suppression –Increase in acid deposition –Lower crop yields and decline in productivity –Disrupts primary productivity in the ocean and marine food chains –Increase in CO 2 in the atmosphere “If the ozone layer depletes, more harmful UV-B radiation will reach the earth through the damaged ozone layer.”

Why Should We Be Worried… Life in the Ultraviolet Zone Less Ozone Also Causes: –increased incidence and severity of sunburn/skin cancer –cataracts/eye irritation –headaches –Breathing/lung problems; asthma; emphysema More About Skin Cancer & Cataracts –increasing in Australia, New Zealand, South Africa, Argentina & Chile because the ozone layer is thin several months a year in those places “More UV-B radiation means more skin cancers, more diseases and eye cataracts, less yield from plants, less productivity from oceans, damage to plastics...”

Links between Global Warming and Climate Change Summary: The ozone hole is caused by ozone depleting chemicals in the atmosphere, which have been produced by industry (for example, CFCs). 1.One link is that CFCs are also 'greenhouse gasses'. Enhanced global warming is a probable consequence of increasing amounts of 'greenhouse gasses', such as carbon dioxide and methane, in the atmosphere. 2.Although the surface of the earth warms, higher up areas of the atmosphere cools, thus increasing the area where polar stratospheric clouds can form. This makes a larger area susceptible to ozone depletion, which provides another link between the two issues.

Management Issues Key issue is whether ozone depletion is natural or human-induced Montreal Protocol Collection and Reuse of CFCs Substitutes for CFCs –HFCs and HCFCs Short-Term Adaptation to Ozone Depletion

Solutions: Protecting the Ozone Layer Montreal Protocol –Treaty created in 1987 by 36 nations –Goal was to cut emissions of CFC’s into the atmosphere by about 35% between 1989 & 2000 –Met 3 more times –Met in 1997 in Montreal –Adopted a protocol accelerating the phase out of key ozone depleting chemicals –CFC production fell by 85%

Solutions: Protecting the Ozone Layer Kyoto Protocol –International agreement that set binding targets for 37 industrialized countries and the European community for reducing greenhouse gas emissions (adopted in Kyoto, Japan in 1997, then spread into force in 2005) –Goal to stabilize greenhouse gas concentrations to prevent dangerous interference with the climate system –Recognized that developed nations were principally responsible for the current high levels of greenhouse gases due to their industrial activity, therefore the protocol placed a heavier burden on developed nations –Countries must monitor, record emissions, and meet benchmarks –The US signed but did not ratify the protocol

Solutions: Protecting the Ozone Layer Stop producing all ozone depleting substances CFC substitutes –HCFCs (hydrochlorofluorocarbon)- contain fewer chlorine atoms per molecule than CFC’s –HFCs (hydrofluorocarbon)- contain fluorine but no chlorine –HCs- hydrocarbons - useful as coolants & insulating foam in refrigerators

Solutions: Protecting the Ozone Layer Technofixes –Physicist Alfred Wong- each year wants to launch blimps football-fields long. –Blimps are radio-controlled and would contain electrical wires that would inject negatively- charged electrons to the stratosphere when exposed to high voltages (to lessen reactivity of the Cl radicals) –Others suggest using lasers to blast CFC’s out, but no one knows how it will affect climate, birds, or planes

Will the International Treaty to Slow Ozone Depletion Work? still a black-market of CFC’s some countries cheating prevention is the best way to deal with global environmental problems

What Can You Do? "Do not release CFCs - recycle them!” “Demand ozone friendly products.”

Please sit in groups of FIVE with people who did NOT do your chemical. Please describe the following ozone depleting chemicals with your table. Halons Methyl bromide Carbon tetrachloride Methyl chloroform Hydrogen chloride Activity