Chapter 3 Global Climate Change • The Ozone Depletion • The Greenhouse Effect
3-1 The Ozone Depletion • Ozone: Good Up High, Bad Nearly • Ozone-Depleting Substances (ODS) • Basic Chemistry of Ozone Depletion • The Antarctic（南極） Ozone Hole
3-1-1 Ozone: Good Up High, Bad Nearly • Ground-level O3—“bad” O3 in troposphere layer (對流層)of the atmosphere (0-10 km) VOC + NOx + Sunlight = Ozone • Stratospheric (同溫層, 10-30 km) O3 layer —“good” O3 , protects life on earth from the sun’s harmful ultraviolet rays (UV-b) • “Good" ozone occurs naturally in the stratosphere and is produced and destroyed at a constant rate.
3-1-1 Ozone: Good Up High, Bad Nearly • What is happening to the “Good” ozone • These ozone depleting substances degrade slowly and can remain intact for many years as they move through the troposphere until they reach the stratosphere. • There they are broken down by the intensity of the sun's UV rays and release chlorine and bromine molecules, which destroy "good" ozone. 1Cl or Br molecule can destroy 100,000 O3 molecules, causing ozone to disappear much faster than nature can replace it. • Gradually being destroyed by manmade chemicals called chlorofluorocarbons (CFCs), halons, and other ozone depleting substances (used in coolants, foaming agents, fire extinguishers, and solvents).
3-1-1 Ozone: Good Up High, Bad Nearly • What is happening to the “Good” ozone • Satellite observations indicate a world-wide thinning of the protective ozone layer. The most noticeable losses occur over the North and South Poles because ozone depletion accelerates in extremely cold weather conditions.
3-1-1 Ozone: Good Up High, Bad Nearly • What is happening to the “Good” ozone
3-1-1 Ozone: Good Up High, Bad Nearly • How Does the Depletion of "Good" Ozone Affect Human Health and the Environment? • Increased UV-b→skin cancer, cataracts（白內障）, and impaired immune systems. • Damage to UV-b sensitive crops, such as soybeans, reduces yield. • High altitude ozone depletion is suspected to cause decreases in phytoplankton（浮游植物）, in the ocean. → affect the marine food chain. • plants "breathe in" CO2 and "breathe out" O2 → CO2 ↑ in the air. ∴Increased UV-b radiation → more ground-level or "bad" ozone
3-1-1 Ozone: Good Up High, Bad Nearly • What is Being Done About the Depletion of Good Ozone? • The Montreal Protocol (effective in 1989)— a series of international agreements on the reduction and eventual elimination of production and use of ozone depleting substances (ODS). • Currently, 160 countries participate in the Protocol. →recovery of the ozone layer in about 50 years.
3-1-1 Ozone: Good Up High, Bad Nearly • What is Being Done About the Depletion of Good Ozone? • In U.S., the U.S. Environmental Protection Agency (EPA) continues to establish regulations to phase out these chemicals. The Clean Air Act requires warning labels on all products containing CFCs or similar substances, prohibits nonessential ODS products, and prohibits the release of refrigerants used in car and home air conditioning units and appliances into the air.
3-1-1 Ozone: Good Up High, Bad Nearly What Causes "Bad" Ozone?
3-1-1 Ozone: Good Up High, Bad Nearly • What is Being Done About Bad Ozone? • The Clean Air Act Amendments(1990) require EPA, states, and cities to implement programs to further reduce emissions of O3 precursors from sources, eg., cars, fuels, industrial facilities, power plants, and consumer/commercial products. • Power plants will be reducing emissions, cleaner cars and fuels are being developed, many gas stations are using special nozzles at the pumps to recapture gasoline vapors, and vehicle inspection programs are being improved to reduce emissions.
3-1-1 Ozone: Good Up High, Bad Nearly • What is Being Done About Bad Ozone? • The ultimate responsibility for our environment is our own. • Minor lifestyle changes can result in major air quality improvements.
3-1-2 Ozone-Depleting Substances (ODS) • Ozone-Depleting Substance(s) (ODS): a compound that contributes to stratospheric ozone depletion • include CFCs, HCFCs, halons, methyl bromide, carbon tetrachloride, and methyl chloroform. • very stable in the troposphere and only degrade under intense ultraviolet light in the stratosphere. • When they break down, they release chlorine or bromine atoms, which then deplete ozone. • A detailed list of class I and class II substances with their ODPs are available.
3-1-2 Ozone-Depleting Substances (ODS) • Class I include CFC's, Halons, Carbon Tetrachloride, and TCA as well as less common substances such as methyl bromide (fumigant) and HBFCs (no Navy/Marine Corps uses). In general, Class I substances cause greater environmental harm than Class II substances • Class II include HCFC substances, thatare interim materials to allow a "rapid" phaseout of Class I substances. Class II substances are also scheduled for phaseout (HCFC-141b by 2003; HCFC-22 and HCFC-142b by 2020; and, all other HCFC's by 2030).
TYPICAL CLASS II ODS SUBSTANCES ** The "ozone depleting potential (ODP)" is a relative index of damage to the environment. The higher the number, the greater the damage.
3-1-2 Ozone-Depleting Substances (ODS) • Chlorofluorocarbon (CFC, Freon): a compound consisting of chlorine, fluorine, and carbon • CFCs are commonly used as refrigerants, solvents, and foam blowing agents. • The most common CFCs are CFC-11, CFC-12, CFC-113, CFC-114, and CFC-115. Their ODPs are, respectively, 1, 1, 0.8, 1, and 0.6. • CFC-11(CCl3F) 、 CFC-l2 (CCl2F2) 及CFC-113(C2Cl3F3)
3-1-2 Ozone-Depleting Substances (ODS) • Hydrochlorofluorocarbon (HCFC): a compound consisting of hydrogen, chlorine, fluorine, and carbon • HCFCs have ODP ranging from 0.01 to 0.1.
3-1-2 Ozone-Depleting Substances (ODS) • Halon: a compound consisting of bromine, fluorine, and carbon (Bromine is many times more effective at destroying ozone than chlorine. ) • used as fire extinguishing agents, both in built-in systems and in handheld portable fire extinguishers. • Halon production in the U.S. ended on 12/31/93 because they contribute to ozone depletion. • ODPs of halon 1301 and halon 1211 were observed to be 10 and 3, respectively. Recent scientific studies, however, indicate that the ODPs are at least 13 and 4, respectively. • Note: technically, all compounds containing carbon and fluorine and/or chlorine are halons, but in the context of the Clean Air Act, "halon" means a fire extinguishing agent as described above.
3-1-2 Ozone-Depleting Substances (ODS) • Methyl Bromide (CH3Br): An effective pesticide, this compound is used to fumigate soil and many agricultural products with ODP 0.6. • Production of methyl bromide ended in the U.S. on 12/31/2000.
3-1-2 Ozone-Depleting Substances (ODS) • Carbon Tetrachloride (CCl4): widely used as a raw material in many industrial uses, including the production of CFCs, and as a solvent with ODP, 1.2. • Solvent use ended when it was discovered to be carcinogenic（致癌的）. • It is also used as a catalyst to deliver chlorine ions to certain processes.
3-1-2 Ozone-Depleting Substances (ODS) • Methyl Chloroform (CH3CCl3): used as an industrial solvent with ODP, 0.11 .
3-1-3 Basic Chemistry of Ozone Depletion • T.E.Graedel and P.J.Crutzen, Atmospheric Change: an Earth System Perspective, 2nd ed., Freeman, New York (1993) Starting on page 141, for a more in-depth treatment of ozone chemistry that is still very readable by the science-layman.
3-1-3 Basic Chemistry of Ozone Depletion • Formation and destruction of ozone (Up to 98% of the sun's high-energy ultraviolet light (UV-B and UV-C) are absorbed) • The global exchange between ozone and oxygen is on the order of 300 million tons per day.
3-1-3 Basic Chemistry of Ozone Depletion • UVA: 320 nm<λ<400 nm (just shorter than visible violet light), not absorbed by ozone. • UVB: 280 nm<λ<320 nm • UVC: λ<280 nm, extremely dangerous, but it is completely absorbed by ozone and normal oxygen (O2).
3-1-3 Basic Chemistry of Ozone Depletion • Halogen catalysis of ozone degradation • Halogens: a chemical family containing fluorine, chlorine, bromine and iodine • Halocarbon: any carbon compound containing halogens. • All halogens have the ability to catalyze ozone breakdown, they have an unequal impact on the ozone layer. • A catalyst is a compound which can alter the rate of a reaction without permanently being altered by that reaction, and so can react over and over again
3-1-3 Basic Chemistry of Ozone Depletion • Halogen catalysis of ozone degradation
3-1-3 Basic Chemistry of Ozone Depletion • Halogen catalysis of ozone degradation • 1 Cl can degrade over 100,000 O3 before it is removed from the stratosphere or becomes part of an inactive compound. • These inactive compounds, for example ClONO2, are collectively called 'resevoirs'. They hold Cl in an inactive form but can release an active chlorine when stuck by sunlight. • stability of the resevior compounds. • Hydrogen fluoride, HF: very stable & have relatively no known impact on O3 . • Bromine resevoirs, eg., HBr and BrONO2, much more easily broken up by sunlight ; causing Br to be from 10 to 100 times more effective than Cl at destroying O3 .
3-1-3 Basic Chemistry of Ozone Depletion • Chlorine Removal In the stratosphere the major mechanisms for chlorine removal involve the formation of HCl: OH + ClO ---->HCl + O2 O2H + Cl ------> HCl + O2 • HCl is water soluble and is eventually precipitated out of the stratosphere by water droplets or crystals. • The estimated lifetime of HCl in the stratosphere is about 2 years.
3-1-4 The Antarctic Ozone Hole • Antarctic Ozone Levels in Fall 2003 (Source: NOAA TOVS satellite ) • The ozone hole is represented by the purple, red, burgundy, and gray areas that appeared over Antarctica in the fall of 2003. The ozone hole is defined as the area having < 220 Dobson units (DU) of ozone in the overhead column
3-1-4 The Antarctic Ozone Hole • The ozone hole is a well-defined, large-scale destruction of the ozone layer over Antarctica that occurs each Antarctic spring. • The word "hole" is a misnomer; the hole is really a significant thinning, or reduction in ozone concentrations, which results in the destruction of up to 70% of the ozone normally found over Antarctica.
3-1-4 The Antarctic Ozone Hole • The ozone hole occurs only over Antarctica. • Two international organizations issue regular bulletins about the ozone hole as it develops each year: the British Antarctic Survey and the World Meteorological Organization. • The University of Cambridge's Ozone Hole Tour provides detailed explanations, with graphics, of the ozone hole and its history.
3-1-4 The Antarctic Ozone Hole • The illustration above shows a column of air, 10 deg x 5 deg, over Labrador, Canada. If all the ozone in this column were to be compressed to standard temperature and pressure (STP) (0 deg C and 1 atmosphere pressure) and spread out evenly over the area, it would form a slab approximately 3mm thick. • 1 Dobson Unit (DU) is defined to be 0.01 mm thickness at STP; the ozone layer over Labrador then is 300 DU. • The unit is named after G.M.B. Dobson, one of the first scientists to investigate atmospheric ozone (~1920 - 1960). He designed the 'Dobson Spectrometer' - the standard instrument used to measure ozone from the ground. • The Dobson spectrometer measures the intensity of solar UV radiation at four wavelengths, two of which are absorbed by ozone and two of which are not.
3-2 The Greenhouse Effect • What is the Greenhouse Effect? • What Gases are Responsible? • What are the Solutions to Greenhouse Gas Warming?
3-2 The Greenhouse Effect • What is the Greenhouse Effect? Greenhouse gases (GHGs) allow incoming solar radiation to pass through the Earth’s atmosphere, but prevent most of the outgoing infra-red radiation from the surface and lower atmosphere from escaping into outer space. ↓ Keep the earth’s temperature about 59 oF(~30oC) warmer
3-2-1 What is the Greenhouse Effect? • http://earthguide.ucsd.edu/earthguide/diagrams/greenhouse/
3-2-2 What Gases are Responsible? • Gases absorb the longer-wavelength energy radiated from the earth (GHG) • H2O (vapor)—dominant GHG, but very little of it is the result of human activities. • Principal GHG resulting from human activities, eg., increased economic activity and changing agricultural practices...:
3-2-2 What Gases are Responsible? • O3—a gaseous molecule contributes to smog, is also a GHG, but exists for only a brief period of time in the lower atmosphere (～weeks) →contribution is still uncertain • Since mid-1800s, atmospheric levels of CO2↑30% (280 ppm → 360 ppm) CH4 ↑100% (→ 1.72 ppm) N2O↑8-15%
3-2-2 What Gases are Responsible? • CO2 Production: Oceans→90 billion tonnes + Decaying vegetation→30 billion tonnes + Natural respiration of living creatures and plants →30 billion tonnes+ Human activities→3% or 7 billion tonnes per year
3-2-2 What Gases are Responsible? • CO2 Removal: Absorption by the oceans & photosynthesis process of green plants • Net of “carbon cycle”→↑3.1-3.5 billion tonnes per year
3-2-2 What Gases are Responsible? • CO2 Manmade: burning of fuels • Chemically stable→remain for many decades
3-2-2 What Gases are Responsible? • Methane
3-2-2 What Gases are Responsible? • Methane Main sources: “Marsh gas (沼氣)” from aerobic decay of vegetation in wetlands and from rice paddies+ natural gas+ Cattle, termites, and other animals release as part of the digestive process • Industrial revolution, 0.8 ppm →1.72 ppm • 600 million tonnes is released & 560 million tonnes is absorbed, annually → 35-40 million tonnes net • Can be destroyed by reactions with other chemicals in the atmosphere and soil → lifetime~10 years • A much greater energy absorber than CO2 (27 times)
3-2-2 What Gases are Responsible? • Nitrous Oxides (laughing gas) Major source: bacterial breakdown of nitrogen components in soils →↑ when land is deforested and then cultivated, particularly if nitrogen-containing fertilizers are used + ocean upswellings during tidal action + fossil fuel combustion (~3% ) • Worldwide, 13-20 million tonnes emitted, but 10-17 millions tonnes are chemically broken down in the stratosphere or otherwise removed from the air →↑4 million tonnes per year • More potent than methane (~165 times than CO2)
3-2-2 What Gases are Responsible? Chlorofluorocarbons(CFCs) & Hydrofluorocarbons(HFCs) • CFCs—most potent GHG, eg., CFC-12 (Freon-12) is 17,700 times than CO2 • Although minute, responsible for ~ 24% greenhouse effect. • CFCs do not exist naturally. Main concern is their role in destroying O3 →Montreal Protocol: phase out their use by 2000 • HFCs has been developed to replace CFCs. • Rare before 1990 and increasing rapidly because in 1994, HFC-134a was adopted as the standard motor vehicle AC refrigerent