Stratospheric Ozone. Science Concepts Ozone Chemistry Creation Process Destruction Processes Equilibrium CFC Chemistry Polar Vortex. Stratospheric Ozone Ozone Chlorofluorocarbons (CFCs) CFCs Antarctic Ozone Hole Causes Ozone and Surface uv Radiation Effects of uv on Life
Stratospheric Ozone Science Concepts Ozone Chemistry Creation Process Destruction Processes Equilibrium CFC Chemistry Polar Vortex Stratospheric Ozone Ozone Chlorofluorocarbons (CFCs) CFCs Antarctic Ozone Hole Causes Ozone and Surface uv Radiation Effects of uv on Life Mitigation The Earth System (Kump, Kastin & Crane) • Chap. 1 (pp. 7-9) • Chap. 11 (pp. 219-220) • Chap. 17 (pp. 343-359)
Ozone Ozone in the Earth’s Atmosphere Stratosphere Stratospheric ozone is “good.” It protects Earth’s surface from Sun’s harmful ultraviolet radiation. 90% of ozone is in the stratosphere. Troposphere Tropospheric ozone is “bad.” It can damage lung tissue and plants. Mesosphere
Ozone Ozone • Three atoms per molecule instead of the normal oxygen molecule with two atoms • Maximum near 25 km • 90% of ozone in stratosphere • Secondary max near ground Fahey, D.W., Twenty Questions and Answers About the Ozone Layer. http://vortex.nsstc.uah.edu/atmchem/recent_events/ upperstrat03_recovery.html
Vis- ible Near IR UV Far Infrared H O 2 CO 2 100 O O , 3 CO , 2 2 CO , 2 Absorption (%) O H O 3 2 H O 2 H O 2 50 0 0.3 0.5 1.0 5.0 10.0 15.0 20.0 Wavelength (microns) Stratospheric Ozone Chemistry Stratospheric Ozone Production • Stratospheric ozone production O2 + uv => O + O O2 + O => O3 Fahey, D.W., Twenty Questions and Answers About the Ozone Layer. http://vortex.nsstc.uah.edu/atmchem/ recent_events/upperstrat03_recovery.html
Stratospheric Ozone Chemistry Four Major Natural Ozone Destruction Processes • Chapman process; uv (0.2 - 0.3 microns) radiation O3 + uv => O2 + O • Collisions with atomic oxygen O3 + O => 2 O2 • Collisions with itself O3 + O3 => 3 O2 • Collisions with nitric oxide; for example NO + O3 => NO2 + O2 NO2 + O => NO + O2 Note nitric oxide molecule ends up being able to participate in another reaction; thus, nitric oxide is said to be catalytic Fifth Natural Destruction Process (Intermittent) Volcanoes add sulfuric gases into the stratosphere that produce particulates that interact to increase ozone destruction
Stratospheric Ozone Chemistry Equilibrium • Bucket with water pouring into it and four holes near the bottom of it - What if we continue the inflow? - What will happen to the water level? - As the depth of water increases, the pressure at bottom increases thereby increasing the rate of outflow until the rate of outflow balances the rate of inflow • State of balance between opposing forces or actions that is either static or dynamic* • A state of adjustment between opposing or divergent influences or elements* * Webster’s New Collegiate Dictionary
Stratospheric Ozone Chemistry Equilibrium (Con’t) • What if we reduce the inflow rate? - Equilibrium level will be lower
Stratospheric Ozone Chemistry Equilibrium (Con’t) • What if we increase the inflow rate? - Equilibrium level will be higher
Stratospheric Ozone Chemistry Equilibrium (Con’t) • What if we decrease the number or size of the outflow holes? - Equilibrium level will be higher • What if we increase the number or size of the outflow holes? - Equilibrium level will be lower
Stratospheric Ozone Chemistry Equilibrium (Con’t) • Equilibrium level changes as the - Rate of inflow changes - Number and/or size of the outflow holes change Principle • Depth (distance between top of water and level of the holes) of water (pressure at the hole) determines force and rate of water exiting tank, i.e., gravity acting on the water forces water through lower-level outflow holes Depth Depth
Stratospheric Ozone Chemistry Ozone Equilibrium • Ozone rate of creation (inflow) is balanced by rate of destruction (outflow) - Creation depends on amount of oxygen and uv while rate of destruction depends on amount of ozone (depth of water) and the destruction processes Creation Ozone Amount Destruction
Stratospheric Ozone Chemistry Ozone Destruction Variability • Solar sunspot activity with 11-year cycle increases cosmic rays (high- energy atomic nuclei and atomic particles) which separate the nitrogen molecule into atomic nitrogen which then combines with oxygen to make NO. Observed 12% variation in ozone amount because of solar cycle. • Increased nitrogen oxides because of increased anthropogenic release (combustion products and fertilizers) • Additional destruction process - Release of manmade chlorofluorocarbons (CFCs)
Chlorofluorocarbons Background • Invented in the late 1930s • Variety of molecules consisting of atoms of hydrogen (H), carbon (C), fluorine (F) and chlorine (Cl) • For example, CCl3 (CFC-11), CCl2F2 (CFC-12), CHClF2 (CFC-22), etc. • Freon, Dupont trade name, used in refrigeration, air conditioners, cleaning solvents for electronic components, foaming agents for plastics, and aerosol propellants• Manufactured to be chemically inert and volatile• Currently releasing about 1 million tons of CFCs per year to the atmosphere• During the 70s, 80s and early 90s CFCs in the atmosphere were increasing by 5-7% per year
Chlorofluorocarbons Background (Con’t) • CFCs in the lower atmosphere are not removed by photodissociation, rainout or oxidation; require ultraviolet (uv; 0.23 microns) light to be destroyed • Solar radiation with wavelength less than 0.29 microns is absorbed by the ozone layer • Thus, CFCs are not destroyed until they are diffused to altitudes 25 to 40 km
Stratospheric Ozone Chemistry Ozone Destruction by CFCs • Chlorine and ozone react in two step chain reaction Cl + O3 => ClO + O2 ClO + O => Cl + O2 • Note chlorine atom ends up being able to participate in another reaction; thus, chlorine is said to be catalytic • Chlorine is finally removed when it combines with hydrogen (H) to make hydrochloric acid (HCl) Cl + H => HCl http://veimages.gsfc.nasa.gov/56/ ozone_destruction_final.mov
Stratospheric Ozone Chemistry Summary • Follow image steps 1 through 5 http://www.cmdl.noaa.gov/infodata/faq_cat-2.html#31
Stratospheric Ozone Chemistry Ozone Destruction by CFCs (Con’t) • Chlorine atoms last 1 to 2 years before combining with hydrogen; during this time they participate in as many as 100,000 reactions with ozone • All in all the chlorine in some CFCs stay in the atmosphere about 100 years from the time they are first released until they are finally rained out Natural Chlorine • Naturally, oceans add chlorine gases to the atmosphere; most of this chlorine does not reach the stratosphere
Stratospheric Ozone Chemistry Ozone Dobson Units (DU) • Note ozone is most frequently measured in Dobson Units O3 If all the Ozone over a certain area were compressed at O°C and 1 atm pressure, it would form a slab about 3 mm thick. This would correspond to 300 DU.
Antarctic Ozone Hole Description • Antarctic ozone in the 70s versus the 80s and 90s http://toms.gsfc.nasa.gov/multi/buv-toms.gif
Antarctic Ozone Hole Description (Con’t) • Comparison of Antarctic ozone in the 70s versus 90s • 60% reduction in early October over Antarctica http://see.gsfc.nasa.gov/edu/SEES/strat/class/Chap_11/11_Js/11-03.jpg
Antarctic Ozone Hole Minimum Folklore has it • 1985 measurements of the stratospheric ozone levels drop were so dramatic, scientists thought their instruments were faulty. • TOMS satellite data didn't show the dramatic loss of ozone because software processing the raw ozone data from the satellite was programmed to treat very low values of ozone as bad readings! http://toms.gsfc.nasa.gov/eptoms/dataqual/oz_hole_annual_min_v8.jpg
Antarctic Ozone Hole September 24, 2006 Development (Con’t) • Global average ozone layer thickness is about 300 Dobson Units • Ozone hole is region over Antarctica with total ozone 220 Dobson Units or lower • Occurs in southern hemispheric spring (October) after southern hemispheric winter that has no sunlight and is very cold • 2005 ozone hole development - July through December http://earthobservatory.nasa.gov/Newsroom/ NewImages/images.php3?img_id=17436 http://earthobservatory.nasa.gov/Newsroom/ NewImages/images.php3?img_id=17116
Antarctic Ozone Hole http://earthobservatory.nasa.gov/Newsroom/ NewImages/images.php3?img_id=17809 September 13, 2007 Depth and Size • 22 million square km is slightly less than North American continent • 9/21-30/06, average area of ozone hole largest ever, at 10.6 million square miles http://svs.gsfc.nasa.gov/vis/a000000/a003100/a003136
Antarctic Ozone Hole Explanation • In winter and early spring, little to no solar radiation. Thus, no uv to create ozone. • Polar vortex (clockwise at high altitudes) wind pattern develops; cuts off air exchange with southern hemisphere midlatitude air. Thus, ozone is not imported. • Recall stratosphere is heated primarily by absorption of solar ultraviolet (uv) radiation by ozone, while stratosphere is primarily cooled by emission of infrared (IR) radiation to space by carbon dioxide, ozone, and water vapor During polar winter, solar heating by ozone ends and the Antarctic stratospheric air becomes very cold http://see.gsfc.nasa.gov/edu/SEES/strat/class/Chap_11/index.htm
Antarctic Ozone Hole Explanation (Con’t) • With temperatures below -80°C (-112°F) during winter, high, thin clouds of water, sulfuric acid, nitric acid (polar stratospheric clouds, PSCs) form at high altitudes (~70 kft; in the stratosphere). - Normally, clouds don’t form in the stratosphere because it is too dry - At high latitudes during winter, stratospheric temperature can become so cold that clouds of other several gases can form Fahey, D.W., Twenty Questions and Answers About the Ozone Layer http://vortex.nsstc.uah.edu/atmchem/recent_events/upperstrat03_recovery.html
Antarctic Ozone Hole Explanation (Con’t) • Cloud droplets provide a surface upon which chlorine species like CFCs can breakdown to yield chlorine molecules (Cl2). These reactions occur during the polar night. By mid winter, most chlorine inside the southern lower stratospheric vortex is in the form of Cl2. • Cl2 reacts to sunlight to form atomic chlorine. Thus, clouds enhance creation of atomic chlorine if sunlight is present. http://see.gsfc.nasa.gov/edu/SEES/strat/class/Chap_11/index.htm
Antarctic Ozone Hole Explanation (Con’t) • Spring arrives and provides sunlight • Now have an abundance of chlorine to destroy ozone • Ozone concentration take a rapid, deep plunge until the vortex breaks up in late spring and re-supply of ozone from midlatitudes can occur http://see.gsfc.nasa.gov/edu/SEES/strat/class/Chap_11/index.htm
Arctic Ozone • Northern Hemisphere ozone is now showing some depletion signs • 1997 spring ozone minimum - March through May Fahey, D.W., Twenty Questions and Answers About the Ozone Layer. http://vortex.nsstc.uah.edu/atmchem/ recent_events/upperstrat03_recovery.html
Global Ozone Depletion • Antarctic depletion up to 50% • 3% depletion in Northern Hemisphere
Global Ozone Depletion Global Total Ozone Change • Comparison of global average ozone in the ‘64 - ’80 versus ‘80s and ‘90s • 3 - 4% reduction • Dramatic dip in 1992 and 1993 caused by eruption of Mt. Pinatubo in Philippines Fahey, D.W., Twenty Questions and Answers About the Ozone Layer. http://vortex.nsstc.uah.edu/atmchem/ recent_events/upperstrat03_recovery.html
Global Ozone Depletion Global Total Ozone Change (Con’t) • Latitudinal distribution of ozone change Global Sunburning uv Change • Change from 1979 to 1992 Fahey, D.W., Twenty Questions and Answers About the Ozone Layer. http://vortex.nsstc.uah.edu/atmchem/ recent_events/upperstrat03_recovery.html
Vis- ible Near IR UV Far Infrared H O 2 CO 2 100 O O , 3 CO , 2 2 CO , 2 O H O Absorption (%) 3 2 H O 2 H O 2 50 0 0.3 0.5 1.0 5.0 10.0 15.0 20.0 Wavelength (microns) Why the big deal? • Ozone absorbs ultraviolet light; uv-B especially • Ultraviolet light is very harmful to living organisms including humans - Destroys acids on DNA molecule that transmit heredity blueprint - Long term exposure can cause skin cancer - Can cause cataracts - Suppressed immune system uv-A Ozone Layer uv-B Fahey, D.W., Twenty Questions and Answers About the Ozone Layer. http://vortex.nsstc.uah.edu/atmchem/ recent_events/upperstrat03_recovery.html
Why the big deal? Global Total Ozone Distribution • Ozone concentration varies with latitude and longitude - More in polar and mid-latitude regions especially northern hemisphere - Less in tropics Annual Average Atmospheric Ozone http://isccp.giss.nasa.gov/products/browsed2.html
Why the big deal? Average Atmospheric Ozone Global Total Ozone Distribution • Ozone concentration varies with season - Lower values in polar regions in winter and spring DJF JJA http://isccp.giss.nasa.gov/products/browsed2.html
Why the big deal? • Change in uv radiation with change in ozone - Note 10% depletion observed to cause about 15% increase in surface uv - Note as ozone depletion increases surface uv increases more rapidly, i.e., this is a non-linear response World Meteorological Organization http://www.wmo.ch/index-en.html
Why the big deal? Erythemal uv • Erythemal uv, sunburn causing uv • Lauder, New Zealand (45.0°S, 169.7°E) • Note annual cycle - maximum in January; Minimum in June • Increasing January maximum; Red line = eyeball fit to peak values http://environment.govt.nz/indicators/ozone/uv.html
Why the big deal? Erythemal uv (Con’t) • EPA estimates 1% increase in uv will cause 2% to 5% increase in skin cancer. According to the NYU School of Medicine risk of developing malignant melanoma was 1 in 250 in 1980 and is 1 in 87 in 1997. • 200 plant species tested, 2/3 react to increased uv • Reduced leaf size, stunted growth, poor seed quality, increased susceptibility to weeds, disease and pests • Can kill phytoplankton • More research needs to be done
What to do? Corrective Measures • Ban CFCs, but not easy to do • 1978 U.S. banned CFCs in aerosol sprays • Dupont is developing new non-chlorine based chemical for automobile air conditioners • 1988 Dupont announced phase out of production by year 2000 • 1988 43 nations signed the Montreal Protocol agreeing to gradually reduce CFC to 50% of the 1986 amounts by 2000. By 1988 many CFC-consuming countries had ratified this agreement.
Montreal Protocol Effects of Corrective Measures • Predictions of stratospheric chlorine and skin cancer from various international agreements to reduce CFCs Fahey, D.W., Twenty Questions and Answers About the Ozone Layer. http://vortex.nsstc.uah.edu/atmchem/ recent_events/upperstrat03_recovery.html
Montreal Protocol Effects of Corrective Measures (Con’t) • Surface measurements of CFCs in the atmosphere show the Protocol is working • Concentrations of other destructive chemicals are still increasing. Must stop increase in production of methylchloride and carbon tetrachloride cleaning agents
Montreal Protocol Effects of Corrective Measures (Con’t) • Model predicted recovery of stratospheric ozone • Note it is around 2050 before ozone recovers to 1980 values Fahey, D.W., Twenty Questions and Answers About the Ozone Layer. http://vortex.nsstc.uah.edu/atmchem/ recent_events/upperstrat03_recovery.html
AMS Ozone Statement Adopted by the American Meteorological Society Council on 5 September 2003) Ozone is an important trace gas in our atmosphere that has both beneficial and damaging aspects. Naturally occurring in both the troposphere and stratosphere, stratospheric ozone has a beneficial effect for life on earth as a filtering agent for damaging ultraviolet radiation. When photochemically produced in the troposphere to sufficiently high levels, however, ozone can be toxic and can result in significant physiological and ecological damage. Bulletin American Meteorological Society, 2004, 85, 297-299
AMS Ozone Statement Human activities are causing changes in ozone levels in much of the atmosphere. By the use of stratospheric ozone depleting chemicals, humankind has caused a decrease in stratospheric ozone. Combustion of fossil fuels in motor vehicles and in stationary power plants has led to increases in nitrogen oxides and volatile organics emissions into our troposphere. Interacting together in sunlight, nitrogen oxides and hydrocarbons are causing increases in tropospheric ozone. This is especially noticeable during pollution episodes in urban centers as photochemical smog events. Tropospheric ozone increases on regional and global scales can lead to agricultural loss and ecological damage. Increases at the global scale can also contribute to global warming. While many facets of ozone's atmospheric behavior are well understood, a large number of important uncertainties remain, whose resolution will require substantial combined efforts by the meteorological and chemical communities. The American Meteorological Society (AMS) strongly supports interactions between these communities focused on obtaining a better understanding of ozone and its behavior.
AMS Ozone Statement The AMS recognizes that human activities are affecting atmospheric ozone by depleting stratospheric ozone and by increasing ground-level ozone worldwide, especially in polluted urban centers. Stratospheric ozone depletion leads to increased amounts of damaging ultraviolet radiation reaching the earth's surface. This is detrimental to the atmosphere, ecosystems, and humankind, and has led to the Montreal Protocol banning stratospheric ozone-depleting chemicals. Increased ground-level ozone concentrations have direct health effects on plants, animals, and humans. Concerns here have led to the Clean Air Act Legislation aimed at the reduction of tropospheric ozone precursor emissions. Tropospheric ozone and its precursors can also have an impact on greenhouse warming.
AMS Ozone Statement 2) The AMS notes that the chemical, radiative, and dynamical components of ozone's behavior are coupled and complex. This complexity adds substantial uncertainty to many of the currently available assessments of ozone's impacts. Despite these uncertainties, however, ample evidence substantiates that atmospheric ozone has been affected in important and even critical ways by human activity. Stratospheric depletion has been established by observations of the Antarctic ozone hole, and our evidence that it results from human-produced halocarbons is overwhelming. Anthropogenic activities also significantly influence tropospheric ozone. Photochemical smog is well documented in most urban centers of the world, and in many cities leads to ozone levels approximately ten times higher than occurs naturally. Air pollution from the combustion of fossil fuels has caused increases in ground-level ozone throughout the Northern Hemisphere, where average ozone levels have increased by 50% or higher. Although it is uncertain how specific emissions of pollutants affect tropospheric ozone, it is certain that the increases in tropospheric ozone are associated with emissions of nitrogen oxides (NOx) and volatile organic compounds (VOCs). The effects in both the stratosphere and troposphere are sufficiently profound to mandate substantial concern, both on a local and global basis.
AMS Ozone Statement 3) While human activity clearly causes changes in the atmospheric concentration of ozone, there remain important gaps in our understanding of ozone's complex behavior. This is particularly the case for tropospheric ozone, where the NOx and VOC interactions are still being unraveled and the importance of long-range transport and mixing is being resolved. In order to satisfactorily forecast future ozone trends in our atmosphere and provide a firm basis for policy analysis and associated policy actions, the lack of understanding needs to be addressed. 4) Many uncertainties arise because of the strong couplings among chemistry, radiation, and atmospheric dynamics. Thus, resolution of the uncertainty will require coordinated effort among scientists having chemical and meteorological backgrounds. The AMS actively supports continuing forums for this scientific interaction and welcomes interactions with other scientific organizations for this purpose. Current ozone-control legislation and international agreements (such as the Montreal Protocol) tend to reflect the uncertainties noted above. Nonetheless, the actions associated with the Montreal Protocol and its associated amendments have been based on the best science available.
AMS Ozone Statement Implementation of the U.S. Clean Air Act is burdened by uncertainties about the relative impact of emissions of NOx and VOCs on tropospheric ozone during pollution events, and by the failure to use observation-based investigations of ozone and ozone precursors to evaluate the impact of control strategies. Directed research should address these issues. Research also needs to identify the increasing impact of international and intercontinental transport of tropospheric ozone and its precursors, as further industrialization leads to increases in ground-level ozone worldwide. With regard to the Montreal Protocol, it is encouraging to note that halocarbon limitations under this agreement appear to have resulted, recently, in decreases of some of the shorter-lived halogen-containing species and an end to increases of chlorofluorocarbons. Increasing reliance on replacement compounds should lead to the recovery of the stratospheric ozone system in the latter part of the twenty-first century. Owing to the noted uncertainties and complexities associated with stratospheric ozone depletion, however, the effects of this and other international agreements must be monitored continuously and carefully to confirm the expected recovery and establish the basic understanding required for more effective maintenance in future years.