ENVS 110 Ozone Depletion
Effects on Biogeochemical Cycles
-terrestrial and aquatic -altering sources and sinks of greenhouse gases and chemically important trace-gases (carbon dioxide (CO2), carbon monoxide (CO), carbonyl sulfide (COS), Ozone, and others) -these changes would contribute to biosphere-atmosphere feedbacks that reduce the force of atmospheric buildup of these gases
Skin Cancer
-1 in 5 americans will develop skin cancer -1 american dies every hour from this -1.3 million cases for 2000
Restoring the Ozone Layer
-1987 United Nations Montreal Protocol: to address ozone depletion -this protocol created industry development of "ozone friendly" substitutes for now controlled chemicals -total global accumulation of ozone-depleting gases has begun to decrease, reducing risk of more ozone depletion -by late 21st century we expect more recovery
Other skin damage
-Actinic keratoses:skin growths that occur on parts exposed to sun -Premature aging of the skin -Cataracts: more curable now, diminish eyesight of many americans and cost millions of dollars each year -Pterygium (tissue growth that can block vision) -Skin cancer around eyes -Degeneration of the macula (part of retina where visual perception is most accurate)
Catalytic reaction
-Allows a single chlorine atom to destroy thousands of ozone molecules -Bromine is involved in second catalytic reaction with chlorine which contributes to the most ozone loss
The Role of Polar Stratospheric Clouds (PSC's) in Ozone Depletion
-Created by the low temperatures in Antartica stratosphere making "ice clouds" (PSC's) -special reactions that occur on PSC's and isolation of polar stratospheric air let chlorine and bromine reactions to produce ozone hole in spring -Chlorine atoms break from CFC's (carbon, chlorine, fluorine) destroy ozone, but it doesn't happen right away, they become part of two chemicals that would be stable under normal weather and are considered "long term reservoirs for chlorine" (they are hydrochloric acid, and chlorine nitrate) -the frozen crystals that make up the clouds provide a surface for the reactions that free chlorine atoms -these reactions convert the inactive "chlorine reservoir"chemicals into more active forms- especially chlorine gas (Cl2) -air from surrounding latitudes mixes into polar region in spring, ozone-destroying forms of chlorine disperse (ozone layer stabilizes until following spring) -ozone hole does NOT occur in arctic, and is more variable in antarctica each year
Radiative Forcing of Climate change from atmospheric gases
-Halogen containing gases are the CFC's- have significant contribution to warming in small quantities -Ozone depletion has cooling effect- warming is cause by long wavelength infra-red radiation getting trapped by greenhouse gases and staying in atmosphere, when there is more depletion more wavelength infra-red escapes and we see cooling -Increase in Tropospheric ozone has a warming effect because ozone traps heat like CO2 -Ozone from troposphere could not replace stratosphere ozone, it is reactive and short lived, and would not last long enough to disperse into stratosphere from troposphere -there is 1000X more Stratospheric ozone so any addition from the Troposphere would be insignificant.
Connections to Global Climate Change
-Marine phytoplankton are a major sink for atmospheric CO2: take it for photosynthesis and convert it to more phytoplankton, if this decreases more CO2 is left in atmosphere -just a 10% decrease in their productivity would leave the same amount of CO2 in the air equal to the amount of all the CO2 released by human activity -Compounds that cause Ozone depletion are also greenhouse gases (CO2 and CH4, CFC's are significant)- 11% of total warming effect -Replacement compounds would also contribute to global warming (HFC's)
How is Ozone formed?
-Oxygen gas is split by HIGH energy UVC (most damaging UV but is usually absorbed) into 2 oxygen atom radicals: O2 +UVC radiation from the sun --> O + O -Then, attach to an Oxygen gas molecule to form an ozone molecule: O + O2 --> O3 (ozone)
Effects of Ozone depletion
-Reductions in ozone levels will lead to higher levels of UVB (which doesn't change in output), less protection -Amount of UVB in antarctic can double during the annual ozone hole -in Canada
Changes in surface erythemal UV radiation
-Solar UV radiation has increased singe 1979 -erythemal radiation- can lead to sunburning, is a component of surface UV radiation that is harmful -it also responds to changes in ozone as well as clouds and aerosols -it has increased (mostly in midlatitudes in both hemispheres), increases in southern hemisphere larger without offsetting changes from clouds and aerosols -smallest estimated change are in the tropics because the ozone hasn't changed that much there
Effects on materials
-Synthetic polymers -Naturally occurring biopolymers -Other materials -today, most of these are protected from UVB by additives but an increase will accelerate their breakdown and limit the length of time they are useful for outdoors
Effect on human health
-UVB causes non-melanoma skin cancer and plays role in malignant melanoma development -linked to cataracts -even with normal ozone levels, all sunlight contains some UVB -Skin Cancer, Melanoma, Nonmelanoma Skin Cancers, Other Skin Damage, Cataracts and Other Eye Damage, Immune Suppression
How are Polar Stratospheric Clouds (PSC's) formed?
-completly dark in winter, there are endlessly circling whirlpool of stratospheric winds called the "polar vortex" isolates the air in the center, air gets so cold that clouds form, chemical reactions take place unlike anywhere else in atmosphere -polar vortex becomes weak in spring when it becomes warmer and lets out all the air in it -this can can occur only on the surface of polar stratospheric cloud particles (water, ice, or nitric acid, depending on temp) -when sunlight returns, UV light rapidly breaks the bond between the two chlorine atoms and releases free chlorine into the stratosphere where it destroys ozone molecules and makes more chlorine (known as a catalytic reaction)
HFC's
-don't release chlorine, have similar properties like other greenhouse gases -used as an alternative for CFC's -when we replace these, we decrease depletion of stratospheric ozone but don't decrease global warming while they are in the troposphere
Ozone depleting chemicals
-in 1970's they found that human produced chemicals could harm ozone layer -increase in skin cancer and eye cataracts because of UV rays -ozone-depleting chemicals increasing in atmosphere (some natural sources, but it was linked to use of chemicals like chlorofluorocarbons (CFCs)- refrigeration and air conditioning, foam blowing- Styrofoam, and industrial cleaning) 1. Free chlorine radical from chlorinated compound broken by high energy UVC and causes ozone loss: XXX-Cl + UVC radiation from the sun --> XXX + Cl 2. Then, reacts with Ozone molecule: Cl + O3 --> ClO + O2 3. CIO reacts with oxygen free radical and release chlorine free radical able to react with another molecule of ozone -cycle that breaks apart ozone molecules, 1 Chlorine containing molecule can destroy 100,000 Ozone molecules. -volcanoes also contribute to ozone depletion, not because of chlorine release but because of creation of sulfur clouds in upper atmosphere
Nonmelanoma Skin Cancers
-less deadly than melanoma -can spread and cause health problems and disfigurement -in 2000 more than 1.2 million people will develop non melanoma skin cancer -more than 1900 will die -two primary types- they have 95% chance if detected and treated early -Basal Cell Carcinomas: most common type of skin cancer tumors, small fleshy bumps or nodules on head or neck or other skin areas, grows slowly and rarely spreads to other parts of the body, can penetrate bone -Squamous Cell Carcinomas: as nodules or red scaly patches, can develop into large masses and spread to other parts of body
Immune suppression
-lower immune system and skins natural defenses -impaired response to immunizations -all people, doesn't matter skin color -increased sensitivity of sunlight -reactions to certain medicines
Melanoma
-most serious form of skin cancer and fastest growing type of cancer in US -link between childhood sunburns and melanoma later in life -more than doubled in past 2 decades and expected to continue
The Ozone Hole
-most severe ozone loss was in springtime over antarctica, this is called the "ozone hole" because depletion is so large and together (it occurs most in antartica than anywhere else in the world because of special weather conditions, low temp creates ice cloudscalld PSC's)- created by chlorine and bromine reactions -in other areas of the globe such as arctic and northern middle latitudes -ozone is now 4% lower over the globe -ozone loss is very small near the equator and increases with latitude toward the poles- larger polar depletion is result of late winter/early spring ozone destruction
Effects on Marin Ecosystems
-phytoplankton are the foundation of aquatic food webs -they are limited to the euphotic zone (upper layer of water where there is sufficient sunlight to produce net productivity) - position of organisms in these parts is controlled by wind and waves -UVB radiation has affected their mobility and orientation mechanisms, reduced survival rates (6-12% reduction in the marginal ice zone) -also causes damage to early developmental stages to fish, crab, shrimp, amphibians and others (decreased reproductivity capacity and impaired larval development) -small increases in UVB could result in the reduction of size of these species who eat smaller creatures
Effects on plants
-plant growth can be directly effected by UVB radiation, even in present-day sunlight -indirect changes caused by UVB: changes in plant form, nutrient distribution, developmental phases, secondary metabolism are all equally or more important than damaging effects of UVB -can also have important implications for plant competitive balance, herbivory, plant diseases, biogeochemical cycles -damage nitrogen fixing bacteria in the soil- decrease availability for nitrogen, effect ecosystem, forcing farmers to increase nitrogen fertilizers
The Ozone Layer
-very small part of atmosphere, same compound (Ozone) that is a problem in the troposphere -Most ozone resides in stratosphere- there are no living systems up there so it is not reactive with anything BUT does absorb UV tradition (UVB, higher energy than UVA) preventing it from reaching planet in large amounts -90% of atmospheric ozone is contained in "Ozone Layer"- shields us from harmful ultraviolet radiation from the Sun -"good up high, bad nearby" -all UVC (100-280 nm) is blocked by O2 (at 100-200 nm) or by ozone (at 200-280 nm) -more energetic UV causes the formation of the ozone layer, when single oxygen atoms produced by UV breaking of O2 (below 240 nm) react with more O2 -band of UV closest to visible light, UVA (315-400 nm), is hardly affected by ozone, and most of it reaches the ground
GWP's
Global Warming Potential -how much heat a greenhouse gas traps in the atmosphere compared to CO2 -CFC's and HFC's can have very high GWP's
