November 18.docx

6 Pages
44 Views

Department
Environmental Studies
Course Code
EVS 205
Professor
James Rotenberg

This preview shows pages 1 and half of page 2. Sign up to view the full 6 pages of the document.
Description
Intro to Stratospheric Ozone • Atmosphere contains layer of ozone that shields earth from UV radiation • Ozone absorbs all UV-C, most UV-B • UV-A is not affected by ozone • The shorted the wavelength the more energetic and dangerous to the UV Ozone hole—History and Discovery • Ozone Depletion: Effects o Ozone: thinned area over Antarctica in Blue  Reached record size o2 September 6, 2000 covering 11.5 million square miles (29.2 million km ) o Ozone Depletion most severe over Antarctica (but also Arctic) o Occurs annually in Antarctica between September-November o Not stationary due to weather patterns. o September 22, 2012—smallest in 20 years • Main Causes of Ozone Depletion o Main problem: CFCs o Other Chemicals:  Halons • Contain bromine and chlorine use in fire retardants  Methyl bromide • Pesticide  Methyl chloroform and Carbon tetrachloride • Industrial solvents used in production of pesticides  Nitrous Oxide • Released from burning fossil fuels o Ozone Depletion: Chemical Reaction  CFCs reach the atmosphere and react with UV light and O 3  O 3plits into O2+ O  CFC-Ozone reactions occurs more frequently than ozone formation  What does this mean eventually? • Ozone Hold Discovery o Joseph Farman—1985, Halley Bay, Antarctica (UK research base) o Measured Ozone layer in Dobsen Unites for about 30 years o Noticed decrease in total ozone in October for each year after mid 1970s • Satellite data for Zone Hole o Data and Ozone Hole had been recorded by satellites since the 1970s; however, the measurements were so low, they were automatically discarded by computers as error o Following Farman’s publication, data was reanalyzed and found correct o Publications  “Continued decline of total ozone over Halley, Antarctica since 1985” (Nature 376: 409-411—August 3, 2002)  Better News—NASA (Fall 2012—smallest ozone in 20 years) • Why Does Ozone Works? o Ozone absorbs at UV radiation at specific wavelengths o Absorbs most strongly at wavelengths of 250 nm  Called the “Hartley band” o Remember!  UV-C = 250-290 nm  Very hazardous and is completely absorbed • Ozone Threats o Chlorine: One of the most important catalysts for ozone destructions o Natural sources:  Mehyl chloride (CH 3l) • 25% of chlorine in stratosphere • Formed in the oceans by marine phytoplankton and from biomass burning in grasslands and forested areas  Hydrogen chloride (HCl) • Volcanoes • Anthropogenic Chlorine sources o Chlorocarbons  Family of chemicals usually derived from an organic compound o Halocarbons  Family of chemicals with halogen atoms • Chlorine, Fluorine, Bromine, Iodine  Include: • Carbon tetrachloride (CCl4)—solvent in dry cleaning • Chlorofluorocarbons (CFCs) Quantifying Ozone Concentration • Gordon Dobson o Dobson spectrophotometer: measures the amount of atmospheric ozone overhead by collection ultraviolet radiation scattered by the atmosphere • Dobson Units (DU) o Measures by the total number of O 3olecules un a 1cm column of air reaching from the ground16ut to space 2 o 1 DU = 2.7 x 10 O m3lecules/cm o On average the Earth has 250-300 DU of ozone coverage  Normally increases from equator to poles Variation of Ozone Layer Ozone and Light Spectrum • UV-A = 320-380 nm o UV-A completely penetrates ozone layer and reaches the ground. • UV-B = 290-320 nm o Biologically hazardous—Sunburn o Most is absorbed by ozone layer, but small amount reaches surface. • UV-C = 250=290 nm o Very hazardous! Completely absorbed by Ozone layer o CFCs • Past Uses o Refrigerators and air conditioners—Freon o Propellants in aerosol spray cans o Plastic foam bubble/peanuts—packaging o Cleaner solvents for electronic parts (computer chips) • Research finds CFCs harmful o 1973: Researchers from the University of California at Irvine found CFC as cause of Ozone depletion o 1985:  First discovered that Ozone thinning was observed to be greater than caused naturally  Battle with Dupont o 1988: Dupont acknowledged CFCs as cause of ozone depletion o 1995: Mario Molina, F. Sherwood Rowland, and Paul Crutzen win Nobel Prize in Chemistry. • Main Chemicals o CFC-11 (CFCl 3 o CFC-12 (CF Cl ) 2 2 o Originally designed as substitute refrigerants and also solvents. • CFCs—a continued Threat o Even though the production and use of CFCs have been banned, they continue to be a threat because of their “atmospheric lifetime” o CFC-11 (76 atm lifetime) o CFC-12 (139 atm lifetime) • The Life of a CFC Molecule o CFCs manufactured o CFC used and travel to lower atmosphere where they accumulate in the Troposphere  10 mt of chlorine present in the form of CFCs o Natural exchange of air between Troposphere and Stratosphere carries CFCs to upper atmosphere. o CFCs are exposed to UV radiation and are broken down releasing Chlorine products o These Chlorine products react with and destroy Ozone o Chlorine further reacts and forms less reactive compounds (HCl) o HCl travels downward to Troposphere and is carried away with rainwater. Unique Atmospheric Features at the Poles • Polar Vortex o Polar vortex is a swirling mass of very cold air that is isolated from the rest of the atmosphere for several months. o Ice crystals in this mass collect CFCs and other chemicals and set up conditions
More Less
Unlock Document

Only pages 1 and half of page 2 are available for preview. Some parts have been intentionally blurred.

Unlock Document
You're Reading a Preview

Unlock to view full version

Unlock Document

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit