1 / 17

What is ozone?

What is ozone?. O 3 a very reactive molecule consisting of 3 oxygen atoms strong oxidant reacts easily by ”giving” one of its oxygen atoms to another molecule. Where do we find ozone?. in the stratosphere (ca 10 - 50 km) absorbing harmful UV-radiation in the troposphere (ground level)

sanchezd
Download Presentation

What is ozone?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. What is ozone? • O3 • a very reactive molecule • consisting of 3 oxygen atoms • strong oxidant • reacts easily by ”giving” one of its oxygen atoms to another molecule

  2. Where do we find ozone? • in the stratosphere (ca 10 - 50 km) • absorbing harmful UV-radiation • in the troposphere (ground level) • as a pollutant • part of photochemical smog • damage on vegetation/crops • damage on respiratory system • produced by electrical discharges • as naturally by lightnings • in useful applications • as desinfecting agent (e.g. for purifying water) • because of its oxidizing effect

  3. What is the ozone layer? • part of the stratosphere (from ca 15-35 km) that is enriched in ozone • but even there the concentrations are very low (between 1 – 20 ppm) • the altitude varies with the latitude, with the seasons and the time of the day

  4. Measuring unit for ozone • Dobson unit (DU) • 100 DU = 1 mm ozone thickness at STP (1 atm, 0ºC) • typical values: 300 – 500 DU • if ozone was compressed to pressure at sealevel it would have a thickness of 3 – 5 mm • if the whole atmosphere was compressed to sealevel pressure it would have a thickness of ca 8 km

  5. Measuring ozone (1) • satellites • ground measurements • balloons • aircrafts • rockets

  6. Measuring ozone (2) • satellites • usually passive instruments that use solar radiation • most instruments register only total ozone • example: TOMS (Total Ozone Mapping Spectrometer) • uses Backscatter Ultraviolet Technique: • 2 measurement (pair measurements) for each used wavelength in the UV-range: • (1) radiation directly from the sun • (2) radiation that is reflected from the ground or backscattered from the atmosphere • measurements at at least 2 different wavelength, one absorbing weakly, one absorbing strongly • changes in the pair measurements for these wavelength are used to calculate ozone amount • for the strong absorbing wavelength: the more ozone, the less is reflected/backscattered

  7. Measuring ozone (3) • ground measurements • passive instruments (Dobson) • measurements of UV-radiation from the sun at 2 wavelength, one strongly absorbed, one weakly absorbed (similar to the backscatter technique on satellites) • other atmospheric phenomenons (clouds, aerosols ….) affect both wavelength in the same way, • the remaining difference between the wavelength is due to ozone. • active instruments (LIDAR) • LIDAR = Light Detection and Ranging • laserlight is used in the same way as radiowaves in a RADAR • beams of two wavelength of UV-light are emitted from a laser • one strongly absorbed by ozone, the other weakly • the reflected/backscattered fotons are measured for both wavelengths • calculations in a similar way as for backscattering method on satellites and the Dobson-instrument • with LIDAR one can also get an ozone profile, not only total ozone • measurements can be done during darkness

  8. Measuring ozone (4) • balloons • in situ measurements (directly measuring the ozone in a sample) • often used: chemical reactions • balloons burst at 30 – 35 km altitude • no data of the highest part of the ozone layer (but above 30 km there is little ozone) • airplanes and rockets(less used than the other platforms) • in situ measurements • (big rockets and planes in the stratosphere are believed to contribute to the destruction of the ozone layer • scientists do not agree on the degree of destruction)

  9. Variations of ozone • Most ozone is produced in the stratosphere above the equator • The highest ozone level is at higher latitude • transportation from the equator • little annual variation in ozone concentration over the equator • about 25% annual variation at higher latitudes • reasons for natural variations: • seasons, suncycle, winds

  10. Annual global ozone variations Source: www.ofcm.gov/jagti/11-03_mtg/long_uviI_jag-it.ppt

  11. How and where is ozone created? • O2+hf  O + O UV-radiation • O2 + O  O3 • in the stratosphere • mainly over the equator • where the UV-radiation is most intense

  12. How is ozone destructed? • Physical processes • O3+hf  O + O2 UV-radiation • O3 + O  2O2 • Chemical processes • O3+RRO + O2 RO + O R + O2 O3+ O  2O2 net reaction • R: free radicals • reactive compounds with an unpaired electron • function as catalysts in the ozone destruction reaction • R: NO, NO2, HO, Cl or Br … • Cl and Br are liberated from e.g. CFC and halons by UV-radiation

  13. How does the Arctic ozone ”hole” develop? 3 necessary conditions: • (1) development of a polar vertex during winter • strong winds around the pole inhibit exchange with air outside the vertex •  no supply of ozone • (2) low temperatures  ice crystals develop • formation of polar stratospheric clouds • ice particles catalyse ozone destruction • with nitric acid (HNO3) ice formation occurs at higher temperatures (ca -80º C) • (3) UV-radiation (sunlight) supplies energy to break down e.g. CFC and halones • formation of more reactive compounds (free radicals) • especially of Cl and Br from CFC and halons  The ozone hole develops just after the sun returns during spring.

  14. Ozone profile from day to day over the South Pole in 2003 Source: http://www.cmdl.noaa.gov/ozwv/ozsondes/spo/ozone_anim2003.html

  15. Amount of UV-radiation on the ground How much UV-radiation we are exposed to depends on: • the total amount of ozone • angle to the sun • latitude • time of the year • time of the day • elevation • cloud cover • aerosols

  16. ERYTHEMAL UV-EXPOSURE • is the energy from UV-radiation that an area on the ground receives during a given period of time • unit: • watt/squaremeter or • joule/squaremeter (measured over the hours with most intense UV-radiation) • this gives an indication of the risk for sunburn

  17. Risks of a low ozone level • higher risk for skin cancer • higher risk for eye diseases • higher risk of DNA damage in organisms • effect on plants vary • some grow better • but e.g. soya grows less (could mean reduced harvest/food) • not enough knowledge to predict exact effect on plankton • some species die at high UV-rates • this effect would propagate through the food chain • others assimilates at higher rates  disturbance of the balance in ecological systems

More Related