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Environmental Impact of Light

Environmental Impact of Light. Fundamental processes in soil, atmospheric and aquatic systems Chemical and biochemical changes 2.iii.c (2 hrs). ‘Dark’ Reactions. Most organic compounds react very slowly, even with oxygen, at normal temperature.

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Environmental Impact of Light

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  1. Environmental Impact of Light Fundamental processes in soil, atmospheric and aquatic systems Chemical and biochemical changes 2.iii.c (2 hrs)

  2. ‘Dark’ Reactions • Most organic compounds react very slowly, even with oxygen, at normal temperature. • As a rule, they can be considered generally nonreactive. • BUT !... Environmental processes / Chemical and biochemical changes / Impact of light

  3. Let Be Light ! • Visible and ultraviolet radiation can promote the reactivity of almost all compounds. • Recall a well known fact that items exposed (northern hemisphere) on southern side of buildings decay more quickly than those on northern side. Environmental processes / Chemical and biochemical changes / Impact of light

  4. On the side facing south, the wooden (and metal) items decay faster Environmental processes / Chemical and biochemical changes / Impact of light

  5. Museum item Side exposed to light Side not exposed to light Environmental processes / Chemical and biochemical changes / Impact of light

  6. Basics of Photochemistry • Primary photophysical process. • Subsequent chemical change(s) Environmental processes / Chemical and biochemical changes / Impact of light

  7. Photophysical process • Actually, it means absorption of light quanta. • It promotes molecule from ground- to excited state (energy rich one). • But, to catch the light quanta, molecule has to have a CHROMOPHORE ! Environmental processes / Chemical and biochemical changes / Impact of light

  8. Chromophores • Chromophores are structural details in molecule(s) that enable high(er) probability of light absorption. • Normally, it comprises double bonds in molecule, i.e., π-electrons: Environmental processes / Chemical and biochemical changes / Impact of light

  9. Chromophore • Double bond • Aromatic ring • Far more efficient are polarized double bonds. Environmental processes / Chemical and biochemical changes / Impact of light

  10. Photophysical process • Once molecule acquires light quantum, it has many ways to decay, involving the chemical change. • Simplified approach tells that molecule can exist in ground state singlet or triplet • The same holds for excited state Environmental processes / Chemical and biochemical changes / Impact of light

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  14. Singlets and triplets are known as multiplicities of state. • Electronic transition among states of different multiplicities is not likely to happen (is ‘forbidden’), • But, as many other things, something forbidden still could happen. Environmental processes / Chemical and biochemical changes / Impact of light

  15. These ‘violations’ could be promoted by, so called, SENSITIZERS. Environmental processes / Chemical and biochemical changes / Impact of light

  16. Sensitizers quickly, and in good yields populate excited triplet states. • Triplets live long enough to encounter other molecules. Environmental processes / Chemical and biochemical changes / Impact of light

  17. Sensitization Environmental processes / Chemical and biochemical changes / Impact of light

  18. Photophysics → Photochemistry Environmental processes / Chemical and biochemical changes / Impact of light

  19. Primary chemical intermediates in photochemical metathesis are organic free radicals. • Free radicals are highly reactive. • Radicals react with almost everything! Environmental processes / Chemical and biochemical changes / Impact of light

  20. Additional sensitization(singlet oxygen) Environmental processes / Chemical and biochemical changes / Impact of light

  21. Coatings & Erosion • VOC-s exposed to light can be promoted to more reactive compounds. • Oxygen-containing derivatives can be aggressive to living organisms and to artifacts. • Reactive intermediates may lead to polymers forming sticky coating. Environmental processes / Chemical and biochemical changes / Impact of light

  22. Everything matters • Ozone is not emitted directly from industrial sources and vehicles. • It is formed in troposphere as a result of reactions involving oxides of nitrogen and volatile organic compounds. Environmental processes / Chemical and biochemical changes / Impact of light

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  24. What pollution we can control? • Industry, • Traffic, • Agriculture • and (….. leisure) Environmental processes / Chemical and biochemical changes / Impact of light

  25. Internet Resources • http://www.iaq.dk/index.html • http://www.airclim.org/airAndEnvironment/AE_chp3.htm • http://www.epa.gov/region4/airqualitytoolkit/10_Glossaries/US NPS - Air Quality Glossary.pdf • http://www.heritage.xtd.pl/pdf/full_czop.pdf • http://www.epa.gov/iaq/voc.html Environmental processes / Chemical and biochemical changes / Impact of light

  26. http://www.environment.gov.au/soe/2006/publications/commentaries/atmosphere/glossary.htmlhttp://www.environment.gov.au/soe/2006/publications/commentaries/atmosphere/glossary.html • http://www.airimpacts.org/documents/local/aqbook.pdf Environmental processes / Chemical and biochemical changes / Impact of light

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