Atmospheric Chemistry

1. Atmospheric Chemistry

2. Stratospheric Ozone 1) Absorbs solar radiation (200-315nm) 2) Three types of UV UV-A (320-400 ) UV-B (280-320nm) UV-C (200-280 nm)

3. 3) The greatest concentration of O3 is from 15-30 km above Earth 4) The amount of Ozone varies 5) Quantified by the Dobson Unit (DU) 100 DU = 1 mm of Ozone The Earth averages about 300 DU Antarctic = 150 DU

4. Ozone Formation: Oxygen molecules are hit with UV light and split into energized atoms that combine with an oxygen molecule to form ozone (O3). 1. O2 + UV  2 O• 2. O• + O2 + M  O3 - this second reaction requires a third party molecule (M) to help absorb the extra energy – usually another atmospheric gas

5. Processes of Ozone destruction Free Radicals: atoms or molecules with a free (non-bonded) electron - highly unstable and reactive - Most responsible for non-oxygen destruction of ozone These include: HOx•, NOx•, ClOx• gases

6. Basic Process: • molecules float to the stratosphere and are bombarded by UV light • molecules are broken apart forming free radicals • free radicals attack ozone molecules causing them to break down and form more free radicals • process continues until the free radicals bind to a sequestering molecule to become stable

7. Generalized Reaction • X2 + UV  X• + X• • X• + O3 XO + O2 • XO + O•  O2 + X•

8. Overall Process: X• is not consumed by the reaction but remains to continue the breakdown of O3. O3 + O  2 O2

9. Hydroxyl Radicals and the HOX Cycle Methods of Hydroxyl Generation: 1. O• (energized oxygen) + H2O  2 •OH 2. H2O + UV  •H + •OH 3. H • + O3 •OH + O2

10. Decomposition of ozone by hydroxyl radical: 1. •OH + O3 HOO• + O2 2. HOO• + O•  •OH + O2

11. NOX Cycle NO2 + UV  NO• + O• This photodissociation makes possible: NO• + O3NO2 + O2 NO2 + O•  NO• + O2 - note the free “O” is there because it is in the stratosphere where atomic density is low

12. The ClOx cycle Cl• are mostly anthropogenic (man made) in source CH3Cl + UV  •CH3 + •Cl

13. MEMORIZE THESE! The main reaction with ozone CFCl3 + UV (<290 nm)  •CFCl2 + Cl• Cl• +O3 ClO• + O2 ClO• + O•  Cl• + O2 Net Reaction = O3 + O  O2 + O2

14. Anthropogenic sources of chlorine • Mostly chlorinated fluorocarbons • Refrigerants, solvents, propellants • Chemically and biologically inert • CFCs do not react in the troposphere but do in stratosphere

15. Properties of CFCs • Can last 60 – 522 years in troposphere • The ODP (ozone depletion potential) is correlated with the # of Cl

16. The Ozone Hole - Antarctica - Results from climatic factors and accumulation of pollutants Process: • Sun sets for the season – dark and very cold • Air currents form a circumpolar vortex that channels pollutants to form stratospheric clouds

17. Clouds form ice crystals of nitric acid, chlorine compounds and water • The sunlight returns to photolyse and create free radicals of chlorine andnitrogen compounds • Rapid degradation of ozone VIDEOVideo #2 Video#3

18. End Result: • Ozone thickness decreases to 150 DU • Free radicals spread north to South America, New Zealand and Australia • Increases UV damage by allowing more UV-B radiation into troposphere

19. Health Effects: - damage to plants - increased damage to skin and DNA (thymine dymers)skin cancer – just like going to the Death Boxes known as tanning bed.

20. Montreal Protocol: Internationalagreement to limit/ban CFC use.

21. Tropospheric Chemistry To form photochemical smog, three main ingredients are needed: • nitrogen oxides (NOx) • hydrocarbons (VOCs) • energy from the sun in the form of ultraviolet light (UV).

22. Process: • Generation of NO, hydrocarbons (VOCs) and carbon monoxide (CO) from combustion in cars N2 + O22 NO 2. In the air, nitrogen monoxide (nitric oxide) combines with molecular oxygen to form nitrogen dioxide within a few hours. 2NO + O22 NO2

23. 3. Nitrogen dioxide absorbs light energy and splits to form nitrogen monoxideand atomic oxygen: NO2NO + O• 4. Then, in sunlight, the atomic oxygen combines with oxygen gas to form ozone O• + O2O3

24. - If no other factors are involved, ozone and nitric oxide then react to form nitrogen dioxide and oxygen gas. O3 + NO  NO2 + O2 - This last reaction is reversible and moves in one direction based on the temperature and the amount of sunlight. - If there is a lot of sunlight, the equation moves to the left, and more ozone is produced. If nothing else gets in the way, an equilibrium is reached, and the ozone level stabilizes.

25. 5. VOCs react with nitric oxide to produce PAN (peroxyacetyl nitrate). NO + hydrocarbonsPAN

26. Two Results: • Volatile, reactive organic compounds are generated directly. • Nitric oxide (NO) reacts with hydrocarbons instead of ozone increasing the amount of ozone in the troposphere to damaging levels. End Product: - an accumulation of ozone and volatile organic compounds such as PAN, which are secondary pollutants - the sun moves the reactions along forming photochemical smog

27. Health Effects of Photochemical Smog • eye irritation and poor visibility • Strong oxidants such as ozone can damage the lungs. • Damage to the lungs may stress the heart. • loss of immune system function, increased susceptibility to infections, and fatigue. • kill plant cells, causing leaves to develop brown spots or drop off the plant, reduce plant growth, and make plants more susceptible to damage from other causes. • corrode and destroy many materials such as rubber, nylon, fabric, and paint.

28. Greenhouse Effect, Enhanced Greenhouse Effect, Global Warming & Climate Change • Greenhouse: glass of greenhouse allows light into the plants and soil. Light is converted to heat (infrared radiation (IR)). The glass traps the heat making the greenhouse warm.

29. Greenhouse Effect on Earth: Atmospheric gases act as the glass. Allow light in but absorb and redirect the IR back to the Earth. • Not all gases do this. Some gases do this more than others. The ability to absorb IR and release it is called the Global Warming Potential. Carbon dioxide has a GWP value of 1 (base measurement) while CFC’s can be hundreds or thousands of times greater than CO2.

30. THIS IS GOOD otherwise the Earth would be about -18 C.

31. Enhanced Greenhouse Effect (aka Global Warming) is the idea that increased amounts of Greenhouse gases will cause the global temperature to increase.

32. Effects: • Change of ocean temperature. • changes ocean currents = change in climate • changes weather patterns = change in climate = loss of biodiversity. Also a change in agriculture. • change in upwelling of nutrients = loss of biodiversity • decreases oxygen content = loss of biodiversity

33. Increased CO2 in water • Loss of Biodiversity • increases acidity of water • decreases productivity • kills coral reefs Loss of Biodiversity

34. Competing Theories