& UV Radiation Exposure

Danielle LeBrun & Bertrand Tematio

*Ozone Depletion

*Ozone Structure

*Ozone exist as a triatomic molecules, containing three oxygen (O3) atoms covalently bonds.

*Ozone is unstable and will readily combine with other atoms.

*Ozone Location

*Ozone is found in the stratosphere between 10 – 50km, where it blocks the sun's ultraviolet (UV) waves and prevents them from reaching the earth's surface.

*Ozone is also found in the troposphere between 0 – 10km, where it can damage living tissue and human-produced objects. It helps keep the air fit to breathe.

*UV radiation is most emitted by the sun and has a shorter wavelength than visible light. It absorbs in the 200 to 400 nm region in the electromagnetic spectrum.

*UV radiation is subdivided into three distinct spectral ranges:

UVA ( 320 – 400 nm) relatively harmless.

UVB (290 – 320 nm) causes sunburn, skin cancer, and other disorders.

UVC ( 200 – 290 nm) extremely harmful

*Ultraviolet Radiation

*Ozone Formation

and Destruction

* Short wavelengths have more energy per photon than long wavelengths.

*Ozone is formed by the action of the sun's ultraviolet radiation shorter than 240nm on oxygen molecules.

*Ultraviolet light splits the molecules apart by breaking the bonds between the atoms. A highly reactive free oxygen atom then collides with another oxygen molecule to form an ozone molecule

O2 + UV (<240nm) O + O Slow (1)

O + O2 + M O3 + M Fast (2)

M denotes particles in the atmosphere that carries off the excess energy of the reaction

*Because ozone is unstable, ultraviolet light quickly breaks it up, and the process begins again.

O3 + h O + O2 Fast (3)

O3 + O 2O2 Slow (4)

Nitrogen Catalytic Cycle NO + O2 NO2 + O2 fast

NO2 + O NO + O2 fast

Net: O3 + O 2O2 fast

Nitrogen dioxide (NO2) is a brownish gas that is observed in major cities

In the lower stratosphere, one NO molecule can destroy hundreds or thousands of O3 molecules.

Chlorine Catalytic Cycle

Cl + O3 ClO + O2 very fast

ClO + O Cl + O2 very fast

Net: O3 + O 2O2 very fast

This cycle is faster than the nitrogen cycle, therefore, destroys more effectively ozone.

NB: Bromine (Br) radicals and hydroxyl (OH) radicals catalytic cycle can also destroy ozone.

*Catalytic Cycles

*Ozone in the Stratosphere

*Good Ozone

*Ozone and oxygen absorb 95 to 99.9% of the sun's ultraviolet radiation

*only ozone effectively absorbs the most energetic ultraviolet light (UV-C and UV-B)

*Life can not exist without the protection provided by the Ozone

*Ozone in the

Troposphere

*10% of the ozone in the earth's atmosphere is found in the troposphere.

*Ozone in high concentration is toxic to plants and irritates both humans eyes and lungs.

*Ozone is a key component of the photochemical smog observe in some cities.

*Ozone in the troposphere cleans the lower atmosphere of pollutants such carbon monoxide (CO) and sulfur dioxide (SO2) that keep the air fit to breath.

*Hole in the

Ozone?!

*The hole in the earth's ozone layer, over Antarctica, was first detected in 1976

*They are caused by the formation of ice particles known as polar stratospheric clouds (PSCs) which alter the chemistry of lower stratosphere by:

(1) coupling between the odd nitrogen and chlorine cycles

ClO + NO2 ClONO2 + M

(2) by providing surfaces on which heterogeneous reactions can occur.

HCl + ClONO2 Cl2 + HNO3

Cl2 + h 2Cl

Atomic chlorine attacks the ozone immediately that is formed

*More research is still needed

*chlorofluorocarbons (CFCs)

*CFCs (chlorofluorocarbons) have been extensively used since the 1960s as refrigerants, industrial cleaning solvents, propellants in aerosol spray cans, and to make Styrofoam. They had interesting thermodynamic properties, they were inert and nontoxic to humans.

*CFCs drift slowly upward to the stratosphere, where they are broken up by ultraviolet radiation, releasing the chlorine that catalytically destroys ozone. The most common compounds are freon-11 (CCl3F) and freon-12 (CCl2F2)

CCl3F + UV (<220nm) CFCl2 + Cl

CCl2F2 + UV (<220nm) CF2Cl + Cl

*Ozone Destructi

on

*1. UV radiation breaks off a chlorine atom from a CFC molecule.

*2. The chlorine atom attacks an ozone molecule, breaking it apart and destroying the ozone.

*3. The result is an ordinary oxygen molecule and a chlorine monoxide molecule.

*4. The chlorine monoxide molecule is attacked by a free oxygen atom releasing the chlorine atom and forming an ordinary oxygen molecule.

*5. The chlorine atom is now free to attack and destroy another ozone molecule. One chlorine atom can repeat this destructive cycle thousands of times.

*Ratification by international community of treaties. The Montreal Protocol in 1987 limited the amount of freons and halons that could be released into the atmosphere by any country.

* Substitution for freons by the chemical industry. One of these is replace one of the chlorine or fluorine atoms with hydrogen atom to make HCFCs

* Engagement of citizens. Consumers should start buying ozone friendly products such as CFC substitutes.

*Ozone Protection

*UV Beads Experiments

*UV Beads as an inquiry based lab

*Beads change color when exposed to UV light

*Design experiments

*UV Beads 1. Do clouds block some or all UV rays?

2. Is old sunscreen as effective as new sunscreen?3. Do T-shirts block some or all UV rays?4. Does windshield glass block some or all UV rays?5. Are all of the windows in a car equal when it comes to blocking UV rays?6. Does SPF 30 sunscreens give twice the protection of SPF 15?7. So UV filtering sunglasses really block UV rays?8. Is exposure to UV rays at midday as great as exposure to UV rays at other times during the day?9. Is sunlight reflected from a white surface as dangerous as direct sunlight?10. Does water reflect all or some UV rays?11. Are UV rays able to travel through water?12. Design your own experiment. Please have your experiment approved by the instructor before you begin.

0 = Bead did not change color (remained white)1 = Very Pale/Light3 = Medium5 = Medium/Dark9 = Very Dark

*Schoenbein Paper

*Gives measurable level of ground level ozone

*Easy to make

GROUND LEVEL OZONE TESTINGThis is the color scale that shows the ozone levels.

Use this graph to get your results from the color above.Schoenbein Color Scale 0-3 Little or no change 4-6 Lavender Hue 7-10 Blue or Purple

*Schoenbien Paper Lab Prep* Preparation of the strip test by the teacher

* Safety: Potassium iodide can cause mild skin irritation

* 1. Place 100 ml of distilled water in a 250 ml beaker.

* 2. Add 1 1/4 teaspoon of corn starch.

* 3. Heat and stir mixture until it gels. The mixture is gelled when it thickens and becomes somewhat translucent.

* 4. Remove the beaker from the heat source and add 1/4 teaspoon of potassium iodide and stir well. Cool the solution before applying to the filter paper.

* 5. Lay a piece of filter paper on a glass plate, or hold it in the air, and carefully brush the paste onto the filter paper. Turn the filter paper over and do the same on the other side. Try to apply the paste as uniformly as possible.

* 6. Wash hands after applying the potassium iodide mixture. (Although potassium iodide is not toxic, it can cause mild skin irritation.)

* 7. Set the paper at a low temperature drying oven.

* 8. Cut the filter paper into 1-inch wide strips.

* 9. To store the paper, place the strips in a sealable plastic bag out of direct sunlight.

* Students will be grouped by 4 and they will construct an ozone map of their area.

*Procedure*1. Each student gets two strips of Schoenbein paper in a sealed bag.

* 2. Each student moistens the paper with distilled water and hangs the test strips at two sites in their home.

* 3. Each student will expose the paper for approximately 3 days, will record the test result every day (To observe and record test results, spray the paper with distilled water. Observe the color)

* 4. Each group will get the map of the city or a map may be posted in the classroom.

* 5. Each student should record their data noting the color change they observe.

* 6. Each group can then plot the relative ozone concentrations on a local, United States or globe.

Schoenbein Color Scale

0 1 2 3 4 5 6 7 8 9 10

0 – 3 Little or no change 4 – 6 Lavender Hue 7 – 10 Blue or Purple

Ideas: Have students mail their Schoenbein paper to relative in other parts of the country or internationally to test ozone levels.

http://www.stevespanglerscience.com/experiment/uv-reactive-beads

http://www.teachersource.com/category/light-ultraviolet

http://www.ucar.edu/learn/1_7_2_29t.htm#procedure

http://beprepared.com/product.asp?pn=FS%20C150&sid=GOOGLE

http://www.flinnsci.com/store/Scripts/prodView.asp?idproduct=20762

http://www.flinnsci.com/store/Scripts/prodView.asp?idproduct=14655

http://www.ucar.edu/learn/1_5_1.htm

The earth system, third edition, Kump. Kasting. Crane

Chemistry, 10th edition, Raymond Chang

References