Ozone, UV, and Nanoparticles Mort Sternheim STEM Education Institute mort@umassk12

1. Ozone, UV, and NanoparticlesMort SternheimSTEM Education Institutemort@umassk12.net STEM ED/CHM Nanotechnology 2012

2. Today’s agenda • Ozone and ultraviolet light • Nanoparticles and sunscreen • Hands on activity Sunscreen PowerPoint and activities based on NanoSense web site: http://nanosense.org/activities/clearsunscreen • Ozone and ultraviolet light • Nanoparticles and sunscreen • Hands on activity (brief) • Sunscreen PowerPoint and activities based on • NanoSense web site: • http://nanosense.org/activities/clearsunscreen

3. The big ideas • Ultraviolet light causes skin damage and cancer • Ozone in the stratosphere blocks UV • Sunscreen blocks UV, partly • Nanoparticles in sunscreen improve blocking

4. 1. Ozone and Ultraviolet LightWhat is ozone? • Ordinary oxygen gas: O2 (2 oxygen atoms) • Ozone: O3 (3 oxygen atoms) • Polar molecule, like water • Ozone is much more reactive, unstable • Pale blue, poisonous gas Bad! • Absorbs ultraviolet radiation! Good!

5. The Sun’s radiation spectrum • ~ 43% is in the visible range • ~ 49% is in the near infrared range • ~ 7% is in the ultraviolet range • < 1% is x-rays, gamma rays, radio waves Most of the sun’s radiation is Ultraviolet (UV), Visible & Infrared (IR) : . Source: Adapted from http://www.ucar.edu/learn/imgcat.htm

6. Some types of electromagnetic radiation • The sun emits several kinds of electromagnetic radiation: Visible (Vis), Infrared (IR) and Ultra Violet (UV). Note the split into UVA, UVB, UVC • Each kind is distinguished by a characteristic wavelength, frequency and energy • Higher energy radiation can damage our skin High Energy Low Energy Source: http://www.arpansa.gov.au/is_sunys.htm

7. What is Radiation? • Light radiation is often thought of as a wave with a wavelength (l), speed (c), and frequency (f) related by • Since c (the speed of light) is constant, the wavelength and frequency are inversely related • This means that light with a short wavelength will have a high frequency and visa versa. Source: http://www.pueblo.gsa.gov/cic_text/health/sun_uv/sun-uv-you.htm

8. E E  f f Radiation energy comes in packets or photons • The size of an energy packet or photon (E) is determined by the frequency of the radiation (f) • Radiation with a higher frequency has more energy in each packet • The amount of energy in a packet determines how it interacts with our skin

9. Skin Damage • Very high energy radiation (UVC) is currently blocked by the ozone layer • High energy radiation (UVB) does the most immediate damage (sunburns) • But lower energy radiation (UVA) can penetrate deeper into the skin, leading to long term damage Source: N.A. Shaath. The Chemistry of Sunscreens. In: Lowe NJ, Shaath NA, Pathak MA, editors. Sunscreens, development, evaluation, and regulatory aspects. New York: Marcel Dekker; 1997. p. 263-283.

10. Ozone layer • Ozone in stratosphere, 10 to 50 km above surface • Ozone Can be depleted by free radical catalysts – NO, OH, Cl, Br – from natural / human sources (CFC’s) • Stratospheric ozone levels decreasing ~4% per year since ’70’s • More skin cancer? • Larger seasonal decrease in lower altitudes (troposphere) in polar regions: the ozone hole • CFC’s phased out globally by 1996 (Montreal Protocol, 1987) – will take decades to leave atmosphere • Ozone levels have stabilized • Recovery will take decades

11. Good ozone • In the stratosphere, absorbs 97+ % of solar UV, protecting life from harm • Produced by solar UV light from O2 : • O2+ UV (radiation < 240 nm) → 2 O • O + O2 → O3 • Ozone – oxygen cycle: • O3+ UV (< 320 nm) → O2 + O • This cycle heats the atmosphere slightly, so ozone is a minor greenhouse gas

12. 2. Nanoparticles and sunscreen • Nanoparticles: 1 to 100 nm in diameter, or about 10 to 1000 atomic diameters • Number of products using nanomaterials is growing very rapidly • Clothing, food and beverages, sporting goods, coatings, cosmetics, personal care, electronics • Sunscreens: many use nanomaterials • Some labeled as containing nanoparticles • Some not labeled

13. http://www.nanotechproject.org/inventories/consumer/analysis_draft/http://www.nanotechproject.org/inventories/consumer/analysis_draft/

14. Why Use Sunscreen? Too much unprotected sun exposure leads to: • Premature skin aging (e.g. wrinkles) • Sunburns • Skin cancer Sources: http://www.oasishospital.org/previousnews.html; http://wohba.com/archive/2005_03_01_archive.html

15. Skin Cancer Rates are Rising Fast • Probability of getting skin cancer: 1930 : 1 in 5,000 2004 : 1 in 65 2050 : 1 in 10… Skin cancer: • Is ~50% of all cancer cases • Has > 1 million cases diagnosed each year • Causes 1 person to die every hour • Causes of the increase: • Decreased ozone protection • Increased time in the sun • Increased use of tanning beds Sources: http://www.msnbc.msn.com/id/8379291/site/newsweek/ ; http://www.skincarephysicians.com/skincancernet/whatis.html; http://www.msu.edu/~aslocum/sun/skincancer.htm

16. A Brief History of Sunscreens: The Beginning • First developed for soldiers in WWII (1940s) to block “sunburn causing rays” These were called UVB rays WWII soldier in the sun Shorter wavelengths (more energy) called UVC Longer wavelengths (less energy) called UVA Sources: http://www.bbc.co.uk/wiltshire/content/articles/2005/05/05/peoples_war_feature.shtml http://www.arpansa.gov.au/is_sunys.htm

17. A Brief History of Sunscreens: The SPF Rating • Sunscreens first developed to prevent sunburn • Ingredients were good UVB blockers • SPF (Sunscreen Protection Factor) Number • Measures the strength of UVB protection only • Higher SPF # = more protection from UVB • Doesn’t tell you anything about protection from UVA • UVA causes cancer, skin aging • No official UVA ratings until now Sources: http://www.shop.beautysurg.com/ProductImages/skincare/14521.jpg and http://www.shop.beautysurg.com/ProductImages/skincare/14520.jpg

18. New FDA UVA Ratings (2012) • The phrase “broad spectrum” is meant to indicate protection against UVA • Products labeled “broad spectrum” will have to provide equal protection against UVB and UVA • Bathing suits: 3 tbsp every 2 hours

19. How much UV is there today • EPA UV index http://www.epa.gov/sunwise/uviscale.html • 1 = low risk, 11+ = extreme risk • Sometimes included in weather reports • Reflective surfaces (concrete, sand, snow, water) may make actual level higher than reported • Free Smartphone App: myUV Alert

20. Clothing • Ordinary clothing provides a good sun shield when dry (the tighter the weave, the better) but little or no protection when wet • Special sun-protective clothing is costly but works well wet or dry; it is a wise investment for children who tend to stay in or around water for hours. http://img.consumersearch.com/files/cs/imagecache/blog-entry/images/blog/sunscreenclothing.jpg

21. Know Your Sunscreen:Look at the Ingredients • Lotion has “inactive ingredients” • Don’t block UV light • UV blocking agents are “active ingredients” • Usually have more than one kind present • UV blocking agents suspended in a lotion • “Colloidal suspension” • Two kinds of active ingredients • Organic ingredients and inorganic ingredients Source: Original Image

22. Organic Ingredients: The Basics • Organic = Carbon Atoms • Hydrogen, oxygen & nitrogen atoms are also often involved • Structure • Covalent bonds • Exist as individual molecules • Size • Molecular formula determines size • Typically < 10 nm Octyl methoxycinnamate (C18H26O3) an organic sunscreen ingredient Sources: http://www.3dchem.com/molecules.asp?ID=135# and original image

23. Organic Ingredients: UV Absorption • Electrons capture the energy from UV rays • They jump to higher energy levels • The energy is released as infrared rays which are harmless (each ray is low in energy) hf=2.48 eV 3hf=2.48 eV Source: Adapted from http://www.3dchem.com/molecules.asp?ID=135#and http://members.aol.com/WSRNet/tut/absorbu.htm

24. Organic Ingredients: Absorption Range • Organic molecules only absorb UV rays whose energy matches difference between electron energy levels • Different kinds of molecules have different peaks & ranges of absorption; usually in UVB region • Using more than one kind of ingredient (molecule) gives broader protection One Ingredient Two Ingredients Three Ingredients Source: Graphs adapted from http://www.aims.gov.au/pages/research/projects/sunscreens/pages/sunscreens02.html

25. Inorganic Ingredients: The Basics • Atoms: Zinc or Titanium, Oxygen • Structure • Ionic molecules: ZnO, TiO2 • Cluster of ions • Formula unit doesn’t dictate size • Cluster (particle) size • Varies with # of ions in cluster • ~10 nm – 300 nm • Absorb thru whole UV spectrum up to 380 nm Detail of the ions in one cluster Group of TiO2 particles Source: http://www.microspheres-nanospheres.com/Images/Titania/TIO2%20P7.jpg and image adapted from http://www.cse.clrc.ac.uk/msi/projects/ropa.shtml

26. Why not use inorganics? • Appearance Matters • Traditional inorganic sunscreens have appear white on our skin • Many people don’t like how this looks, so they don’t use sunscreen with inorganic ingredients • Of the people who do use them, most apply too little to get full protection Source: http://www.4girls.gov/body/sunscreen.jpg

27. Why Do They Appear White? • Traditional ZnO and TiO2 clusters are large • (> 200nm) • Large clusters scatter visible light • (400-700 nm) • Maximum scattering occurs for wavelengths twice as large as the clusters • The scattered light is reflected to our eyes, appearing white Source: Original image

28. Waves and obstacles • Waves go around small obstacles • Waves scatter all around from obstacles of sizes comparable to a wavelength • Water wave (ripple tank) simulation: http://www.falstad.com/ripple/ • Organic sunscreen molecules are too small to scatter light ( < 10 nm) • How does absorption of light by inorganic compounds differ from absorption by organic molecules?

29. Inorganic Compounds: Energy Levels • Inorganic ingredients exist as particle clusters • Very large number of atoms involved • Electrons’ energy depends on their position in relation to all of them • Huge number of different energy levels possible ~200 nm TiO2 particle Source: Images adapted from http://www.cse.clrc.ac.uk/msi/projects/ropa.shtml

30. Inorganic Compounds: Absorption I • Because the energy levels are so closely spaced, we talk about them together as energy “bands” • Normal energy band for electrons (ground states) is called the “valence band” • Higher energy band (electrons are more mobile) is called the “conduction band” • In each band, there are many different energies that an electron can have • The energy spacing between the two bands is called the "energy gap” or "band gap“ Source: Original Image

31. Inorganic Compounds: Absorption II • Electrons can “jump” from anywhere in the valence band to anywhere in the conduction band • Inorganic Compounds are able to absorb all light with energy equal to or greater than the band gap energy Source: Original Images

32. Inorganic Compounds: Absorption Curve • This is the same as saying that all light absorbed must have a wavelength equal to or less than the wavelength corresponding to the band gap energy • Absorption curves have sharp cutoffs at this l • Cutoff l is characteristic of the kind of compound • Doesn’t depend on size of the cluster Source: Graph adapted from http://www.aims.gov.au/pages/research/projects/sunscreens/pages/sunscreens02.html

33. Inorganic Compounds: UV Protection • Inorganic Compounds with cut off wavelengths around 400 nm (ZnO and TiO2) are able to absorb almost the whole UV spectrum • Can be the only active ingredient in a sunscreen • Can also be combined with other ingredients for reasons such as appearance or cost • True for both nano and traditional forms (not dependant on size) Source: Graph adapted from http://www.aims.gov.au/pages/research/projects/sunscreens/pages/sunscreens02.html

34. Absorption Summary

35. Nanosized Inorganic Clusters • Maximum scattering occurs for wavelengths twice as large as the clusters • Make the clusters smaller (100 nm or less) and they won’t scatter visible light Source: Graph adapted from http://www.aims.gov.au/pages/research/projects/sunscreens/pages/sunscreens02.html

36. In Summary… • Nanoparticle sunscreen ingredients are small inorganic clusters that: • Provide good UV protection by absorbing both UVB and UVA light • Appear clear on our skin because they are too small to scatter visible light Source: http://www.smalltimes.com/images/st_advancednanotech_inside_.jpg

37. 3. Testing sunscreen activity • Use UV sensitive beads • Compare opacity/ transparency of samples for visible light and UV light • Beads absorb UV from 300 nm to 360 nm (UV A is 320 – 400 nm, UV B is 280 – 320 nm) • Make UV detector necklaces

38. Teacher note highlights • Safety. Do not look directly at the UV lamp • Liquids. Apply directly to bead or to clear plastic strips • Purchasing. See teacher notes handout • Making the testers. Melt beads in oven, glue to sticks http://graphics8.nytimes.com/images/2011/06/15/science/SUNSCREEN/SUNSCREEN-articleLarge.jpg

39. Available documents Handouts More on the website UV violet color guide Controlled Experiment On The Transmission Of Ultra-Violet Radiation (Jennifer) Web links UVA standards articles Sunscreen clothing – does it work? • This PowerPoint • Teacher guide • Student write-up • Consumer Reports sunscreen ratings