Good Ozone and Bad Ozone

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1 Good Ozone and Bad Ozone MEES, March 5, 2008 Mort Sternheim, Rob Snyder, STEM Education Institute Center for Hierarchical Manufacturing University of Massachusetts Amherst

Our sponsors National Science Foundation grant to the UMass Center for Hierarchical Manufacturing, award # 0531171 NASA grant to the STEM Education

2 Our sponsors National Science Foundation grant to the UMass Center for Hierarchical Manufacturing, award # NASA grant to the STEM Education Institute (ended), award # NNG05GN64G Advertisement: We are accepting teacher applications for International Polar Year and Nanotechnology Summer Institutes

3 Today s agenda Ozone and ultraviolet (UV) light Nanoparticles and sunscreen Hands on sunscreen activity Ozone is a health problem Measuring ozone handouts Today s materials on line:

4 The big ideas Ultraviolet light causes skin damage and cancer Ozone in the stratosphere absorbs UV, partly Sunscreen blocks UV, partly Nanoparticles in sunscreen improve blocking Tropospheric ozone is a major part of smog, damages plants, animals, and people

5 1. Ozone and UV 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!

6 The Sun s radiation spectrum Most of the sun s radiation is Ultraviolet (UV), Visible & Infrared (IR) : ~ 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 Source: Adapted from

Some types of electromagnetic radiation The sun emits several kinds of electromagnetic radiation: Visible (Vis), Infrared (IR) and Ultra Violet (UV).

7 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 High Energy Low Energy Each kind is distinguished by a characteristic wavelength, frequency and energy Higher energy radiation can damage our skin Source:

8 What is Radiation? Light radiation is often thought of as a wave with a wavelength (λ), 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:

9 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) E 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 E f f

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

10 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; p

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 + O 2 O3 Ozone oxygen cycle: O3 + UV (< 320 nm) O2 + O This cycle heats the atmosphere slightly, so ozone is a greenhouse gas

12 Ozone In the Atmosphere Thermosphere 50 Mesosphere % of ozone is in the stratosphere Troposphere 10% of ozone is in the troposphere Ozone (parts per 12 million) 8 0 Altitude (miles) Altitude (km) 80

Ozone is the Earth s natural sunscreen 100 60 Thermosphere UVc - 100% Absorption Mesosphere UVb - 90% Absorption UVa - 50%

13 Ozone is the Earth s natural sunscreen Thermosphere UVc - 100% Absorption Mesosphere UVb - 90% Absorption UVa - 50% Absorption & Scattering Troposphere Ozone (parts per million) Altitude (miles) Altitude (km) 80

14 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 sources Also from chlorofluorocarbons (CFCs) (freons) and bromofluorocarbons (halons) UV light produces free Cl, Br radicals Cl, Br catalyze chain reactions destroying ~100,000 ozone molecules Used in aerosols, refrigerators, air conditioners, fire extinguishers

15 Chemicals that Destroy Stratospheric Ozone Cl is much more abundant than Br Br is about 50 times more effective at O3 destruction From Ozone FAQ - see

16 Ozone depletion 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

17 Low level (tropospheric) ozone Formed by interaction of UV with hydrocarbons, nitrogen oxides from natural sources plus car exhausts, etc. Major air pollution (smog) component Can cause serious damage to lungs Fatal in very high concentrations for people, animals Damage to plants UNH Forest Watch looks at white pine needles which store data for 3 years Excellent school project Measure with ozone sensitive paper, new meters

18 Ozone levels 3 10 ppb: Threshold of perception. Typical indoor level when outdoor levels are low 50 ppb: Maximum allowed indoor levels 100 ppb: Maximum allowed in industrial work area ppb: Typical outdoor peak urban levels 300 ppb: Threshold for nasal, throat irritation 500 ppb: Smog alert #1 in Los Angeles. Can cause nausea, headaches; lead to lung edema.

19 Higher ozone levels ppb: Smog alerts #2, 3 in LA. Headaches, chest pains after 2 hours 12,000 ppb: Lethal for guinea pigs after 3 hrs 50,000 ppb: Lethal for humans after 60 minutes

20 2. Nanoparticles and sunscreen 1 nanometer = 10-9 meter ~ 10 atomic diameters Nanoparticles: 1 to 100 nm in diameter, or about 10 to 1000 atomic diameters Sunscreen PowerPoint and activities based on NanoSense web site

21 Nano Products Number of products using nanomaterials is growing very rapidly Doubling every year? Clothing, food and beverages, sporting goods, coatings, cosmetics, personal care Sunscreens: many use nanomaterials Some labeled as containing nanoparticles Some not labeled

22 pdf/workshop/rejeski.pdf

23 Why Use Sunscreen? Too much unprotected sun exposure leads to: Premature skin aging (e.g. wrinkles) Sunburns Skin cancer Sources:

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

increase: Decrease ozone protection Increased time in the sun Increased use of tanning beds Sources: http://www.msnb

24 Skin Cancer Rates are Rising Fast Probability of getting skin cancer: 1930 : 1 in 5, : 1 in : 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: Decrease ozone protection Increased time in the sun Increased use of tanning beds Sources: ;

25 Sun Radiation Summary UVC UVB UVA Vis IR Characteristic Wavelength (λ) I n c r e a si n g W a v e l e n g t h Radiation Type ~ nm (Short-wave UV) ~ nm (Mid-range UV) ~ nm (Long-wave UV) Energy per Photon I n c r e High Energy a si n Mediumg Energy E n e r g Low Energy y ~ nm % of Total Radiation Reaching Earth ~0% DNA Damage No Sunburn DNA Damage Skin Cancer No Tanning Skin Aging DNA Damage Skin Cancer No ~43 % None Currently Known Yes ~49% Heat Sensation (high λ IR) No (<1% of all UV) ~.35% (5% of all UV) ~6.5% (95 % of all UV) Lower Energy ~ ,000 nm Lowest Energy Effects on Visible to Human Skin Human Eye?

26 Which Sunscreen Should You Use??? New and Improved Now with Nano-Z Broadband Protection Safe for Children SPF 50 Goes on Clear

(more energy) called UVC Longer wavelengths (less energy) called UVA Sources: http://www.bbc.co.

27 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:

SPF # = more protection from UVB Doesn t tell you anything about protection from UVA Sources: http://www.shop.

28 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 Sources: and

A Brief History of Sunscreens: The UVA Problem UVA rays have no immediate visible effects but cause serious long term damage Cancer Skin aging Sunscreen

29 A Brief History of Sunscreens: The UVA Problem UVA rays have no immediate visible effects but cause serious long term damage Cancer Skin aging Sunscreen makers working to find UVA blockers No official rating of UVA protection yet Source: Twenty different skin cancer lesions

30 How do you know if your sunscreen is a good UVA blocker?

Know Your Sunscreen: Look at the Ingredients UV blocking agents suspended in a lotion Colloidal suspension Lotion has inactive ingredients Don t block UV light UV

31 Know Your Sunscreen: Look at the Ingredients UV blocking agents suspended in a lotion Colloidal suspension Lotion has inactive ingredients Don t block UV light UV blocking agents are active ingredients Usually have more than one kind present Two kinds of active ingredients Organic ingredients and inorganic ingredients Source: Original Image

formula determines size Typical a few to several dozen Å (<10 nm) Sources: http://www.3dchem.

32 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 Typical a few to several dozen Å (<10 nm) Sources: and original image Octyl methoxycinnamate (C18H26O3) an organic sunscreen ingredient

Organic Ingredients: UV Absorption 1. 2. 3.

48 ev The energy is released as infrared rays which are harmless (each ray is low in

33 Organic Ingredients: UV Absorption Electrons capture the energy from UV rays They jump to higher energy levels hf=2.48 ev The energy is released as infrared rays which are harmless (each ray is low in energy) 3hf=2.48 ev Source: Adapted from

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 and ranges

34 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 and ranges of absorption Using more than one kind of ingredient (molecule) gives broader protection One Ingredient Two Ingredients Three Ingredients Source: Graphs adapted from

35 Organic Ingredients: Absorption Range cont. Most organic ingredients that are currently used were selected because they are good UVB absorbers The FDA has approved 15 organic ingredients Sunscreen makers are trying to develop organic ingredients that are good UVA blockers Avobenzone (also known as Parasol 1789) is a new FDA approved UVA blocker Source:

36 How are inorganic sunscreen ingredients different from organic ones? How might this affect the way they absorb UV light?

Inorganic Ingredients: The Basics Atoms Involved Zinc or Titanium Oxygen Structure Ionic attraction Cluster of ions Formula unit doesn t dictate size Size Varies with # of ions in cluster ~10 nm 300

37 Inorganic Ingredients: The Basics Atoms Involved Zinc or Titanium Oxygen Structure Ionic attraction Cluster of ions Formula unit doesn t dictate size Size Varies with # of ions in cluster ~10 nm 300 nm Detail of the ions in one cluster Group of TiO2 particles Source: and image adapted from

Inorganic Ingredients: Cluster Size Inorganic ingredients come in different cluster sizes (sometimes called particles ) Different number of ions can cluster together Must be a multiple of the formula

38 Inorganic Ingredients: Cluster Size Inorganic ingredients come in different cluster sizes (sometimes called particles ) Different number of ions can cluster together Must be a multiple of the formula unit ZnO always has equal numbers of Zn and O atoms TiO2 always has twice as many O as Ti atoms ~100 nm TiO2 particle ~200 nm TiO2 particle Source: Images adapted from

39 Inorganic Ingredients: UV Absorption Inorganics have a different absorption mechanism than organics Absorb consistently through whole UV range up to ~380nm Source: Graph adapted from

40 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:

41 Why Do They Appear White? Traditional ZnO and TiO2 clusters are large (> 200nm) Large clusters scatter visible light ( 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

42 Organic Sunscreen Molecules are Too Small to Scatter Light ~200 nm TiO2 particle (Inorganic) Methoxycinnamate (Organic) (Note that these images are not drawn to scale) Source: Images adapted from and

43 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:

44 What could we do to inorganic clusters to prevent them from scattering visible light? Source: Adapted from

Nanosized Inorganic Clusters Maximum scattering occurs for wavelengths twice as large as the clusters Make the clusters smaller (100 nm or less)

45 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

46 Nano-Sunscreen Appears Clear Nanosized ZnO particles Source: Large ZnO particles

In Summary Nanoparticle sunscreen ingredients are small inorganic clusters that: Provide good UV protection by absorbing both UVB and UVA light

47 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:

48 Essential Questions: Time for Answers 1. What are the most important factors to consider in choosing a sunscreen? 2. How do you know if a sunscreen has nano ingredients? 3. How do nano sunscreen ingredients differ from other ingredients currently used in sunscreens?

49 Testing sunscreen activity Use UV sensitive beads Compare opacity/transparency of samples for visible light and UV light

50 How can we measure ground level ozone? Ozone paper Moderate cost Adequate for relative measurements Used for NASA Globe project But: Inconsistent sensitivity one batch to the next Insensitive to low ozone levels

51 Sources for ozone sensitive papers Vistanomics Eco badge kit (30 test cards), $38.95 Eco badge lesson books middle school, 150 cards, Ozone Services Ozone test strips, 105 ppb, 12 strips, $ strips, $33.50

52 Miniature Ozone Sensor for K-12 Outreach Joyce Cheung, Paul Voss, Smith College David Greenberg, Greenfield Community College

53 Miniature ozone sensor Under development at Smith College Measures ozone, pressure, pressure Uses a semiconductor to detect ozone Works at low and high ozone levels Measure at 10 minute intervals and store 2 weeks of data Accurate data at parts per billion level Moderate cost

54 Instrument Intercomparison Red: AIRNow-Tech, Chicopee Station Blue: Smith College, McConnell Building Black: Smith College, Whately AirMap Station

Ozone: Earth s shield from UV radiation

Outline Ozone: Earth s shield from UV radiation Review electromagnetic radiation absorptivity by selective gases temperature vs. height in atmosphere Ozone production and destruction natural balance anthropogenic