1. Ozone, UV, and Nanoparticles
Mort Sternheim
STEM Education Institute
6/29/2008

2. Ozone, UV, and Nanoparticles
Today’s agenda
Ozone and ultraviolet light
Nanoparticles and sunscreen
Hands on activity
Sunscreen PowerPoint and activities based on
NanoSense web site:
Ozone and ultraviolet light
Nanoparticles and sunscreen
Hands on activity
Sunscreen PowerPoint and activities based on
NanoSense web site:

3. Ozone, UV, and Nanoparticles
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. Ozone, UV, and Nanoparticles
1. What 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
Ozone, UV, and Nanoparticles
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

6. Some types of electromagnetic radiation
Ozone, UV, and Nanoparticles
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:

7. Ozone, UV, and Nanoparticles
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:

8. Radiation energy comes in packets or photons
Ozone, UV, and Nanoparticles
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  f E 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. Ozone, UV, and Nanoparticles
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

10. Ozone, UV, and Nanoparticles
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

11. Ozone, UV, and Nanoparticles
Ozone is the Earth’s natural sunscreen
100 60
Thermosphere 80 50
UVc - 100% Absorption
Mesosphere
UVb - 90% Absorption
UVa - 50% Absorption & Scattering 40 60
Altitude (km)
Altitude (miles) 30 40 20 20 10
Troposphere 2 4 6 8
Ozone (parts per million) 11 11

12. Ozone, UV, and Nanoparticles
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

13. Chemicals that Destroy Stratospheric Ozone
Ozone, UV, and Nanoparticles
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
From Ozone FAQ - see 13

14. Ozone, UV, and Nanoparticles
Ozone depletion
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

15. 2. Nanoparticles and sunscreen
Ozone, UV, and Nanoparticles
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
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

16. Ozone, UV, and Nanoparticles

17. Ozone, UV, and Nanoparticles
Why Use Sunscreen?
Too much unprotected sun exposure leads to:
Premature skin aging (e.g. wrinkles)
Sunburns
Skin cancer
Sources:

18. Skin Cancer Rates are Rising Fast
Ozone, UV, and Nanoparticles
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: ;

19. Ozone, UV, and Nanoparticles
Sun Radiation Summary
Radiation
Type
Characteristic
Wavelength (l)
Energy per Photon
% of
Total Radiation
Reaching Earth
Effects on Human Skin
Visible to Human Eye?
UVC
~ nm
(Short-wave UV)
High Energy
~0%
(<1% of all UV)
DNA Damage No
UVB
~ nm
(Mid-range UV)
Medium Energy
~.35%
(5% of all UV)
Sunburn
Skin Cancer
UVA
~ nm
(Long-wave UV)
Low Energy
~6.5%
(95 % of all UV)
Tanning
Skin Aging
Vis
~ nm
Lower Energy
~43 %
Yes IR
~ ,000 nm
Lowest Energy
~49%
Increasing
Energy
Increasing
Wavelength

20. Which Sunscreen Should You Use???
Ozone, UV, and Nanoparticles
Which Sunscreen Should You Use???
New and Improved
Now with Nano-Z
Broadband Protection
Safe for Children
SPF 50
Goes on Clear

21. A Brief History of Sunscreens: The Beginning
Ozone, UV, and Nanoparticles
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:

22. A Brief History of Sunscreens: The SPF Rating
Ozone, UV, and Nanoparticles
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

23. A Brief History of Sunscreens: The UVA Problem
Ozone, UV, and Nanoparticles
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
Twenty different skin cancer lesions
Source:

24. Ozone, UV, and Nanoparticles
How do you know if your sunscreen is a good UVA blocker?

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

26. Organic Ingredients: The Basics
Ozone, UV, and Nanoparticles
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)
Octyl methoxycinnamate (C18H26O3)
an organic sunscreen ingredient
Sources: and original image

27. Organic Ingredients: UV Absorption
Ozone, UV, and Nanoparticles
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

28. Organic Ingredients: Absorption Range
Ozone, UV, and Nanoparticles
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

29. Organic Ingredients: Absorption Range cont.
Ozone, UV, and Nanoparticles
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:

30. Ozone, UV, and Nanoparticles
How are inorganic sunscreen ingredients different from organic ones?
How might this affect the way they absorb UV light?

31. Inorganic Ingredients: The Basics
Ozone, UV, and Nanoparticles
Inorganic Ingredients: The Basics
Atoms involved
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
Detail of the ions in one cluster
Group of TiO2 particles
Source: and image adapted from

32. Inorganic Ingredients: Cluster Size
Ozone, UV, and Nanoparticles
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

33. Inorganic Ingredients: UV Absorption
Ozone, UV, and Nanoparticles
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

34. Ozone, UV, and Nanoparticles
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:

35. Why Do They Appear White?
Ozone, UV, and Nanoparticles
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

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

37. Ozone, UV, and Nanoparticles
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:

38. Ozone, UV, and Nanoparticles
What could we do to inorganic clusters to prevent them from scattering visible light?
Source: Adapted from

39. Nanosized Inorganic Clusters
Ozone, UV, and Nanoparticles
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

40. Ozone, UV, and Nanoparticles
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:

41. Essential Questions: Time for Answers
Ozone, UV, and Nanoparticles
Essential Questions: Time for Answers
What are the most important factors to consider in choosing a sunscreen?
How do you know if a sunscreen has “nano” ingredients?
How do “nano” sunscreen ingredients differ from other ingredients currently used in sunscreens?

42. 3. Testing sunscreen activity
Ozone, UV, and Nanoparticles
3. Testing sunscreen activity
Use UV sensitive beads
Compare opacity/ transparency of samples for visible light and UV light