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Today’s agenda
1. Ozone and ultraviolet light2. Nanoparticles and sunscreen3. Hands on activity
Sunscreen PowerPoint and activities based on
NanoSense web site: http://nanosense.org/activities/clearsunscreen
1. Ozone and ultraviolet light2. Nanoparticles and sunscreen3. Hands on activity
Sunscreen PowerPoint and activities based on
NanoSense web site: http://nanosense.org/activities/
clearsunscreen
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
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!
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
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
Source: http://www.arpansa.gov.au/is_sunys.htm
High Energy Low Energy
What is Radiation?
• Light radiation is often thought of as a wave with a wavelength (), speed (c), and frequency (f) related by
Source: http://www.pueblo.gsa.gov/cic_text/health/sun_uv/sun-uv-you.htm
• 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.
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 fE
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
• 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.
Skin Damage
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
UVc - 100% AbsorptionUVb - 90% Absorption
UVa - 50% Absorption & Scattering
Ozone is the Earth’s natural sunscreen
Ozone (parts per million)
0
20
40
60
80
100
Alt
itud
e (k
m)
Troposphere
Mesosphere
Thermosphere
Altitude (m
iles)
10
0
20
30
40
50
60
0 2 4 6 8
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
16%
32%
23%
12%
7%5%
1%4%
0
3400
3000
2000
1000
(CH3CCl3)
(e.g., HCFC-22 = CHClF2)
(CCl2FCClF2)
Naturalsources
Other gasesMethyl chloroform
HCFCs
CFC-113
Carbon tetrachloride (CCl4)
CFC-11 (CCl3F)
CFC-12 (CCl2F2)
Methyl chloride (CH3Cl)
0
20
15
10
5
15%
27-42%
5-20%20%
14%
4%
Methyl bromide (CH3Br)
Halon-1211 (CBrCIF 2)
Halon-1301 (CBrF3)
Other halons
Very-short lived gases (e.g., bromoform = CHBr3)
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 http://www.unep.org/ozone/faq.shtmlFrom Ozone FAQ - see http://www.unep.org/ozone/faq.shtml
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
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
http://www.masspolicy.org/pdf/
workshop/rejeski.pdf
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
Skin Cancer Rates are Rising Fast
Skin cancer:• Is ~50% of all cancer
cases• Has > 1 million cases
diagnosed each year• Causes 1 person to
die every hour
Probability of getting skin cancer:1930 : 1 in 5,0002004 : 1 in 652050 : 1 in 10…
http://www.skincarephysicians.com/skincancernet/whatis.html; http://www.msu.edu/~aslocum/sun/skincancer.htm
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/ ;
Radiation
Type
Characteristic Wavelength
(
Energy per Photon
% of Total
Radiation Reaching
Earth
Effects on Human
Skin
Visible to
Human Eye?
UVC ~200-290 nm(Short-wave UV)
High Energy
~0%
(<1% of all UV)
DNA Damage
No
UVB ~290-320 nm(Mid-range UV) Medium Energy
~.35%
(5% of all UV)
SunburnDNA
DamageSkin Cancer
No
UVA ~320-400 nm (Long-wave UV)
Low Energy
~6.5%
(95 % of all UV)
TanningSkin Aging
DNA Damage
Skin Cancer
No
Vis ~400-700 nmLower Energy
~43 % Yes
IR ~700-120,000 nm Lowest Energy
~49% No
Sun Radiation Summary
Increasing Energy
Increasing Wavelength
Which Sunscreen Should You Use???
New and Improved
Now with Nano-Z
SPF 50Goes on Clear
Safe for Children
Broadband Protection
Sources: http://www.bbc.co.uk/wiltshire/content/articles/2005/05/05/peoples_war_feature.shtml http://www.arpansa.gov.au/is_sunys.htm
A Brief History of Sunscreens: The Beginning
• First developed for soldiers in WWII (1940s) to block “sunburn causing rays”
Shorter wavelengths (more energy) called UVC
Longer wavelengths (less energy) called UVA
These were called UVB rays
WWII soldier in the sun
Sources: http://www.shop.beautysurg.com/ProductImages/skincare/14521.jpg and http://www.shop.beautysurg.com/ProductImages/skincare/14520.jpg
A Brief History of Sunscreens: The SPF Rating
• 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
• Sunscreens first developed to prevent sunburn– Ingredients were good UVB blockers
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 yetSource: http://www.cs.wright.edu/~agoshtas/fig8.jpg
Twenty different skin cancer lesions
How do you know if your sunscreen is a good UVA
blocker?
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
Source: Original Image
• UV blocking agents suspended in a lotion– “Colloidal suspension”
• Two kinds of active ingredients– Organic ingredients and inorganic ingredients
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: http://www.3dchem.com/molecules.asp?ID=135# and original image
Octyl methoxycinnamate (C18H26O3)
an organic sunscreen ingredient
Organic Ingredients: UV Absorption
1. Electrons capture the energy from UV rays
2. They jump to higher energy levels
3. The energy is released as infrared rays which are harmless (each ray is low in energy)
Source: Adapted from http://www.3dchem.com/molecules.asp?ID=135#and http://members.aol.com/WSRNet/tut/absorbu.htm
hf=2.48 eV 3hf=2.48 eV
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 http://www.aims.gov.au/pages/research/projects/sunscreens/pages/sunscreens02.html
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: http://jchemed.chem.wisc.edu/JCEWWW/Features/MonthlyMolecules/2004/Oct/JCE2004p1491fig4.gif
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 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
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
Group of TiO2 particles
Detail of the ions in one cluster
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 http://www.cse.clrc.ac.uk/msi/projects/ropa.shtml
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 http://www.aims.gov.au/pages/research/projects/sunscreens/pages/sunscreens02.html
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
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
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 http://www.cse.clrc.ac.uk/msi/projects/ropa.shtml and http://www.3dchem.com/molecules.asp?ID=135#
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/
What could we do to inorganic clusters to prevent them from
scattering visible light?
Source: Adapted from http://www.loc.gov/rr/scitech/mysteries/images/sunscreen2.jpg
Nanosized Inorganic Clusters
Source: Graph adapted from http://www.aims.gov.au/pages/research/projects/sunscreens/pages/sunscreens02.html
• 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
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
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?
3. Testing sunscreen activity
• Use UV sensitive beads
• Compare opacity/ transparency of samples for visible light and UV light