Good Ozone and Bad Ozone

MEES, March 5, 2008

Mort Sternheim, mort@umassk12.netRob Snyder, snyder@umassk12.net

STEM Education InstituteCenter for Hierarchical ManufacturingUniversity of Massachusetts Amherst

MEES, March 5, 2008

Mort Sternheim, mort@umassk12.netRob Snyder, snyder@umassk12.net

STEM Education InstituteCenter for Hierarchical ManufacturingUniversity of Massachusetts Amherst

Our sponsors• National Science

Foundation grant to the UMass Center for Hierarchical Manufacturing, award # 0531171

• NASA grant to the STEM Education Institute (ended), award # NNG05GN64G

Advertisement: We are accepting teacher applications for International

Polar Year and Nanotechnology Summer Institutes

Today’s agenda1. Ozone and ultraviolet (UV) light2. Nanoparticles and sunscreen

• Hands on sunscreen activity3. Ozone is a health problem

• Measuring ozone handouts

Today’s materials on line:www.umassk12.net/nano/MEES

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

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!

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 skinSource: 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 (λ), 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 greenhouse gas

12Ozone (parts per million)

0

20

40

60

80

100

Alti

tude

(km

)

Troposphere

Mesosphere

Thermosphere

Ozone In the AtmosphereA

ltitude (miles)

10

0

20

30

40

50

60

90% of ozone is in the stratosphere

0 2 4 6 8

10% of ozone is in the troposphere

13

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

Alti

tude

(km

)

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

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• 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

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

– www.forestwatch.sr.unh.edu– Excellent school project

• Measure with ozone sensitive paper, new meters

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• 150 - 500 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.

Higher ozone levels• 1000 – 1500 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

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– http://nanosense.org/activities/clearsunscreen

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

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 FastSkin 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:• Decrease 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 (λ)

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 DamageSkin Cancer

No

Vis ~400-700 nmLower Energy

~43 % None Currently Known

Yes

IR ~700-120,000 nmLowest Energy

~49% Heat Sensation(high λ IR)

No

Sun Radiation Summary

Increasing Energy

Increasing Wavelength

Which Sunscreen Should You Use???

New and ImprovedNow 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 raysWWII 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 yet

Source: 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 attraction– Cluster of ions– Formula unit doesn’t dictate

size• 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

Nano-Sunscreen Appears Clear

Source: http://www.science.org.au/sats2003/images/barber-slide3.jpg

Nanosized ZnO particles

Large ZnO particles

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?

Testing sunscreen activity

• Use UV sensitive beads• Compare

opacity/transparency of samples for visible light and UV light

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

Sources for ozone sensitive papers• Vistanomics

– www.ecobadge.com– Eco badge kit (30 test cards), $38.95– Eco badge lesson books “middle school,” 150 cards,

119.95• Ozone Services

– www.ozonelab.com/products/OLM/o3ts.htm– Ozone test strips, 105 ppb, 12 strips, $13.50– 30 strips, $33.50

Miniature Ozone Sensor for K-12 Outreach

Joyce Cheung, Paul Voss, Smith College

David Greenberg, Greenfield Community College

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

Instrument IntercomparisonRed: AIRNow-Tech, Chicopee StationBlue: Smith College, McConnell BuildingBlack: Smith College, Whately AirMap Station