WHAT IS OZONE DEPLETION?

WHAT IS OZONE?

Triatomic form of oxygen (O3) Strong oxidant (chemically reactive) In lower atmosphere = pollutant In stratosphere = protective “shield” • 90% of O3 found b/w 15-40 km altitude • 99% of UV radiation screened by

ozone Ozone absorbs ultraviolet (UV) radiation

WHAT IS UV LIGHT? Ultraviolet (UV) Radiation Smaller wavelength, more

energy 3 types (wavelength): 1. UVC: shortest, most

energetic, most absorbed in stratosphere

2. UVA: longest, transmitted to Earth, causes some damage

3. UVB: MOST DANGEROUS! Strongly absorbed by O3 in stratosphere

but with less O3 there is more UVB…

WHAT DAMAGE DOES LESS OZONE CAUSE? Skin Cancer Epidemic Most common cancer in US Ultraviolet radiation (UVB)

damages skin 90% increase since 1970; 1

in 5 will contract; 40 – 50% over 65

Related to ozone depletion PROTECT YOURSELF! • 50% of exposure by 18 • Cumulative effect

WHERE IS THE OZONE HOLE?

British Antarctic Survey scientists first measured O3 in 1957

They published depleted levels of O3 in 1985

Show clear decrease since 1970’s

NOT an actual “hole” but decreased concentration

WHY DOES IT FORM OVER ANTARCTICA?

IT’S COLD!

Polar stratospheric clouds form ~20 km above poles in temps 195-190 K (-78 to -83 C) when sulfuric acid freezes

Polar vortex isolates air mass Clouds hold nitrogen,

removing chlorine sink (nitrogen oxides help remove Cl)

In the spring, sunlight sets off ozone depletion reactions

WHAT CAUSES OZONE DEPLETION?

Hypothesis that anthropogenic CFCs havedepleted O3 suggested in 1974 Immediately controversial!! Everyday products had CFCs • Propellants in spray cans • Refrigerants • Cleaning agents • Styrofoam

Two reactions define cycle of destruction, a catalytic chain reaction:

1. Cl + O3 ¯> ClO + O2

2. ClO + O ¯> Cl + O2

Estimated that single Cl atom can gothrough cycle 200 times in stratosphere! Further estimated that single Cl atomdestroys ~100,000 ozone molecules in 1-2 years

MONTREAL PROTOCOL 1987

Plan for eventual reduction of global CFCs by 50% of 1986 levels; stop by 1999

Because of dramatic evidence of destruction, timetables shortened; US ended production in 1995

Even if all production of bad chemicals stopped today, problem would not go away

About 35% of CFC-12 will still be around in 2100, and ~15% in 2200

SUMMARY Ozone is a pollutant in lower atmosphere, and an

effective measure of poor air quality. Ozone is a GOOD thing, up in the stratosphere We have caused a decrease in the stratospheric

ozone concentration, leading to increased incidents of skin cancer, cataracts, suppressed immune system, damage to food crops

Take precautions in the sun!