2 WHAT IS OZONE? Triatomic form of oxygen (O3) Strong oxidant (chemically reactive)In lower atmosphere = pollutantIn stratosphere = protective “shield”• 90% of O3 found b/w km altitude• 99% of UV radiation screened by ozoneOzone absorbs ultraviolet (UV) radiation
3 WHAT IS UV LIGHT? Ultraviolet (UV) Radiation Smaller wavelength, more energy3 types (wavelength):1. UVC: shortest, most energetic, most absorbed in stratosphere2. UVA: longest, transmitted to Earth, causes some damage3. UVB: MOST DANGEROUS! Strongly absorbed by O3 in stratospherebut with less O3 there is more UVB…
4 WHAT DAMAGE DOES LESS OZONE CAUSE? Skin Cancer EpidemicMost common cancer in USUltraviolet radiation (UVB) damages skin90% increase since 1970; 1 in 5 will contract; 40 – 50% over 65Related to ozone depletionPROTECT YOURSELF!• 50% of exposure by 18• Cumulative effect
5 WHERE IS THE OZONE HOLE?British Antarctic Survey scientists first measured O3 in 1957They published depleted levels of O3 in 1985Show clear decrease since 1970’sNOT an actual “hole” but decreased concentration
6 WHY DOES IT FORM OVER ANTARCTICA? IT’S COLD!Polar stratospheric clouds form ~20 km above poles in temps K (-78 to -83 C) when sulfuric acid freezesPolar vortex isolates air massClouds hold nitrogen, removing chlorine sink (nitrogen oxides help remove Cl)In the spring, sunlight sets off ozone depletion reactions
7 WHAT CAUSES OZONE DEPLETION? Hypothesis that anthropogenic CFCs havedepleted O3 suggested in 1974Immediately controversial!!Everyday products had CFCs• Propellants in spray cans• Refrigerants• Cleaning agents• Styrofoam
8 Two reactions define cycle of destruction, a catalytic chain reaction: 1. Cl + O3 ¯> ClO + O22. ClO + O ¯> Cl + O2Estimated 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
9 MONTREAL PROTOCOL 1987Plan for eventual reduction of global CFCs by 50% of 1986 levels; stop by 1999Because of dramatic evidence of destruction, timetables shortened; US ended production in 1995Even if all production of bad chemicals stopped today, problem would not go awayAbout 35% of CFC-12 will still be around in 2100, and ~15% in 2200
10 SUMMARYOzone is a pollutant in lower atmosphere, and an effective measure of poor air quality.Ozone is a GOOD thing, up in the stratosphereWe have caused a decrease in the stratospheric ozone concentration, leading to increased incidents of skin cancer, cataracts, suppressed immune system, damage to food cropsTake precautions in the sun!
Your consent to our cookies if you continue to use this website.