Do Now:

• We know that our ozone layer is critical for life on earth. However, can it also be harmful if Ozone is found in other atmospheric layers?

Aim: How is ozone formed and destroyed?

Ozone layer/shield

• Ozone (O3) absorbs most of the UV radiation from the sun and filters its rays

• This UV absorbtion causes it to heat up the part of the stratophere that’s closer to the sun (farthest from Earth)

Ozone’s effects

• Tropospheric O3= BAD

– Causes lung damage because we breathe it in

– Greenhouse gas so it traps heat near Earth’s surface

• Stratospheric O3 = GOOD

– Shields us from UV rays• Earth’s sunscreen :)

Ozone Depletion

• Thinning of the stratospheric ozone shield

• Mostly occurring over South Pole

• What problems can result because of this?

Destruction of ozone

• Chlorofluorocarbons (CFCs) react to destroy ozone

• UV rays easily break the bond between the Cl-FC

• Free chlorine attacks Ozone in the reaction O3 +Cl --> O2 + (Cl+O)

• The bond between Cl – O is unstable so it is easily broken leaving the Cl to attack another ozone molecule

Pic: CFC destroying Ozone

CFCs • developed in the early 1930s • desirable safety characteristics

– non-toxic, non-flammable, and non-reactive with other chemical compounds.

• stable thermodynamic properties

• used in a variety of industrial, commercial, and household applications. – coolants for commercial and

home refrigeration units, aerosol propellants, electronic cleaning solvents, and blowing agents.

Greenhouse Gas Build up

#1 Carbon Dioxide (CO2)

– Fossil fuel use– Deforestation

#2 Methane (CH4)

– Microbial fermentation at landfills– Coal & oil deposits– Natural gas pipelines– Cows waste (manure)

Greenhouse Gas Build up cont’d…

#3 Nitrous Oxides (NOx)

– Biomass burning– Chemical fertilizers – Fossil fuels burning

Chart: Greenhouse vs Ozone Shield

Greenhouse Effect

Ozone Shield

Where? Troposphere Stratosphere

What happens? Traps heat near Earth’s surface

Filters UV radiation

Benefits Keeps Earth warm enough for life to exist

Protects us from sun’s harmful rays forming cancer & from overheating

Which gases? Water vapor, carbon dioxide, methane

Oxygen gas, Ozone

Problem Global warming Ozone depletion

If problem persists

Annual increase in temp. leads to ecosystem destructions

More UV radiation exposure resulting in more cancer

Pic: Too many greenhouse gases