Ozone depletion E.4.2-Ozone depletion E.4.2-4.34.3

Presentation by Dina GoodmanPresentation by Dina Goodman

What is the ozone layer, What is the ozone layer, anyway?anyway?

A layer that occurs in stratosphere between 12 A layer that occurs in stratosphere between 12 km and 50 km above the Earth’s surface.km and 50 km above the Earth’s surface.

The natural “steady state” of the ozone layer has The natural “steady state” of the ozone layer has been lost because of ozone-depleting pollutant.been lost because of ozone-depleting pollutant.

About 4% of the ozone layer has been lost per About 4% of the ozone layer has been lost per decade since the 1970s.decade since the 1970s.

The ozone layer prevents most harmful UVB The ozone layer prevents most harmful UVB wavelengths (270–315 nm) of UV light from wavelengths (270–315 nm) of UV light from passing into the Earth’s atmosphere. Thus several passing into the Earth’s atmosphere. Thus several biological consequences as increases in skin biological consequences as increases in skin cancer, cataracts, damage to plants, and cancer, cataracts, damage to plants, and reduction of plankton populations are attributed reduction of plankton populations are attributed to ozone depletion.to ozone depletion.

E.4.2- Ozone-Depleting E.4.2- Ozone-Depleting PollutantsPollutants

Chlorofluorocarbons (CFCs)Chlorofluorocarbons (CFCs) Contains: Cl, F, C Contains: Cl, F, C Sources: developed in 1930s for various of industrial, Sources: developed in 1930s for various of industrial,

commercial, and household applications. CFC have commercial, and household applications. CFC have desirable safety characteristics (non-toxic, non-desirable safety characteristics (non-toxic, non-flammable, and non-reactive) and stable flammable, and non-reactive) and stable thermodynamic properties, so they are ideal for many thermodynamic properties, so they are ideal for many applications, e.g coolants for commercial and home applications, e.g coolants for commercial and home refrigeration units, aerosol propellants, electronic refrigeration units, aerosol propellants, electronic cleaning solvents, and blowing agents. cleaning solvents, and blowing agents.

In 1973 discovered to be a catalytic agent in ozone In 1973 discovered to be a catalytic agent in ozone destruction because the ultraviolet radiation breaks the destruction because the ultraviolet radiation breaks the weak C-Cl bond and form radicals.weak C-Cl bond and form radicals.

E.4.2- Ozone-Depleting Pollutants E.4.2- Ozone-Depleting Pollutants

cont.cont.

Oxides of nitrogen (NOOxides of nitrogen (NOxx) ) Nitric Oxide: produced during combustion. So in areas Nitric Oxide: produced during combustion. So in areas

with a large amount of vehicle traffic, e.g. Atlanta, with a large amount of vehicle traffic, e.g. Atlanta, the amount of nitrogen oxides emitted into the the amount of nitrogen oxides emitted into the atmosphere can be quite significant.atmosphere can be quite significant.

Nitrous oxide: laughing gas, propellant Nitrous oxide: laughing gas, propellant When exposed to sunlight, Oxides of nitrogen react When exposed to sunlight, Oxides of nitrogen react

and form photochemical smog.and form photochemical smog.

E.4.3 Alternatives to E.4.3 Alternatives to CFCsCFCs

Since the creation of the Montreal Protocol in 1987, fewer Since the creation of the Montreal Protocol in 1987, fewer CFCs have been used. CFCs have been used.

Alternatives should have similar properties, such as low Alternatives should have similar properties, such as low reactivity, low toxicity, and low flammability, but they do reactivity, low toxicity, and low flammability, but they do not contain the weak C-Cl bond. Furthermore they not contain the weak C-Cl bond. Furthermore they shouldn’t absorb infrared reaction, or else will be shouldn’t absorb infrared reaction, or else will be greenhouse gases.greenhouse gases.

Examples: - Hydrocholorofluorocarbons (HCFCs) e.g. Examples: - Hydrocholorofluorocarbons (HCFCs) e.g. CHFCHF22ClCl

- Hydrofluorocarbons (HFC) e.g. CF- Hydrofluorocarbons (HFC) e.g. CF33CHCH22FF

- Hydrocarbons e.g. C- Hydrocarbons e.g. C44HH1010