Topic 6 - Atmosphere

composition of the earths atmosphere

• nitrogen 78%

• oxygen 21%

• argon 0.93%

• neon 0.002%

• helium, krypton and xenon

• water

• carbon dioxide

• ozone

the atmosphere is maintained by earths…

gravitational forces which create air pressure

layers of the earths atmosphere

• troposphere

• stratosphere

• mesosphere

• thermosphere

troposphere

• closest to the earth’s surface, extends up to about 10km above sea level

• The earth surface absorbs heat from the sun

• Wind speeds increase with height

• Most of the atmospheric mass is found, includes nearly all the water vapour, clouds and pollutants

• Most of our weather occurs

• Humans and other organisms have most interaction through exchange of gases or through introduction of pollutants

• The greenhouse effect occurs and helps to regulate the temperature of the earth

what is the greenhouse effect?

atmospheric heating phenomenon in which the Earth experiences rise in temperature because of greenhouse gasses in the atmosphere allow incoming sunlight to pass through but trap heat radiated from the earth's surface

energy from the sun enters as…

short wave radiation

heat energy is radiated as…

long wave radiation

green house gasses absorb…

long wave radiation

albedo effect

when solar energy is reflected back into the atmosphere through clouds, ice and snow

greenhouse gasses

• water vapour

• carbon dioxide

• methane

• nitrous oxide

• CFC and HCFC

• Perfluorocarbon

• Sulphur hexa-fluoride

water vapour

• the most abundant GHG

• A rise in temperature results in more water vapour leading to further warming, which allows more water to evaporate

• positive feedback cycle continues

Carbon dioxide

• concentrations are increased by burning of fossil fuels, respiration, volcanic activity and deforestation

methane

arises from emissions from livestock, anaerobic decomposition of waste, rice cultivation and fossil fuels

nitrous oxide

sources include fertilizers, combustion and industrial processes

CFCs and HCFC

have been used as liquid coolants (in refrigerators and air conditioning systems), in the production of plastic foam and as industrial solvents

Perfluorocarbon

is used in production of aluminium

Sulphur hexa-fluoride

is used in production of magnesium

Stratosphere

• extends from 10 to 50km above sea level

• Stratospheric ozone absorbs UV radiation from the sun.

• Temperature is constant at about -60°C in the lower part of the stratosphere, which is shielded by the ozone layer but then increases with altitude

• The air is dry

• Winds increase with height

mesosphere

• ranges from about 50 to 80km

• Without the presence of ozone or other particulates to absorb UV radiation, the temperature declines with height

• It is the coldest part of the atmosphere with temperatures falling to -100°C.

• There are strong winds with speeds up to around 3,000km/h

thermosphere

• This layer extends beyond about 80km to between 500km and 1,000km

• UV and X-radiation from the sun is absorbed which breaks apart molecules into atoms (oxygen, nitrogen and helium atoms are the main components in the upper thermosphere).

• The temperature increases with height and can reach beyond 2,000°C. This heat can cause the layer to expand causing variation in depth overtime from 500 to 1,000km

ionosphere

located within the thermosphere and comprises of an area in which the particles are electrically charged

what absorbs the most amount of UV

• ozone in the stratospheric layer

which types of UV rays can ozone absorb

• UV-B (some is absorbed)

• UV-C (all is absorbed)

UV-A wavelength

• longest wavelength

• 315-400nm

UV-B wavelength

280-315nm

UV-C wavelength

• shortest wavelength with highest energy

• 100-280nm

which is the most dangerous UV to humans?

UV-B

Ozone levels are measured in …

• Dobson Units (DU)

• which is the depth the ozone molecules would occupy at standard temperature and pressure (STP) of 0°C (273 Kelvin) and 1 Atmosphere

1DU =

= 0.01mm of ozone

thereats to staratosphere

• CFC’s

• Natural emissions of ozone depleting substances (volcano eruptions, release nitrogen oxide and sulphate particles)

management of stratospheric ozone

• international agreements (montreal protocol 1987)

secondary pollutants

pollutants formed when primary pollutants react in the atmosphere

types of secondary pollutants

• acid rain

• ozone

how is acid rain formed

formed when nitrogen oxide and sulphur dioxide react with water

how is ozone formed?

formed when nitrogen dioxide and hydrocarbons react in the presence of sunlight energy

photochemical smog

Photochemical smog occurs when sunlight activates reactions between nitrogen oxides (NOx) and volatile organic compounds (VOCs) resulting in the formation of ozone and peroxyacyl nitrates (PAN)

what are VOC’s (volatile organic compounds)

VOCs are carbon based compounds with a low boiling point such as propane, butane and formaldehydes

ozone in the statosphere

• “good ozone”

• reflects UV B and UV C rays

• protects life on earth from UV ray damage

ozone in the troposhere

• “bad ozone”

• secondary polutant formed through reaction between nitrogen oxides (NOx) and oxygen molecules driven by solar radiation

• contributes to smog, harmful to health, damaging to ecosystems

policies to reduce air pollution

• Altering human activity that produces air pollution

• Legislation to prevent or regulate the release of air pollutants

• Clean up and restoration of damaged system

acid deposition

refers to the falling of acidic substances from the atmosphere to the Earth's surface

the pH of natural deposition is …

usually acidic at between pH 5 and 6

why is natural deposition acidic?

due to the presence of carbon dioxide in the atmosphere which forms carbonic acid

how does acid deposition occur?

• occurs as a result of primary pollutants of sulphur dioxide and nitrogen oxides reacting in the atmosphere

• form secondary pollutants of sulphuric acid and nitric acid

types of deposition

• dry deposition

• wet deposition

wet deposition

when pollutants are incorporated into the clouds or falling raindrops and result in acidified rain or snow

dry deposition

when atmospheric pollutants are removed by gravity or direct contact under dry conditions (emissions of ash or dry particles from power stations are absorbed directly onto plants and buildings)

The impact of acid deposition on aquatic and terrestrial ecosystems also depends on …

the capacity of the environment to neutralise the acidic input

buffering capacity

alkaline calcium, magnesium compounds, and calcium carbonate (limestone)