Atmospheric Pollution and its Causes

• Acid rain: precipitation with a pH value of less than 7

  • Burning of fossil fuels in factories and power stations release sulfur dioxide and nitrogen oxides.
  • Vehicle emissions add further nitrogen oxides.
  • When these gases mix and react with the water vapour in the atmosphere, they form weak nitric and sulfuric acid solutions.
  • Prevailing winds carry them.
  • They eventually fall to Earth as acid rain.
• Smog:

  • Burning of fossil fuels in industry, homes, and vehicles provides particles like smoke and dust for fog to form around.
• Photochemical smog:

  • Involves chemical reactions induced by sunlight on certain pollutants.
  • These reactions convert them into harmful substances like ground-level or tropospheric ozone (‘bad’ ozone).
• Volatile Organic Compounds (VOCs):

  • Chemicals that easily enter the atmosphere as gases, mainly from evaporation.
  • Examples: hydrocarbons (like methane), ammonium nitrate, carbon monoxide (incomplete combustion), etc.
• Temperature inversion: a weather condition when the air temperature increases with altitude rather than decreasing.

  • During the day, the surfaces are heated due to longwave radiation.
  • On calm and clear nights, the Earth's surface quickly cools, emitting radiation and cooling the air above it.
  • At higher altitudes, the air doesn’t cool as quickly, so this air becomes warmer than the air below it.
  • This layer of warm air is the inversion layer that disrupts the regular convection currents.
  • The concentration of smog (pollutants) increases, often in valleys surrounded by steep-sided hills.
• Enhanced greenhouse effect: created by adding greenhouse gases to the atmosphere through human activities.

  • More heat is retained in the atmosphere.
  • Increased temperature of the Earth's surface leads to global warming and climate change.
• Ozone Layer Depletion (1)

  • The ozone layer protects the Earth from the Sun’s harmful radiation.
  • It is formed when oxygen (O2) filters from the top of the troposphere and reacts under the influence of ultraviolet radiation to form ozone (O3).
  • It is continually formed, destroyed and replaced naturally, creating a dynamic balance disturbed by human activities.
• Ozone Layer Depletion (2):

  • When CFCs reach the stratosphere, the ultraviolet radiation breaks them down, releasing chlorine.
  • Chlorine reacts with oxygen in a destructive process, breaking down the ozone molecules to chlorine monoxide and oxygen, depleting the layer and forming a hole.
  • This hole allows harmful radiation to enter the Earth’s atmosphere
• Ozone (O3) is a greenhouse gas

  • greenhouse gas - a gas that traps heat into our planet
• The good ozone layer is located in the stratosphere (90% of the ozone is in this layer)

  • this layer protects us from UV radiation and also heats up the planet
• Sunlight reacts with oxygen molecules (O2) and the oxygen molecules undergoes splitting where it turns into oxygen atoms (O)

  • With the oxygen molecules and the oxygen atom both in the atmosphere together, they collide and become ozone (O2 + O => O3)
• The bad ozone consists of 10% of the total ozone supply in the troposphere
• In the presence of sunlight, nitrogen oxides, and VOCs, there is a chemical reaction that creates bad ozone which is the main ingredient of smog

  • nitrous oxides - pollutants that come to the atmosphere through emissions from industrial processes, transport etc.
  • VOCs - volatile organic compounds that come from paint, household products, tobacco smoke, solvents, coolants, emissions etc.
• Atmospheric or air pollution occurs when the atmosphere contains gases and substances in harmful amopunts

  • pollutants - substances that cause atmospheric pollution
• Smog (smoke and fog) - occurs where the burning of fossil fuels in industry, homes and vehicles provides additional particles that act as condensation nuclei for fog to form around

  • a problem associated with industrial and urban areas
  • more frequent during winter months as people use more heating
• Photochemical smog - air pollution in the atmosphere accompanies by high levels of ozone and nitrogen oxides from vehicles and caused by the action of sunlight on the pollutants

  • chemical reactions induced by sunlight of certain pollutants that converts them into harmful substances such as ground-level or tropospheric ozone
  • occurs during warm and sunny conditions
  • vehicles are major sources of particulate matter (PM) and volatile organic compounds (VOCs) which cause photochemical smog
• Short-wave radiation - incoming or short-wave solar radiation, visible light and UV radiation are commonly called shortwave radiation
• Long-wave radiation - outgoing or terrestial radiation as the Earth produces very little visible light or UV radiation as the Earth produces very little visible light or UV radiation, all radiation from the Earth is infrared
• Primary pollutant - a pollutant that is emitted directly from the source
• Secondary pollutant - a pollutant that forms through chemical reactions with primary pollutants
• Particulate matter - a mixture of very small particles and liquid droplets suspended in the air

  • categorised by the size of the particles
  • can be derived from human e.g. fuel combustion, engine emissions, tyre wear, mining, quarrying and construction
  • can be derived from nature e.g. sea spray, soil and dust
• Volatile organic compounds (VOCs) - chemicals that easily enter the atmosphere as gases, mainly from evaporation

  • comprise a wide range of organic compounds e.g. hydrocarbons
  • evaporate and exist as vapour in the atmosphere
  • emissions of VOCs result from incomplete combustion of fuel, leakages from petrol tankers and fuel tanks etc.
  • methane produced by certain agricultural practices is also a VOC
  • agricultural smog can form when ammonium nitrate from fertilisers and manure is carried in the air
• Certain physical conditions can create a temperature inversion that then traps and increases the concentration of smog

  • dustbin lid effect - smog may be thick enough to block out the sun
• Temperature inversion

  A) sinking air

  B) high pressure

  C) warmer air

  D) pollution

  E) trapped

  F) temperature inversion

  G) cold air

  H) flows

  I) valley sides

  J) night

  K) warm air

  L) urban area

  M) rise

  N) cold air

  
• Conditions needed for a temperature inversion:

  • high air pressure (anticyclone) which causes the upper air to sink
  • calm conditions resulting from high pressure as winds will disperse smog
  • valleys surrounded by steep-sided hills which trap the smog
• Acid rain - precipitation with a pH value of less than 6

  • acidity results from burning fossil fuels in factories and power stations which release sulfur dioxide and nitrogen oxides into the atmosphere
  • dry deposition - vehicle emissions add further nitrogen oxides
  • if toxic gases mix with water vapour and oxygen in the atmosphere, weak solutions of nitric and sulfuric acids are created which can then be moved by winds
  • wet deposition - solutions will eventually fall to earth as acid rain and can occur at some distance from the source
• Ozone - a greenhouse gas can be found in the troposphere (bad ozone) and stratosphere (good ozone) but it is concentrated at a height of about 25 km in the stratosphere
• Ozone layer exists because oxygen filtering from the top of the troposphere reacts under the influence of UV radiation to form zone

  • screens the earth from harmful radiation from the sun
  • stratosphere’s ozone is continually being produced, destroyed and replaced by this chemical process, creating a dynamic balance between our atmosphere and UV radiation
  • chemical reaction is greatested above the equator and tropics, where solar radiation is strongest and is more direct, and ozone is distributed to other regions by wind in the stratosphere
• The natural balance of the ozone layer has been disrupted by human activities, causing the concentration of ozone to fall

  • main danger is chlorine as it reacts with oxygen in a destructive process
• Chlorine is found in the CFCs released by plastic manufacturing, air cooling systems, refrigeration fluid and aerosol sprays

  • long lived and eventually reach the stratosphere where UV radiation breaks them down, releasing chlorine
• As ozone depletes in the stratosphere, it forms a ‘hole’ (1)

  • ‘hole’ allows harmful UV radiation to enter the Earth’s atmosphere
  • in the Southen Hemisphere, the ‘hole’ caused the air over Antartica to cut off from the rest of the atmosphere by the polar vertex and strong winds sweeping around the continent
  • high in the stratosphere, clouds form from tiny ice particles in the intense cold
• As ozone depletes in the stratosphere, it forms a ‘hole’ (2)

  • on the cloud surfaces, chemical reactions involving CFCs take place, releasing chlorine which reacts with the oxygen in the ozone layer
  • destruction of the ozone layer begins when spring Sun arrives as the clouds evaporate in summer and the chlorine converts into other compounds, the hole filling in until next year
  • ozone hole is more developed over Antartica than the Arctic because Antartica is separated from the rest of the world by the polar vertex
• Depletion - a reduction or loss
• Polar vertex - a circulation of strong upper level winds that surround Antartica and keep cold air locked in above the continent
• Enhanced greenhouse effect - the addition of greenhouse gases to the atmosphere through human activities

  • results in more heat being retained in the atmosphere and an increase in the Earth’s temperature
  • leads to global warming and climate change
• • Sources of main greenhouse gases

  A) human activities

  B) abudndance

  C) burning

  D) fossil fuels

  E) deforestation

  F) cattle and rice

  G) coal

  H) mine

  I) deforestation

  J) decomposition

  K) aerosol sprays

  L) fire extinguishers

  M) refrigeration

  N) air conditioning

  O) vehicle exhausts

  P) chemical

  Q) fertilisers

  R) chemical reactions

  S) nitrogen dioxides

  T) unburnt

  U) fuel