pollution dispersal and degradation

• environmental conditions that affect the severity of pollution

  -dispersal by winds and water

  -temperature

  -light

  -aerobic and anaerobic conditions

  -pH

  -presents of other chemicals

  -temperate inversions

  -transformations to secondary pollutants
• wind and water currents

  prevailing winds: higher risk of trans-boundary pollution, speed and direction can disperse pollutants over large areas

  proximity to water: pollutants can percolate into water and be transported far and also decrease quality of water

  rainfall: dilute terrestrial or water pollution, wash it away and can lead to leaching soil pollutants into water bodies
• temperature


  atmospheric temperatures in the troposphere normally decline with increasing altitude

  -warm pollutants rise and disperse into the atmosphere due to being more buoyant
• temperate inversions


  -under certain circumstances (temp inversions), the layer of air closest to the ground may be colder then normal

  -a temperature inversion is a break from normal troposphere temperature gradient

  -air higher in the troposphere is warmer than air closer to the ground

  -the cooler air is more dense and less buoyant so any pollutants released there may also become cold and dense, this means the pollutants can't disperse and can become more concentrated
• factors that allow temperate inversions to form

  valleys: where the cooler denser air can collect

  low wind velocity: so that the air layers with different temps do not mix

  cloudless skies:so that infrared energy can be radiated from the ground, allowing the ground to cool

  mist or fog during the day: water vapor that condenses in the cooler ground layer has a high albedo and will reflect sunlight and slow heating of the ground that would cause the temp inversion to be broken down
• what effect do temperature inversion have on the dispersal of pollutants?

  -pollutants become trapped by the temperature inversions

  -they remain more dense and less buoyant so not dispersed or diluted

  -the pollutants become concentrated and can form photochemical smog
• the presence of absorbent materials

  pollutants may absorb onto material such as clay particles or organic materials in aquatic sediments

  absorption may immobilise the pollutant and stop it causing problems
• example of adsorbent materials


  -radioactive caesium-137 released into the atmosphere by the nuclear accident, at Chernobyl in 1986, was washed out of the atmosphere by rain
• effects of point and diffuse sources of pollution

  -
• a point source


  a single, identifiable source of pollution such as a pipe or a drain

  -industrial wastes are commonly discharged into rivers and the sea
• diffuse sources


  refer to those inputs which occur over a wide area and are ont easily attributed to a single source

  associated with particular land uses: urban and agricultural land use, forestry
• factors that affect degradation of chemical transformations

  temperature

  light

  aerobic and anaerobic conditions

  pH

  presents of other chemicals
• temperature


  high temp can increase the volatility and reactivity of various pollutants, enhancing their potential to spread and cause harm
• temperature effects on degradation of chemicals

  chemical reactions occur faster when temperatures are increased

  warmer temps cause deoxygenation of water because oxygen is less soluble
• example of temperature


  -insecticides degrade quicker in warmer temperature

  -mosquitoes become resistant to insecticides

  -mosquitoes life cycle time shortens

  -as temp rises, so do the survical odds insecticide resistant mosquitoes
• light


  can produce the activation energy for chemical reactions

  -photo degradation of pesticides
• photochemical smog


  mixture of pollutants that are formed when nitrogen oxides and volatic organic compounds (VOC) react to sunlight creating a brown haze above the cities

  occurs more often in summer
• oxygen


  required for many chemicals and biological reactions
• example of oxygen


  aerobic bacterial decomposition of sewage oxidation of sulphide ore, producing sulphur dioxide oxidation of metals
• pH


  pH can affects the solubility of substances

  pH of the soil- the acidity or alkali of the soil can affect the availability and toxicity of certain pollutants
• example of pH


  acidic soils can mobalise heavy metals (e.g lead) making them more hazadous
• pollutant interactions


  the behavior of a pollutant can be affected by its interactions with other pollutants

  -some increase effects of pollutants or its toxcity
• example of pollutant interactions

  allergen, irritants and pollutants may increase asthma

  interaction of NOx and hydrocarbons in photochemical smog