chem p2

• Proportions of different gases in the atmosphere:

  • For 200 million years, the proportions of different gases in the atmosphere have been much the same as they are today:
  • ~4/5 (80%) nitrogen
  • ~1/5 (20%) oxygen
  • Small proportions of various other gases, i.e. CO2, H2O(g) and noble gases
• • CO2 dissolved in the water and carbonates were precipitated, reducing the amount of CO2 in the atmosphere
• The Earth's early atmosphere:

  • One theory suggests that during the first billion years of the Earth's existence:
  • Intense volcanic activity released gases that formed the early atmosphere
  • At the start of this period, the atmosphere may have been like the atmospheres of Mars and Venus today: mainly CO2 with little or no O2(g)
  • Volcanoes also produced nitrogen (N2) which gradually built up in the atmosphere, and there may have been small proportions of methane (CH4) and ammonia (NH3)
  • Water vapor condensed to form the oceans
• How oxygen increased:

  • Algae & plants produced the O2 that is now in the atmosphere by photosynthesis:
  • 6CO2 + 6H2O -> C6H12O6 + 6O2 (carbon dioxide + water -(light)-> glucose + oxygen)
  • Algae first produced oxygen about 2.7 billion years ago, and soon after this, oxygen appeared in the atmosphere
  • Over the next billion years, plants evolved, and the % oxygen gradually increased to a level that enabled animals to evolve
• How carbon dioxide decreased:

  • Algae and plants decreased the % CO2 in the atmosphere by photosynthesis
  • CO2 was also decreased by the formation of sedimentary rocks that contain carbon (e.g. limestone and coal) and by the production of fossil fuels from the remains of dead plants and animals when they decay
• Greenhouse gases maintain temperatures on earth high enough to support life
• Greenhouse gases include: water vapour, CO2, and CH4
• The greenhouse gas effect:

  • Electromagnetic radiation from the sun passes through the Earth's atmosphere
  • The Earth absorbs some radiation and warms up
  • Some heat is radiated from the Earth as infrared radiation
  • Some of this IR radiation is absorbed by greenhouse gases in the atmosphere
  • Atmosphere warms up leading to the greenhouse effect and global warming
• Human activities that contribute to an increase in greenhouse gases in the atmosphere:

  • Activities increase levels of CO2 and CH4
  • Examples of human activity include driving (CO2), consuming electricity (CO2), raising livestock (cows - CH4), and decay of organic waste in landfill sites (CH4)
• Many scientists believe that human activities will cause the temperature of the Earth's atmosphere to increase at the surface, resulting in global climate change
• Global climate change:

  • An increase in average global temperature is a major cause of climate change
  • Potential effects of global climate change include extinction of species, raising sea levels due to the melting of polar ice caps, migration of people from areas suffering drought/flooding, and decrease in crop yield for all major world crops
• Carbon footprint: the total amount of CO2 and other greenhouse gases emitted over the full life cycle of a product, service, or event
• Ways to reduce carbon footprint:

  • Reduce emissions of carbon dioxide and methane
  • Use less electricity (using less fossil fuels or alternative sources of electricity)
  • Reduce the amount of travel or transportation of goods or people
  • Plant more trees
• Challenges in reducing carbon footprint:

  • Action may be limited because it's more difficult and expensive
  • Planting trees takes away land that could be used to grow crops
• Atmospheric pollutants from fuels:

  • Combustion of fuels is a major source of atmospheric pollutants
  • Most fuels (including coal) contain carbon and/or hydrogen and may also contain some sulfur
  • Gases released into the atmosphere when a fuel burns may include carbon dioxide, water (vapour), carbon monoxide, and oxides of nitrogen (formed at high temperatures)
  • Solid particles and unburned hydrocarbons may also be released, forming particulates in the atmosphere
• • In partial/incomplete combustion, if there's not enough oxygen, some of the fuel doesn't burn, releasing solid particles of soot (carbon), carbon monoxide, and unburnt fuel
  • Combustion of hydrocarbons releases energy, with carbon and hydrogen oxidising to form carbon dioxide and water
• Properties and effects of atmospheric pollutants:

  • Carbon monoxide: toxic gas that is colourless and odourless, making it hard to detect
  • Sulfur dioxide and oxides of nitrogen: cause acid rain and respiratory problems in humans
  • Particulates: cause global dimming and human health problems