C4 Chemistry of the Atmosphere

• Acid rain: Rain that is acidic due to dissolved gases, such as sulfur dioxide, produced from the burning of fossil fuels.
• Carbon footprint: The total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product.
• Environmental implication: The effect that the activity has on the environment.
• Global climate change: A long-term shift in global climate patterns.
• Greenhouse gases: Greenhouse gases include water vapour, carbon dioxide and methane. Greenhouse gases in the atmosphere maintain temperatures on Earth high enough to support life.
• Particulates: Causes global dimming and health problems for humans.
• particulates (soot) are a product of incomplete combustion.
• Equation for photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2
• Pollutants: A substance introduced into the environment that has undesired effects.
• For 200 million years, the proportions of different gases in the atmosphere have been much the same as they are today: approximately 4/5 (80%) nitrogen, 1/5 (20%) oxygen, and small proportions of various other gases such as carbon dioxide, water(gas), and noble gases.
• During the first billion years of the Earth’s existence, there may have been intense volcanic activity that 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 carbon dioxide with little or no oxygen (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 vapour condensed to form the oceans.
• Carbon dioxide dissolved in the ocean and carbonates were precipitated, producing sediments, reducing the amount of CO2 in the atmosphere.
• Algae and plants produced the oxygen that is now in the atmosphere by photosynthesis (6CO2 + 6H2O -> C6H12O6 + 6O2).
• 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 levels gradually increased to a level that enabled animals to evolve.
• Algae and plants decreased the carbon dioxide levels in the atmosphere by photosynthesis.
• Carbon dioxide levels were 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 decayed.
• Greenhouse gases maintain temperatures on earth high enough to support life. Examples include: water vapour, carbon dioxide & methane
• The greenhouse gas effect:

  Electromagnetic radiation at most wavelengths (both long and short) from the sun passes through the Earth’s atmosphere. The Earth absorbs some radiation and thus warms up (essential for life on Earth). But 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.
• Some human activities contribute to an increase in greenhouse gases (e.g carbon dioxide and methane) in the atmosphere.

  Examples of human activities include: driving (carbon dioxide released), consuming electricity (carbon dioxide released), raising livestock i.e cows (methane released), decay of organic waste in landfill sites (methane released)
• Based on peer-reviewed evidence, many scientists believe that human activities will cause the temperature of the Earth’s atmosphere to increase at the surface and that this will result in global climate change.

  But, it is difficult to model such complex systems as global climate change. This leads to simplified models, speculation and opinions presented in the media that may be based on only parts of the evidence and which may be biased.
• An increase in average global temperature is a major cause of climate change. The potential effects of global climate change includes: extinction of species; raising sea levels due to the melting of polar ice caps; migration - people will move from areas suffering drought/flooding; decrease in crop yield for all major world crops.
• Carbon footprint can be reduced by reducing emissions of carbon dioxide and methane e.g. by using less electricity (so using less fossil fuels or using an alternative source of electricity), by reducing the amount of travel or transportation (of either goods or people) and by planting more trees. However, action may be limited because it’s more difficult, can be more expensive and planting trees takes away land that could be used to grow crops.
• 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.
• The gases released into the atmosphere when a fuel burns may include carbon dioxide, water (vapour), carbon monoxide, and oxides of nitrogen (which are formed at high temperatures). Solid particles and unburned hydrocarbons may also be released, forming particulates in the atmosphere. If there’s not enough oxygen, some of the fuel doesn’t burn – this is partial/incomplete combustion. Here, solid particles of soot (carbon), carbon monoxide and unburnt fuel are released.
• The combustion of hydrocarbons releases energy. During combustion, the carbon and hydrogen in the fuels are oxidised to form carbon dioxide and water.
• Carbon monoxide: toxic gas which is colourless and odourless so not easy to detect
• Sulfur dioxide and oxides of nitrogen: cause acid rain and respiratory problems in humans.