Chemistry of the atmosphere

• The Earth’s early atmosphere is a topic of limited evidence due to the time scale of 4.6 billion years and theories have changed/developed over time.
• One theory suggests that during the first billion years of the Earth’s existence, there was 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 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 vapour condensed to form the oceans.
• CO2 dissolved in the water and carbonates were precipitated producing sediments, reducing the amount of CO2 in the atmosphere.
• Algae and plants produced the O2 that is now in the atmosphere by photosynthesis.
• 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.
• 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 decayed.
• Greenhouse gases maintain temperatures on earth high enough to support life and include water vapour, CO2 & CH4.
• The greenhouse gas effect involves electromagnetic radiation at most wavelengths (both long and short) from the sun passing through the Earth’s atmosphere, with the Earth absorbing some radiation and thus warming up, and some heat being radiated from the Earth as infrared radiation.
• Some of the infrared radiation is absorbed by greenhouse gases in the atmosphere, warming up the atmosphere and leading to the greenhouse effect and global warming.
• Human activities contribute to an increase in greenhouse gases in the atmosphere by increasing levels of CO2 & CH4, with examples including driving, consuming electricity, raising livestock, and decay of organic waste in landfill sites.
• 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 result in global climate change.
• Global climate change may cause effects such as extinction of species, raising sea levels due to the melting of polar ice caps, migration of people due to drought or 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.
• Carbon footprint can be reduced by reducing emissions of carbon dioxide and methane, for example by using less electricity, reducing the amount of travel or transportation, and planting more trees.
• Combustion of fuels is a major source of atmospheric pollutants, with most fuels including coal containing 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, with solid particles and unburned hydrocarbons also being released, forming particulates in the atmosphere.
• If there’s not enough oxygen, some of the fuel doesn’t burn – this is partial/incomplete combustion, with solid particles of soot, carbon monoxide and unburnt fuel being released.
• During combustion, the carbon and hydrogen in the fuels are oxidised to form carbon dioxide and water.
• Carbon monoxide is a toxic gas which is colourless and odourless, making it difficult to detect.
• Sulfur dioxide and oxides of nitrogen cause acid rain and respiratory problems in humans.
• Particulates cause global dimming and human health problems.