Atmospheric Processes

1. Atmospheric Processes The composition of the atmosphere

2. Key questions… • What is the importance of the atmosphere as a life support system? • What are the main gases and aerosols of the lower atmosphere? • What are the main processes associated with such gases and aerosols which influence life on Earth?

3. Our atmosphere… 10 reasons why we need it; • Gives us oxygen (O2) to breathe! • Provides Nitrogen (N2)which are essential to make proteins and DNA • CO2 for photosynthesis • Water vapour released as precipitation (Fresh water supply – Hydrological Cycle) • Protects us from meteorites – most burn up in thermosphere • Absorbs harmful UV radiation from the sun (Ozone Layer – O3) • Absorbs heat which regulates temperature allowing Earth to be habitable • Creates climates by the circulation of gases and particles • Circulation of hot and cold air to regulate different climate zones – this is important as different species of flora and fauna require certain climatic conditions to survive • …….. Can you think of any others? quite important?

4. The Earth’s atmosphere • A mixture of transparent, odourless gases and aerosols held to Earth by gravity • Three main types of constituents • Permanent gases – e.g. nitrogen, oxygen, argon • Variable gases (greenhouse gases and reactive gas species) – e.g. carbon dioxide, methane, water vapour • Aerosols (non-gaseous components of atmosphere) – e.g. sea salt, soot particles, volcanic ash

5. Permanent gases • Mostly passive in weather-related processes • N2, O2 and Ar constitute 99.9% of atmosphere Variable gases and aerosols • Occur as a result of both natural processes (e.g. carbon cycle) and human activities (e.g. burning coal) • Affect transmission of radiation through atmosphere The composition of the atmosphere

6. Other present gases and aerosols of the lower atmosphere

7. Sources, sinks and atmospheric residence times • Source = point from which a gas or aerosol is released into atmosphere • Sink = point where a gas or aerosol is removed from atmosphere • by chemical reaction • by absorption into other components of earth-atmosphere system (e.g. oceans, ice sheets) • Photosynthesis (Plankton blooms) • Atmospheric residence time = average period of time a molecule or particle resides within atmosphere • Determined by relative rates of emission (from source) and removal (via sink)

8. The Greenhouse Gases • Naturally occurring greenhouse gases include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone (O3) and water vapour (H2O) • Play an important role in regulating atmosphere’s energy budget by absorbing some of outgoing terrestrial radiation • Increases global mean surface temperature • Process = natural greenhouse effect • Atmospheric concentrations of almost all these gases have increased since 1800s (Industrial Revolution) due to: • Combustion of fossil fuels • Deforestation and agricultural change (livestock/food production increase) • Anthropogenic greenhouse gases include chlorofluorocarbons, methyl bromide (pesticides), solvents, halons • Released into atmosphere since 1930s • Consequence = enhanced Greenhouse Effect

9. Changes in atmospheric concentrations of greenhouse gases ppmv = parts per million by volume ppbv = parts per billion by volume *Figures for 1750 based on proxy records ( ice core samples)

10. Carbon dioxide (CO2) • Most important greenhouse gas after water vapour –involved in complex ‘carbon cycle’ • Natural sources • Respiration • Decomposition of organic matter • Forest fires • Volcanic eruptions • Evaporation from oceans • Anthropogenic sources • Fossil fuel combustion • Deforestation & biomass burning • Manufacture of cement • Sinks (removal from atmosphere) • Plant photosynthesis • Absorption by oceans Volcanic eruption Industrial pollution

11. The global carbon cycle

12. Atmospheric CO2 concentrations at Mauna Loa, Hawaii – 1958-2006 AD Why might CO2 levels increase in N hem spring and reduce in N hem autumn? • world’s longest instrumental record of atmospheric carbon dioxide

13. Atmospheric CO2 concentrations – Ice Core Data, 1850-1950 AD– Mauna Loa, Hawaii, 1958-present AD • Antarctic and Greenland ice sheets preserve a record of past atmospheric composition • Ice sheets are cored and studied by extracting air bubbles trapped in layers of ice

14. Methane (CH4) • Primary natural source • natural anerobic (i.e. oxygen-deficient) processes in wetlands & rice paddyfields (c.40% of total) • Other natural sources • Animal digestive processes, cows can produce up to 200 litres a day! • Termites • Forest fires • Anthropogenic sources • Fossil fuel combustion • Biomass burning • Disposal of refuse in landfill sites • Sinks • Oxidized to CO2 and H2O by complex photochemical reactions in troposphere Paddyfields Landfill site

15. Nitrous oxide (N2O) • Primary natural source • Microbial activity (nitrification) in soils and oceans • Anthropogenic sources • Fossil fuel combustion • Biomass burning • Nylon, nitric acid & nitrogen fertilizer production • Sinks • Oxidized to nitrogen oxides (NOX) by photochemical reactions in stratosphere Fossil fuel combustion

16. CFCs • Chlorofluorocarbons (11,12) Anthropogenic uses include: • Used as coolants in refrigeration • Propellants in aerosols • Expanders in foam products Concentrations: • Distinct increase in concentrations between 1960 - 1990 Impacts: • Montreal Protocol – led to a huge decline

17. Tropospheric Ozone (O3) • Produced by a series of complex chemical reactions • Including pollutants from car exhausts (nitrous oxide and Hydrocarbons reacting with sunlight) • More vehicles = greater concentration thus increasing the ‘greenhouse effect’ • Can damage human health and vegetation • Key ingredient of ‘urban smog’

18. Greenhouse gases in Greenland ice cores • Atmospheric concentrations of four greenhouse gases over the last 1,000 years as preserved within ice cores • SO4, CH4, N20 and CO2 • All show fairly constant or very slowly increasing atmospheric concentrations before c.1800 AD • Increasingly rapid rise in atmospheric concentrations since c.1800 AD • Close correlation between atmospheric concentrations of greenhouse gases and world population

20. Inert or not? • Look at the cards with gases and aerosols on which may or may not be present in the lower atmosphere • In pairs – categorise the gases • You must choose your own categories (try to have no more than 5)

21. Research questions… • Read the article • Highlight key facts or information throughout the passage • Answer the questions (take note of the mark allocation for each question)