Atmospheric Processes

The composition of the atmosphere

Key questions…1. What is the importance of the atmosphere as a

life support system?

2. What are the main gases and aerosols of the lower atmosphere?

3. What are the main processes associated with such gases and aerosols which influence life on Earth?

Our atmosphere…10 reasons why we need it;1. Gives us oxygen (O2) to breathe!

2. Provides Nitrogen (N2) which are essential to make proteins and DNA

3. CO2 for photosynthesis

4. Water vapour released as precipitation (Fresh water supply – Hydrological Cycle)5. Protects us from meteorites – most burn up in thermosphere6. Absorbs harmful UV radiation from the sun (Ozone Layer – O3)

7. Absorbs heat which regulates temperature allowing Earth to be habitable8. Creates climates by the circulation of gases and particles9. 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

10. …….. Can you think of any others?

quite important?

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

The composition of the atmosphere

Gas % by volume

Parts per million (ppm)

Symbol Importance

Nitrogen 78.08 780 840.0 N2 Biologically inert – remains stable. Needed to make proteins

and DNA

Oxygen 20.95 209 460.0 O2 Needed for aerobic respiration

Argon 0.93 9 340.0 Ar Inert

Carbon dioxide

0.03 350.0 CO2 Major contribution to the Greenhouse Effect but essential for

Photosynthesis

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

Other present gases and aerosols of the lower atmosphere

Gas % by Volume

Parts per Million (ppm)

Symbol Importance

Neon 0.0018 18.0 Ne Inert

Helium 0.00052 5.2 He Inert

Methane 0.00014 1.4 CH4 Major contribution to the Greenhouse Effect and Acid Rain

Krypton 0.00010 1.0 Kr Inert

Nitrous Oxide 0.00005 0.5 N2O Major contribution to the Greenhouse Effect

Hydrogen 0.00005 0.5 H2 None

Xenon 0.000009 0.09 Xe Inert

Ozone 0.000007 0.07 O3 Stratospheric – filters UV radiationTropospheric – health hazard

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)

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

Changes in atmospheric concentrations of greenhouse gases

Gas Symbol Conc. in 1750*

Conc. In 2011

Carbon dioxide

CO2 278 ppmv 390.4 ppmv

Methane CH4 0.72 ppmv 1.80 ppmv

Nitrous oxide

N2O 270 ppbv 324 ppbv

CFC-11 CFC-11 0 0.24 ppbv

CFC-12 CFC-12 0 0.53 ppbv

ppmv = parts per million by volumeppbv = parts per billion by volume

*Figures for 1750 based on proxy records ( ice core samples)

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

The global carbon cycle

Atmospheric CO2 concentrations at Mauna Loa, Hawaii – 1958-2006 AD

• world’s longest instrumental record of atmospheric carbon dioxide

Why might CO2 levels increase in

N hem spring and reduce in N hem autumn?

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

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

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

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

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’

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

Nitrogen Neon Nitrous Oxide CFC – 11

Oxygen Helium Hydrogen Helium

Argon Methane Xenon Radon

C02 Krypton Ozone Chlorine

Inert or not?

1. Look at the cards with gases and aerosols on which may or may not be present in the lower atmosphere

2. In pairs – categorise the gases3. You must choose your own categories (try

to have no more than 5)

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)