Air

The Ocean of Air• We live in a vast ocean of air, (called

atmosphere) which extends upwards for over 1000 km. It has a mass of about 5 x 1015 tonnes and is spread over an area of 5x108 km2.

• There is no definite boundary between the atmosphere and outer space. It slowly becomes thinner and fades into space.

• An altitude of 120 km marks the boundary where atmospheric effects become noticeable during atmospheric reentry

The Ocean of Air• Three quarters of the atmosphere's mass

is within 11 km of the surface. This lowest part of this ocean of air is known as the troposphere. It contains about 75% of the total mass of the atmosphere and 90% of water vapour.

• 99% of the atmosphere is spread approximately about 30 km from the sea level

• As we move away from the earth, the density of air decreases

The Ocean of Air• Apart from providing us air to breathe, this

blanket of air traps the sun's heat that is essential for life on the earth, and also acts as a barrier against harmful and excessive radiation.  

• This ocean of air provides us O2, which is essential for life; CO2, which is used by the plants to manufacture food for the living organisms; N2 which plants use to make proteins and water vapour that condenses to form life and thus gives us rain and determines the climatic conditions of the globe.

Composition of Air• Filtered air includes trace amounts

of many of the chemical elements. • Substantial amounts of argon,

nitrogen, and oxygen are present as elementary gases.

• Note the major greenhouse gases: water vapor, carbon dioxide, methane, nitrous oxide, and ozone.

Composition of Air• Many additional elements from natural

sources may be present in tiny amounts in an unfiltered air sample.

• Various industrial pollutants are also now present in the air, such as chlorine (elementary or in compounds), fluorine (in compounds), elementary mercury, and sulfur (in compounds such as sulfur dioxide [SO2]).

Composition of Dry Air• Gas Volume

• N2 780,840 ppmv (78.084%)• O2 209,460 ppmv (20.946%)• Ar 9,340 ppmv (0.9340%)• CO2 383 ppmv (0.0383%)• Ne 18.18 ppmv (0.001818%)• He 5.24 ppmv (0.000524%)• CH4 1.745 ppmv

(0.0001745%)• Kr 1.14 ppmv (0.000114%)

• Gas Volume

• H2 0.55 ppmv (0.000055%)• N2O 0.3 ppmv (0.00003%)• Xe 0.09 ppmv (9x10-6%)• O3 0.0 to 0.07 ppmv (0%-

7x10-6%)• NO2 0.02 ppmv (2x10-6%)• I 0.01 ppmv (1x10-6%)• CO 0.1 ppmv• NH3 trace

ppmv: parts per million by volume

Not included in above dry atmosphere:Water vapor (H2O): ~0.40% over full atmosphere, typically 1%-4% at surface

Parts of the Atmosphere• The troposphere is the lowest layer

of the atmosphere; it begins at the surface and extends to between 7 km (23,000 ft) at the poles and 17 km (56,000 ft) at the equator, with some variation due to weather factors

• All the activities of living beings are possible in this region, so this area is suitable for living beings

Troposphere

Parts of the Atmosphere• Though part of the Stratosphere, the ozone

layer is considered as a layer of the Earth's atmosphere in itself because its physical and chemical composition is far different from the Stratosphere.

• Ozone (O3) in the Earth's stratosphere is created by UV light splitting O2 atoms into individual oxygen atoms which then combine with unbroken O2 to create O3.

• Hence, ozone provides protection against UV rays

Ozone Layer

Parts of the Atmosphere• The stratosphere extends from the

troposphere's 7–17 km (4.3–11 miles; 23,000–56,000 ft) range to about 51 km (32 miles; 170,000 ft).

• The stratosphere contains the ozone layer, the part of the Earth's atmosphere which contains relatively high concentrations of ozone.

• Temperature increases with height

Stratosphere

Parts of the Atmosphere• The mesosphere extends from about

50 km (31 mi; 160,000 ft) to the range of 80–85 km (50–53 mi; 260,000–280,000 ft).

• Temperature decreases with height, reaching −100 °C (−148.0 °F; 173.1 K) in the upper mesosphere.

• This is also where most meteors burn up when entering the atmosphere.

Mesosphere

Parts of the Atmosphere• The thermosphere extends from 80–

85 km (50–53 miles; 260,000–280,000 ft) to over 640 km (400 miles; 2,100,000 ft)

• The temperature increases with height. The temperature of this layer can rise to 1,500 °C (2,730 °F).

• The International Space Station orbits in this layer, between 320 and 380 km (200 and 240 mi).

Thermosphere

Parts of the Atmosphere• The part of the atmosphere that is ionized

by solar radiation stretches from 50 to 1,000 km (31 to 620 miles; 160,000 to 3,300,000 ft) and typically overlaps both the exosphere and the thermosphere.

• It plays an important part in atmospheric electricity.

• Because of its charged particles, it has practical importance because it influences, for example, radio propagation on the Earth.

Ionosphere

Parts of the Atmosphere• The exosphere extends from 500–

1,000 km (310–620 miles; 1,600,000–3,300,000 ft) up to 10,000 km (6,200 miles; 33,000,000 ft)

• This region contains free-moving particles

Exosphere

Atmospheric Pressure• Atmospheric pressure is a direct result of

the total weight of the air above the point at which the pressure is measured

• The average atmospheric pressure, at sea level, is about 1 atmosphere (atm) = 101.3 kPa (kilopascals)

• The density of air decreases with height, thereby causing a corresponding decrease in pressure. This explains the difficulty in breathing at high altitudes

Oxygen (O2)

Oxygen – An Introduction• Oxygen is the third most abundant

element in the universe by mass after hydrogen and helium and the most abundant element by mass in the Earth's crust.

• Diatomic oxygen gas constitutes 20.9% of the volume of air.

• Oxygen is present in compound state in almost all the minerals and rocks

• Oxygen is present in water as compound to 88.8% by weight

Obtaining Oxygen ……• Electrolysis of water (containing

strong acid or strong base to make it conduct electricity)

2H2O electrolysis 2H2 + O2

• Oxygen is evolved at the positive electrode and hydrogen at the negative electrode

• This method gives 100% pure oxygen

Obtaining Oxygen ……• Oxygen can also be obtained from its

important compounds like oxides, nitrates and chlorates

4CrO3 2Cr2O3 + 3O2

2NaNO3 2NaNO2 + O2

2KClO3 2KCl + 3O2 (Lab method)• In the lab method, manganese dioxide

is used as a catalyst – something that does not take part in a reaction, only affects the rate

Obtaining Oxygen ……• Another method involves the

addition of water to sodium peroxide and the collection, over water, of the liberated oxygen

• 2Na2O2 + 2H2O 4NaOH + O2

Oxygen – Properties• It is colourless, odourless and

tasteless• Oxygen is not inflammable, but it is

a supporter of combustion• It occurs in a diatomic form in

nature – O2

• It easily forms compounds with other elements

Oxygen – Uses• Required for breathing in all living

organisms (animals) and by plants for respiration

• Oxygen inhalers for patients suffering from asthma, pneumonia etc

• Oxygen cylinders are used by scuba divers and mountaineers

• Oxy-hydrogen and oxy-acetylene flame used for cutting and welding metals

• For producing chlorine, nitric and sulphuric acid

Nitrogen (N2)

Nitrogen – An Introduction• Nitrogen constitutes 78% (by

volume) of the atmosphere• Nitrogen is an inert gas and is not

directly used by plants and animals, but it occurs in all living organisms.

• It is a constituent element of amino acids and thus of proteins, and of nucleic acids (DNA and RNA).

Obtaining Nitrogen ……• Air is passed over heated copper or

coke to remove oxygen• Carbon dioxide formed due to coke

is removed by dissolving in water• The remaining air is liquefied and

nitrogen is separated

Nitrogen Cycle

Nitrogen Cycle• The nitrogen cycle is the biogeochemical

cycle that describes the transformations of nitrogen and nitrogen-containing compounds in nature.

• The conversion of nitrogen (N2) from the atmosphere into a form readily available to plants and hence to animals and humans is an important step in the nitrogen cycle, which distributes the supply of this essential nutrient.

• There are four ways to convert atmospheric N2 gas into more chemically reactive forms:

Nitrogen Cycle• Biological fixation: some symbiotic

bacteria (most often associated with leguminous plants) and some free-living bacteria are able to fix nitrogen as organic nitrogen.

• Industrial N-fixation: Under great pressure, at a temperature of 600oC, and with the use of a catalyst, atmospheric nitrogen and hydrogen can be combined to form ammonia (NH3).

Nitrogen Cycle• Combustion of fossil fuels:

automobile engines and thermal power plants, which release various nitrogen oxides (NOx).

• Other processes: Additionally, the formation of NO from N2 and O2 due to photons and especially lightning, are important for atmospheric chemistry, but not for terrestrial or aquatic nitrogen turnover

Properties of Nitrogen• It is a colourless, odourless and

tasteless gas• It is not inflammable and neither

does it support combustion• It is non-poisonous, although it

inhibits breathing• It is present in nature as a diatomic

molecule• It has the capacity to form

compounds with various elements

Uses of Nitrogen• It is useful in the preparation of

chemicals like ammonia, nitric acid etc.

• It is used to create inert atmosphere – for e.g., many volatile / inflammable liquids are stored in containers that contain nitrogen. It helps reduce the possibility of fire

Pollution

Pollution• Due to industrialization, many

unwanted chemical compounds in the form of gas, liquid and solid are thrown into the soil and atmosphere

• When these chemical compounds start showing adverse effect, it is called pollution

• The compounds spreading pollution are called pollutants

Types of Pollution• Pollution is of different types:• Air pollution• Water pollution• Soil pollution• Noise (sound) pollution

Pollution• Pollutants bring about physical, chemical

and biological changes in the air, water and soil

• These changes may prove fatal to man as well as other living organisms

• They also destroy the delicate balance of the eco-system

• Pollutants are produced in our daily life – when we use detergents, drive a petrol / diesel car, generate rubbish, dump effluents in rivers etc.

Air Pollution

Air Pollution• Pollutants in the air, mainly in the form of

gas or minute particles, consist of:– Gaseous state of some solid/liquid

compounds– Dust and Fog– Minute particles of unnecessary

chemicals and carbon– Smoke produced as gaseous residue due

to incomplete combustion of C, Fe, Si, Al, Pb, Zn, hydrocarbons, acid, base etc

– Radiation

Air Pollution - Effects• Diseases of the oesophagus and lungs,

intestinal cancer, damages to the kidney, blood pressure

• Can affect the reproduction power of people working in chemical industries

• Life expectancy of animals and men is reduced

• Physical and sometimes genetic defects result

• Vegetation affected – reduced crop output, slowing down of photosynthesis etc.

Air Pollution - Remedies• Reduction of dust particles, polluting

gases at source• Changing the raw materials and improving

process systems• Diffusing the pollutants over a larger area• Separation of industrial and residential

areas• Regular checking and maintenance of

vehicles• Use of ‘clean’ and ‘alternative’ fuel (CNG,

bio-fuels)

Air Pollution - Remedies• Developing hybrid vehicles that run

on electricity, hydrogen cells etc• Increasing the green cover by

planting more trees• Developing forests and bio-

reserves, parks etc., which act as ‘lungs’

• Recycling trash, rather than burning it

Greenhouse Effect• The greenhouse effect is the

heating of the surface of the earth due to the presence of an atmosphere containing gases that absorb and emit infrared radiation.

• Greenhouse gases, which include water vapor, carbon dioxide and methane, trap heat within the surface-troposphere system

Greenhouse Gases• In order, Earth's most abundant

greenhouse gases are:– water vapor– carbon dioxide – methane– nitrous oxide – ozone– CFCs

Greenhouse Gases• When these gases are ranked by

their contribution to the greenhouse effect, the most important are:– water vapor, which contributes 36–

70% – carbon dioxide, which contributes

9–26% – methane, which contributes 4–9% – ozone, which contributes 3–7%

Greenhouse Effect - Mechanism• The carbon dioxide proportion in

the air is maintained at around 0.3% by the actions and activities of:– animals (who release it during

respiration) – plants (which use it during

photosynthesis)– sea water that absorbs CO2

Greenhouse Effect - Mechanism• The earth receives energy from the

sun mainly in the form of light and this is absorbed by the surface of the earth

• The earth radiates this absorbed energy in the form of heat

• Carbon dioxide absorbs heat and along with the other greenhouse gases helps to maintain the average surface temperature of the earth (14oC).

Exchange of EnergySolar

radiation absorbed by the Earth

Thermal Energy into

spaceDirectly radiated from the surface

Heat and energy in the atmosphere

Greenhouse gas

absorption

Earth’s land and ocean surface warmed to a

temp. of 14oC

Greenhouse Effect - Impact• When the proportion of CO2

increases, the temperature of the earth also increases as more heat is now absorbed by the atmosphere

• Polar ice-caps start melting leading to a rise in water levels, submerging of coastal areas, flooding etc.

• An overall increase in the temperature of the earth leading to ‘hotter’ summers and ‘warm’ winters

Acid Rain• "Acid rain" is a popular term referring

to the deposition of wet (rain, snow, sleet, fog and cloud-water, dew) and dry (acidifying particles and gases) acidic components.

• A more accurate term is “acid deposition”.

• Acid rain is mostly caused by human emissions of sulfur and nitrogen compounds which react in the atmosphere to produce acids.

Acid Rain• Dry form: This can be responsible for as

much as 20 to 60% of total acid deposition.• This occurs when acidic gases like Sulfur

dioxide spread in the atmosphere and stick to the ground, plants or other surfaces.

• Wet form: when humidity increases, atmospheric gases like SO2 and NOx turn into sulphuric acid and nitric acid.

• When this acid falls along with the precipitation (rain, snow) it is called ‘acid rain’

Acid Rain - Causes• The principal cause of acid rain is sulfur

and nitrogen compounds from human sources, such as electricity generation, factories, and motor vehicles.

• Coal power plants are one of the most polluting.

• Sulphur dioxide is produced in the atmosphere due to the sulphur present in coal

• Vehicles are responsible for nitrogen oxides, hydrocarbons and carbon monoxide

Origin of Acid Rain

Acid Rain - Effects• The higher aluminum concentrations in

surface water that occur as a result of acid rain can cause damage to fish and other aquatic animals

• As lakes and rivers become more acidic biodiversity is reduced

• Soil biology and chemistry can be seriously damaged by acid rain

• Microbes producing essential fertilizers are killed and essential minerals are leached

Acid Rain - Effects• High altitude forests are especially

vulnerable as they are often surrounded by clouds and fog which are more acidic than rain.

• Fine particles, a large fraction of which are formed from the same gases as acid rain (sulfur dioxide and nitrogen dioxide), have been shown to cause illness and premature deaths such as cancer and other diseases

• Acid rain can also cause damage to certain building materials and historical monuments

Effect of Acid Rain on Trees

Effect of Acid Rain on Statues

Acid Rain - Prevention• Use fuel containing less sulphur• Removal of sulphur containing gases

before release to atmosphere• Production of crude oil with less

sulphur content• Usage of calcium carbonate to

absorb sulphur dioxide• Stricter automobile emission

controls to reduce the emission of nitrogen oxides