The Multidisciplinary Nature of Environmental Studies 1.4.2. Atmosphere The atmosphere is the thin layer of gases separating earth from the outer space. The lower atmosphere is a mixture of molecules of three important gases - Oxygen (02)' itrogen (N 2 )and Carbon dioxide (C0 2 ) - alongwith water va- pour and trace amounts of several other gases that have no immediate biologi- cal importance. The gases in the atmosphere are normally stable but under some circumstances they react chemically to form new compounds. The atmos- phere is a major source of carbon and oxygen for all organisms and a source of nitrogen for a few organisms. The gaseous mixture of the troposphere (lowest layer of atmosphere in which living organisms operate) is called air containing oxygen, nitrogen and carbon dioxide, all of which cycle in nature through biogeochemical cycles. Most of the organisms make use of these gases not only to liberate chemical energy from food during respiration but in different ways, e.g. plants use CO 2 in photosyn- thesis and nitrogen is used by nitrogen fixing bacteria ofthe roots of some plants. An imbalance in the mixture of these gases will, therefore, affect the processes that are involved in reduced aeration of soil bringing about a number of mor- phological and physiological effects on plants. Excess of CO 2 in soil and air may result in the production of such toxins which are lethal to soil organisms and plants. All this explains the ecological significance of air. The entire world and its materials can be grouped into non-living (abiotic) and living (biotic) components. The abiotic environment can further be classified into atmosphere, lithosphere and hydrosphere whereas biotic environment is called as biosphere. The gaseous envelope, held to the planet by gravitational attraction ofthe earth is called atmosphere. The total mass of the atmosphere amounts to 5.7 x 10 15 tons of air. It blends at about 1000 km or so above the surface of the earth. Atmosphere is a reservoir of several life supporting elements that serve many functions such as filtration of radiant energy from the sun, insulation of heat to check loss from earth's surface and stabilization of climatic conditions. 1.4.2.1. Origin of Atmosphere The origin of atmosphere is related to the origin of earth itself. The earth was formed by the accretion ofsolid materials that condensed from the solar nebula. The atmosphere at that time was totally different from the atmosphere today. In the first stage, the earth by its gravitational force attracted gaseous constitu- ents of the cosmic dust viz. hydrogen, methane, ammonia, water vapour and noble gases. There was no oxygen at this stage and it was a reducing or hydro- gen rich atmosphere. It lasted about 3.5 x 10 9 years ago. The second stage of evolution of atmosphere lasted about 2 x 10 9 years ago. Volcanic eruptions took place during this period. Large quantities of magma, saturated with dissolved gases moved towards the surface of the earth. They passed over iron present in the mantle. The gases such as nitrogen, hydrogen, hydrogen sulphide, carbon monoxide and water vapour existed in a reduced state. Any free oxygen that escaped from the interior of the earth combined with hydrogen, residual methane or ammonia. In the second stage also there was no free oxygen in the atmosphere. 9
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The Multidisciplinary Nature of Environmental Studies
1.4.2. AtmosphereThe atmosphere is the thin layer of gases separating earth from the outer space.The lower atmosphere is a mixture of molecules of three important gases -Oxygen (02)' itrogen (N2)and Carbon dioxide (C02) - alongwith water va-pour and trace amounts of several other gases that have no immediate biologi-cal importance. The gases in the atmosphere are normally stable but undersome circumstances they react chemically to form new compounds. The atmos-phere is a major source of carbon and oxygen for all organisms and a source ofnitrogen for a few organisms.The gaseous mixture of the troposphere (lowest layer of atmosphere in whichliving organisms operate) is called air containing oxygen, nitrogen and carbondioxide, all of which cycle in nature through biogeochemical cycles. Most of theorganisms make use of these gases not only to liberate chemical energy fromfood during respiration but in different ways, e.g. plants use CO2 in photosyn-thesis and nitrogen is used by nitrogen fixing bacteria of the roots of some plants.An imbalance in the mixture of these gases will, therefore, affect the processesthat are involved in reduced aeration of soil bringing about a number of mor-phological and physiological effects on plants. Excess of CO2 in soil and air mayresult in the production of such toxins which are lethal to soil organisms andplants. All this explains the ecological significance of air.The entire world and its materials can be grouped into non-living (abiotic) andliving (biotic) components. The abiotic environment can further be classifiedinto atmosphere, lithosphere and hydrosphere whereas biotic environment iscalled as biosphere.The gaseous envelope, held to the planet by gravitational attraction of the earthis called atmosphere. The total mass of the atmosphere amounts to 5.7 x 1015
tons of air. It blends at about 1000 km or so above the surface of the earth.Atmosphere is a reservoir of several life supporting elements that serve manyfunctions such as filtration of radiant energy from the sun, insulation of heat tocheck loss from earth's surface and stabilization of climatic conditions.
1.4.2.1.Origin of AtmosphereThe origin of atmosphere is related to the origin of earth itself. The earth wasformed by the accretion of solid materials that condensed from the solar nebula.The atmosphere at that time was totally different from the atmosphere today.In the first stage, the earth by its gravitational force attracted gaseous constitu-ents of the cosmic dust viz. hydrogen, methane, ammonia, water vapour andnoble gases. There was no oxygen at this stage and it was a reducing or hydro-gen rich atmosphere. It lasted about 3.5 x 109 years ago.The second stage of evolution of atmosphere lasted about 2 x 109 years ago.Volcanic eruptions took place during this period. Large quantities of magma,saturated with dissolved gases moved towards the surface of the earth. Theypassed over iron present in the mantle. The gases such as nitrogen, hydrogen,hydrogen sulphide, carbon monoxide and water vapour existed in a reducedstate. Any free oxygen that escaped from the interior of the earth combinedwith hydrogen, residual methane or ammonia. In the second stage also therewas no free oxygen in the atmosphere.
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Thermosphere
-200 0 200 400 600 800 1000 1200 °C
Mesosphere
Stratosphere
700r-----------------------------r-~
Fig. 1.1. : Temperature profile of the atmosphere (From Miller)
In the third and present day atmosphere oxygen production began to exceedoxygen consumption. Two atmosphere phenomena contributed in the inductionof oxygen. Firstly, it was the photo chemical dissociation of water molecules.Water molecules absorbed ultraviolet rays and splitted into hydrogen and oxy-gen. The major part of oxygen was inducted by photosynthesis. This processbegan after the advent of life on the earth. Multi-cellular marine organismsappeared during this period. They consumed phyto plankton and floated onwater. With the decrease ofphytoplankton, the number of heterotrophic bacte-ria also declined. This led to increase in the oxygen in atmosphere.
-100-80-60 -40 -20 0 20 40Temprature,°C
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]a) 200"C::l
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The Multidisciplinary Nature of Environmental Studies
1.4.2.2.Structure of the AtmosphereThe vertical structure of atmosphere consists of several layers which are sepa-rated from one another by change in slope of the graph of temperature us. alti-tude. In the lowest level (the troposphere) the temperature decreases with in-creasing altitude until at the tropopause (10-12 kms), the temperature is -70"C. The next layer (the stratosphere) is characterized by increasing tempera-ture. Near the top ofthe layer is a region where the ultraviolet solar radiation isabsorbed by ozone. This makes stratopause a warm area of the atmosphere andalso provides an effective shield keeping the harmful ultraviolet radiation fromthe ground.
TroposphereThe lowest layer ofatmosphere in which living organisms operate is called tropo-sphere. It is the region of strong air movements and cloud formations. It was amixture of several gases which remained fairly in abundance. However, watervapour and dust occurred in troposphere in extremely variable concentrations.The air in the troposphere, the air which we breathe, consists volume of about78 percent nitrogen (N2), 21percent oxygen (02)' 1percent argon (Ar) and 0.03percent carbon-dioxide (C02). Also present are traces of other gases, most ofwhich are inert. Details of all these gases are given below in table 1.2.
Table 1.2.Details of different gases in the world's atmosphere
Gas or Vapour Mass Concen- Concen-(trillions tration, tration,oftonnes) ppm %
The layer of greatest interest in pollution control is this layer of troposphere.since this is the layer in which most living things exist. One of the more recent
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change in the troposphere involves the phenomenon of acid rains. Acid rain oracid deposition results when gaseous emissions of sulphur oxides (SOx) andnitrogen oxides (NOx)interact with water vapour and sunlight and are chemi-cally converted to strong acidic compounds such as sulphuric acid (H2S04) andnitric acid (HN0:J. These compounds alongwith other organic and inorganicchemicals, are deposited on the earth as aerosols and particulates (dry deposi-tion) or are carried to the earth by rain drops, snow flakes, fog or dew (wetdeposition). Details of acid rain are given in chapter on "Social issues and theenvironment" .
StratosphereStratosphere is the air mass extending from the uppermost level of the tropo-sphere to uppermost level of stratosphere, about 50 kms above the surface ofthe earth. Ozone present there forms an ozone layer called as ozonosphere. It isformed from oxygen through a photochemical reaction where oxygen moleculesplits to form oxygen.
02 + (h = radiation) = 20The atomic oxygen combines with molecular oxygen and ozone is formed.
02 + °= 03
It forms an umbrella called as ozone umbrella that absorbs the ultraviolet ra-diation from the Sun. Moreover, it serves as a blanket in reducing the coolingrate of earth. Therefore, an equilibrium between ozone and rest of the air is asignificant factor of the environment.
MesosphereAbove to stratosphere is the mesosphere in which there is cold temperature andlow atmosphere pressure. The temperature drops reaching a minimum of-95°C at 80-90 kms above the earth's surface. The zone is called as mesopause.
ThermosphereAbove mesosphere is the thermosphere which extends upto 500 kms above theearth's surface. It is characterised by an increase in temperature from themesosphere. Upper zone to thermosphere where ionization ofmolecules oxygenoccur is called ionosphere.
ExosphereAtmosphere above the ionosphere is called exosphere ofouter space which takesatmosphere except that of hydrogen and helium and extends upto 32190 kmsfrom the surface of the earth. It has very high temperature due to radiations ofSun.
1.4.2.3.Elemental Properties of the AtmospherePollution problems arise from the confluence of atmospheric contaminants, ad-verse meteorological conditions and at times certain topographical conditions.Because of the close relationship that exists between air pollution and certainatmospheric conditions, it is' necessary to have some understanding of meteor-ology.
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The source of all meteorological phenomenon is a basic, but variable ordering ofthe elemental properties of the atmosphere - heat, pressure, wind and mois-ture. All weather including pressure system, wind speed and direction, humid-ity, temperature and precipitation ultimately result from variable relationshipof heat, pressure, wind and moisture.The interaction of these four elements may be observed on several differentlevels of scale. These scales ofmotion are related to mass movement of air whichmay be global, continental, regional or local in scope. According to their geo-graphical range ofinfluence, the scale ofmotion may be designated as macroscale,mesoscale or microscale.Macroscale : Atmospheric motion on this scale involves the planetary pat-terns of circulation, the grand sweep of air currents over hemisphere. Thesephenomenon occur on scales of thousands of kilometers and are exemplified bythe semi-permanent high and low pressure areas over oceans and continents.The air movement on the global scale is not simply in the longitudinal directionfrom equator to poles or vice versa because the dual effect of heat differentialbetween poles and equator and of the rotation of the earth along its axes estab-lishing a more complicated pattern of air circulation. It is under this dual influ-ence of thermal conversion and the corolis force (effect ofthe earth's rotation onwind velocity and direction) that high and low pressure areas, cold or warmfronts, hurricanes and winter storms are formed.One of the primary elements influencing air mass movement on this scale is thedistribution of land and water masses over the surfaces of the earth. The greatvariance between conductive capacities of land and ocean masses account forthe development of many of our weather systems.
Mesoscale: Circulation pattern develop over regional geographic units, pri-marily because of the influence of regional or local topography. These phenom-enon occur on scales of hundreds of kilometers. Air movement of the earth'ssurface - the location ofmountain ranges, of oceanic bodies, of forestation andof urban development.
Microscale :Microscalephenomenon occur over areas ofless than 10kilometers:It occurs within the friction layer, the layer ofatmosphere at ground level whereeffects of friction stress and thermal changes can cause winds to deviate appre-ciable from a standard pattern. The frictional stress encountered as air movesover and around irregular physical features such as buildings, trees, bushes orrocks causes mechanical turbulence which influences the pattern of air move-ment. Radiant heat from stretches of urban asphalt and concrete, desert sandsor other such surfaces causes thermal turbulence that also influences air move-ment patterns.Macroscale circulation patterns have little direct influence on air quality inmost cases. It is the movement of air on-mesoscale and microscale levels that isof vital concern to those responsible for the control of air pollution.Heat: Heat is a critical atmosphere variable. It is a major catalyst of climaticconditions. The heat energy in the atmosphere comes from the Sun as shortwave radiation (about 0.5 um), mostly in the form of visible light. The earthemits much longer waves (average of 10 um) than it receives, mostly in the formof non visible heat radiation.
