Contents
Immunology is one of the Biology Topics focused on understanding the immune system and its response to pathogens and diseases.
Air is a Natural Resource and cannot be Exhausted by Human Activities.
The multilayered gaseous envelope surrounding the planet Earth is called the atmosphere. The atmosphere filters sunlight reaching the Earth, affects climate, and is a reservoir of several elements which are essential for life. It is divided into five distinct layers or zones: troposphere, stratosphere, mesosphere, thermosphere (ionosphere), and exosphere. Troposphere is the lowest region of the atmosphere which contains air and is subject to differential heating. It extends from the surface of Earth upto 8 to 20 km. Many important climatic events such as cloud formation, lightening; thundering, thunderstorm formation, etc., all take place in the troposphere.
On Earth, we human beings along with all other biota are surrounded by air. Air is a mixture of gases such as nitrogen, oxygen, and carbon dioxide. Air also contains water vapour and suspended dust particles. Oxygen is required by all living beings for respiration and for burning (combustion) of materials. Air contains about 20 percent oxygen and its percentage in air is balanced by the process of photosynthesis. Photosynthesis occurs in chloroplasts of green plants and this metabolic activity requires carbon dioxide, water, and sunlight but releases oxygen gas.
Composition of Gases in Air
Component | Percentage of Volume |
1. Nitrogen (N2) | 78.09 |
2. Oxygen (O2) | 20.93 |
3. Argon (Ar) | 0.93 |
4. Carbon dioxide (CO2) | 0.03 |
5. Miscellaneous (moisture, dust, etc.) | 0.02 |
The Atmosphere: Earth’s Security Blanket – Climate Change
1. Role of Atmosphere in Climate Control
Air is an inexhaustible natural resource. In a world without air, there would be no plant or animal life, no winds, clouds, or rain, no fires, and no protection against harmful solar radiation. This is because the atmosphere covers the Earth, like a blanket. Air is a bad conductor of heat. The atmosphere keeps the average temperature of the Earth fairly steady during the day and even during the course of the whole year.
The atmosphere prevents the sudden increase in temperature during the daylight hours. And at night, the atmosphere slows down the escape of heat into outer space. For instance, the moon is about the same distance from the sun that the Earth, but it lacks an Earth-like atmosphere. As a consequence, on the surface of the moon, the temperature ranges from -190° C to 110° C. Thus, the moon’s temperature rises during the sunlit period (day) to about 110°C and cools to -190°C during the dark period (night).
To measure the temperature of water, soil, sand, and air in bright sunlight and shade.
Take (i) a beaker full of water, (ii) a beaker full of soil, and sand, and (iii) a closed bottle containing a thermometer. Keep them in bright sunlight for three hours. Now measure the temperature of all three vessels. Also, take the temperature reading in the shade at the same time.
You will observe that the temperature of soil/sand is more than the temperature of water in bright sunlight. It is so because soil/sand gets heated by solar radiation faster than water. Therefore, the land would become hot faster than the seas. You will also observe that the temperature of air (in shade) is different from the temperature of soil/sand and water (in bright sunlight) because of the direct effect of radiation in the latter case.
The temperature should be measured in the shade because in the bright sunlight direct solar radiations will affect the thermometer reading which will not be uniform.
You will observe that the temperature of the air in the closed glass bottle is more than the temperature taken in the open air. It is due to the greenhouse effect. The solar radiations enter the glass bottle through the glass walls. However, the reradiated rays can not pass through the glass and they heat up the air inside the closed glass container. We come across this phenomenon of the greenhouse effect in our daily life. For example, when a car is parked in the sun, it gets heated from inside due to the greenhouse effect.
2. The Movement of Air: Wind
A cool evening breeze after a hot day or rain after a few days of hot weather brings us considerable relief. The following questions may strike our mind:
- What causes the movement of air?
- What decides whether this movement of air will be in the form of a gentle breeze, a strong wind, or a terrible storm?
- What brings the rain?
All the phenomena in the above-mentioned questions are the result of changes that take place in our atmosphere due to the heating of air and the formation of water vapours.
When the solar radiations fall on the Earth, some are absorbed and the majority of these are reflected back or reradiated by the land and water bodies. These reflected or reradiated solar radiations heat the atmosphere from below. As a result, convection currents are set up in the air. But since the land gets heated faster than the water, the air over land also gets heated faster than the air over water bodies.
Air movement in coastal areas: In coastal areas, during the daytime, there is a regular flow of cool air from the sea towards the land. At night, there is a reverse flow of air from land to sea. This happens because, during the daytime, the land gets heated faster than water. Re-radiation of heat from land heats the air above it. The hot air rises and creates an area of low pressure. Sea water does not get heated so rapidly, so the air above the sea is relatively cool. A high-pressure area forms above seawater as compared to air over land. Therefore, cooler air over the sea flows toward the land, where a low-pressure area exists. The movement of air from one region to the other creates winds.
During the night, a reverse flow of air occurs. Land cools down rapidly. The air above the land becomes cooler. Sea water cools down slowly. The air above the sea is hotter and has a lower air pressure as compared to air pressure above the land. Therefore, cooler air present over land flows towards the sea.
Wind Belts
At a much larger scale, temperature differences across the Earth generate the development of the major wind belts. Such wind belts, to some degree, define the climate zones of the world.
To demonstrate that-air currents are caused by the uneven heating of air.
Place a candle in a beaker or wide-mouthed bottle and light it. Now, light an incense stick (Agarbatti) and bring it to the edge of the mouth of the beaker or bottle. Observe the direction of the flow of smoke. In the next step, keep the lighted incense stick a little above the candle and note the direction of the flow of smoke. Keep the lighted incense stick in other regions above the beaker or bottle and again note the direction of smoke above the beaker or bottle and again note the direction of the smoke.
You will observe that the direction of the flow of smoke is different (i) when a lighted incense stick is kept at the edge of the mouth of a beaker or bottle, (ii) a little above the candle, and (iii) in different regions above the beaker or bottle when the incense stick is kept at the edge of the mouth of the beaker or bottle, the smoke will flow toward the candle and then above.
When the incense stick is placed at different regions above the beaker or bottle, the direction of the flow of smoke will be towards the candle and then upwards. The patterns revealed by the smoke show us the direction in which the hot and cold air move. The air above the burning candle gets heated and therefore rises, creating a low pressure below. Therefore, air from adjacent cold areas moves towards this low-pressure zone.
The movement of air does not follow the quickest straight-line path. In fact, the air moving from high to low pressure follows a spiraling route, outwards from high pressure and inward towards low pressure. This is due to the rotation of the Earth beneath the moving air which causes an apparent deflection of the wind to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The deflection of air is caused by the Coriolis force. Consequently, air blows anticlockwise, around a low-pressure center (depression), and clockwise, around a high-pressure centre (anticyclone) in the Northern Hemisphere. This situation is reversed in the Southern Hemisphere.
Coriolis Effect
A force that, like centrifugal force, apparently acts on moving objects when observed in a frame of reference that is itself rotating. Because of the rotation of the observer, a freely moving object does not appear to move steadily in a straight line as usual, but rather as if, besides an outward centrifugal force, “Coriolis force” acts on it, perpendicular to its motion, with a strength proportional to its mass, its velocity, and state of rotation of the frame of reference. The effect, first described in 1835 by Gaspard de Coriolis (1792 – 1843) accounts for the familiar circulation of airflow around cyclones, etc.
Fronts: Air temperature is generally higher at ground level due to heating by the sun, and decreases with increasing altitude. This vertical temperature difference creates a significant uplift of air, since warmer air near the surface is lighter than cold air above it. This vertical uplift of air can generate clouds and rain. Sometimes, air from warmer regions of the world collides with air from colder regions. This air mass conversion occurs in the mid-latitudes, where the warm air rises above the colder air, generating fronts and depressions.
Factors Influencing Movements of Air
Depending upon the energy levels and air pressure, diverse types of atmospheric phenomena occur, such as breezes, wind storms, thunderstorms, monsoon rains, cyclones (tempests/typhoons), etc. Various factors controlling these phenomena are:
- Uneven heating of land at different parts of Earth.
- Differences in heating and cooling of land and water bodies.
- Vaporisation and condensation of water vapours.
- Rotation of Earth.
- Presence of high mountain ranges in the path of winds.
- The difference in topography over which the wind passes.
3. Rain
When water bodies get heated by solar radiation during the day, a large amount of water evaporates and goes into the air. Some amount of water vapour also goes into the atmosphere because of various biological activities such as transpiration by plants. The air carrying water vapour also gets heated. This hot air rises up, carrying water vapours with it. As the air rises, it expands and cools. This cooling causes the water vapour in the air to condense in the form of tiny droplets. Such a process of condensation of water is facilitated when dust and other suspended particles act as the ‘nucleus’ for these droplets to form around.
An enormous collection of tiny droplets of water appear in the form of clouds. These droplets of water, once formed, slowly grow bigger due to the condensation of more water droplets. When the droplets become big and heavy, they fall down in the form of rain. Occasionally, when the temperature of the air is very low, precipitation then may occur in the form of snow, sheet, or hail.
To demonstrate the role of some factors influencing climatic changes such as the formation of clouds and rain.
Take an empty plastic bottle in which bottled water is generally sold. Pour 5-10 ml water into it and close the bottle tightly with a cap. Shake the bottle well and then place it in the sun for 10 minutes. Now open the cap of the bottle and allow some smoke from the lighted incense stick to enter the bottle. Quickly close the bottle tightly with the cap. Now, press the bottle hard between your hands as much as possible. After a few seconds release the bottle. Press the bottle again as hard as you can.
This simple experiment replicates, on a very small scale, the happenings when air with a very high content of water vapour goes from a region of high pressure to a region of low pressure. When a bottle containing water is kept in the sun, the water evaporates and air inside the bottle gets saturated with water vapour. When the bottle is pressed between your hands, the pressure inside becomes high and air inside the bottle moves in a region of low pressure. It expands and cools.
The smoke particles act as ‘nuclei’ on which water vapours condense in the form of tiny droplets. When you release the pressure, the air inside the bottle becomes foggy. When the bottle is again pressed, the fog will disappear, it is so because due to high pressure condensed water vapours will fall down and collect as water at the bottom of the bottle. When the experiment is repeated without smoke inside the bottle, one will not observe foggy air inside the bottle as smoke particles are absent and nothing is available in the air to act as a ‘nucleus’ for water vapours to condense as tiny droplets.
To collect information from newspapers and weather reports on rainfall patterns across the country
Read the newspapers daily or alternatively listen to the weather reports on television. Record the relevant information about rainfall patterns across the country daily in your notebook.
You will notice that rainfall patterns in different regions/cities/towns are not uniform throughout the year. Different regions or cities or towns get a varied amount of rainfall in specific months of the year only. In large parts of India, rains are mostly brought by the southwest or northeast monsoons. You will also observe the month in which your city/town/village got the maximum rainfall. Similarly, you will observe the month in which your state or union territory got the maximum rainfall. Rain is not always accompanied by thunder and lightning. However, it is generally accompanied by thunders and lightning in monsoon months.
Air Pollution – Causes and Effects
Air pollution is the addition of air pollutants such as particulate matter, gases, and vapors into the atmosphere, which has an adverse effect on humans, animals, vegetation, and human assets. In fact, air pollution is of two main types:
- Natural (e.g., forest fire, dust storm, pollen).
- Human-made (e.g., burning of fossil fuels in industries, vehicles and thermoelectric plants, gaseous emission from industries, mining, processing, stone crushing).
Particulate air pollutants are also called suspended particulate matter or SPM because they remain suspended in the air for a good period of time. SPM consists of smoke, soot (a black powder substance that is produced when coal, wood, etc., is burnt), fly ash, and dust (i.e., particles of silica, grit, lead, asbestos, cement, sulphur, etc.).
Gases that cause air pollution are sulphur dioxide, nitrogen oxides, carbon monoxide, hydrogen sulphide, hydrogen cyanides, hydrogen fluorides, chlorine, methane and ammonia. They are formed from nitrogen, sulphur, and carbon compounds of fossil fuels and decaying organic matter. Pollutant vapours include unburnt hydrocarbons (benzene).
Effects of Air Pollution on Human Beings
- SPM causes asthma, bronchitis, and allergic cold.
- Pollutant gases cause irritation in the eyes, throat, and lungs.
- They injure the lungs, liver, kidneys, spleen, and nervous system.
- Heart-related diseases tend to increase. Many people develop terminal ailments such as cancer.
- Hydrocarbon vapours not only damage the internal organs but also cause cancer.
Other Effects of Air Pollution
Many injurious effects such as falling of leaves, reduced growth, degeneration of chlorophyll, mottling of leaves, etc., have been noticed in plants. Lichens are very sensitive to the levels of contaminants, such as sulphur dioxide, present in polluted air.
To study lichens growing on the bark of trees in your area
Make a visit to trees growing along busy roads, less busy roads, and some distance away from the roads. Record the lichens growing on the barks of trees in. above mentioned areas. Compare the lichens growing on trees near busy roads with those on trees some distance away. On the trees near roads, compare the incidence of lichens on the side facing the road with the side away from the road.
Normally, you will observe lichens on the bark of trees as the greenish-white crust. On the trees near busy roads, the incidence of lichens would be less as compared to those on the trees some distance away from the roads. You will also observe more incidence of lichens on the barks of trees on the sides away from the roads as compared to the sides towards the roads. It is so because on busy roads, automobiles regularly, emit air pollutants including sulphur dioxide by burning fossil fuels (diesel, petrol). Increased levels of air pollutants such as sulphur dioxide in the air around busy roads reduce the incidence of lichens on the trees near roads as they are sensitive to increased levels of air pollutants such as sulphur dioxide.
Further, SO2 reacts with water in the atmosphere to form sulphuric acid. This sulphuric acid is washed down into the soil by rain (acid rainfall) which it may make the soil highly acidic, thus, affecting the growth of plants and ultimately the forest growth. The acid rainfall severely affects salmon reproduction and fish yield and also eats into the surface of buildings, eroding the stone (e.g., Taj Mahal) and brickworks.
Air pollution also results in two serious ecological problems of global magnitude-green house effect and the peeling of the ozone umbrella (hole in the ozone layer). The carbon dioxide of the atmosphere keeps the Earth warm, much like a glass wall that keeps a greenhouse warm. This effect is called the greenhouse effect. The increase in carbon dioxide in the atmosphere intensifies the greenhouse effect and leads to global warming, i.e., an increase in the average temperature of the Earth.
Ozone Layer Depletion – Cause, Effects, and Solutions
Ozone is an allotrope of oxygen. (Allotropy refers to an occurrence of one element in more than one form). It is triatomic (O3) as compared to diatomic elemental oxygen (O2). Ozone gas is a blue gas with a pungent odour. It is highly poisonous to living systems. It, however, does not exist in an appreciable quantity in the lower atmosphere region called the troposphere. Ozone is present in significant amounts in the stratosphere region of the atmosphere. Maximum concentration occurs at a height of 23-25 Km above the equator or at slightly lower altitudes at other places. The density of the ozone layer varies greatly, being thickest at high latitudes in late summer and much thinner over the tropics.
The part of the atmosphere which is rich in ozone may be called the ozone layer, ozonosphere, ozone umbrella, or ozone shield. The ozone layer is highly important as it filters out the harmful, high-energy ultraviolet radiations coming from the sun. The high-energy ultraviolet radiations split ozone into molecular and atomic oxygen:
Heat is liberated which warms the stratosphere. Ozone re-forms as atomic oxygen is highly reactive:
O2 + [O] → O3
In 1985, Farman et al., found that the ozone layer had thinned out over Antarctica. It was called an ozone hole. A similar but smaller hole was also found over the Arctic region by Augestein (1987). The hole is more prominent in the spring season in these regions. Over the years, the antarctic ozone hole has widened. It has grown in size from 13 million km2 in 2000. The amount of atmospheric ozone is measured by a Dobson spectrometer and is expressed in Dobson units (DU).
Ozone Depleting Substances (ODS): A reduction in the concentration of the ozone layer is called ozone depletion. It is caused by certain chemicals called ozone-depleting substances (ODS). The important ODS are chlorofluorocarbons (CFCs), halons, methyl bromide, nitrogen oxides, and chlorine, CFCs such as carbon tetrachloride, CCl3; dichlorodifluoromethane, (CCl2F2). They are rich in chlorine, fluorine, and carbon. CFCs are commonly used as aerosol propellants, refrigerants, shaving foams, spray agents in scents, etc. Some ODS are released in the stratosphere by jets flying at height.
Effects of Ozone Depletion:
Depleting the ozone layer allows more ultraviolet (UV) radiation to pass through it, which reaches the Earth’s surface. These UV rays cause various harmful effects on human beings, animals, plants, and the environment such as
- Skin cancer.
- Damage to eyes; also increase in the incidence of cataract disease in eyes.
- Damage to the immune system.
- Increased embryonic mortality in animals and humans.
- Decreased crop yields.
- Reduced populations of phytoplankton, zooplankton, and certain fish larvae are important constituents of aquatic food chains.
- Smog formation
Smog Definition & Meaning
Smog is a photochemical haze (dark brown or greyish smoky mist) caused by the action of solar ultraviolet radiation on the atmosphere polluted with primary pollutants such as hydrocarbons (methane, ethane, toluene, etc.) and oxide of nitrogen (NO2) from automobile exhaust:
Atomic oxygen sometimes reacts with hydrocarbons to form radicals. These radicals ultimately combine with oxygen, NO2, and hydrocarbons to produce secondary pollutants such as formaldehyde, aldehydes, and peroxyacetyl nitrate (PAN). All these pollutants collectively form photochemical smog. Smog not only reduces visibility but is highly suffocating and toxic (harmful to humans, animals, and plants).
Plans are in pipelines to phase out the use of ozone-depleting substances (ODS) such as CFCs by 2020. The use of methyl bromide as a pesticide has already been stopped, as it acts as a powerful ozone-depleting reagent.