Lecture 11 :: Causes, effects and control of noise and thermal pollution

Noise pollution
Noise is perhaps one of the most undesirable by products of  modern mechanized lifestyle. It may not seem as insidious or harmful as the contamination of drinking water supplies from hazardous chemicals, but it is a problem that affects human health and well-being and that can also  contribute to the  general deterioration of environmental quality. It can affect people at home, in their community, or at their place of work.
Sound waves cause eardrums to vibrate, activating middle and inner organs and sending bioelectrical signals to the brain. The human ear can detect sounds in the frequency range of about 20 to 20,000 Hz, but for most people hearing is best in the range of 200 to 10,000 Hz. A sound of 50 Hz frequency, for example, is perceived to be very low-pitched, and a 15,000 - Hz sound is very high pitched.
Simply defined, noise is undesirable and unwanted sound. It takes energy to produce  sound, so, in a manner of speaking, noise is a form of waste energy. It is not a substance that can accumulate in the environment, like most other pollutants, but it can be diluted with distance from a source. All sounds come from a sound source, whether it be a radio, a machine, a human voice, an airplane, or a musical instrument. Not all sound is noise. What may be considered music to one person may be nothing but noise to another. To a extent, noise pollution is a matter of opinion. Noise is measured in terms of Decibel units.
Sources of noise
Based on the type of noise include
a) Industrial Noise
b) Transport Noise
C) Neighbourhood Noise
Industrial Noise
It is caused by machines used for the technological advancement. There exist a long list of sources of noise pollution including different machines of numerous factories, industries and mills.



Transport Noise:

Main source is transport. In addition to adversely impacting urban air quality, heavy automobile traffic creates seemingly unbearable noise pollution. Ever since industrial revolution   doubling of noise for every 10 years


Pointed nose that angles downward during takeoff, the Anglo-French Concorde flies at more than twice the speed of sound.  Supersonic plane is very noisy, and some believe its sonic booms harm the environment.


Animals such as whales use water to communicate with one another over great distances. Human-generated noises in the ocean, such as engine noises by boats, may interfere with animal communication.

Measurement of noise
The noise is usually measured either by i) Sound Pressure or ii) Sound Intensity.  The Sound intensity is measured in Decibel (dB), which is tenth part of the longest unit “Bel” named after Alexander Graham Bell. Decibel (dB) is a ratio expressed as the logarithmic scale relative to a reference sound pressure level. The db is thus expressed as

Sound Intensity Level = 10 log Intensity Measured (I)
Reference intensity (I0)
    or            dB = 10 log I / I0

Intensity of Noise sources





Trickling clock


Normal conversation


Office noise

60 - 80



Motor cycle


Jet fly

100 - 110

Effects of Noise Pollution
Auditory effects

    • Auditory fatigue   -- Whistling &                 buzzing in ears( noise level - 90dB)
    • Deafness               --  Permanent hearing loss ( noise level- 100dB)


  • Persistent sound in one or both ears.
  • Tinnitus is often experienced as a high-pitched hiss, ring, buzz, or roar.
  • It is usually continuous, but it may pulsate, and the beats may coincide with the heartbeat.

Non auditory effects

  • Interference with speech  communication - 50dB
  • Annoyance, ill temper, bickering
  • loss in working efficiency - tiredness, deterioration or complete loss of ability to work

Physiological disorders
Neurosis, anxiety, hypertension, increased sweating, giddiness, nausea, fatigue, visual disturbance, reduces depth and quality of sleep ,  peptic ulcers, Increases cholesterol level resulting in constriction of blood vessel , Low weight children to  mothers

Noise intensity

Health hazards




Hearing damage


Very annoying


Stimulation of reception in skin


Pain threshold




Pain in ear


Burning of skin


Rupture of tymphonic membrane


Permanent damage

Even the nonliving things such as buildings undergo physical damage by cracks, breakage of windows, doors, and glasses etc. by sudden and explosive sounds.

Control of Noise Pollution
Noise definitely affects the quality of life. It is therefore important to ensure the mitigation or control of noise pollution. Noise pollution can be controlled

Control of Noise Pollution

Noise definitely affects the quality of life. It is therefore important to ensure the mitigation or control of noise pollution. Noise pollution can be controlled
•           At source level – Can be done by  i) Designing and fabricating silencing devices in air craft engines, automobiles industrial machines and home appliances, ii) By segregating the noisy machines

•           During Transmission – can be achieved by adding insulation and sound-proofing to doors, walls, and ceilings; covering the room walls with sound absorbers as acoustic tiles and construction of enclosures around industrial machinery. Zoning urban areas to maintain a separation between residential areas and zones of excessive noise. Sound absorbents can be used for the reduction of noise.
a)         Acoustillite : made up of Compressed wood pulp, wood fibers and is available in the form of tiles
b)         Acoustical blanket : Prepared from mineral wool or glass fibres
c)         Hair Felt: Consists of wool fibres, Coarse Cotton Fibres.
d)         Fibre Glass
e)         Cork Carpet: Prepared out of pieces of corks treated with linseed oil and is used for covering floors.
f)         Acoustic Plaster: Mainly consists of gypsum in the form of plaster.
•           Protecting the  exposed person
•           By creating vegetation cover – Plants absorb and dissipate sound energy and thus act as Buffer Zone. Trees should be planted along highways, schools and other places.

Planting vegetation to absorb and screen out noise pollution – Trees can act as a noise barrier

          1. Through law  
          2. Silence Zones must be created near Schools, hospitals
          3. Indiscriminate use of loudspeakers at public places should be banned/restricted  by laws
          4. Restriction on unnecessary us e of horns and vehicles plying without silencers
          5. Restrictions on aircraft flight at midnight


Permissible Ambient Noise Level in Different areas




Code category

Noise level (dB)

Day Time
(6 to 9 Am)

Night Time
(9 to 6 PM)


Industrial Area




Commercial Area




Residential Area




Silence Zone



      1. The Air (prevention and control of pollution) Act, 1981
      2. The Motor Vehicles Act,1988
      3. Indian Penal Code – Sections 268 & 290
          1. Through education - We Indians are Noisy people. Every occasion, it may be religious or family functions or elections; we used to celebrate with noise. Educating  the people that noise is a pollutant, not a part of our routine life.


Thermal Pollution
The term thermal pollution has traditionally been used more often to refer to the heating of lakes, river, streams, and other  water bodies  usually by electric power generating plants or by factories

          1. The combustion of fossil fuels always produces heat, sometimes as a primary desired product, and sometimes as a secondary, less desired by-product i.e. noise
          2. Heat is also produced when fossil fuels are burned to generate electricity. In this case, heat is a by-product, not the main reason that fuels are burned.
          3. Electricity is also generated in nuclear power plants, when no combustion occurs.
          4. The decay of organic matter in landfills also releases heat to the atmosphere.

It is clear, therefore, that a vast array of human activities result in the release of heat to the environment. As those activities increase in number and extent, so does the amount of heat released. In many cases, heat added to the environment begins to cause problems for plants, humans, or other animals. This effect is then known as thermal pollution.
Sources of Thermal pollution

  1. Coal fired power plant effluents
  2. Domestic sewage
  3. Hydroelectric  power effluent
  4. Industrial effluents
  5. Nuclear power plants



Effects of thermal Pollution

                  A one megawatt nuclear power plant may require 1.3 billion gallons (five million m3) of cooling water each day. The water used in such a plant has its temperature increased by about 63oF (17oC) during the cooling process. For this reason, such plants are usually built very close to an abundant water supply such as a lake, a large river, or the ocean.

When thermal pollution drives water temperatures up, most aquatic and marine wildlife cannot survive. Immobile organisms, such as plants and shellfish, simply die. One inevitable result of thermal pollution is a reduction in the amount dissolved oxygen in water. The amount of any gas that can be dissolved in water varies inversely with the temperature. As water is warmed, therefore, it is capable of dissolving less and less oxygen. Organisms that need oxygen to survive will, in such cases, cant be able to survive.

When heated water is released from a plant or factory, it does not readily mix with the cooler water around it. Instead, it forms a stream-like mass known as a thermal plume that spreads out from the outflow pipes. It is in this thermal plume that the most severe effects of thermal pollution are likely to occur. Only over an extended period of time does the plume gradually mix with surrounding water, producing a mass of homogenous temperature

Invasion of Destructive Organism

                Water temperatures can have other, less expected effects also. As an example, trout can swim less rapidly in water above 66oF (19oC) making them less efficient predators. Organisms may become more subject to disease in warmer water too. The bacterium Chondrococcus columnaris is harmless to fish at temperatures of less than 50oF (10oC). Between temperatures of 50o - 70oF (10o - 21oC), however, it is able to invade through wounds in a fish's body and at temperatures above 70oF (21oC) it can even attack healthy tissue.
Urban Heat dome
Another example of thermal pollution is the development of urban heat islands. An urban heat island consists of a dome of warm air over an urban area caused by the release of heat in the region. Since more human activity occurs in an urban area than in the surrounding rural areas, the atmosphere over the urban area becomes warmer than it is over the rural areas.
It is not uncommon for urban heat islands to produce measurable climate changes. For example, the levels of pollutants trapped in an urban heat island can reach 5 to 25 percent greater than the levels over rural areas. Fog and clouds may reach twice the level of comparable rural areas, wind speeds may be produced by up to 30 per cent, and temperatures may be 32.9o - 35.6oF (0.5o - 2oC) higher than in surrounding rural areas. Such differences may cause both personal discomfort and, in some cases, actual health problems for those living within an urban heat island.

Undesirable changes in Algal population: Excess Nutrients from the washout water from farm lands combined with thermal pollution cause an excessive algal growth with consequent changes. High Temperature promotes blue green algal blooms which disrupts the aquatic food chain.
Control of Thermal pollution
The water heated by thermal pollution also has a number of potential useful applications. For example, it may be possible to establish aquatic farms where commercially desirable fish and shellfish can be raised. The Japanese have been especially successful in pursuing this option. Some experts have also suggested using this water to heat buildings, to remove snow, to fill swimming pools, to use for irrigation, to de-ice canals, and to operate industrial processes that have modest heat requirements. Hot water is pumped into one end of the pond and cooler water is removed from the other end. The heat gets dissipated from the pond into the atmosphere. The main disadvantage is large amounts of water are lost due to evaporation

Here at Westport, Kentucky the Ohio River provides the large amount of water required by this coal-fired power plant. Thermal pollution is abated by the use of the large cooling tower which emits only steam into the atmosphere. The emission of the smokestack is largely steam but still contains pollutants.