Heat, light, electricity, water and sound, besides a number of things are provided by nature. If the five agents of nature are under control they are rather beneficial to an individual, a society or a nation. If they are in excess and go beyond the control of man or are misused by man they pollute the environment and affect the personal and social health.
Excess of heat (measured in units of temperature) may decompose anything. To take a simple example the burning of coal in mills and factories the chimnies belch carbon dioxide, carbon monoxide and a number of other gases that pollute the atmosphere. Even the un-burnt gas released in a heating process pollutes the environment.
A combination of heat and light that emnates from the sun creates radio activity if the ozone layer grows thin. Electricity generated in the clouds may fall in the shape of lightening burning forests creating pollution. Pollution through dirty water is a common aspect.
That sound (or noise) too pollutes the environment may look funny to many. But it does. It may be some times imperceptible but no less harmful. Noise is directly related to man both in creation and experience. City roads are as much pestered with noise from automobiles, bands, mikes and the down towns with quarrelling men and women and the elite areas with strange associations like the share market that is worst even than the vegetable market as the areas on the banks of rivers with polluted water.
The worse preys of noise pollution are the big cities like New York, London, and Shanghai that have perfect air connection with other cities. A flight a minute disturbs the whole city. Equally infested by noise are the areas by the side of a busy railway track.
That noise too is a serious pollutant is a recent research. It is based on how sound (or noise) affects human ear. It may affect even animals. Before the advent of automobiles horse carriages carried men and material. The driver won’t hit the horse. He will move the hunter in air creating sound that jarred the ears of the horse that gave a jerk to let the horse gain speed—exploiting the animal through noise pollution. The excessive pitch of the noise created by the trumpeting of an elephant or the roaring of a I ion pollutes the whole atmosphere of the jungle. So does the cries of an unruly husband in a house or a residential area. It is the ear that tells whether a particular noise pollutes the environment or not. Ear and sound (or noise) has a direct relationship.
The ear has three parts—the outer, the middle and the inner ear. The auricle i.e. the outer ear collects the sound stimuli. They pass through a canal, widest at the middle ear outer wall i.e. the ear drum. The tympanic membrane of the ear drum receives the sound vibrations from the outer ear. The hammer, the anvil and the stirrup are three minute pieces of bone that transmit the vibrations to the inner ear. The inner ear has two organs—one for hearing and the other for balance. Cochlea the hearing organ is a snail 5-aped container. It transmits sound vibrations as nerve impulses to the brain. The brain initiates the whole system of the body. In a way it guides the different organs to respond to the sound in different ways.
The brain activates the pituitary glands. These glands activate the thyroid and adrenal glands to excrete hormones. As it stimulates the sympathetic nervous system it indirectly influences the heart, the stomach, the pupil, blood vessels and motor nerves that control muscle reactions. Such reactions decide the response of our body to sound. Some sounds are jarring or unpleasant to the ear while some are pleasant. The unpleasant sounds create discomfort and affect the nerves. These unpleasant impacts are collectively called as noise pollution.
Almost all the cities and towns come under noise pollution. In big cities like New York, London, Kolkata and Delhi the noisy traffic is the biggest menace. In cities like New York and the capitals of European countries the noise pollution comes from the sky too because of the high frequency of aeroplanes. Some lower level noises like barking dogs and fighting animals during night hours are also pollutants as they disturb sleep. They can be detrimental to health in the long run. The high pitch sounds affect the ear drum and those who have to hear these constantly are more prone to losing their hearing capacity early as they ascend the age ladder. Some people do more work in noisy environment. But they invite great trouble for the future. The constant exposure to noise deteriorates the tender parts of the mid ear. It, in the long run fails to transmit sound impulses to the inner ear. The result is inefficient responses to sound.
Sound is produced by the vibrations of an object and is transmitted in the form of waves. Sound has two important properties—frequency and intensity (loudness). Frequency means pitch. It is measured in Hertz (Hz) units and is determined by the number of times the vibrating waves fluctuate in a second. The pitch is higher if the fluctuation is more. The loudness is measured in decibels (db). A decibel is one-tenth of a bell. It is the physical unit based on the weakest sound that can be caught or detected by human ear. ‘bel’ is after the name of Alexander Graham Bell who invented the telephone.
The scale of decibel is logarithmic i.e. an increase of 1Odb means 10 times increase. But if the increase is 20 db it means 100 times. Thus 30 db would mean a 1000 times increase. A whisper is about 10 db A decent conversation is around 20 db while a normal talk is 30 db To decide a noise pollution we may start with a loud conversation which is 60 db The playing children have a noise scale of 60 to 80 db While the traffic noise may go to 90 db Heavy truck traffic reaches 100 db while a motorcycle reaches 105.
Beat Music amplified electrically reaches 120 db While an aircraft—a jet take off touches 120 db a jet engine (at 25 m. distance) is generally not less than 140 db But the highest and the most harmful is the space vehicle launch noise that reaches 170 db
Looks strange but is equally true that the human ear cannot hear sounds having frequencies higher than 20,000 Hz (20,000 vibrations per second). It explains why one can’t hear the extraordinary high pitch sound created by a flying bat which is 20,000 to 1, 00,000 Hz. The sound is at ultrasonic levels. The ultrasonic waves are a tool of research and are useful in the sub-marine echo sounding and in detection of flows in casting, drilling glasses and other processes. As such it is hard to say if they pollute the environment as they do not affect the hearing process.
The speed at which sound travels can of course some times go on polluting the area it covers. Sound can travel in certain media at different speed with which it travels in air. It is 331 meters per second in air at sea level. In water 4965 in per second, in glass it is 6000 in per second while in iron or steel it is generally 15000 m per second. In granite, ice cold water, bricks and even in wood its speed is greater than in air. This explains how sound pollutes sea water through sub-marine and also how noise can pollute the mines and closed buildings too.
But the most experienced pollution through speed is in the air media. That is how the thundering clouds deafen people when the thunder reaches the earth. The railway trains too leave their mark of sound all the way they travel. But the most injurious is the sound of aeroplanes that travels to the earth passage over which they fly. When they start travelling with a speed more than 331m per second they cross, the sound barrier making a quake like vibration in the atmosphere.
Supersonic speed is about 1216 km per hour. It is measured in Mach (after the name of Ernst Mach, a German Scientist who worked it out). Now Mach is the ratio of the speed of flight to the speed of sound. At the speed of sound it is Mach 1, at half it is 0.5, at twice the speed it is mach 2 and so on. Since the modern fast aeroplanes cross the speed barrier they pollute the area all the way when they fly low on cities. As the speed of the plane is more than that of sound the sound remains behind and those in the planes are not affected by it.
Any way noise pollution has been increasing in different ways with the growth of urbanization. Besides taking the environmental pollution, water pollution, nuclear pollution and the depletion of ozone layer seriously the world will have to develop a culture—sophistication in life to remove or lessen noise pollution too or half the world will be partly or totally deaf in decades to come.