Inquinamento acustico en

From "Physics, Waves, Music": a website about the physics of waves and sound, acoustics of musical instruments, musical scales, harmony and music.

What is acoustic pollution and what causes it?

  • If the sound level in a particular area exceeds the limits set by law (for example 55 dB during the day in a residential area, that is, an effective sound pressure of about 0.01 Pa), we say that the area is acoustically polluted.
  • Acoustic pollution is present: near busy roads, because of the noise of engines and of tyres rolling on the asphalt; near construction or manufacturing areas; wherever "noisy" devices are being used. Nowadays, there are numerous sound sources that cause acoustic pollution, which affects the quality of life and health of a large part of the European population: according to the European Environment Agency, more than 20% of Europeans, that is about one person in five, are exposed to levels of road traffic noise harmful to health.

Regulations

  • In 1993, in its "Fifth Environmental Action Programme", the European Commission stated that noise is a serious environmental problem and - in the following "Sixth Environmental Action Programme", which was valid for the decade of 2002-2012 - a regulation was changed to help control the problem. It called for using "sound maps" (acoustic zoning) during urban planning and setting new limits on noise produced by all machines. These measures would reduce the total population exposed to acoustic pollution by 15% with respect to the year 2000.
  • The action plan called for alternatives to current pollution situations and, above all, was a serious attempt to make the population aware of the problem and responsible for contributing positively to a solution.
  • In Italy, the region of Lombardy has the most cities that have conducted acoustic zoning.
  • To carry out acoustic bonification, there is a need for both local technical competences and the political will to implement Bonification Plans.
  • The Italian DPCM 14/11/97 (Prime Minister's Decree 14 November 1997) sets the maximum limit of exposure to noise in both internal and external environments. Various types of areas were identified:
type of area maximum dB daytime maximum dB nighttime
exclusively industrial 70 70
primarily industrial 70 60
intense commercial activity, high population density, railway lines, ports, etc. 65 55
mix of average population density and average industrial/rural activity 60 50
residential 55 45
protected (hospitals, schools, recreational buildings) 50 40

What can be done?

  • To deal with acoustic pollution, the first thing needed is legislative interventions that set parameters to be respected regarding the construction of new buildings and the improvement of existing ones.
  • A good example is building road surfaces with porous, phono-absorbent material or, even better, constructing main thoroughfares that move heavy traffic away from city centres. Another two highly effective interventions are creating bicycle paths and insulating closed environments where sounds are produced with phono-absorbent material.
  • Acoustic pollution near railway lines is caused by friction between the train wheels and the train tracks, as well as traction and braking systems. High-speed trains cause even more noise due to friction between the trains and the air.
  • Currently, many interventions are being implemented to solve these problems, such as improvement of braking systems and track welding techniques. With regards to the aerodynamic noise, new solutions are being sought, particularly considering that many more high-speed trains will be used in the future.
  • Acoustic pollution caused by air traffic is being dealt with through preventive strategies that call for the replacement of obsolete, noisy airplanes, the limiting of night flights and the use of noise maps, especially near airports during take-offs and landings.

To preserve your hearing

Many measures can be adopted to preserve one's hearing. A good example is to try using headphones or earphones without putting the volume at maximum level. This prevents the sound intensity reaching the eardrum from rising to harmful levels.

Hearing damage depends not only on the sound level but also on the duration of exposure. An exposure of 8 hours a day at 85 dB is generally considered acceptable; for every 3 dB more, that is, for every doubling of the sound intensity, the acceptable exposure time halves: 4 hours at 88 dB, one hour at 94 dB, a quarter of an hour at 100 dB. Ringing in the ears or "muffled" hearing after a concert are signs that the limit has been exceeded.

Sound pressure levels in discotheques often reach levels not far from the pain threshold and frequent exposure of eardrums to this situation at a young age can cause hearing loss.

Check your understanding

In a residential area the limit is 55 dB by day and 45 dB by night. How much lower must the sound intensity be at night? Answer. A difference of 10 dB corresponds to a factor of 10 in sound intensity: at night the intensity must be ten times lower than by day (see Perception of loudness).

An exposure of 8 hours at 85 dB is considered acceptable. How long can you safely stay in a venue where the level is 97 dB? Answer. 97 dB is 12 dB more, that is four times 3 dB: the time halves four times, from 8 hours to 4, 2, 1 and finally half an hour.

Why does porous asphalt reduce traffic noise? Answer. Much of the noise of a car, especially at medium and high speeds, comes from the tyres rolling on the asphalt. Porous asphalt absorbs part of the sound instead of reflecting it, and reduces the compression of the air trapped between the tyre and the road, which is one of the sources of the noise.

In-depth study and links

"Physics, Waves, Music": a website about the physics of waves, acoustics of musical instruments, musical scales, harmony and music.