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Studies about Noise Pollution in Urban Areas

GABRIELA DEMIAN, MIHAI DEMIAN, LUMINIŢA GRECU, VALENTIN GRECU

Engineering Department University of Craiova

13 A. I. Cuza street, Craiova ROMANIA

[email protected]; [email protected]; [email protected]; [email protected]

Abstract: - The problem of the traffic noise pollution from the urban areas amplified in the last years. The evolution of the traffic volume values in Romania is continuously increasing. The present paper presents measurements of traffic noise on the street in south western Romania (Drobeta Turnu Severin). The study was performed between January-April 2007. The paper presents the ways to reduce emissions from urban traffic and noise pollution prevention. Key-Words: - Acoustic pressure, Noise, Pollution, Sonometer, Decibel 1 Introduction Global problem of population protection against noise is very important and should be treated with great responsibility by the authorities. By joining the EU, Romania had to adapt legislation to the European; the first step in this direction is the preparation of noise maps. Noise is a neglected form of pollution in our country but the form has a significant impact on human society, affecting the health of the population. Industry, shipments, car traffic are strong current and potential sources of pollution. Methods and apparatus for measuring noise are complex and must comply with standards that are applied to the measurement noise. Standards contain the necessary conditions for measuring instruments, methods of measuring noise for different activities or types of equipment, assessing the harmful effects of noise. The most important standards are those published by ISO (International Standards Organization) and IEC (International Electrotechnics Commission). ISO deals primarily in the measurement methods, experimental conditions, measurement parameters and methods for evaluating the results, while his prime objective is to design and construction of measuring instruments. 2 Noise Measurement

Equipment In measurement noise on the field, essential condition is that the equipment is easily installed and calibrated on the ground, have the power

independence, to be slight, to say the equipment is portable. Sonometer is a portable device that serves to measure the level of acoustic pressure. Audio signal is converted into an electrical signal identical, through a microphone. Signal noise is low must be amplified before it can read the screen on the instrument. After further amplification, the signal is high enough to be shown on the instrumental reading. The display instrument gives in dB the level of acoustic pressure. The potential harmfulness of noise is not only depending on the level of this noise but also it depends on the duration. To measure the potential harm of a noise should measure both the level and duration of noise. 3 Sound Power, Intensity and

Pressure The basic unit of level in acoustics is the “decibel” (abbreviated dB). Decibel is a logarithmic unit used to describe physical values like the ratio of the signal level - power, sound pressure, voltage or intensity.

⎟⎟⎠

⎞⎜⎜⎝

⎛=

refPPlg10decibel

where: P is the signal power (W); Pref is the reference power (W) . Sound power is the energy rate - the energy of sound per unit of time (J/s, W in SI-units) from a sound source. Sound power can more practically be

Proceedings of the 10th WSEAS International Conference on ACOUSTICS & MUSIC: THEORY & APPLICATIONS

ISSN: 1790-5095 87 ISBN: 978-960-474-061-1

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expressed as a relation to the threshold of hearing - in a logarithmic scale named Sound

Power Level - . W10 12−

WLThe sound power level is given the symbol LW or SWL.

⎟⎟⎠

⎞⎜⎜⎝

⎛=

0W N

Nlg10L (1)

where: is the sound power level in WL

10 12−

( )SWLdecibel (dB); is the sound power (W);

. N

WN0 =The lowest sound level that people of excellent hearing can discern has an acoustic sound power about , . The intensity, or power per unit area, is simply given by where P is the power emitted by the source and r is the distance from the source. The intensity I would be measured in watts per square meter. The sound level (sometimes called the intensity level - a term which I think is too easily

confused with "intensity" which is measured in

W10 12− dB0

2mW

)

associated with any sound is determined by the intensity ratio relative to the threshold of hearing and is measured in decibels. According to theory ignorable the effect of absorption in a spherical wave radiated in an open space of power P, I sound intensity decreases inversely as the square of r to the source:

24 rPIπ

= (2)

The Sound Intensity Level can be expressed as:

⎟⎟⎠

⎞⎜⎜⎝

⎛=

refI I

Ilg10L (3)

where: = sound intensity level (dB); = sound

intensity (W/m2);

IL I

⎟⎠⎞

⎜⎝⎛= −

212

ref mW 10I reference

sound intensity. The Sound Pressure is the force (N) of sound on a surface area (m2) perpendicular to the direction of the sound. The SI-units for the Sound Pressure are N/m2 or Pa. The sound pressure level (SPL) or Lp is defined as:

⎟⎟⎠

⎞⎜⎜⎝

⎛=⎟

⎟⎠

⎞⎜⎜⎝

⎛=

ref2ref

2

p pplg20

pplg10L (4)

where: = sound pressure level (dB); = sound

pressure (Pa); reference sound pressure (Pa).

pL P

Pa102P 5ref

−⋅=

The sound pressure level is expressed in units of decibels (dB), where P is measured in Pascals (Pa) and is ostensibly the audible limit of the human

ear, with a value defined as . refP

Pa102 5−⋅ 4 Noise Environment in Urban Areas

of Drobeta Turnu Severin When comparing two different sound intensities, and , the difference in sound levels would be given by:

1I

2I

0

1

1

21I2II I

Ilg10IIlg10LLL −=−=Δ (5)

which would reduce to

⎟⎟⎠

⎞⎜⎜⎝

⎛=

1

2I I

Ilg10LΔ (6)

When the source of sound is a "point source" - the sound spreads out uniformly in all directions - the

intensity is given by 2r4PIπ

= . So the sound level

difference between the two points at different distances from the same source is given by

⎟⎟⎠

⎞⎜⎜⎝

⎛=⎟

⎟⎠

⎞⎜⎜⎝

⎛=

2

122

21

I rrlg20

rrlg10LΔ (7)

Absorption of sound energy in air is very small and can be considered only if large distances. High sounds are absorbed much more intense than the low. Thus at a fixed distance from two sources of sound intensity equal to a frequency of 50Hz and 1000Hz down the sound will be heard with more intensity than the high sound. This explains the fact that the noise of a plane flying at a great height and the noise of distant strong sources, eg bench test stand for engines, sounds are perceived as low. All that sounds high are in noise composition and are attenuate during the propagation due to absorption in the air to such an extent that becomes inaudible. Distance at which the low tones can be heard can be explained that having long low sounds they can by pass obstacle by


ISSN: 1790-5095 88 ISBN: 978-960-474-061-1

http://www.engineeringtoolbox.com/decibel-d_341.html

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diffraction to their propagation, while it sounds high, with short-wave, are reflected by obstructions and therefore screened by them. Audibility distance of sound sources vary greatly depending on atmospheric condition. The same source can be heard sometimes from 10 km distance, and sometimes only from 1-2 km. Often the sound of a strong source (siren signaling, by shooting cannon, etc...) Is not heard at a distance of several miles but at a bigger distance, is heard again. These differences, between the distances of audibility are because at different heights above the earth's temperature and speed of movement of air are not the same. Usually windy with periods of air layers of the surface of the earth have a travel slower than the upper. Sound wave propagation in the wind, the higher areas will move at speed higher than lower. Following this the wave front will move towards the earth, which will increase distance and improve audibility source. In the case of contrary wind the sound waves are deviate from vertical and the audibility decrease. The temperature difference between layers of air is also a question of changing the direction of propagation of sound. In the lower layers of warmer air, the speed of propagation of sound is greater than the upper layers of sound waves that cause deviate vertically, which leads to reducing the distance of audibility. Evening after a hot day, the earth and with it, the layers of air close to cold quickly, upper layers are warmer than the lower, direction of sound waves change to the contrary direction, so the audibility distance increases. The simultaneous temperature action and variable wind as speed and direction at a different heights, leading to a more complicated propagation of sound waves, and variations in atmospheric condition leading to sudden variations of propagation conditions and distance of audibility. Apart from these phenomena is necessary to take into account that the noise source is higher for the surface of the earth, the sound spreads at longer distances. Study the propagation of sound waves in the atmosphere has a scratchy high significance in determining the distance of audibility of powerful sound sources such as sirens signaling, noise from various gas discharges, etc.. In choosing noisy targets location near the cities, for example a bench test stand for engines or noisy factories, must take into account the direction of prevailing winds in the region and to seek such a location as a factory to wind direction from town to the factory and not vice versa.

To investigate the effect of large sounds simultaneously emitted from multiple sources, decibels are added. The formula is below. This method of summation is called "energy combination" (power combination)".

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛+++= 10

nL10

2L10

1L

10..........1010lg10L (8)

To compensate for background noise, the difference in decibels is calculated. The formula is below. Background noise compensation uses L1 (dB) as the A-weighted sound pressure level sum of the targeted noise and the background noise, and L2 (dB) as just the background noise. It then estimates the targeted noise L3 (dB) by obtaining the difference.

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛−= 10

2L10

1L

3 1010lg10L (9)

The decibel value of the average is called the "average power" (average energy)". It is expressed with the following formula:

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛+++= 10

nL10

2L10

1L

ave 10..........1010n1lg10L (10)

5 Description Of Noise Measurement The location of the analyzed intersection is shown in the figure above.

Fig. 1. The location of the measurement points Noise monitoring activity involves determination of the noise level in 11 points in different areas of the


ISSN: 1790-5095 89 ISBN: 978-960-474-061-1

city, where measurements are made twice times in a month. These measurements led to the conclusion that there are points where the noise level is often exceeded, for example: district Crihala-Splai M. Viteazul belt, area where heavy traffic is diverted, and the unprotected area to intense noise pollution due to road traffic; district Crihala-Gas Station, Industrial areas, Street Timişoara-Way- affected areas of road noise, but low impact on humans, since it is mostly populated. Table 1. Level of the noise values ( dB ) January -February

No. Check points

Medium values January

dB

Medium values

February dB

1 Crihala-Splai M Viteazul - belt 65.7 67.3

2 Crihala ( Gas Station ) 61.0 64.9

3 Alunis 59.8 64.0

4 Way Timisoara- Gas Station 69.3 71.9

5 Weather Station 51.1 53.6 6 Roses Park 51.5 51.7 7 Industrial area 1 58.9 69.2 8 Industrial area 2 65.3 66.8 9 F.E.Halanga 55.7 64.0

10 Industrial area 3 67.1 71.3 11 Podul Gruii 60.5 64.5

Fig. 2. Evolution of the noise level to the radius of city (January –February) In the graph is observed that the rate curves, the light exceeded the permissible limits of the expertise artery located in the vicinity of the town belt.

Table 2. Level of the noise values ( dB) February- March

No. Check points

Medium values

February dB

Medium values March

dB


2 Crihala ( Gas Station ) 67.6 66.0

3 Alunis 63.4 64.8




Fig. 3. Evolution of the noise level to the radius of city (February- March) Table 3. Level of the noise values ( dB)) March- April

Nr.Cr. Check points

Medium values March

dB

Medium values April dB


2 Crihala ( Gas Station ) 66.0 64.2 3 Alunis 64.8 68.1





ISSN: 1790-5095 90 ISBN: 978-960-474-061-1

[3] M. Grumăzescu , A. Stan, N. Wegener – Combaterea zgomotului şi vibraţiilor, Ed. Tehnică, 1986.

[4] Alexandru Darabont, Ştefan Pece – Protecţia Muncii, manual pentru învăţământul universitar , E.D.P. , Bucureşti, 1996. [5] Inspectoratul de Protecţie a Mediului Mehedinţi – Raport de mediu. [6] http://www.engineeringtoolbox.com [7] http://www.calpoly.edu Fig. 3 Evolution of the noise level to the radius of

city (March- April) [8] Nicolae Herisanu, Vasile Bacrie, Mihai Toader, Smaranda Popa Radovan Investigation and reduction of ambient noise in an urban area, Proceedings of the 7th WSEAS International conference on Acoustic & Music: Theory & Applications, Croatia, June 13-15 2006 . pp 48-53.

6 Analysis of the results of measurements and

Conclusion Measurements for urban traffic noise have been made in Drobeta Turnu Severin, Romania. Form graphs is observed that the rate curves is relatively the same for the analysis period (January-April 2007) which shows that there were significant changes in the pressure exerted by the noise in the set for sonometer expertise. These measurements have led the following conclusions: there are points where the noise level is often exceeded, for example: District - Crihala-Splai M.Viteazu - belt area where heavy traffic is diverted, the area populated mostly unprotected and noise pollution due to road traffic; Cartier-Crihala-PECO, roundabout; Street Timisoara-Way-area heavily affected by road noise, but low impact on humans, since it is mostly populated. Note that the trend curves reflecting noise level is relatively equivalent for the same period January to April 2007 which suggests that there were significant changes in the pressures exercised by the noise in the set for sonometric expertise in general level city of Drobeta Turnu Severin.

Reducing emissions from traffic can be achieved by bringing the belt road and a plan fluidity of traffic in the city (one-way streets) rehabilitation of road infrastructure, the arrangement of plant protection curtains. Having regard to the effects of noise, it is recommended the development of a greater magnitude, in order to obtain statistics that allow the achievement of a complete mapping of the scientific, referring to a form of pollution neglected so far and search solutions to reduce the amount required by legislation (50 dB). References: [1] Valer Teuşdea – Protecţia mediului, Ed. Fundaţiei „România de Mâine”, Bucureşti, 2000. [2] http://www.calpoly.edu.


ISSN: 1790-5095 91 ISBN: 978-960-474-061-1

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