ASSESSMENT OF NOISE POLLUTION IN DHAKA CITY
Sanjib Chandra Chowdhury, M. Mahbubur Razzaque, and Md. Maksud Helali
Department of Mechanical Engineering, Bangladesh University of Engineering and Technol- ogy, Dkaka-1000, Bangladesh.
e-mail: sanjib@me.buet.ac.bd
Hans Bodén
The Royal Institute of Technology, Teknikringen 8, 10044 Stockholm, Sweden
Like many other mega cities of developing countries, noise pollution in Dhaka city of Bang- ladesh is a big concern. Here noise is produced from different sources like traffic, loud- speaker, people gathering etc. To mitigate the noise pollution in Dhaka city, the government of Bangladesh has recently passed a new ordinance and has modified the existing traffic con- trol rules. However, the condition did not improve as much as expected. Exposure to high level noise may cause severe stress on the auditory and nervous system of the city dwellers, particularly the children. The extreme effects e.g. deafness and mental breakdown are also occasionally reported. This paper reports the level of noise pollution in Dhaka city. For this purpose noise levels have been measured at ten major locations of the city from 8 AM to 10 PM during the working days. The data have been analyzed to calculate various noise parame- ters such as Leq, and Lnp. It is observed that at all the locations, the level of noise remains far above the acceptable limit for all the time. Comparison of present results with the existing previous results shows that noise level in the Dhaka city is increasing day by day. The paper suggests that urgent measures should be taken into consideration to control the level of noise pollution in the city and vulnerable institutions like kinder gardens, schools and hospitals should be located far away from the road side.
1. Introduction
Noise can be defined in different ways. People who study acoustics define noise as complex sound waves that are aperiodic, in other words, sound waves with irregular vibrations and no defi- nite pitch. In engineering, noise is defined as a signal that interferes with the detection of or quality of another signal [1]. Basically, noise is unwanted sound. It is a pollutant and a hazard to human health and hearing. Noise in our environment affects physical health. Noise also has psychological
and social implications and affects our wellbeing and quality of life [2]. Frequent exposure to high level of noise hampers physical and mental peace and may cause damage to the health.
Like other mega cities of developing countries, noise pollution in Dhaka city of Bangladesh is a big concern. Along with the increasing degree of air and water pollution, the inhabitants of Dhaka City are being exposed to high level of noise pollution. The level of noise pollution is very closely related with urbanization and motorization. Although there are many sources of noise which include industries, construction works, indiscriminate use of loudspeakers, people gathering, etc., the prin- cipal source of noise in Dkaka City is motorized traffic. To mitigate the noise pollution in Dhaka city, the government of Bangladesh has recently passed a new ordinance and has modified the exist- ing traffic control rules. However, the condition does not improve as much as expected. During the 70s and early 80s, noise pollution was not a major concern for the dwellers of Dhaka City. With the increase of the number of motorized vehicles in the city, the hazard of noise pollution has increased and exceeded the level of tolerance. Exposure to high level of noise is causing severe stress on the auditory and nervous system of the dwellers of Dhaka City. Ahmed [3]reported that the hearing ability of the inhabitants of Dhaka City has reduced during the last ten years. About five to seven percent of the patients admitted to the Bangabandhu Sheikh Mujibur Rahman Medical University (BSMMU) Hospital, Dhaka are suffering from permanent deafness due to noise pollution. Distur- bances created by noise may cause hypertension, headache, indigestion, peptic ulcer, etc. [4-5].
This paper reports the level of noise pollution in Dhaka city. For this purpose noise levels have been measured at several locations of the city from 8 AM to 10 PM during the working days.
The data have been analyzed to calculate various noise parameters such as Leq, and Lnp. To estimate the trend of noise pollution, present results have been compared with the existing previous results.
2. Measurement of Noise Parameters
Sound level, its frequency spectrum and its variation over time characterizes the nature of noise. Although the level of noise largely depends on the subjective perception of the listener about the loudness, the term sound level refers to a physical measure which is a function of the magnitude of the sound pressure fluctuations. The most common measures of sound level are sound intensity and sound pressure. Sound intensity (also called sound power density) is the average rate of sound energy transmitted through a unit area perpendicular to the direction of sound propagation, typically measured in pW/m2. Since no instrument is available to directly measure the power level of a source, sound pressure is employed as a measure in this regard. Sound pressure is usually propor- tional to the square root of sound power. Because of dealing with large range of numbers, a loga- rithmic measure called decibel (dB) is used to describe sound level. The sound level in decibel is defined as follows:
Sound level, L(dB)=10log10(P/P0)2 =20log10(P/P0) (1) where, P is root mean square value of the sound pressure (N/m2) and P0 is the standard reference pressure (20 µN/m2). For practical purpose, the decibel scale ranges from zero, the threshold of hearing, to about 140 dB, the onset of pain. For every 3 decibel increase in sound level, the apparent loudness of sound is doubled. In order to account for the ear’s response to different levels of noise, weighing filters are used while measuring the sound level. The A-weighting sound level is devised to represent a person’s subjective response to the variation of sound more accurately. A-weighting, though originally intended only for the measurement of low-level sounds, is now commonly used for the measurement of environmental noise and industrial noise, as well as when assessing potential hearing damage and other noise health effects at all sound levels.
Environmental noise levels show a good amount of variability with respect to time. It is, there- fore, necessary to establish meaningful statistical noise measures that describe the magnitude of the problem while capturing the variability. The parameter universally used in discussions of noise pol- lution of environment is Leq, the energy equivalent continuous noise level expressed in dB(A) which
is the average rate at which energy is received by the human ear during the period mentioned [6].
Mathematical expression of Leq is as follows,
=
=
∫ ∑
i L T
eq dt N i
f f
L T 10 ( /10)
0 2 0
2
10 1 10
log 1 10
log
10 (2)
where, T is the period of measurement and Li is the average noise level during interval i. Another parameter, termed as Noise Pollution Level (Lnp), is also used to express varying level of noise [7].
It can be computed from the time varying noise level using following equation.
) 60 (
) (
90 10 2 90 10
50 L L L L
L
Lnp = + − + − (3)
where L10, L50 and L90 indicate the levels exceeded for 10%, 50% and 90% of time respectively in a set of records of noise level in a given interval of time (Fig.1). Lnp is expressed in the units of dB(A). Leq provides the energy equivalent sound level received by the ear and hence an indicator of the physiological disturbance to the hearing mechanism. Lnp takes into account the variations in sound signal and hence serves as better indicator of noise pollution in the environment for physio- logical and psychological disturbance of the human system. Noise climate (NC) provides the range over which the sound levels fluctuate in an interval of time and is given by the following equation.
90
10 L
L
NC= − (4)
Figure 1. Different noise parameters.
3. Impacts of Noise on Health
The most notable physical effect of noise exposure is loss of hearing [2]. Noise Induced Hear- ing Loss (NIHL) affects children, adolescents, young adults and older adults. Because of noise pol- lution, hearing loss is appearing much earlier in life. Noise not only affects hearing, it affects other parts of the body and body systems. Noise can also hamper performance of daily tasks, increase fatigue, and cause irritability. Noise can reduce efficiency in performing daily tasks by reducing attention to tasks. This is a concern of employers when it comes to assuring workers' safety. Be- cause of noise, we often find ourselves fatigued and irritable. We do not even realize the effect until the noisy hubbub stops and we feel relief. From another perspective, due to noise one’s own inabil- ity to hear and understand others clearly can cause one to feel angry and frustrated. Instead of ac-
cepting the problem is his/her, he/she misdirects his/her feelings to others and blows up at them.
Noise also makes speech communication harder. More concentration and energy is needed not only to listen and hear over the noise but also to speak louder above the noise. As a result, voices can be strained and vocal cord abuses, such as laryngitis, develop. It is a physical strain to carry on even an enjoyable conversation in the presence of noise.
Noise is both a public health hazard and an environmental pollutant. Many of its effects are well known and many of its effects continue to unfold through research. The World Health Organi- zation (WHO) has documented seven categories of adverse health effects [8] of noise pollution on humans which are: hearing loss, speech interference, sleep disturbance, cardiovascular and physio- logical effects, mental health disturbance, impaired task performance and negative social behavior and annoyance.
4. ACCEPTABLE NOISE LIMIT
Various standards are being used in different countries regarding the acceptable levels of noise depending on the situation. Limits of acceptable noise level established by different organiza- tions [3, 5] are given in Table 1.
Table 1. Acceptable Noise Level (dBA) Noise Level (dBA)
Description of Area DOE FHA AASHTO
Sensitive Areas such as parks,
schools, hospitals, mosques etc. 45 60 55-60
Residential Area 50 70 Exterior
55 Interior 70 Exterior 55 Interior
Mixed Area 60 70 70
Commercial Area 70 75 75
Industrial Area 75 75 75
5. STUDY DESIGN
Noise levels have been measured at ten major locations in Dhaka City during 8 AM to 10 PM on working days. The locations are BSMMU, Azimpur, DMCH, Science Laboratory, Dhanmondi, Motijeel, Gulshan, Banani, Farmgate and Sayedabad. Almost all the locations are situated in mixed areas whereas few of these are situated in residential and commercial areas. Noise levels have been measured at the roadside as well as at a distance of about 50 m away from the roadside. This is done to analyze the effects of distance and existing roadside barriers on the reduction of noise level.
Sound Level Meter (SLM) was placed at a height of about 1.5 m with the help of a tripod. Before noise level measurement, SLM was calibrated by Tenmars sound level calibrator at 94 dB and 114 dB with 1 kHz. During noise level measurement, ‘A-weighting’ scale was selected and the SLM was switched to fast response mode. Noise levels have been measured at every 5 min intervals and the values of these measurements have been recorded as the noise level for the corresponding loca- tion and time. From the recorded values of noise level, noise parameters have been estimated using the equations described earlier.
6. RESULTS AND DISCUSSION
Noise levels have been measured at ten locations on ten different working days from January 02, 2010 to January 20, 2010. The weather was dry and the wind speed was negligible on these
50 60 70 80 90
8:00 10:00
12:00 14:00
16:00 18:00
20:00 22:00 Time
Sound Pressure Level (dBA)
Road side Inside
0.0 20.0 40.0 60.0 80.0 100.0 120.0
BSMMU Azimpur
DM CH BCSIR
Dhanmondi Motijeel
Gulshan Banani
Farmgate Sayedabad Loacation
Leq (dBA)
Inside Roadside
days. Figure 2 depicts the variation of noise level with time at BSMMU location. It is observed that in morning, with the increase of time noise level increases whereas at night noise level decreases with the increase of time. It is due to the increase and decrease of traffic flow and people gathering with time at the morning and night, respectively. During the day time noise level remains almost same. However, noise level at the inside position is lower than that of the roadside position at a par- ticular time. This may be due to effects of distance and existing roadside barriers on the reduction of noise level. The trend of variation of noise level observed for other locations is almost same.
Figures 3-5 show different noise parameters at different locations of Dhaka city. From these figures it is found that values of different noise parameters are higher in commercial and mixed ar- eas compared to those in residential areas. However, in a particular area, inside position is exposed to less noise level compared to roadside position.
Figure 2. Variation of noise level with time at BSMMU of Dhaka city.
Figure 3. Variation of Leq at different locations of Dhaka city.
0.0 20.0 40.0 60.0 80.0 100.0 120.0
BSMMU Azimpur
DMC H
BCS IR
Dhanmondi Motijeel
Gulshan Banani
Farmga te
Sayedabad Loacation
Lnp (dBA)
Inside Roadside
0.0 4.0 8.0 12.0 16.0
BSMMU Azimpu
r DM
CH BCSIR Dhanmondi
Motijeel Gulshan
Banani Farmg
ate Sayedabad Loacation
NC (dBA)
Inside Roadside
Figure 4. Variation of Lnp at different locations of Dhaka city.
Figure 5. Variation of NC at different locations of Dhaka city.
Citywide aggregated noise levels and dwellers exposure time to that level are summarized in Table 2. From this table, it is observed that average noise levels and its degree of fluctuation as given by Leq and Lnp are higher in roadside locations whereas the range of variation in noise level as given by NC is higher in inside locations. It is observed that average noise level in roadside and inside positions are about 82 dBA and 73 dBA, respectively which exceeds the acceptable limit for mixed and commercial areas set by the Department of Environment (DOE), Bangladesh. Moreover, the measured existing noise levels are higher than the values measured in the previous year [9]
which implies environmental noise level in Dhaka city is increasing day by day. Dwellers of Dhaka city including school going children to retired persons are exposed to this high level environmental noise for minimum 2 hours per day on an average which implies that they are in the risk of serious health hazards.
Table 2. Dhaka city wide average noise level and dwellers exposure time
Average value Noise parameters
Road side Inside
Exposure time (Hours)
Leq (dBA) 82 73
Lnp (dBA) 87 79
NC (dBA) 6.7 7.8
Minimum 2
7. CONCLUSIONS
Noise is undesirable or unwanted sound. Extended exposure to excessive sound has been proved to produce physical and psychological damage. Because of its annoyance and disturbance implications, noise adds to mental stress and hence affects the general wellbeing of those exposed to it.
This paper reported an assessment of the level of noise pollution in Dhaka city. For this pur- pose noise levels have been measured at ten major locations of the city from 8 AM to 10 PM during the working days. Various noise parameters are calculated from the data. It is observed that noise pollution in Dhaka city far exceeds the acceptable limits set by the Department of Environment, Bangladesh. Comparison of present results with the existing previous results shows that noise level in Dhaka city is increasing day by day. Dwellers of Dhaka city are exposed to high level environ- mental noise for a sufficient duration of time which puts them in the risk of serious health hazards.
Therefore, urgent measures should be taken to control the level of noise pollution in the city. More- over, magnitude of environmental noise is relatively lower in the inside locations. Therefore, vul- nerable institutions like kinder gardens, schools and hospitals should be located far away from the roadside unless special arrangement to alleviate the sound is adopted.
Acknowledgments
This work is done under the “Assessment of Environmental Noise Impacts in Dhaka” project jointly conducted by Bangladesh University of Engineering and Technology (BUET), Dhaka, Bang- ladesh and The Royal Institute of Technology (KTH), Stockholm, Sweden and funded by the Swed- ish Research Council.
REFERENCES
[1] M. J. Crocker, Handbook of Acoustics, John Wiley, New York, 1998.
[2] K.D. Kryter, Handbook of Hearing and the Effects of Noise, New York Academic Press, 1996.
[3] K. Ahmed, “A Study on Noise Pollution in Dhaka City”, Department of Environment, Bang- ladesh, 1998.
[4] W. Passchier-Vermeer, “Noise and Health”, The Hague: Health Council of the Netherlands, publication No A93/02E, 1993.
[5] OECD, “Road Side Noise Abatement, Road Transport Research”, Organization for Economic Cooperation and Development, Publication Services, OECD, France, 1995.
[6] C. S. Papacostas, and P. D. Prevedouros, Transportation Engineering and planning, 2nd Edi- tion, Prentice Hall Publishers, USA, 1993.
[7] P. R. Rao and M. G. Rao, “Urban Traffic Intensity and Prediction of Leq Noise Level”, Indian Journal of Environmental Health, 33(3), pp. 324-329, 1991.
[8] B. Berglund, T. Lindvall, and D. H. Schwela, Guidelines of community noise, Geneva, WHO, April 1999.
[9] M. J. B. Alam, A. F. M. A. Rauf, and M. F. Ahmed, “Traffic Induced Noise Pollution in Dhaka City”, Journal of Civil Engineering, IEB, Bangladesh, CE 29(1), pp 55-63, 2001.
Nomenclature and Abbreviations
DOE = Department of Environment, Bangladesh FHA = Federal Highway Agency
AASHTO = American Assoc. of State Highway and Transportation Officials
