Monitoring of the Environmental Noise Level in San Juan, Puerto Rico

Transcription

1 Monitoring of the Environmental Noise Level in San Juan, Puerto Rico José Alicea-Pou Olga Viñas-Curiel Wanda Cruz-Vizcarrondo Osvaldo Alomar Noise Control Area, Puerto Rico Environmental Quality Board Box 11488, San Juan PR Address for principal author (*): Envioronmental Quality Board, Nacional Plaza Building, 431 Ponce de León Avenue, Hato Rey, Puerto Rico Phone Number: (787) Fax: SUMMARY The aim of the study was to describe the behavior of environmental noise levels in communities around the city of San Juan, Puerto Rico. Fourteen noise stations were monitored for twenty-four hours in order to describe the levels of environmental noise. The project is in progress with an expected number of ninety stations by the end of The locations were selected using a random protocol of quadrants in the city map. The sound levels were obtained with the use of four Norsonic Nor-121 sound analyzers. The different statistics (L eq, L 10, L 90, L max, L min, ect) were plotted and the behavior of the graph described. Our current model for the behavior of the noise graphs includes characteristics such as the "sustained noise level zone", the "noise drop zone", the "minimum reach level" and the "sonic rise zone". The study is part of the development of Puerto Rico s first Noise Action Plan. The Noise Plan will include as goals, the reduction of the average environmental noise levels in urban areas, the reduction of the difference between the sustained levels and the minimum reached level and the increase in the duration of the minimum reach levels. Key Words: Environmental Noise, Urban Noise, Noise Criteria INTRODUCTION Until now the noise pollution problem in Puerto Rico has not been sufficiently documented and the need for local environmental noise research (Finegold 2001) is required in order to take further action. The Noise Control Area (NCA) of the Environmental Quality Board (EQB) is in the process of conducting the first citywide noise study project with the purpose of documenting the current decibel levels in various exterior locations around San Juan, Puerto Rico. In this phase of the project, NCA will determine the status of San Juan s acoustic environment (soundscape) (Bronzaft 2000) as the first step towards setting plans to combat city noise and to educate people about the quality of their acoustic environment. To facilitate the sampling and monitoring, the research plans included dividing the city up into six sections and randomly select various locations within these sections. Stations were set up at each of the sites and the sound levels were monitored for 24 hours. So far, we have studied twenty-four sites and the project is expected to continue most of next year, expanding to other cities and rural areas of the country. By the end the project, the goal is to encompass several hundred monitoring sites in order to create an accurate representative sound pattern of the cities studied. To create effective noise legislation and understand how noise behaves in the urban areas of Puerto Rico, it is necessary to measure different sounds types and sound intensities throughout multiple locations in the city. Although many possible methodologies can be used to accomplish

2 these types of studies, and since the study of environmental noise can be complex, our idea was to describe in a simple way what was the behavior of sound levels over time in different locations, and to use these characteristics to define concepts of environmental acoustic quality for Puerto Rico (Figure 1). In the long run, we want this data and the results to be as simple as possible for the general public and policy makers to comprehend and use in urban planning and policymaking. METHODS The main goal of the project was to create a sound level profile for the city based on the behavior of the levels vs. time of the sound data for 24 hours. This profile contains information gathered from randomly selected locations that were monitored for a period of 24 hours using four units of the sound analysis system Norsonic NOR-121. The stations where selected to ensure a sample of all possible acoustic conditions and locations representative of the entire city. For San Juan, the city was divided into six areas and to each area a grid was applied, where each square encompassing approximately one city block. Each square was numbered and then locations were selected randomly from the map. The sites were then visited and evaluated for the safety of the location and types of possible attachment setting for the exterior microphones. After each site was selected as a monitoring location, one Norsonic NOR-121 unit was place and programmed to start its analysis at 7:00 am, for a total period of 24 hours. Usually, four stations were placed on each randomly selected day, which included weekends. Locations were residential properties, parks, highways, neighborhood streets, industrial zones, and even close to shore, among other kinds of sites. The equipment came from the distributor with an exterior case, but we also built a case with fans, to control the temperature, and various sets of attachments for electric poles, fences and walls. We also configured a vehicle to carry the system inside, with the exterior microphone on the roof of the SUV vehicle; giving us the flexibility of locating the station anywhere the vehicle could be parked. Data was extracted from the Norsonic system and stored on a computer. The analysis started by plotting the sound levels of each monitored location on a line graph of time vs. L 10 or L eq sound levels. After each site was completed, each line was included into a multilane graph from all the locations, creating a profile of the different sound patterns in San Juan. From this data, we can identify periods during the day where sound levels need to be reduced and areas where the behavior on the noise line could identify locations in need of specific actions to reduce noise levels. With the help of four students from the Worcester Polytechnic Institute that visited us on an internship program, we also did multiple censuses of noise sources in each site, identifying the prominent sources and its level. With this information, we will make definitive suggestions regarding what sources of noise are the primary causes of the noise pollution at that site and how they can be controlled by immediate or long-term strategies. We use various units of Brüel & Kjær 2236 sound level meters to describe the noise levels of these sources. RESULTS Based on some of the first stations studied, we defined a basic 24-hour sound pattern that is summarized by the model shown in Figure 1. The line begins at a daytime level, with a steady level that starts dropping at some time after sun down, reaching a minimum level and increasing to a higher sound level as the sun rises. These are some of the characteristics of the environmental sound level behavior of our model. This model has become a very useful tool to explain to the general public what is expected of the study, helps with the establishment of noise reduction goals at the city level and to educate people about how different acoustically it can be during the day and night times, and what are the main reasons for these differences.

3 Sustained level Minimum Level Reach L e v l e s db(a) Sonic Drop Sonic Rise Time of Minimum reach Time (min) Figure 1. Model of the 24 hours Behavior of Environmental Sound Levels. After twenty-three stations monitored all over San Juan, the majority of the data followed the general curve of the hypothesis for the sound profile proposed (Figure 1). Other locations had lines that were mostly flat through the whole 24 hours period; characteristics that we feel are not ideal and need further studies and stronger noise control strategies. To form a general profile for the entire area we averaged all 30 minutes L 10 and L eq levels for all the station for all 24 hour, resulting on one line that collected of the data. These profiles are shown in Figure Average Leq and L10 values for all sites with 5th order polynomial trendlines 68.0 Sound pressure level (db) Average Leq Values Average L10 Values Poly. (Average Leq Values) Poly. (Average L10 Values) :30 AM 8:30 AM 9:30 AM 10:30 AM 11:30 AM 12:30 PM 1:30 PM 2:30 PM 3:30 PM 4:30 PM 5:30 PM 6:30 PM 7:30 PM 8:30 PM 9:30 PM 10:30 PM 11:30 PM 12:30 AM 1:30 AM 2:30 AM 3:30 AM 4:30 AM 5:30 AM 6:30 AM Time Figure 2: Sound Level Profile of San Juan Displaying the 24 Monitored Sites

4 After fitting the averaged data with a best-fit line, it is easy to see how similar the overall sound levels of the city are with the anticipated profile. As a general concept, through the day, sound levels remained fairly high (over L 10 = 63 db(a), until late into the night (around 11:00 pm), then levels reach a low level under and L 10 value of 58 db (A) around 3:00 am, dropping only for a few hours. Additional to the behavior of the L 10 and L eq lines, the data reflects the average levels that people can potentially be expose in exterior environments around the city, representing this line a powerful, scientific base, awareness tool against noise. This levels could be considered high since according to the World Health Organization (WHO), most people are moderately annoyed by levels above 50dB and seriously annoyed by levels around 55dB (WHO 2000). One of our objectives, as explained to the general public, is to decrease the high decibel levels sustained during daytime hours to a lower average level. By explaining to the communities that by taking multiple, site specific, noise control strategies, it could lower these daytime level, they comprehended, in a simple way, how this would benefit their community. Another goal is to achieve that the drop in sound level occurs as early in the night as possible, especially in residential areas. By increasing the duration of the reached minimum noise levels during the nighttime, would then result in quieter communities for longer periods of time at night. Another objective is to take steps toward understanding all the factors (human activities) that could contribute to the abrupt increases in decibel levels as the night transitions into day time hours, and how to reduce that increase. Eventually we would like to study in more details the contribution on nature (fauna, mainly amphibian) to the background environmental sound levels. CONCLUSION The preliminary data that we have collected reinforces our assertion of San Juan s noise problem and suggests the necessity for noise reduction measures. The most pertinent verification of the problem is displayed in the sound level database that we compiled which summarized the general sound profile of the city. Of the twenty-three sites that have been monitored, we found that the L eq during daytime hours remained around 64dB (A). With appropriate funding and cooperation from law enforcement and other agencies, the Environmental Quality Board can begin to establish different short term and long term goals and plans of action to improve the acoustic urban environment. Definitive legislation will lead to more efficient enforcement, while additional funding will provide other forms of noise reduction. At the culmination of this project, a reduction of noise will create a more enjoyable and acoustically favorable environment for the residents of San Juan and Puerto Rico, ensuring both peaceful living and an increase in the quality of life. Noise pollution is a serious problem that must be dealt with because it has numerous adverse effects on personal health and community. A vital step in creating noise legislation is to first assess and document noise levels throughout different areas of the city. This is crucial because it expands the researchers knowledge of the studied city. As previously discussed, there are a number of factors, such as the type of sound, the context of the sound, the location, the people involved, and their culture, that contribute to the perception of noise and must be taken into consideration when proposing legislation. Once all factors of noise pollution in a given region are studied and assessed, any noise pollution problem can be efficiently managed using new or modified legislation that is dependent on the needs and characteristics of that city. The sound levels recorded and studied, the opinions of citizens through surveys and the analysis of our data base of complaints (both not discussed in this paper) would all be incorporated with all other concepts needed to develop an effective, but reasonably simple, noise action plan for Puerto Rico. By documenting each of these components of the noise pollution problem in San Juan, ideas and suggestions regarding more efficient legislation for the city will be easier to formulate because the future legislation will be based upon the characteristics of San Juan s noise problem and data collected on the field.

5 References A. L. Bronzaft, Acoustic Ecologist and Environmental Psychologists: Working Toward a Quieter and Healthier Soundscape.Journal of Acoustic Ecology, Vol I, number 2 (2000). L. S. Finegold, E. G. Henning, P. D. Schomer, B. F. Berry, Proposal for monitoring worldwide noise exposure and assessing the effectiveness of noise exposure policies and noise control technologies. Noise Control Eng. J. 49 (4), 2001 July-Aug. WHO, Guidelines for Community Noise, B. Berglund, T. Lindvall, D. Schewela, and Kee-Tai Goh, World Health Organization, Geneva, Ministry of the Environment, Singapore (2000).