People who live in Terrassa and usually move around it, know the streets and avenues where there is a lot of noise, but do we know what noise means? When is the most noise generated? What is the difference between sound and noise? What does noise pollution mean? When do we go from sound to noise pollution? How is sound quality evaluated? How can noise pollution affect our health? We will discuss it below, but first we will describe some concepts that can create a bit of confusion.

It is strange to find a place on our planet naturally without being able to perceive any sound around us but it is true that, for different reasons, we can ignore it. A sound begins when a body or object at rest starts moving due to an external factor (for example, if we push it, we hit it ...). It is at this moment, when the body begins to emit vibrations and produces different compression waves that propagate in the environment that surrounds it (either through air, water, earth ...) until it reaches our ears. It is then when the energy of these waves is transformed into nervous impulses and they arrive to our brain where the received information is processed.

We speak of sound when it may give us a pleasant sensation when hearing it. This is because the original vibration is regular and uniform. An example of a sound would be when we listen to a melody by a cellist at a concert; this sound has “musical” or “harmonic” characteristics. It is nice to hear and it can have positive physiological or psychological effects for example, when we get excited when listening to a certain song.

Instead, we talk about noise when the sound we hear is annoying, unpleasant, and short-lived. For instance, the noise made by chalk when something is underlined on the blackboard. It should be borne in mind that the noise will be more or less annoying depending on the duration, intensity, frequency, but above all on the hearing sensitivity of the people affected.

Once the difference between sound and noise has been introduced, we can begin to speak of noise pollution. Let's imagine that we are walking on Jacquard Avenue at 9:30 in the morning, just when the shops open and, in a matter of minutes, we hear many blinds of different types (manual and automatic) being raised, buses and cars circulating, a truck of EcoEquip unloading a glass container, people and children screaming or speaking very loud... At one point, we have a lot of banging noises. This is what we know as noise pollution; an excess of noise that accumulates, is maintained continuously over time and alters the normal environmental conditions of a given area.

Recent studies indicate that there is a direct relationship between noise pollution and health. The noise level is measured in decibels (dB) and, according to the World Health Organization (WHO), the "tolerable" noise limits cannot exceed 65dB during the day and 55dB at night. The main problem is that we have become accustomed to withstanding the noise of the city and also to generating it, but we are not aware of the impact that its exposure has on our body.

An exposure above the "tolerable levels" of noise, depending on the intensity, duration and sensitivity of the person, can generate in our body: hearing problems (loss of hearing, beeping ...), psychological (irritability, stress, anxiety ...) and other  physiological (increase in heart, respiratory, blood pressure ...) problems and sleep disorders (insomnia, daytime sleepiness, tiredness ...). As you can see, apart from environmental pollution in cities, noise pollution is another of the municipalities' concerns, since it negatively impacts health if it is not regulated.

For this reason, the Terrassa City Council started a project, in collaboration with different areas (environment and Smart City), to study acoustic quality in different parts of the city. Eleven strategic points were chosen (Fig. 1) to install noise sensors capable of measuring, in real-time, the noise level in decibels (dB).

Figure 1. Location of noise sensors in the city of Terrassa. Source: Visor Sentilo de Terrassa.

From the collected data, published on the Sentilo platform, a study of the noise type, distribution and evolution throughout the day is being carried out in order to subsequently develop noise maps, as can be seen in the Terrassa's Strategic Noise Map. Many projects that are currently under way in our city are related in a cross manner to different areas of the city Hall. Although at first sight this relationship is not observed. For example, the change of direction of Nou Street was made to improve mobility in the centre (driven by the mobility area).

Once implemented, the acoustic and environmental quality of the area has been observed to improve (involving the Smart City area in the collection of sensor data and the Environment area in the realization of maps of noise). On various occasions, the data analyses have served as a factor favouring changes in our city. For example, the purchase of the new municipal hybrid buses was made within the theme of energy efficiency, but analysing the data from the noise sensors, it has been reflected on paper that there is a reduction in noise pollution as well.

Gradually, changes are being made in our city to improve air quality and noise, thus improving the health of its inhabitants.


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