Assessing and managing environmental noise, reducing the number of people exposed to excessive sound, ensuring quality of life parameters and improving the quality of the acoustic environment are some of the current and future concerns in city management.

Municipalities are responsible for assessing and managing environmental noise(Decree-Law no. 146/2006).

Lisbon City Council, through its technical Noise Assessment team, has the mission of providing information to Lisbon residents on environmental noise and its effects, monitoring noise exposure in the external environment, drawing up Strategic Noise Maps for the city and approving action plans to prevent and reduce environmental noise and its effects in Lisbon, as well as raising awareness among the population of measures and behaviors to adopt.

Noise has always affected cities, increasing as they grow and evolve. As early as 600 BC in ancient Greece, craftsmen were forced to locate their workshops outside the city so as not to disturb the peace of the inhabitants with excessive noise. With the industrial revolution, a period of great technological development, the noise problem worsened. Today, this is a global challenge, prioritized differently in each city and country.

In our daily lives we are exposed to a wide range of sound intensity levels. There are various sources of noise in urban areas, such as traffic, cultural activities, commercial activities, events, demonstrations, among others. A busy street with a large concentration of people and cars can reach 90 dB ( A) and a rock concert can reach 115 dB(A). These are considered high noise levels.

Recently, Lisbon has invested in increasing its green structure, offering citizens the chance to practice sports, go for walks and encourage healthy lifestyles in the various parks and gardens, where the sounds of nature can be heard quietly.

In the city of Lisbon, noise is managed by the Municipality, the Portuguese Environment Agency, the Lisbon and Tagus Valley Regional Coordination and Development Commission, the General Directorate of Health, the Regional Health Authority, the National Emergency and Civil Protection Authority and the entities that manage road, rail, air and port infrastructures.

Legislation on noise prevention and noise pollution control has existed since 1987 and is currently regulated by the General Noise Regulation - RGR (Decree-Law no. 9/2007, of January 17). This is intended to regulate the noisy activities that usually disturb us, whether permanent or temporary, such as transport, construction work, shows, night-time activities, as well as neighborhood noise and other noise sources.

The State is responsible for safeguarding the health and well-being of the population with regard to environmental noise, and rest and sleep are considered in the Constitution of the Portuguese Republic to be fundamental rights of personal integrity(Article 25) and of the environment and quality of life(Article 66).

The World Health Organization (WHO) considers environmental noise to be a very important issue for public health and has therefore developed environmental guidelines for Europe to protect human health when exposed to environmental noise from various sources, defining noise limit levels for day and night.

The General Noise Regulation (RGR) establishes the legal framework applicable to the prevention and control of noise, always with the health and well-being of the population in mind. This regulation considers residential, school, hospital or similar buildings and leisure spaces to be sensitive receptors.

Noisy activities have different rules of action defined by the RGR, aimed at the various sources of noise. These are classified as

1. Permanent noisy activity: any activity that produces permanent and annoying noise in its vicinity (bars, nightclubs or concert halls).
2. Temporary noisy activity: any activity that produces noise as an isolated and temporary act (construction work, festivals, pilgrimages, fairs, rallies, dances, etc).
3. Neighborhood noise: noise associated with residential use and its activities, produced by someone or an animal under their responsibility, which affects public health and/or the tranquility of the neighborhood.

The municipality intervenes according to the RGR in the various activities, with the aim of minimizing the effects of noise on the city's population.

This regulation defines three reference periods with different limits to minimize noise nuisance:

• thedaytime period defined as from 7:00 a.m. to 8:00 p.m;
• theevening period from 20h00 to 23h00;
• night time from 23h00 to 7h00.

The acoustic tests and measurements required to verify compliance with the General Noise Regulation (RGR) are carried out at the Lisbon City Council Acoustic Testing Laboratory (LEA), which has been accredited by the Portuguese Accreditation Institute(IPAC) since April 2013, under accreditation number L0651.

The Acoustic Testing Laboratory (LEA) analyzes an average of 50 cases every year.

It has a frequency measured in hertz (Hz), and an amplitude which expresses the intensity of that sound. Sound needs a material medium to propagate and its speed of propagation depends on that medium, with air being considered the main propagation medium.

Sound becomes noise when it becomes unpleasant, disturbs rest, is uncomfortable, annoying, undesirable and affects human health, sometimes irreversibly. The level of annoyance of noise varies depending on the source, the distance from the place of reception, the means of propagation, the time of exposure, the intensity of hearing, the time of day and the sensitivity of the receivers.

How is sound measured?

Sound levels are measured based on the sound pressure level, measured in Decibels (dB), which is the unit used to measure sound intensity.

The sound level meter is the most commonly used piece of equipment for measuring sound by frequency and sound pressure level (SPL), which corresponds to the human sense of hearing in terms of sound.