Understanding Environmental Noise and Its Impact

Description of Environmental Noise

Noise is the most common contaminant and can be defined as any sound that the recipient qualifies as annoying, undesirable, inappropriate, or objectionable. What is music to one person may be classified as noise to another. In a broader sense, noise is any unwanted sound perceived by the receiver, and sound is defined as any physical agent that stimulates the sense of hearing.

Noise Pollution

Noise pollution is defined as interference in normal activities. That is, not simply the existence of high levels of noise, but people at risk and carrying out activities incompatible with such noise levels.

Noise Characteristics

• It is a spontaneous phenomenon that is linked to the activity schedule producing it.
• It does not leave any residue (it has a cumulative effect on the environment, but it can have a cumulative effect on humans).
• Its quantification is complex.
• It is one of the pollutants that requires less energy to be produced.
• It has a small radius; that is, it is localized.
• It is not susceptible to movement through natural systems, such as air pollution carried by wind or runoff carried by a river for great distances.
• It is perceived by only one sense: the ear. This makes estimating its effect different from other pollutants, such as water, for example, where pollution can be perceived by its appearance, smell, and taste.

Decibel

The weakest sound that a good ear can hear or detect has an amplitude of one-twentieth-millionth of a Pascal (20µPa) - something like 5,000,000,000 times less than normal atmospheric pressure. A change in pressure of 20µPa is so small that it makes the ear membrane deflect a distance less than the diameter of a single molecule of hydrogen. The decibel is a logarithmic-type mathematical relationship where if noise increases by 3 dB, it means that the sound energy received doubles. The hearing threshold is at 0 dB, and the pain threshold is at 120 dB.

Sound Level Meter

A sound level meter is an instrument designed to respond to sound in approximately the same manner as the human ear and to provide objective and reproducible measurements of sound pressure level. There are many sound measuring systems available. Although different in detail, each system consists of a microphone, a processing section, and a reading unit.

CONAMA's Work

Noise has emerged as a cross-cutting issue to be addressed. The work in this area has had special emphasis on coordination with stakeholders and developing guidelines for the design of environmental standards.

Description

The first standard issued addressed noise nuisance generated by fixed sources (DS 146/97 Ministry General Secretariat of the Presidency), which establishes maximum permissible levels for daytime and evening, according to land use (residential or industrial, for example), of the affected area. This regulation was the first standard developed under the procedure for issuing environmental standards that CONAMA coordinates.

In the case of mobile sources, the work started with the noise emission standard for buses in urban and rural public transportation (DS 129/02 Ministry of Transport and Telecommunications). This regulation establishes maximum emission levels that should be verified by standardized and controlled testing before the bus enters the vehicle fleet and during periodic technical reviews. In 2008, work began to develop rules for the noise emitted by light vehicles, medium vehicles, and motorcycles. CONAMA also supported the development of a technical standard for setting minimum requirements for acoustic insulation of houses.

CONAMA's Work (Continued)

• It has developed a Model Municipal Noise Ordinance.
• It supports the environmental impact assessment of projects.
• It has a program of education and information through seminars, lectures, and activities, such as the International Day of Awareness on Noise.