By definition, noise is "sound without value" or "any noise that is undesired by the recipient". Thus, the kind of environmental impact of noise pollution is slightly different from other kinds of pollution.
Generally, there is much more noise in the urban areas because of larger concentration of population as well as industrial and other activities like transportation vehicular movements, etc. Non-industrial sources of noise can come from public address systems for religious or political propaganda, recreation, hawkers or other street noise. Noise can also arise from the natural sources like thunder.
Noise as a potent menace can be evaluated in terms of a 'noise level' scale, or in decibels (dB). However, the health hazard is a matter of perceived noise level decibels (pNdB), which according to the W.H.O.'s prescribed optimum noise level as 45 dB by day and 35 by night; and anything above 80 dB is hazardous. Table 10.2 lists noise sources and their intensity.
The hazards of noise pollution are many and varied. For example, people exposed to noise levels reaching 110 db may reveal mental trauma, deafness, physical fatigue and hypertension, cardiovascular disease, insomnia, peptic ulcer, eczema and asthma. Psychologists are of the opinion that prolonged exposure to noise for a day alone, may lead to severe mental disorientation, and in a few cases, result in a violent behavior.
The noise properties and their reasonable level, in general, can be controlled only through enlightened and co-operative authorities. However, in a few cases, noise pollution can be minimized only through rigorous law and conscious efforts of the law enforcement department.