High noise levels are an irritation and, at very high levels, a health hazard. Several new applications allow smart phone owners to turn their phone into a sound meter. A number are reviewed at healthyhearing.com.
For more about the connections between noise and health see the noise section of the Design for Health web site.
Noise Mapping England is a terrific online resource providing highly localized noise mapping for a number of English cities. Noise sources include raid, rail, industry, and air and users can create separate maps for day and night.
For more information about health and noise see the noise section of the Design for Health web site.