Monitoring Noise Pollution

How is sound measured?

decibels (dB)

What scale is used for human hearing?

dB(A) scale

dB(A) scale

It takes into account the sensitivity of human hearing by weighing sounds between 1000 and 4000Hz

This is because the nerve cells in the ear are more sensitive to sounds in this frequency range, so they are heard more easily

Measuring Road Traffic Noise levels:

LA10

LA90

Traffic Noise Index (TNI)

L10 (18h)

LA10

LA10 measures noise exceeded for 10% in any set period.

What is LA10 a good measure of?

It is a good measure of the noisiest areas. It represents the louder parts of traffic noise, like during busy moments or when many vehicle pass.

Example of LA10

If you're measuring noise for 1 hour, LA10 is the noise level that was exceeded for 6 minutes (10% of 1 hour)

LA90

LA90 measures the noise level exceeded for 90% in any set period. It is a good measure of the quietest periods.

Example of LA90

In a 1 hour measurement, LA90 is the noise level exceeded for 54 minutes (90% of 1 hour).

Traffic Noise Index (TNI)

This produces a representative measure of traffic noise using LA10 and LA90

L10 (18h)

This measure assumes that traffic noise is only a problem during the 18 hours between 6am and midnight.

The noise level that is exceeded during the noisiest 10% of each of these 18 hours is measured. The mean of these 18 levels is then calculated.

Measuring Aircraft Noise levels:

- Effective Perceived Noise Levels (EPNL)

- Noise and Number Index (NNI)

- Leq 57dB

Effective Perceived Noise Levels (EPNL)

This is an estimate of the relative loudness of a particular type of aircraft during take-off, overflight, and landing

It is calculated from many observations, recorded at 450m, to the side of the flight path

Noise and Number Index (NNI)

It combines the number of flights and the noise levels of aircraft above 80dB, as it is presumed that aircraft below 80dB do not cause serious annoyance

(It has been replaced with Leq 57dB)

Leq 57dB

Leq is an average sound level over a particular period.

For UK airports, an average of 57dB between 7am and 11pm in the summer is used

Considerations about 57dB

- Levels above this are considered annoying

- Areas with noise above this level will experience 'significant community annoyance'