In a city the noise levels represented by equivalent sound pressure level over 8 years period were reported as 80 dB (A). What does 'A' refer to

Decibel (dB) is a unit for expressing the ratio between two physical quantities, usually amounts of acoustic or electric power, or for measuring the relative loudness of sound. 

dB (A) measurement:

• A dB (A) measurement has been adjusted to consider the varying sensitivity of the human ear to different frequencies of sound.
• Very low or high frequencies are given less weight than on the standard decibel scale.
• Many regulated noise limits are specified in terms of dB (A) based on the belief that dB (A) is better correlated with the relative risk of noise-induced hearing loss.
• Compared to dB, dB (A) is a type of weighting measurement used that underestimate the perceived loudness, annoyance factor, and stress-inducing capability of noises with low-frequency components, especially at moderate or high volumes of noise. 

Therefore, in a city the noise levels represented by equivalent sound pressure level over 8 years period were reported as 80 dB (A), here 'A' refers to a type of weighting used in the measurement.

Measurement of some common sounds: