(620 ILCS 35/5) (from Ch. 15 1/2, par. 755)

Sec. 5. Definitions. As used in this Act:

(a) "Airport" means an airport, as defined in Section 6 of the Illinois
Aeronautics Act, that has more than 500,000 aircraft operations (take-offs
and landings) per year.

(a-1) "Airport sponsor" means any municipality, as defined in Section 20 of the Illinois
Aeronautics Act, that can own and operate an airport.

(a-3) "Annual community noise equivalent level" or "annual CNEL" means the average sound  level (on an energy basis), in decibels, of the daily community noise equivalent level over a 12-month period. The annual CNEL is calculated by the following:

Annual CNEL = 10 log₁₀[(1/365) SIGMA antilog (CNEL(i)/10)]
Where:
        (1) CNEL(i) = the daily CNEL for each day in a continuous 12-month period; and
        (2) SIGMA means summation.

When the annual CNEL is approximated by measurements on a statistical basis, the number 365 is replaced by the number of days for which measurements are obtained.

(a-5) "Daily community noise equivalent level" or "CNEL" means the 24-hour day average sound level,
in decibels, adjusted to an equivalent level to account for the lower tolerance of people to noise during evening and night time periods relative to the daytime period. The daily community noise equivalent level is calculated from the hourly noise levels by the following:

CNEL = 10 log (1/24) [SIGMA antilog (HNLD/10) + 3 SIGMA antilog
(HNLE/10) + 10 SIGMA antilog (HNLN/10)]

Where:
        (1) HNLD means the hourly noise levels for the period 7:00 a.m. through 6:59 p.m.;
        (2) HNLE means the hourly noise levels for the period 7:00 p.m. through 9:59 p.m.;
        (3) HNLN means the hourly noise levels for the period 10:00 p.m. through 6:59 a.m.; and
        (4) SIGMA means summation.

(a-8) "Noise exposure level" means the level, in decibels, of the time-integrated A-weighted squared sound pressure for a stated time interval or event, based on the reference pressure of 20 micronewtons per square meter and reference duration of one second.

(a-9) "Noise level" means the sound level measure, in decibels, of an A-weighted sound pressure level as measured using the slow dynamic characteristic for sound level meters specified in American National Standard Specification for Sound Level Meters (ANSI S1.4-1983 as revised by ANSI S1.4A-1985), which is hereby incorporated by reference. The A-weighting characteristic modifies the frequency response of the measuring instrument to account approximately for the frequency characteristics of the human ear. The reference pressure is 20 micronewtons/square meter (2 x 10

^-4 microbar).

(b) "Permanent noise monitoring system" or "system" means a system that
includes at least:

(1) automated noise monitors capable of recording noise levels 24 hours per day 365 days