E	unit potential energy (J kg−1)
F()	function of
f	frequency (Hz)
fk	Fourier transformation at frequencies n = 0, 1, 2,…, n − 1 and k = 0, 1, 2,…, n − 1
g	gravity (=9.81 ms−2)
H, H’	stack full height (m), normalized stack full height H’ = 1
Hd, H’d	stack discharging height (m), normalized stack discharging height (-)
Hp, H’p	stack height of air pressure measurement (m), normalized stack height of air pressure measurement (m wg.)
k	frequency factor
max	maximum value
n	number of samples
p	probability (-)
P	air pressure (m wg.)
$\overline{\mathit{P}}$	average air pressure (m wg.)
q	stack water discharging flow rate (Ls−1)
R	risk index defined in Equation (9) (-)
r	correlation coefficient (-)
T	T-statistics for t-test (-)
t	time period of a fluctuation cycle (s)
Subscript
1	of reference condition of transmission risk concerned
m	of measured value
max	of maximum value
p	of predicted value