Table 2. Main parameters of stimulated rain intensity.

	The level of rainfall	Intensity a mm/h	Flow rate of eluting solution b (mL/h)
1	light rain	1	0.31
2	moderate rain	5	1.57
3	heavy rain	15	4.71
4	rainstorm	30	9.42

^aIntensity is collected based on weather parameters;

^bFlow rate = intensity of rainfall × area of column.