Why Static Charges are Affected on Dry Days

[eureka_beyond]

Homework Statement

why should experiemnts related to static charges be carried out on dry days?

Homework Equations

I know this somehow relates to the moisture in air. yet, I do not understand the concept behind.

The Attempt at a Solution

Do the sparks created by the wan der graff generator or lightlings seen in thunderstorms relate to this concept. if so, how?

 

[Borek]

How does the conductivity of the air depend on amount of moisture?