From AMS Glossary
In atmospheric electricity, a measure of the rate at which a given electrically charged object loses its charge to the surrounding air.
If the object bears a charge q at time t, then according to a law established by Coulomb,
where k is the object's dissipation constant expressed in reciprocal time units. It is found that k depends not only upon the geometry of the charged object but also upon the density of the surrounding air, its humidity, and its motion relative to the object.