DC and low frequency humidity dependence of an air-gap capacitor

We have measured both the 0.01 Hz (quasi-DC) and 1.0 kHz value of a room temperature air-gap capacitor as a function of environment (pressure, temperature, humidity). A huge difference in the humidity dependence was discovered in both measurements. This proves that surface layers containing adsorbed water have a significant effect on the frequency dependence of the capacitance value of air-gap capacitors.