The detection efficiency of electrostatic collection radon monitors is influenced by the humidity of the air in the collection cell. This is due to the recombination of positively charged 218Po with OH− ions, whose concentration depends on humidity. A novel design of an electrostatic collection cell, in which the air pressure in the cell is less than the atmospheric pressure, is proposed to eliminate the impact of humidity. As a result of the lower air pressure, the drift velocity of the positively charged 218Po in the electric field increases...