To better understand the influence of air parameters such as pressure, humidity and temperature on the counting efficiency of a radon monitor based on solid state silicon detectors and radon daughter electrostatic collection, a number of experimental and theoretical studies have been performed. This study has been carried out using a multiparameter acquisition system used to monitor radon, temperature, pressure and relative humidity. Results show that air humidity and temperature inside the cell influence radon daughter collection in a significant way. For the tested cell, a decrease of the 218Po counting efficiency vs. humidity and temperature increase was measured in the ranges from 10% to 90% and from 15 degrees C to 35 degrees C, respectively. These effects were also theoretically studied by using Monte-Carlo software, which takes into account electrostatic collection of radon daughters in the cell, by considering the recombination process as a function of climatic parameters. A satisfactory agreement was obtained between experimental measurements and theoretical calculations.