A systematic study of the mechanism of interaction of 218po(raa) formed by the decay of 222rn with airborne particulate matter has been made. The rate of attachment of raa to particles in the diameter range of 0.1 Um to 10.0 Um was measured as a function of particle size, concentration, and composition, radon concentration, time of interaction, relative humidity, and temperature. It was found that under the conditions in these experiments the attachment rate was proportional to the square of the particle diameter and varied with temperature and relative humidity. The composition of the particles apparently has no effect on the attachment. The variation in attachment rate was related to a sticking probability coefficient of approximately 0.02 That varies systematically with temperature and humidity. In addition, the rate of deposition of raa on the walls of the attachment kinetics system was measured and also found to change with temperature and relative humidity.