We investigate analytically and numerically trapping of submicron aerosol particles in a three-dimensional quadrupole acoustic chamber having hyperbolical configuration. The particle trajectories are described by the Langevin equation accounting for particle random Brownian motion. The particle trapping efficiency is investigated for a range of acoustic field parameters and particle properties. It is shown that submicron diffusive particles can be trapped in a small region near the chamber center. The effect of Brownian motion is to broaden the trapping region. The dimensions of the trapping region can be reduced by increasing the acoustic strength parameter.