Charge transfer experiments were carried out in walk-in clod room to investigate the sign and amount of charge that is transferred to the graupel(soft-hail) during the collisions of ice crystal with graupel. Different concentration of aqueous solution of sulfuric acid were used to produce polluted cloud during the experiments. A cloud of supercooled droplets is formed inside the cloud chamber by heating the same aqueous solution and ice crystal formation in cloud is initiated by momentarily introducing a metal rod dipped in liquid nitrogen into the cloud.

It is observed that the charge transfer values increase with the increasing of sulfuric acid concentrations in aqueous solution.If aqueous solution contains 25% and 50% of sulfuric acid by weight, dark film like coat on the crystal surface is observed. Due to this film, the crystals boundaries are no longer sharp and well defined like that observed for pure water cloud. It is suggested that during the collisions between ice crystal and graupel this film could be transferred to the graupel resulting in higher values of charge transfer.