Upward-propagating discharges from thunderstorms, called blue jets and blue starters and high altitude near-cloud top discharges have been reported over strong convective storm systems. The electrodynamics involved in these high altitude electrical phenomena are not clarified, though several models have been proposed, including initiation by run-away high energy electron beams and breakdowns related to quasi-electrostatic fields. We suggest that the occurrence of such high altitude discharges may, under some conditions, be instigated by decreases in electrical conductivity (and therefore increases in electric field strength) near and above cloud tops, the conductivity decrease resulting from the presence of large ions. We hypothesize that the large ions are pollution aerosols which are systematically transported to the lower stratosphere/upper troposphere from the lower troposphere by convective currents. In addition we propose that large ion production in the region above cloud is further enhanced by: 1. creation of new large ions by photolytic gas-to-particle conversion; and 2. by the upward transport of cloud top ions across the tropopause into the lower stratosphere. ¿ 1998 American Geophysical Union