Our measurements of ion size distributions near a waterfall provided new evidence for a waterfal I- induced modification of air ion sizes. The ion size spectrum near a waterfall permanently differs from that in ordinary tropospheric air. In this paper we investigated the near-waterfall air ions chemical nature in detail. We carried out a simulation series of air small negative ion evolution, proposing that falling water, as a new environmental component, increases the concentration of OH- cluster ions. The produced OH- ions were employed as an extra input for our ion evolution model. The presence of additional OH- ions resulted in a decrease of typically model-provided NO (3) and/or HSO4- cluster ion concentrations and an increase of the abundance of HCO (3) cluster ions. Near the waterfall the latter ions became dominant in our simulations.