Rate constants for room-temperature reactions involving atmospheric cluster ions have been measured using two laboratory facilities: (1) a stationary afterglow facility employing photoionization and separate mass analysis for ions and neutrals, and (2) a drift tube facility employing thermionic emission of alkali ions and mass analysis of ions. In the afterglow facility, the sequence of reactions initiated by NO+ ions reacting in a gaseous mixture of nitric oxide and water vapor and terminated by H3O+·4H2O has been studied at 296°K with each rate constant measured independently. Likewise the sequence of reactions initiated by NO+ ions reacting in a gaseous mixture of nitric oxide and ammonia and terminated by NH4·3NH3 has been studied at 296°K. In the drift tube facility, the clustering of atmospheric gases to the alkali ions Li+, Na+, and K+ has been studied. From laboratory studies of the clustering of atmospheric gases to alkali ions, a map of the minimum values for initial clustering reaction rate constants and equilibrium constants has been drawn. The importance of the formation of a weakly bound cluster ion followed by a switching reaction to form a strongly bound cluster ion to the ion chemistry of the D region has been shown.