Gas-phase ion-molecule reactions of HO2-. CO2 with the neutrals CO, N2O, NO, NO2, N2O5, HNO3, and SO2 in helium at 290 K were studied using a fast flow reactor. For CO, N2O, NO, and NO2, no detectable reaction was observed to occur. The primary reaction channels of HO2-. CO2 with HNO3 lead to NO3- and HO2-. HNO3, while the reaction with N2O5 yields only NO3-. With SO2, the ion product is HSO4-. Measured rate constants for the observed reactions are at or close to tile collisional rate. The implications of these studies for atmospheric chemistry are discussed.