Synergistic effect in the humidifying process of atmospheric relevant calcium nitrate, calcite and oxalic acid mixtures

► Synergistic effect among mixed aerosol exists during humidifying process. ► The coexisting Ca(NO3)2 promoted the reaction in CaCO3/H2C2O4 mixture. ► Substitution of HNO3 by H2C2O4 occurs during the humidifying process of Ca(NO3)2/H2C2O4 mixture. ► The physicochemical properties of mixtures were greatly changed after humidifying process.