The third-order rate constants for NaOH + CO2 +M were measured in a flow tube at 298 K. The rate constants for N2 and N2 O buffer gases are (1.3¿0.3)¿10-28 and (2.9¿0.6)¿10-28 cm6 molecule-2 s-1, respectively. We expect the product of this reaction, NaHCO3 , to be relatively stable with respect to 0 atom reaction and photolysis and to be a dominant reservoir species for Na in the mesosphere. The association reaction of NaOH with CO2 is at least 40 times faster than NaOH + HCl at all altitudes below the Na layer. Na species will not affect stratospheric ClOx and O3 chemistry. ¿American Geophysical Union 1987