We have succeeded in observing the structure-sensitive reaction of CO2 with TiO2(110)-(1 x 1) surfaces modified with Na adatoms by scanning tunneling microscopy. At low coverages (0.4 atom/nm(2) or less) Na adatoms are ionized and adsorbed on the exposed Ti-rows of the substrate. A p(4 x 2) order locally appears at 0.6 atom/nm(2), and a c(4 x 2) order develops at 0.9 atom/nm(2). Those Na-modified surfaces are exposed to 10(2) L CO2 at room temperature. Post-exposure observation finds chains of bright particles on the c(4 x 2) surface. The asymmetric topography of the individual particles is assigned to the distribution of the LUMO of the adsorbed carbonate. In contrast, dispersed Na adatoms at lower coverages are unable to react with CO2 at all. The genesis of strong basic sites is thus suggested not to be linearly correlated with Na quantity, but to be correlated with the ordered structure of Na adatoms.