Cerium dioxide, CeO2, plays an important role in catalysis, due to its ability to store and release oxygen depending on the conditions present in the catalyst environment. To understand the role of ceria in catalytic reactions, we need to study the details of the interaction of ceria surfaces with environmentally sensitive molecules. In this work, we examine the adsorption of the NO2 molecule onto defective (reduced) surfaces of ceria using density functional theory with a correction for on-site Coulomb interactions (DFT+U), which allows for a consistent description of pure and reduced ceria. The interaction of NO2 with defective (111), (110), and (100) surfaces gives an adsorbate-surface structure in which the bond lengths around one Ce(III) ion from the reduced surface shorten, while one N-O bond lengthens. Analysis of the electronic structure and spin density distributions demonstrates that one Ce(III) has been reoxidized to Ce(IV), with the formation of adsorbed NO2-. Finally, we discuss the energetics of the interaction of NO2 with ceria.