NO2 interacts with soot in the atmosphere and, at higher temperatures, is used as an oxidant to regenerate filters on the exhausts of diesel cars. This work investigates the adsorption and reaction of NO2 (forming NO) with either carbon black or soot (from a diesel engine) held at near ambient temperatures (20-75 degrees C) in a packed bed. It was found that initially NO2 very rapidly adsorbed; approximately half the NO2 adsorbed was converted to NO, leaving behind O-containing functionalities on the surface of the carbon. These adsorbed species can be made to produce CO2 and CO by heating the carbon to a temperature above 100 degrees C. At 20 degrees C, the number of O-containing species, C(O), formed on the carbons was found, surprisingly, to be equal to the amount of NO2 remaining stably adsorbed. A mechanism of elementary reactions is postulated, in which NO2 is only adsorbed on the newly formed C(O). A model of adsorption and reaction in a packed bed was used to estimate kinetic parameters for the surface reactions giving overall C(_) + 2NO(2) -> C(O + NO2) + NO. The measurements of [NO2] and [NO] against time were represented best by the reactions C(_) + NO2 -> C(NO2), C(NO2) -> C(O) + NO, and C(O) + NO2 -> C(O + NO2); each is first order with respect to NO2. Excellent agreement between the results of modeling and experiment is obtained by assuming that there are two types of active site, C(_), with different reactivities.