The uptake coefficients of NO2 on buffered solutions containing m-dihydroxy benzene (resorcinol) or 2,7-dihydroxynaphthalene (Np(OH)(2)) were determined over the pH range from 3 to 11 using the wetted. wall flow tube technique. The nominal reactant concentration was also varied by several orders of magnitude. Taking into account gas phase as well as liquid-phase diffusion, the uptake coefficients were interpreted using a simple model of, stepwise deprotonation of these two weak bivalent acids. This model yields the rate constants for the reaction of NO2 with the neutral, singly, and doubly deprotonated forms of both compounds. While the reaction of NO2 with the neutral form is very slow (i.e., with rate constants of a few times 10(2) M-1 s(-1)), the reaction of NO2 with the deprotonated species is much faster (rate constants are reaching levels of several 10(6) M-1 s(-1)). The rate constant of 3.8 x 10(8) M-1 s(-1) for NO2 with the doubly deprotonated resorcinol ion is in good agreement with the one found by Alfassi, the only reported literature value.