Uptake of gas-phase NO2 by water was studied in both the droplet train and bubble train flow reactors. Aqueous surface reaction of NO2(g), reported previously in the literature, is not substantiated by these studies. The uptake of NO2(g) is a function of Henry＇s law coefficient (H-NO2) and the second-order NO2(aq)-NO2-(aq) hydrolysis reaction rate coefficient (k(2)), in the form H-NO2(k(2))(1/2). The NO2(aq)-NO2(aq) hydrolysis rate coefficient is defined by: -d[NO2(aq)]/dt = 2k(2)[NO2(aq)](2). The coupled nature of the uptake makes it difficult to obtain reliable separate values for the two parameters H and k(2). Literature values for these parameters vary by as much as a factor of 5. With the bubble train apparatus it was possible to separate clearly the effects of solubility and reaction on NO2 gas uptake. From these measurements and analysis of literature values, recommended values of these parameters at 293 K are H-NO2 = (1.4 +/- 0.2) x 10(-2) M atm(-1) and k(2) = (3.0 +/- 0.9) x 10(7) M-1 s(-1). At 276 K, our best estimates are H-NO2 = 2.3 (+0.3-0.9) x 10(-2) M atm(-1) and k(2) = (2.2 +/- 0.6) x 10(7) M-1 s(-1).