Heterogeneous Interactions of NO2with Aqueous Surfaces

Uptake of gas-phase NO 2 by water was studied in both the droplet train and bubble train flow reactors. Aqueous surface reaction of NO 2 (g), reported previously in the literature, is not substantiated by these studies. The uptake of NO 2 (g) is a function of Henry's law coefficient ( H NO 2 ) and the second-order NO 2 (aq)−NO 2 (aq) hydrolysis reaction rate coefficient ( k 2 ), in the form H NO 2 ( k 2 ) 1/2 . The NO 2 (aq)−NO 2 (aq) hydrolysis rate coefficient is defined by: −d[NO 2 (aq)]/d t = 2 k 2 [NO 2 (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 NO 2 gas uptake. From these measurements and analysis of literature values, recommended values of these parameters at 293 K are H NO 2 = (1.4 ± 0.2) × 10 -2 M atm -1 and k 2 = (3.0 ± 0.9) × 10 7 M -1 s -1 . At 276 K, our best estimates are H NO 2 = 2.3 (+0.3−0.9) × 10 -2 M atm -1 and k 2 = (2.2 ± 0.6) × 10 7 M -1 s -1 .