Evaluation of the rate of uptake of nitrogen dioxide by atmospheric and surface liquid water

Abstract

The rate of uptake of NO 2 by liquid water according to (R1), 2NO 2 (g) + H 2 O(1) → 2H + + NO 3 − + NO 2 − , is shown to be unaffected by O 2 (0.2 atm). Hence the rate constant and Henry's law solubility constant of NO 2 previously obtained may be employed to evaluate the rates of aqueous phase reactions of NO 2 in the ambient atmosphere. Reactions (R1) and (R2), NO 2 (g) + NO(g) + H 2 O(1) → 2H + + 2NO 2 − , are quite slow at representative atmospheric partial pressures and cloud liquid water content; the characteristic times range upward from 10 3 –10 4 hours at 10 −7 atm, increasing with decreasing partial pressures of the gases. Direct acidification of cloud liquid water by (R1) or (R2) is also unimportant. Catalytic enhancement of (R1) is potentially important for catalyst concentrations of order 10 −7 M , assuming sufficiently fast rate constants (∼10 8 M −l s −1 ). Iron‐catalyzed reaction in particular, however, is found to be unimportant. Reaction of NO 2 with dissolved S(IV) is potentially mportant, based upon an assumed upper limit rate constant of 2.5×10 7 M −1 s −1 . Deposition of NO 2 to surface (ocean or lake) water is shown to be controlled by aqueous phase mass transport and/or reaction and is much slower than heretofore assumed.