Mechanistic insight into the competition between interfacial and bulk reactions in microdroplets through N₂O₅ ammonolysis and hydrolysis.

Abstract

Reactive uptake of dinitrogen pentaoxide (N₂O₅) into aqueous aerosols is a major loss channel for NO_x in the troposphere; however, a quantitative understanding of the uptake mechanism is lacking. Herein, a computational chemistry strategy is developed employing high-level quantum chemical methods; the method offers detailed molecular insight into the hydrolysis and ammonolysis mechanisms of N₂O₅ in microdroplets. Specifically, our calculations estimate the bulk and interfacial hydrolysis rates to be (2.3 ± 1.6) × 10^-3 and (6.3 ± 4.2) × 10^-7 ns^-1, respectively, and ammonolysis competes with hydrolysis at NH₃ concentrations above 1.9 × 10^-4mol L^-1. The slow interfacial hydrolysis rate suggests that interfacial processes have negligible effect on the hydrolysis of N₂O₅ in liquid water. In contrast, N₂O₅ ammonolysis in liquid water is dominated by interfacial processes due to the high interfacial ammonolysis rate. Our findings and strategy are applicable to high-chemical complexity microdroplets.