Mechanistic insight into the competition between interfacial and bulk reactions in microdroplets through NO ammonolysis and hydrolysis.

Reactive uptake of dinitrogen pentaoxide (NO) into aqueous aerosols is a major loss channel for NO 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 NO in microdroplets. Specifically, our calculations estimate the bulk and interfacial hydrolysis rates to be (2.3 ± 1.6) × 10 and (6.3 ± 4.2) × 10 ns, respectively, and ammonolysis competes with hydrolysis at NH concentrations above 1.9 × 10mol L. The slow interfacial hydrolysis rate suggests that interfacial processes have negligible effect on the hydrolysis of NO in liquid water. In contrast, NO 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.