A possible atmospheric source of HNO3: the ammonolysis reaction of t-N2O4 in the presence of water monomer, water dimer, and sulfuric acid

Although the ammonolysis of t-N2O4 is one of the potential sources of HNO3 formation, the available studies have only focused on its naked reaction. Herein, the effect of important neutral and acidic trace gases, water monomer, water dimer, and sulfuric acid, on the formation of HNO3 from the ammonolysis of t-N2O4 was studied by the quantum chemical method of CCSD(T)/aug-cc-pVTZ//B3LYP-D3/6-311++G(3df,2pd) and the Master equation/Rice–Ramsperger–Kassel–Marcus (ME/RRKM) rate calculations. The quantum chemical results revealed that the ammonolysis of t-N2O4 with (H2O)2 and H2SO4 are barrierless or nearly barrierless reactions, potentially lowering the energy barrier to 3.4–4.1 kcal mol−1. The calculated effective rate constant illustrates that (H2O)2 (100% RH) dominates over H2O and H2SO4 within the range of 280–320 K (0 km), with an effective rate constant that is 1–3 orders of larger magnitude, whereas H2SO4 (108 mol cm−3) is the most favorable catalyst within the troposphere between 5 and 30 km. However, the contributions of H2O, (H2O)2, and H2SO4 are not apparent in the gas-phase ammonolysis of t-N2O4 within the range of 213–320 K and 0–30 km because their effective rate constants were at least 4 orders of magnitude lower than the corresponding rate constant of the ammonolysis of t-N2O4. In general, the current findings shed fresh light on neutral (H2O and (H2O)2) and acidic (H2SO4) catalysts that not only affect energy barriers but also have an impact on the ammonolysis of t-N2O4 in neutral and acidic conditions.