Estimating the NH3:H2SO4 ratio of nucleating clusters in atmospheric conditions using quantum chemical methods

[摘要] We study the ammonia addition reactions of H₂SO₄·NH₃molecular clusters containing up to four ammonia and two sulfuric acidmolecules using the ab initio method RI-MP2 (Resolution of Identity 2nd orderMøller-Plesset perturbation theory). Together with results from previousstudies, we use the computed values to estimate an upper limit for theammonia content of small atmospheric clusters, without having to explicitlyinclude water molecules in the quantum chemical simulations. Our resultsindicate that the NH₃:H₂SO₄ mole ratio of small molecularclusters in typical atmospheric conditions is probably around 1:2. Highammonia concentrations or low temperatures may lead to the formation ofammonium bisulfate (1:1) clusters, but our results rule out the formation ofammonium sulfate clusters (2:1) anywhere in the atmosphere. A sensitivityanalysis indicates that the qualitative conclusions of this study are notaffected even by relatively large errors in the calculation of electronicenergies or vibrational frequencies.

[学科分类] 大气科学