Index Geophysics

Amines are likely to enhance neutral and ion-induced sulfuric acid-water nucleation in the atmosphere more effectively than ammonia

We have studied the structure and formation thermodynamics of dimer clusters containing H₂SO₄ or HSO₄^− together with ammonia and seven different amines possibly present in the atmosphere, using the high-level ab initio methods RI-MP2 and RI-CC2. As expected from e.g. proton affinity data, the binding of all studied amine-H₂SO₄ complexes is significantly stronger than that of NH₃•H₂SO₄, while most amine-HSO₄^− complexes are only somewhat more strongly bound than NH₃•HSO₄^−. Further calculations on larger cluster structures containing dimethylamine or ammonia together with two H₂SO₄ molecules or one H₂SO₄ molecule and one HSO₄^− ion demonstrate that amines, unlike ammonia, significantly assist the growth of not only neutral but also ionic clusters along the H₂SO₄ co-ordinate. A sensitivity analysis indicates that the difference in complexation free energies for amine- and ammonia-containing clusters is large enough to overcome the mass-balance effect caused by the fact that the concentration of amines in the atmosphere is probably 2 or 3 orders of magnitude lower than that of ammonia. This implies that amines might be more important than ammonia in enhancing neutral and especially ion-induced sulfuric acid-water nucleation in the atmosphere.

Kurtén, T.

Loukonen, V.

Vehkamäki, H.

Kulmala, M.

2018-01-15

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10.5194/acp-8-4095-2008

https://acp.copernicus.org/articles/8/4095/2008/

eISSN: 1680-7324

eng