Abstract
Abstract. The exchange kinetics and thermodynamics of amines for ammonia in small (1–2 nm diameter) ammonium bisulfate and ammonium nitrate clusters were investigated using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Ammonium salt clusters were reacted with amine gas at constant pressure to determine the kinetics of exchange. The reverse reactions, where aminium salt clusters reacted with ammonia gas, were also studied, and no substitution of ammonia for amine was observed. Gibbs free energy changes for these substitutions were determined to be highly exothermic, −7 kJ/mol or more negative in all cases. Uptake coefficients (reaction probabilities) were found to be near unity, implying that complete exchange of ammonia in small clusters by amine would be expected to occur within several seconds to minutes in the ambient atmosphere. These results suggest that if salt clusters are a component of the sub-3 nm cluster pool, they are likely to be aminium salts rather than ammonium salts, even if they were initially formed as ammonium salts.
Highlights
New particle formation (NPF) has been linked to the production of cloud condensation nuclei (CCN) (Lihavainen et al, 2003; Kerminen et al, 2005; Laaksonen et al, 2005), which can affect global climate
Predictions of the contribution of boundary layer (BL) particle formation to global and regional distributions of CCN suggest that NPF is an important contributor to the global aerosol number budget (Merikanto et al, 2009; Spracklen et al, 2006, 2008)
In the 3– 2 dimethylaminium bisulfate cluster, substitution of TMA for DMA becomes unfavorable after the second substitution, which is what would be predicted based on enthalpy of solvation values
Summary
New particle formation (NPF) has been linked to the production of cloud condensation nuclei (CCN) (Lihavainen et al, 2003; Kerminen et al, 2005; Laaksonen et al, 2005), which can affect global climate. The authors observed that amines will usually bind more strongly than ammonia to these complexes, suggesting that amines may be more important than ammonia in enhancing both neutral and ion-induced sulfuric acid-water nucleation in the atmosphere (Kurten et al, 2008). Another recent modeling study indicated that amines may be an important contributor to organic salt formation in the atmosphere (Barsanti et al, 2009). The results of this work are directly relevant to the composition of salt nuclei in the atmosphere
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