Amine–Amine Exchange in Aminium–Methanesulfonate Aerosols

Abstract

Aerosol particles are ubiquitous in the atmosphere and have been shown to impact the Earth's climate, reduce visibility, and adversely affect human health. Modeling the evolution of aerosol systems requires an understanding of the species and mechanisms involved in particle growth, including the complex interactions between particle-and gasphase species. Here we report studies of displacement of amines (methylamine, dimethylamine, or trimethylamine) in methanesulfonate salt particles by exposure to a different gas-phase amine, using a single particle mass spectrometer, SPLAT II. The variation of the displacement with the nature of the amine suggests that behavior is dependent on water in or on the particles. Small clusters of methanesulfonic acid with amines are used as a model in quantum chemical calculations to identify key structural elements that are expected to influence water uptake, and hence the efficiency of displacement by gas-phase molecules in the aminium salts. Such molecular-level understanding of the processes affecting the ability of gas-phase amines to displace particlephase aminium species is important for modeling the growth of particles and their impacts in the atmosphere.

New particle formation and growth from methanesulfonic acid, trimethylamine and water

“…The ion pair formed from MSA and TMA is a particularly stable unit in the MSA-TMA system. 65 The interaction energy between MSAÁTMA units is significant, but not as great as that between ions in the ion pair due to the lack of hydrogen bonding. As discussed in Ortega et al 71 for the sulfuric acid-DMA system, a deep local minimum on the free energy surface can lead to evaporation of clusters that will affect particle formation rates.…”

Reactions of Methanesulfonic Acid with Amines and Ammonia as a Source of New Particles in Air

“…50 For comparison, the binding energies of ion pairs in forming (MSA) 2 ·(MA) 2 and (MSA) 2 ·(DMA) 2 clusters (ΔH = −36 and −37 kcal mol −1 , respectively) are close and are significantly larger than the binding energy informing (MSA) 2 ·(TMA) 2 due to a cyclic hydrogen-bonding structure between alternating cations and anions. 72 However, the availability of an NH group that is not hydrogen-bonded in the MA cluster may lead to an extended hydrogen-bonding network, an arrangement seen in the crystal structure of ammonium methanesulfonate. 75 While growth of a perfect crystal may not occur in this case, the additional hydrogen-bonding site may play a role in more effectively growing the MSA-MA clusters to detectable sizes even under dry conditions.…”

“…The growth of DMA and TMA particles is also significantly faster than the MA particles (Figure 2 and S2). This can be due to (1) a larger contribution of growth from water because of their higher hygroscopicities, 72 (2) a larger molecular volume, and/ or (3) smaller particle formation rates so that higher concentrations of gas precursors and small clusters that can contribute to growth are left in the DMA and TMA systems.…”

Overview: Homogeneous nucleation from the vapor phase—The experimental science

“…In particular, experimentalists are introducing new techniques such as vibrational spectroscopy 56,171,176,249 and mass spectrometry, 193,233,234,[237][238][239][240]244,[250][251][252][253][254][255] combining multiple complementary techniques to generate redundant data with which to test experimental self-consistency, 68,162,175,249 improving the sophistication of models, 74,231 and conducting complementary quantum chemical calculations. 248,256,257 In this section, we present several examples that highlight recent experimental advances.…”