Atmospheric nucleation occurs all around the world, leading to seed clusters that can further grow by uptake of trace gases and water. They ultimately grow to sizes sufficient to impact visibility, public health and climate. Despite these observations, many questions still remain regarding the mechanisms of nucleation and growth of the initial molecular clusters, and the nature of the precursors involved. Experimental and quantum chemical calculations have previously shown that small amines are key players in sub-3 nm particle formation through reactions with acids such as sulfuric acid (H2SO4) and methanesulfonic acid (MSA). However, in the atmosphere, ammonia usually coexists with the amines. We report here the influence of ammonia on particle formation from the reactions of MSA with small amines (methylamine, dimethylamine, trimethylamine). Experiments were performed in a glass flow reactor coupled to different particle counters and particles were measured at various reaction times ranging from 2 to 42 sec. Ammonia is shown to systematically enhance particle formation from MSA/amines, but to various degrees depending on the amine investigated. Ab initio calculations are also presented for these systems to characterize the nature of proton transfer and hydrogen bonding between the species involved, providing molecular insights into particle formation.

Influence of ammonia on particle formation from methanesulfonic acid and amines: Combined experimental and theoretical studies

254th National Meeting (2017)

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