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Title: Integrated experimental and theoretical approach to probe the synergistic effect of ammonia in methanesulfonic acid reactions with small alkylamines
While new particle formation events have been observed worldwide, our fundamental understanding of the precursors remains uncertain. It has been previously shown that small alkylamines and ammonia (NH 3 ) are key actors in sub-3 nm particle formation through reactions with acids such as sulfuric acid (H 2 SO 4 ) and methanesulfonic acid (CH 3 S(O)(O)OH, MSA), and that water also plays a role. Because NH 3 and amines co-exist in air, we carried out combined experimental and theoretical studies examining the influence of the addition of NH 3 on particle formation from the reactions of MSA with methylamine (MA) and trimethylamine (TMA). Experiments were performed in a 1 m flow reactor at 1 atm and 296 K. Measurements using an ultrafine condensation particle counter (CPC) and a scanning mobility particle sizer (SMPS) show that new particle formation was systematically enhanced upon simultaneous addition of NH 3 to the MSA + amine binary system, with the magnitude depending on the amine investigated. For the MSA + TMA reaction system, the addition of NH 3 at ppb concentrations produced a much greater effect ( i.e. order of magnitude more particles) than the addition of ∼12 000 ppm water (corresponding to ∼45–50% relative humidity). The effect of NH 3 on the MSA + MA system, which is already very efficient in forming particles on its own, was present but modest. Calculations of energies, partial charges and structures of small cluster models of the multi-component particles likewise suggest synergistic effects due to NH 3 in the presence of MSA and amine. The local minimum structures and the interactions involved suggest mechanisms for this effect.  more » « less
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Journal Name:
Environmental Science: Processes & Impacts
Page Range / eLocation ID:
305 to 328
Medium: X
Sponsoring Org:
National Science Foundation
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