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Download fileComputational Study of the Effect of Mineral Dust on Secondary Organic Aerosol Formation by Accretion Reactions of Closed-Shell Organic Compounds
journal contribution
posted on 2019-10-10, 14:45 authored by Fatemeh Keshavarz, Anna Shcherbacheva, Jakub Kubečka, Hanna Vehkamäki, Theo KurténThe effect of dust
aerosols on accretion reactions of water, formaldehyde,
and formic acid was studied in the conditions of earth’s troposphere
at the DLPNO-CCSD(T)/aug-cc-pVTZ//ωB97X-D/6-31++G** level of
theory. A detailed analysis of the reaction mechanisms in the gas
phase and on the surface of mineral dust, represented by mono- and
trisilicic acid, revealed that mineral dust has the potential of decreasing
reaction barrier heights. Specifically, at 0 K, mineral dust can lower
the apparent energy barrier of the reaction of formaldehyde with formic
acid to zero. However, when the entropic contributions to the reaction
free energies were accounted for, mineral dust was found to selectively
enhance the reaction of water with formaldehyde, while inhibiting
the reaction of formaldehyde and formic acid, in the lower parts of
the troposphere (with temperatures around 298 K). In the upper troposphere
(with temperatures closer to 198 K), mineral dust catalyzes both reactions
and also the reaction of methanol with formic acid. Despite the intrinsic
potential of mineral dust, calculation of the catalytic enhancement
parameter for a likely range of dust aerosol concentrations suggested
that dust aerosols will not contribute to secondary organic aerosol
formation via dimerization of closed-shell organic compounds. The
main reason for this is the relatively low absolute concentration
of tropospheric dust aerosol and its inefficiency in increasing the
effective reaction rate coefficients.