Featured on the cover page of the American Chemical Society Earth and Space Chemistry Earth and Space Chemistry : an article published by PhLAM laboratory and SAGE department.
Primarily emitted from biomass burning or from anthropogenic sources, atmospheric aerosols contain a significant part of organic compounds and, in particular, organic acids. Molecular dynamics is used to model the formation of valeric (C5H10O2) and glutaric (C5H8O4) acid nanometer-sized aerosol particles at room temperature and two different humidities.
As a result of a higher propensity to form hydrogen bonds, glutaric acid aggregates are shown to be denser than their valeric counterpart. The addition of water molecules with water/acid ratios of 1:1 and 2:1 has then been studied in the case of the diacid. At a low water content, water primarily forms small islands on the surface. When the amount of water increases, it penetrates deeper into the aggregate but a significant fraction remains at the surface. A Connolly surface analysis reveals that the surface is mostly covered by hydrogen atoms from CH2 groups, with acidic hydrogens being saturated and not available at the surface, for both dry and wet particles. These atomic distributions could impact the reactivity of such particles with gas-phase oxidants and the uptake of trace gases.
Classical Molecular Dynamics Study of Small-Chain Carboxylic Acid Aerosol Particles
Antoine Roose, Céline Toubin , Sébastien Dusanter , Véronique Riffault, and Denis Duflot
ACS Earth Space Chem., 2019, 3 (3), pp 380–389