Understanding the properties of methyl vinyl ketone and methacrolein at the air-water interface: Adsorption, heterogeneous reaction and environmental impact analysis

Abstract

Air-water interfaces are ubiquitous in nature, as manifested in the form of the surfaces of oceans, lakes, and atmospheric aqueous aerosols. The aerosol droplets interface, in particular, plays a critical role in numerous atmospheric chemistry processes. Methyl vinyl ketone (MVK) and methacrolein (MACR), two abundant volatile organic compounds, are the significant precursors of Criegee intermediates and secondary organic aerosol. In this work, the physicochemical properties of MVK and MACR at the air-water interface are studied from a theoretical perspective. The free energy wells of MVK and MACR occur at the air-water interface, and the absorption probabilities of them are 71% and 67%, respectively. Repulsion dominates the interactions between MVK/MACR and water molecules in the bulk region, while attraction is dominant at the interface. The two molecules tend to tilt at the interface, with the CC bond exposed at the outer interface. The most likely reaction scenario of O3-initiated MVK/MACR reaction in the troposphere is also determined for the first time. Based on the molecular dynamics simulation results, the activity sequence of MVK + O3 is given at four different environments by the density functional theory method: air-water interface, mineral clusters interface, bulk solution, and homogeneous gas. The interfacial water molecule can catalyze the reaction of MVK with O3, and the rate constant at the air-water interface is ~6 times larger than that on the mineral surface model. Compared with mineral particles, aqueous particles play a more significant role in modifying the reaction properties of atmospheric organic species.