[AAS13-P02] Role of water molecule in aerosol nucleation and air-water interface reaction: quantum chemical and molecular dynamic simulation
Keywords:nucleation, interface, quantum simulation
Recently, quantum chemical calculation and molecular dynamic simulation methods have important theoretical significance and practical application value to study the formation and degradation of atmospheric pollutants, especially the micro-mechanism of atmospheric photodegradation, aerosol nucleation and heterogeneous reaction, and to identify structural information and energy information of the intermediates and products in the reaction process.
Water is the third most abundant species in the atmosphere after N2 and O2, corresponding to 50% of relative humidity at 298 K. Water plays an important role in several gas-phase chemical processes occurring in the atmosphere. For example, we carried out quantum calculation to study the interactions between benzoic acid (BA) and sulfuric acid (SA)/ammonia (NH3)/dimethylamine (DMA) with hydration by 1 to 6 water molecules, and found water molecules have different effect on BA-SA/NH3/DMA nucleation (Figure 1). For BA-DMA-(0-6)H2O, increasing water molecules can inhibit nucleation. For BA-NH3-(0-6)H2O, the most negative Gibbs free energy occur when NH3 are hydrated with 2/6 water molecules and BA is unhydrated. For BA-SA-(0-6)H2O, the most negative Gibbs free energy occur when SA is unhydrated and BA are hydrated with 6 water molecules. Moreover, the Born-Oppenheimer molecular dynamics (BOMD) was used to simulate ammonium bisulfate formation from a series of amines, SO3, and H2O molecules at the air-water interface. The results show that reactions between amines and SO3 involve multiple water molecules at the air-water interface. The reaction center’s ring structure (amine-SO3-nH2O) promotes the transfer of protons in the water molecules (Figure 2). The formed ammonium cation (-RNH3+) and the bisulfate anion (HSO4-) are present and stable by means of hydrogen bond interaction.
Water is the third most abundant species in the atmosphere after N2 and O2, corresponding to 50% of relative humidity at 298 K. Water plays an important role in several gas-phase chemical processes occurring in the atmosphere. For example, we carried out quantum calculation to study the interactions between benzoic acid (BA) and sulfuric acid (SA)/ammonia (NH3)/dimethylamine (DMA) with hydration by 1 to 6 water molecules, and found water molecules have different effect on BA-SA/NH3/DMA nucleation (Figure 1). For BA-DMA-(0-6)H2O, increasing water molecules can inhibit nucleation. For BA-NH3-(0-6)H2O, the most negative Gibbs free energy occur when NH3 are hydrated with 2/6 water molecules and BA is unhydrated. For BA-SA-(0-6)H2O, the most negative Gibbs free energy occur when SA is unhydrated and BA are hydrated with 6 water molecules. Moreover, the Born-Oppenheimer molecular dynamics (BOMD) was used to simulate ammonium bisulfate formation from a series of amines, SO3, and H2O molecules at the air-water interface. The results show that reactions between amines and SO3 involve multiple water molecules at the air-water interface. The reaction center’s ring structure (amine-SO3-nH2O) promotes the transfer of protons in the water molecules (Figure 2). The formed ammonium cation (-RNH3+) and the bisulfate anion (HSO4-) are present and stable by means of hydrogen bond interaction.