Understanding physical and chemical processes at a molecular level is crucial for identifying root causes of environmental problems and in developing innovative solutions for a sustainable environment. For example, understanding the physical principles underlying desalination processes can lead to more efficient and sustainable water treatment technologies. Similarly, studying chemical reactions involved in ozone depletion can help improve our understanding of this chemistry behind the process, and inform better chemical strategies to protect the ozone layer. By using advanced computational techniques, including high level quantum chemical methods, classical molecular dynamics simulations and ab initio molecular dynamics simulations, the chemical and physical interfacial processes involved in environmental sustainability can be investigated systematically. This thesis explores the chemical and physical interfacial processes fundamental to desalination and ozone depletion chemistry. Enhanced sampling methods such as umbrella sampling and metadynamics are used understand the energy requirements of the processes, as aided by free energy profiles. Additionally, further analysis is conducted to study the effects of intermolecular interactions, hydration number, and forces in the systems on these interfacial processes. Studies from this thesis yield several important results: (1) an understanding of the anomalous behavior of water flow through narrow-diameter carbon nanotubes (CNTs) caused by cross-CNT-orifice hydrogen bonds; (2) an understanding of the effects of the dipole moment of nanopore rims on water desalination and the underlying mechanism; (3) an understanding of the reactive uptake of chlorine nitrate (ClONO2) at the air-water interface and near-barrierless reversible hydrolysis of ClONO2; (4) a molecular-level insight into the formation of Cl2O resulting from ClONO2 exposure to the interface of cloud droplet surfaces and the ensuring reaction between ClONO2 and HOCl on cloud droplet surfaces; and (5) an understanding of the catalytic decomposition of NH2NOx (x=1,2) at the air-water interface and the molecular mechanisms involved. By studying these physical and chemical processes, we have uncovered the fundamental molecular interactions and chemical processes to explain anomalous and observed chemical behavior of interacting chemical systems at interfaces.