Microfluidics and Interfacial Chemistry in the Atmosphere

The air-liquid interface plays an important role in atmospheric chemistry. Surface spectroscopic techniques such as Raman, surface-enhanced Raman spectroscopy, and sum-frequency generation have been used to detect chemical reactions at the air-liquid interface. However, in situ characterization using vacuum-based surface techniques has been a technical challenge; as a result, these techniques have limited applications in atmospheric research. This review summarizes popular techniques applied to the study of atmospheric surfaces and introduces the basics of microfluidics and their novel application in atmospheric interfacial studies. Specifically, we highlight a recent technical innovation for the investigation of in situ air-liquid interfacial chemistry enabled by a vacuum compatible microfluidic reactor, namely, the System for Analysis at Liquid and Vacuum Interface. The air-liquid interface is approximated by the vacuum-liquid interface. With the chemical imaging capabilities offered by time-of-flight secondary ion mass spectrometry, detailed molecular mapping of species at the interface has become possible. A perspective on how to advance the study of air-liquid interfaces is presented in summary.