The Bigger Picture
Humans spend ∼90% of their time indoors. However, understanding the chemistry that occurs on indoor surfaces and its impact on air quality is still in its nascent stages due to the complexity of indoor surfaces. High surface-to-volume ratios indoors increase gas-surface collisions, but molecular mechanisms for surface reactions are often poorly understood, despite their importance becoming increasingly clear. Equilibrium thermodynamics poorly explain indoor surface chemistry, with key kinetic effects observed. Drivers of surface reactivity include relative humidity, temperature, light, and surface pH. Highlighted findings are the ubiquitous presence of aqueous and secondary organic films, their ability to act as reservoirs of contaminants, and impacts on gas and particle lifetimes. Indoor surface chemistry impacts multiple U.N. Sustainable Global Goals that point to the importance of further integration of laboratory, modeling, and real-world measurements to understand the air we breathe indoors.