According to the World Health Organization (WHO), air pollution is responsible for 7 million deaths worldwide. Air pollutants are present both outdoor and indoors. The indoor air quality is more important than ever during the pandemic, as people are forced to stay home for a prolonged period. Atmospheric chemistry plays a vital role in the formation, evolution, and fate of air pollutants. Fundamental laboratory experiments have been an essential aspect of atmospheric research to provide kinetic and mechanistic information. The theme of this talk is related to the role of water in the outdoor and indoor air. The aqueous-phase is the largest condensed phase in the context of atmospheric chemistry, and water plays a convoluted role in the reactivity and partitioning of air pollutants. In this talk, I will be giving an overview of two projects conducted by my research group. The first project is the investigation of the pH-dependence of cloudwater photochemistry. The interplay between acid-base chemistry and photochemistry is a unique yet unexplored aspect of aqueous-phase atmospheric chemistry. In the second project, the potential contributions of ultrasonic humidifiers to indoor air pollutants are discussed. Household humidifiers are commonly employed to combat dry indoor air, which is particularly relevant to cold and dry Canadian Winter. Our study shows that ultrasonic humidifiers are giving rise to very high concentrations of particulate matter in a household. Emissions from humidifiers may induce previously unrecognized chemical processes in the indoor environment.