Chemistry provides the underlying mechanisms for understanding the impacts of surfaces in the environment. These environmental interfaces play pivotal roles in processes that affect air quality, water quality, climate, and HEALTH (planetary, ecosystem, and human health). For the Willard Lectureship in Analytical Chemistry, my presentation will focus on the chemistry and impacts of atmospheric aerosols as well as larger aqueous microdroplets found in clouds and fog. Aerosol and microdroplet surfaces represent important components of the Earth’s atmosphere where chemical reactions can occur. Utilizing molecular-based tools, we have gleaned mechanistic details of how these reactions proceed to better understand their global impacts.