Indoor and outdoor building surfaces constitute important environmental compartments that mediate the fate and transport of gaseous and particulate pollutants. Studying chemical transformations at these interfaces is a challenge, but also a key element in understanding how contaminants and surface materials impact human health and energy efficiency. This seminar will describe two examples of interfacial chemistry. The first example shows how chemical reactions taking place between cigarette smoke residues (e.g. nicotine and particles) and atmospheric reactive species (e.g., ozone and HONO) can be long-term sources of secondary pollutants, including carcinogens, irritant gas phase chemicals and ultrafine particles. The experimental work was carried out using conventional analytical techniques (GC-MS/MS, HPLC-UV) as well as state-of-the-art aerosol instrumentation at the Advanced Light Source (ALS). These findings raise concerns about tobacco smoke residues that have recently been dubbed “thirdhand smoke”, and their potential health effects. The second example illustrates how soiling and weathering of exterior building surfaces can lead to a significant loss of their initial solar reflectance, resulting in higher air conditioning energy use in buildings. At the Heat Island Group we have developed an accelerated laboratory approach that mimics these multi-year natural processes that can facilitate the development of advanced roofing products. Examples will be also shown for a new generation of building envelope materials that resist soiling, along with discussion of their potential impacts on urban air quality.