The chemical composition of the atmosphere controls the quality of the air we breathe, and the radiative balance of the planet. Reactive organic carbon plays a particularly important role in the atmosphere, acting as the fuel for oxidation reactions, a source of secondary organic aerosol, and a key ingredient for ozone production. Various sources emit organic carbon into the atmosphere, including plants, wildfire smoke, and vehicles. Once in the atmosphere, the organic carbon chemically evolves, and then can be removed through wet or dry deposition. Our group uses mass spectrometry and other analytical techniques to provide observational constraints on the emissions, evolution, and fate of atmospheric organic carbon. This talk will explore three aspects of our work: (1) wildfire emissions and evolution; (2) dry deposition of particles to Earth’s surfaces; and (3) indoor chemistry. While each aspect of the atmosphere represents unique measurements and chemistry, they all demonstrate the importance of observational constraints on the processes controlling organic carbon in both gas and particle phase to better understanding and controlling sources of air pollution.