Fossil fuels, such as coal, petroleum, and natural gas, have supplied the energy that powered the Industrial Revolution and economic development, serving as the “life blood” of modern societies (Andres et al. 2012). While the use of fossil fuels has lifted millions out of poverty and dramatically improved living standards in the United States and other parts of the world, the adverse effects of fossil fuel combustion are becoming increasingly evident. When coal, petroleum, and natural gas are combusted for energy, the carbon that serves as the backbone of these fossil fuels is mostly emitted to the atmosphere as carbon dioxide (CO2), the key greenhouse gas that is responsible for the bulk of anthropogenic climate change (IPCC 2014; Gurney et al. 2015). Fossil fuel combustion simultaneously releases other air pollutants, such as mercury, nitrogen oxides (NOx), particulate matter (PM), and volatile organic compounds (VOCs) (Akimoto 2003; Watts et al. 2016). Cities, with their large, dense populations, are where substantial fossil fuel combustion takes place (International Energy Agency 2008) and where air pollution impacts are concentrated (see the sidebar for additional information). As the global population increasingly resides in cities (Seto et al. 2012), the role of urban areas in determining the future trajectory of carbon emissions is magnified. Because anthropogenic carbon emissions are intimately tied to socioeconomic activity through fossil fuel combustion, research efforts into cities’ carbon emissions provide opportunities for reduction efforts away from the federal level to state and local levels, where cities are playing a central role. Despite many cities’ ambitious goals for greenhouse gas reduction, verifying whether these targets are met is a difficult task. The urban environment is characterized by extreme heterogeneity in land use and human activity (Gurney et al. 2015). However, cities are also arenas where diverse observations and data streams are available. Examples include meteorological data, air quality monitoring, and a variety of socioeconomic datasets, such as detailed census data, cell phone network data, traffic information, and building characteristics. When these assets are combined with advances in instrumentation, computing, and communications that lie at the heart of the “Smart City” revolution (Dameri and RosenthalSabroux 2014), progress can be made on quantifying and understanding the underlying processes that control carbon emissions from cities, leading to informed decisions about how to most effectively implement emissions reduction goals. In this paper we describe a research effort centered in the Salt Lake City (SLC), Utah, metropolitan region, which is the locus for one of the longest-running urban CO2 networks in the world. This network is enhanced with a) air quality observations, b) novel mobile observations from platforms on light-rail public transit trains and a news helicopter, c) dense meteorological observations, and d) modeling efforts that include atmospheric simulations and high-resolution emission inventories. Thus, the Salt Lake area provides a rich environment for studying anthropogenic emissions and for understanding the relationship between emissions and socioeconomic activity. In addition to describing the observations, we present three sample applications of the data. This work has benefited from and contributed to the interests of multiple stakeholders, including policymakers, air quality managers, municipal government, urban planners, industry, and the general public.