The goal of this project is to address uncertainties and knowledge gaps in the carbon cycle of densely populated areas by developing a model�?�data framework for prediction and assessment of C fluxes in the Boston Metro region. The measurement component is built around an advanced network of surface CO2 observations, 14CO2 campaigns, ecological and biogeochemical measurements, and remote sensing of total column CO2 from space and from the ground. The model component integrates sub�?�models describing natural and human sources and sinks of CO2 (fossil fuel emissions, ecosystems fluxes, and land cover dynamics) with a high�?�resolution atmospheric transport model. The model�?�data framework will produce optimal CO2 fluxes for the urban�?�to�?�rural domain by inverse modeling, allowing us to quantitatively characterize the spatial and temporal variations in CO2 component fluxes and net CO2 exchange with strong constraints from observed data. The project deliverables include (1) regional estimates of net CO2 exchange partitioned into ecosystem and anthropogenic contributions; (2) improved characterization and modeling of the nitrogen cycle in urban environments; (3) improved models for atmospheric transport, anthropogenic emissions, and ecosystem fluxes of CO2; (4) analytical tools for greenhouse gas assessments and management in urban areas; and (5) process�?�level assessment of how alternative patterns of urban development and land cover change affect ecosystem and coupled human�?�carbon dynamics.