Urban areas are major emitters of greenhouse gases with the most important being carbon dioxide (CO2). Traditionally, urban CO2 emissions have been determined  from inventory techniques which however commonly lack high spatial and temporal resolution needed to understand intra-city variability of emissions. In recent years, growing number of observational methods to determine urban emissions have emerged with One of the most direct mean being the micrometeorological eddy covariance (EC) technique. EC technique measures the turbulent transport of CO2 (or other scalars) between the surface and the atmosphere providing the total surface exchange or flux in a neighborhood or local scale.

In Helsinki, Finland, continuous urban eddy covariance measurements of carbon dioxide are conducted at two contrasting sites: semi-urban and dense city center sites with the first being ICOS (Integrated Carbon Observation System) Associated Ecosystem Station. The power of the EC technique in identifying anthropogenic activities and emissions, as well as biogenic sinks will be demonstrated based on observations from the two sites. In addition, examples on how the different sources and sinks of the net surface exchange can be separated and uncertainties in the measurements evaluated are demonstrated using micrometeorological modeling.