More than 50% of the global population and three-quarters of Europeans live in cities. Cities are ‘hot spots’ for greenhouse gas (GHG) emissions and also key areas for emission reduction efforts. Although fossil fuel inventories can provide information on long-term emissions, there is growing interest to constrain GHG emission estimates and assess reduction efforts at urban and intra-urban scales. Developing and improving techniques for directly measuring GHG emissions into (and uptake from) the urban atmosphere, requires us to combine atmospheric measurements of GHGs, information on airflow, and surface databases.

This seminar will focus on selected micrometeorological measurement approaches we explored and developed at fine scales. We will highlight the potential and discuss the challenges of atmospheric measurements in cities to quantify and attribute GHG emissions at various scales. For example, the presentation shows how we can exploit data from direct eddy covariance flux tower measurements in cities to determine emission factors. We will ask the question whether stable isotope ratios can add additional information on fuel sources. Finally, we will explore the potential of mobile sensor-networks to spatially map and quantify CO2 emissions at block and street level using mid-cost sensors on moving vehicles.

An intelligent and effective integration of established and new techniques to map, quantify and attribute emissions in complex configurations can form the basis for long-term city observatories. Such observatories can support GHG emission reduction policy on several scales, for example the European Green Deal, by providing geographic information on the effectiveness and timeline of emission reduction efforts and targeting emission hot-spots.

Prof. Dr. Andreas Christen is Chair of Environmental Meteorology, Institute for Earth and Environmental Sciences, Faculty of Environment and Natural Resources, University of Freiburg, Germany