The road to measuring GHG emissions in urban spaces: How the City of Zurich – at the heart of an EU-funded project – is paving the way.
Cities are at the heart of emission reduction efforts, as they are key contributors to a large proportion of fossil fuel emissions: around 70% of anthropogenic emissions are produced in, around, and by cities. Yet, measuring greenhouse gas (GHG) emissions in urban areas is not easy. Dr Stavros Stagakis, from the University of Basel, explains that the city ecosystem poses a challenge due to its complexity and variety of human activities and various land uses. All these components of a city have different functionalities with different CO2 flux patterns, making it difficult to apply existing methods for measuring CO2 emissions. The most common method for direct CO2 flux measurements, called Eddy Covariance, is well established in very homogenous environments, such as grasslands and forests. However, this methodology is still challenging to apply in the urban environment. This is where the ICOS Cities project comes in.
PAUL, Pilot Applications in Urban Landscapes – Towards Integrated City Observatories for Greenhouse Gases (ICOS Cities) is funded by the EU’s Horizon 2020 research and innovation programme. PAUL recognises the critical role of urban areas in achieving GHG emissions reductions, and aims to develop the most innovative systematic observation approaches to GHG emissions in these areas. To do this, three pilot cities of varying size were selected – Zurich, Paris, and Munich – to test the feasibility of different measurements and modelling approaches. Twelve further cities joined the network, to ensure that the concepts developed can be applied to cities in other countries and landscapes. Through a collaborative approach, the project ensures that the measurement concepts fit the needs of cities, as tools and services are co-designed with city representatives. The project, which started on 1 October 2021, is nearing its end and will conclude on 31 December 2025. It is therefore timely to reflect on the contributions of ICOS Cities, and what the future holds for measuring CO2 in urban areas. In line with the co-design approach of ICOS Cities, interviews were conducted with administrators from the City of Zurich (Ms Sabine Marbet), the research institute EMPA (Dr Lukas Emmenegger), and the University of Basel Department of Environmental Sciences (Dr Stavros Stagakis).
Zurich was not selected out of the blue: a careful and long process led to its final success. Dr Stagakis explains that the University of Basel was involved in the project from the beginning, due to their expertise in the Eddy Covariance method. Back in 2019, a small group came together in Helsinki and participated in a workshop at the ICOS Hyytiälä Forestry Field station on how urban areas could be included in ICOS (i.e., the European research infrastructure for the observation of GHGs). When the proposal phase commenced, the project was coordinated by the ICOS Head Office. Proposing the pilot cities followed a bottom-up approach, with each group from ICOS to submit a proposal to the Head Office. The Swiss partners joined forces and proposed the city of Zurich. In fact, Dr Emmenegger and Dr Stagakis highlight Zurich’s extremely good bottom-up inventory of GHG emissions, the existence of the city’s digital twin, and the willingness of local authorities to work with and support advancements of new methods in this area. Combining EMPA’s strong know-how in GHG measurements and top-down emissions monitoring, the University of Basel’s longstanding expertise in CO2 flux measurements, and the established collaboration with the City of Zurich made sense, and thus a collaboration was born.
However, such a project comes with its challenges. For Dr Emmenegger, challenges arise on two levels: on a scientific and on an infrastructure level. The scientific challenge is the measuring of anthropogenic CO2 emissions. Around half of the existing emissions are natural and the other half are human made. Although both types of emissions are at the same order of magnitude, it is the anthropogenic emissions that are of the main interest for city stakeholders. This means that the natural and human-made emissions have to be disentangled from one another, which is challenging, particularly in a city like Zurich with its complicated topography which requires detailed wind information and sophisticated atmospheric transport models. On an infrastructure level, implementing an extensive measurement network is highly challenging. This is where the importance of collaboration is clearly visible: the private sector provided access to the antennas of the Swiss telecommunications provider ’Swisscom‘, the City of Zurich granted access to parks and trees, and the city police supported the installation of an Eddy Covariance system on their antenna which is situated on one of the tallest buildings in Zurich. Without this joint effort, the measurements needed to drive and constrain the models would not have been possible.
And while PAUL may be coming to an end at the end of the year, the work does not stop here. Both Dr Emmenegger and Ms Marbet affirmed that there are ongoing discussions between the City of Zurich and EMPA on how to use the measurements and findings of the project beyond 2025. As Dr Emmenegger highlights, one cannot lose weight by stepping on the scale once. Achieving a desired result requires consistent effort and tracking. Thus, while ICOS Cities has presented cities with different methodologies, it is now up to other stakeholders and the city administration to make use of these methodologies to support their respective climate ambitions and targets. In the same vein, Ms Marbet highlighted the ongoing contact with some cities, particularly Paris, to compare methodologies with the aim of evaluating what possibilities arise with the measurements; knowledge exchange is continuous on how other cities are using the new possibilities and opportunities created by ICOS Cities. The knowledge generated from these exchanges will also benefit other cities in the future: once the pilot cities have found the best way of using the measurements in their respective cities, smaller cities that may lack the resources to conduct their own similar project can learn from the ICOS Cities network. Moreover, events like the recent Urban Greenhouse Gas Conference and Stakeholder Summit 2025 provide ample networking opportunities for research institutes, scientists, and interested parties to learn more about the latest findings from urban GHG researchers.
The knowledge generated through this EU-funded project has positive spillover effects in other research areas related to measuring CO2 emissions in urban spaces. Dr Stagakis, for example, will work on a new 3-year project funded under Horizon Europe: CLMS-Cities. The project recognises that cities often lack precise tools to monitor GHG emissions and track progress to support evidence-based decisions. While CLMS-Cities will build on a method developed by its predecessor project CURE, so as to provide detailed environmental data for 10 leading cities, Dr Stagakis emphasises that knowledge gained from ICOS Cities will be invaluable here too.
What is clear is that the Horizon grant was instrumental for ICOS Cities being able to happen, as this was a large-scale and resource-intensive project. While the grant itself was only for four years, the project’s legacy will continue to live on.