In 2017, the Netherlands generated 10 percent more renewable energy than it did in 2016. However, the country is far from meeting its climate goal to be CO2-neutral by 2050. Four researchers from Wageningen University and Research (WUR), published a paper on December 2017, reporting on the temporal variability of CO2 fluxes in the city center of Arnhem, a middle-sized Dutch city, home to 157,277 people.

During the four years between 2012 and 2016, the fluxes were continuously measured using the eddy-covariance (EC) method. Continuous meteorological measurements were also carried out. “We also analysed data from 30-minute traffic counts performed during those years,” write the researchers. Results indicate that the city center of Arnhem is a strong emitter of CO2 compared to many other cities across the country.

Diagram of Arnhem's CO2 emissions.

Land use in and around the main footprint of the EC measurements (black circle, with the six sectors indicated by wedges with a black outline). The red dot at the center of the circular footprint shows the location of the EC station. The Ing. J.P. van Muijlwijkstraat is shown in blue. CC: Netherlands’ Cadastre, 2014

Weekly and daily variations in CO2 flux are clearly correlated with traffic intensity, whereas seasonal variation can largely be explained by space heating demand. The study found that traffic- and heating-related burning of natural gas are the main emission sources.

Dividing up the total flux into a heating-related and traffic-related flux helped the researchers find out that space heating accounts for up to 60 percent of the total flux during the winter. Traffic intensity remains more or less constant throughout the year. In summer, when space heating is absent, CO2 emission is almost entirely related to traffic intensity.

“However, our estimations suggest that human respiration could have a non-negligible share in this,” the researchers argue. The contribution of the small fraction of urban green in the city center is probably minimal. The annual emissions for Arnhem’s city center estimated by EC measurements are 20 to 25 percent lower than those reported for the whole city by the official emission inventory. Moreover, The Netherlands’ climate goals for 2050 aspire to reduce Heating Degree Days by 27 percent, resulting into a 32 percent reduction of heating-related emission flux, without a change in fossil fuel use.

“In this study we analysed the data from the first Dutch multiyear urban EC study that measured CO2 fluxes,” the researchers conclude. They still recommend that more urban EC CO2 flux studies to be conducted as there are currently not enough data to provide reliable city-wide emission estimates.”