Methane and carbon dioxide observations at Debrecen, Hungary: mole fraction and isotope ratio measurements in three different seasons

The increasing level of atmospheric greenhouse gases and the effect of this trend, climate change, is one of the greatest environmental issues of the anthropogenic era. The increasing trend of greenhouse gas levels after industrialization is related to urban environments, where industrial and traffic-related activity and emissions are concentrated. In response to this, the European system, the ICOS (Integrated Carbon Observation System) was established and started the ICOS cities program, where coordinated greenhouse gas observations are carried out besides the regional background measurements and samplings. Similarly to this program, atmospheric air samples were collected at the Institute for Nuclear Research, Debrecen. During the sampling campaigns in three different seasons (winter, spring and summer), a minimum of 23 samples were collected in the morning and afternoon during weekdays and weekends as well. The samples are processed within a collaboration between Utrecht University, where the stable isotope composition of CO₂ and CH₄ were measured, and the Institute for Nuclear Research, Hungary, where the mole fraction of CO₂ and CH₄ and radiocarbon ratio of CO₂ were measured. Based on the isotope composition results and stable isotope fingerprint of carbon dioxide and methane sources, the differentiation of the possible emission sources of these gases can be made. Using the radiocarbon, we can estimate the fossil CO₂ contribution in urban areas. The preliminary results show that there is a great fossil contribution to the CO₂ fraction, on the other hand, a great local biological contribution was observed in the CH₄ fraction in every season. Based on measurements and literature, the source of the massive biological discharge could be the sewage pipeline system, even in winter. Our dataset shows that this kind of CH₄ emitter can exceed fossil sources in Debrecen, Hungary.