A comprehensive carbon isotopic analysis of seasonal carbon dioxide variability from an urban environment in Hungary

Urban areas as important sources of industrial and transport emissions, have a key impact on the atmospheric greenhouse gas trends. In order to study these emissions we collected atmospheric air samples at the HUN-REN Institute for Nuclear Research (ATOMKI) of Debrecen, Hungary, in three different seasons (winter, spring and summer). Sampling was done to reflect differences between weekdays and weekends and between morning and afternoons. For this study we collected at least 23 samples each season. We compared carbon dioxide (CO₂) concentration and radiocarbon (¹⁴C) results with observations from the Hungarian ICOS (Integrated Carbon Observation System) regional background station. Within the project, stable isotope analysis was performed at Utrecht University while CO₂ mole fraction and ¹⁴C were measured at ATOMKI.

The results show that depleted δ¹³C and Δ¹⁴C values observed during morning hours -especially winter- may indicate fossil fuel emission sources.  On the other hand, summer shows enriched isotopic values because of the stronger biogenic uptake. We analyzed strong correlations between δ¹³C and Δ¹⁴C values in winter, compared to weaker correlations in spring, suggesting that isotopic signals may be influenced by different processes depending on the season. The findings provide important information in the field of carbon isotopic measurements that could simplify distinguishing between CO₂ sources or understanding seasonal shifts between biogenic and anthropogenic sources.

Project number C2295145 has been implemented with the support provided by the Ministry of Culture and Innovation of Hungary from the National Research, Development and Innovation Fund, financed under the KDP-2023 finding scheme.