Investigating the impact of COVID-19 on the atmospheric 14C trend and fossil carbon load at urban and background sites in Hungary

The global impact of COVID-19 on communities and economies has led to questions about decreasing environmental risks and pollution due to the decreased industrial and transport activity. One of the key concerns revolves about the atmospheric rise in CO2 levels and the associated arising fossil carbon load, constituting the global climate change. The quantification of fossil-origin atmospheric carbon load is addressed through the use of natural radiocarbon (14C), a unique scientific tool. Fossil sources lack 14C activity, while recent biogenic carbon contains radiocarbon. This study centers on revealing long-term trends in atmospheric 14C levels, particularly during the year of the pandemic, in comparison to the preceding five years in Hungary. Atmospheric CO2 and tree rings from the studied six years were subjected to 14C analysis from three distinct locations. One of the examined cities, Budapest - Hungary's capital - is a highly urbanized land with a reported 1.7 million population. Despite the city's extensive vehicular and human activity, a "state of danger" was in effect in Hungary from March to June 2020 due to the first wave of COVID-19. The sampling sites had been characterized by a busy urban environment, with a mix of vehicular activities contributing to the local atmosphere. The second urban sampling site is Debrecen, a smaller but evolving city that can be found in the eastern part of Hungary. It’s the second largest Hungarian city - around 200 thousand citizens – and it is currently experiencing an industrial revolution by the construction of major factories. Significant contribution to pollution in this area come from urban vehicular traffic and the surrounding agricultural regions. The background 14C signal used in the study is from the easternmost Integrated Carbon Observation System(ICOS) atmospheric regional background station (HUN) and NOAA background site, at Hegyhátsál. Mole fraction has been continuously monitored at four elevations at HUN station since September 1994. For this research integrated atmospheric 14CO2 samples, supplemented with CO2 mole fraction measurements, were used from October 2014 to December 2020. The data was studied from the aspect of temporal variation and altitudinal differences. CO2 mole fraction data of the free tropospheric background ICOS station at Jungfraujoch (Switzerland) were used. The outcomes of the trend analysis reveal the fluctuations in atmospheric fossil carbon load throughout the pandemic, which offers valuable insights into the environmental effects of reduced human activities in Hungary. Prepared with the professional support of the Doctoral Student Scholarship Program of the Co-operative Doctoral Program of the Ministry of Innovation and Technology financed from the National Research, Development and Innovation Fund and supported by the PARIS project (Grant Agreement No. 820846), which is funded by the European Commission through the Horizon 2020 research programme.