Evaluation of combined radiocarbon and carbon stable isotope data of PM2.5 carbonaceous aerosol in Debrecen, Hungary

Comprehensive atmospheric studies have demonstrated that carbonaceous aerosol is one of the main components of atmospheric particulate matter over Europe. Despite its significant role in atmospheric processes, the characteristic of carbonaceous particle sources and the contributions from modern and fossil sources in the Pannonian Basin are still less known. Using radiocarbon as a tracer, the ratio of modern (biological aerosol, wood burning etc.) and fossil (coal or oil burning, transportation) sources for an aerosol sample can unambiguously be determined but identification of exact sources is not possible. Considering other isotopic techniques, carbon stable isotope results can provide us such supplementary information that can be used in separating different large source clusters (e.g. burning of C3 type wood, coal burning or transportation). Different aerosol sources have well defined carbon stable isotope ranges, which can be used in source apportionment models. Nevertheless, these ranges often overlap each other, making the accurate source identification rather difficult. Combined radiocarbon and carbon stable isotope measurements can however help us to differentiate more precisely numerous modern or fossil sources.

In our study, the isotopic composition of carbon in the PM_2.5 atmospheric aerosol collected on weekly basis in Debrecen, Hungary was investigated. In doing so, the organic and elemental carbon content, the specific ¹⁴C content and the δ¹³C values of total carbon were measured using a Sunset OC/EC analyser, an accelerator mass spectrometer (AMS) and an EA/IRMS instrument, respectively. Based on our three-year long carbon stable isotope data of carbonaceous aerosol, relatively enriched δ¹³C results can be observed in each wintertime period, which are supposed by other authors to be related to the effect of coal combustion (mainly in heavily industrialised areas). Contrarily, radiocarbon measurements imply the dominance of modern sources for the same wintertime periods when the biological activity of vegetation is moderate. Consequently, according to our assumption, these values are caused by modern sources having more positive δ¹³C value such as biomass burning of residences. In contrast to single stable isotope or radiocarbon measurements our study sheds light on the importance of combined carbon isotopic investigations. The research was supported by the European Union and the State of Hungary, co-financed by the European Regional Development Fund in the project of GINOP-2.3.2-15-2016-00009 ‘ICER’