Source identification of PM_2.5 carbonaceous aerosol using combined carbon fraction, radiocarbon and stable carbon isotope analyses in Debrecen, Hungary

In this study, PM_2.5 aerosol samples collected continuously in Debrecen, Hungary from December 2011 to July 2014 were processed and analysed. Mass concentration and ratios of PM_2.5 aerosol, organic and elemental carbon fractions, in addition, radio and stable carbon isotopes were evaluated together to obtain a better sight into the possible local and regional sources. For the studied period, the mean mass concentration of PM_2.5 aerosol and the constituting total, organic and elemental carbon were 23.6, 5.8, 5.0 and 0.8 μg m⁻³, respectively. In all cases, the mean for the heating periods were on average 2–3 times that of the vegetation (i.e. heating-free) periods. The relatively high mean secondary organic carbon concentration of 4.1 μg m⁻³ and OC/EC ratio of 6.9 suggested the dominance of combustion processes in winter and, based on the higher contemporary carbon fraction of 0.77, wood fuels prevailed over coal or oil. The average δ¹³C of the tested wood fuels implies that combustion of black locust, oak and beech was a significant factor in forming the mean δ¹³C of PM_2.5 of −25.6‰ during the heating months. The mean δ¹³C of −26.7‰ in summer was more influenced by emissions from transportation and the surrounding vegetation. In addition, using coupled backward trajectory modeling (HYSPLIT) and visualization of open fire events (FIRMS), we presume that the conspicuously enriched δ¹³C values of PM_2.5 collected in October of the observation years were probably caused by long-range transport of particles derived from agricultural combustion of C₄ plants close to the southern and eastern Hungarian borders.