Exploring seasonal variations in δ13C of dicarboxylic acids in fine aerosols: Insights from a Central European background site

Abstract

In this study, we present the measurement results of stable carbon isotope ratio (δ13C) performed on a one-year aerosol samples (n = 96, 24h time resolution during Sep. 2013 - Aug. 2014) for dicarboxylic acids (hereafter “diacids”) and related compounds in PM1 at a rural background site National Atmospheric Observatory Košetice (NAOK), Czech Republic, Central Europe. In previous study on the molecular distributions of diacids (Vodička et al., 2023a), we observed a distinct seasonal variation in the composition of diacids in PM1. In winter, approximately 75% of the organic aerosols originated from anthropogenic sources, whereas in summer, over 75% were attributed to biogenic sources. The objective of this study was to investigate whether these differences are reflected in δ13C of diacids. In general, we observed higher δ13C values for lower carbon molecules (Vodička et al., 2023b). A comparison of δ13C values of major diacids (oxalic (C2), succinic (C4), malonic (C3), azelaic (C9)) with those from other background sites, especially in Asia, shows similar values to those from the European site. This comparison also demonstrated that C2 is more enriched with 13C at background sites than at urban ones. In general, we did not observe significant seasonal differences in δ13C values of diacids at NAOK. We observed statistically significant differences (p value < 0.05) between winter and summer δ13C values solely for C4, glyoxylic (ωC2), glutaric (C5) and suberic (C8) acids. The only significant correlations between δ13C of C2 and δ13C of C3 were found in spring and summer, suggesting that the oxidation of C3 to C2 is significant in these months with a strong contribution from biogenic aerosols. The strongest season-independent annual correlation was observed between C2 and C4, the two dominant dicarboxylic acids. Therefore, C4 appears to be the main intermediate precursor of C2 throughout the whole year. Acknowledgement: This conference contribution was supported by the Ministry of Education, Youth and Sports of the Czech Republic under the project ACTRIS-CZ-LM2023030, by the Czech Science Foundation grant No. 20–08304J and by the Japan Society for the Promotion of Science (JSPS) through Grant-in-Aid No. 24221001. We appreciate the financial support of JSPS fellowship to P. Vodička (P16760) in Japan.