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

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.

References:

Vodička, P., Kawamura, K., Deshmukh, D.K., Pokorná, P., Schwarz, J., Ždímal, V., 2023a. Anthropogenic and biogenic tracers in fine aerosol based on seasonal distributions of dicarboxylic acids, sugars and related compounds at a rural background site in Central Europe. Atmos. Environ. 299, 119619. doi:10.1016/j.atmosenv.2023.119619

Vodička, P., Kawamura, K., Schwarz, J., Ždímal, V., 2023b. A year-round observation of δ¹³C of dicarboxylic acids and related compounds in fine aerosols: Implications from Central European background site. Chemosphere 337. doi:10.1016/j.chemosphere.2023.139393