A year-round observation of δC of dicarboxylic acids and related compounds in fine aerosols: Implications from Central European background site.

Isotopic analysis of specific compounds in aerosols can be a useful tool when studying atmospheric processes. Here, we present the results of stable carbon isotope ratio (δC) measurements performed on a one-year set (n = 96, Sep. 2013-Aug. 2014) of dicarboxylic acids and related compounds in PM at a rural Central European background site, Košetice (Czech Republic). The most C enriched acid was oxalic (C, annual average = -16.6 ± 5.0‰) followed by malonic (C, avg. = -19.9 ± 6.6‰) and succinic (C, avg. = -21.3 ± 4.6‰) acids. Thus, δC values decreased with an increase in carbon numbers. Azelaic acid (C, avg. = -27.2 ± 3.6‰) was found to be the least C enriched. A comparison of δC of dicarboxylic acids from other background sites, especially in Asia, shows similar values to those from the European site. This comparison also showed that C is more C enriched at background sites than at urban ones. In general, we did not observe significant seasonal differences in δC values of dicarboxylic acids at the Central European station. We observed statistically significant differences (p value < 0.05) between winter and summer δC values solely for C, glyoxylic acid (ωC), glutaric acid (C) and suberic acid (C). The only significant correlations between δC of C and δC of C were found in spring and summer, suggesting that the oxidation of C to C is significant in these months with a strong contribution from biogenic aerosols. The strongest season-independent annual correlation was observed in δC values between C and C, the two dominant dicarboxylic acids. Therefore, C appears to be the main intermediate precursor of C throughout the whole year.