Seasonal changes in stable nitrogen isotopic composition in fine aerosols at a rural background station Košetice (Central Europe).

The stable nitrogen isotope ratios (δ¹⁵N) of total nitrogen (TN) were studied for fine aerosol particles (PM₁) collected with a 24-h time resolution every two days at a Central European rural background site from September 27, 2013, to August 9, 2014 (n=146).
We observed a seasonal cycle of enrichment and depletion of ¹⁵N in aerosol particles with lower values in winter and higher values in summer. The majority of the yearly data showed a strong correlation between δ¹⁵N and ambient temperature, supporting an enrichment of ¹⁵N via isotopic equilibrium exchange between the gas and particulate phases. This process seemed to be one of the main mechanisms for ¹⁵N enrichment at the Košetice site, especially during spring. The most ¹⁵N-enriched summer and most ¹⁵N-depleted winter samples were limited by the partitioning of nitrate in aerosols and suppressed equilibrium exchange between gaseous NH₃ and aerosol NH₄⁺. During winter, we observed an event with the lowest δ¹⁵N values which deviate from temperature dependence. The winter event was connected with prevailing southeast winds and the lowest δ¹⁵N values were probably associated with agriculture emissions of NH₃ under low-temperature conditions (<0°C).

Acknowledgement:
This conference contribution was supported by the Ministry of Education, Youth and Sports of the Czech Republic under the project No. LM2018122, by the ERDF project "ACTRIS-CZ RI" (No. CZ.02.1.01/0.0/0.0/16_013/0001315) 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.

Reference:
Vodička, P., Kawamura, K., Schwarz, J., Kunwar, B. and Ždímal, V.: Seasonal study of stable carbon and nitrogen isotopic composition in fine aerosols at a Central European rural background station, Atmos. Chem. Phys., 19, 3463–3479, 2019.