The city of Ostrava, NE Czech Republic, is known for its industrial pollution. It has well-characterized emission sources and stable air movement patterns. These features are conveniently used to generalize on atmospheric NOx and SO2 oxidation processes. In 2021, we conducted a series of sampling campaigns to assess the isotopic fractionation conducive to NO3− and SO42− aerosols in PM10. These sampling campaigns were timed to capture varying atmospheric conditions, including climatic inversion periods, providing also insights into urban emission dynamics over the course of the year. Gaseous NOx and SO2 were collected on passive filters, while their oxidized forms, NO3− and SO42, were captured on PM10 particle filters, enabling us to analyze the transformation dynamics of these pollutants. Isotopic analyses distinguished the sources of NOx emissions—coal combustion (δ15N = −3‰) and vehicular emissions (δ15N = −7 ‰)—and allowed quantifying isotope fractionation during their conversion to NO3− (εNOx-NO3- = 11.5 ± 1.15 ‰). This fractionation, however, was influenced by seasonal variations, and appears to be notably affected by NH4NO3 decomposition during warmer months. The correlation of the NO3− to NOx ratio with PM10 and atmospheric moisture highlighted the interplay between particulate matter and humidity in relevant atmospheric transformations. Similarly, for SO2, primarily emitted from coal combustion (δ34S = −2‰), we identified distinct fractionation patterns during oxidation to SO42− encompassing both kinetic (εSO2-H2O = −1.3 ± 0.5‰) and equilibrium (εSO2- SO42- = 2.24 ± 0.67‰) effects. The SO42−/SO2 ratio was correlated with PM10 but showed no dependence on humidity. Significantly, atmospheric inversion conditions accelerated oxidation, modifying the fractionation patterns for both NOx (εNOx-NO3- = 7‰) and SO2 (εSO2- SO42-= −0.9 ± 0.3‰). Our methodology elucidates pivotal mechanisms in atmospheric pollution transformation, underlined by the tracing of NOx and SO2 to aerosol conversions via δ15N and δ34S isotopic analyses. The isotope fractionation underscores equilibrium processes in oxidation reactions, while the effect of PM10 and humidity reveals the complexity of these atmospheric oxidative transformations. The role of wet deposition in removing SO2 highlights an essential pathway in the atmospheric sulfur cycle.
Cold Wind Cave, located at elevations ranging between 1,600 and 1,700 m a. s. l. in the main range of the Nízke Tatry Mountains (Slovakia), is linked in origin with the adjacent Dead Bats Cave. Together, these caves form a major cave system located within a narrow tectonic slice of Triassic sediments. Both caves have undergone complex multiphase development. A system of sub-horizontal cave levels characterized by large, tunnel-like corridors was formed during the Tertiary, when elevation differences surrounding the cave were less pronounced than today. The central part of the Nízke Tatry Mountains, together with the cave systems, was uplifted during the Neogene and Lower Pleistocene, which changed the drainage pattern of the area completely. The formation of numerous steep-sloped vadose channels and widespread cave roof frost shattering characterized cave development throughout the Quaternary. In the Cold Wind Cave, extensive accumulations of loose, morphologically variable crystal aggregates of secondary cave carbonate ranging in size between less than 1 mm to about 35 mm was found on the surface of fallen limestone blocks. Based on the C and O stable isotope compositions of the carbonate (δ13C: 0.72 to 6.34 ‰, δ18O: –22.61 to –13.68 ‰ V-PDB) and the negative relation between δ13C and δ18O, the carbonate crystal aggregates are interpreted as being cryogenic cave carbonate (CCC). Published models suggest the formation of CCC in slowly freezing water pools, probably on the surface of cave ice, most probably during transitions from stadials to interstadials. Though the formation of these carbonates is likely one of the youngest events in the sequence of formation of cave sediments of the studied caves, the 230Th/234U ages of three samples (79.7±2.3, 104.0±2.9, and 180.0±6.3 ka) are the oldest so far obtained for CCC in Central Europe. This is the first description of CCC formation in one cave during two glacial periods (Saalian and Weichselian).
