Multi-seasonal pattern in 5-year record of stable H, O and S isotope compositions of precipitation (Wrocław, SW Poland)

Abstract

Sulphur dioxide is still a major industrial pollutant in the atmosphere. However, its origin is not always easily traceable, particularly at regional scale where numerous sulphur sources coexist. Geochemical tracers, such as the stable sulphur (δ34S) and oxygen (δ18O) isotopic compositions of sulphates in precipitation, have been successfully applied for estimation of the S-contribution from multiple sources to the atmosphere. However, the majority of previous studies conducted over relatively short time spans have revealed a short-term seasonal trends only and were unable to capture multi seasonal systematics. Here, we present results from a five-year monitoring program conducted in Wrocław (SW Poland). We have determined the Local Meteoric Water Line of δ2H= (6.91 ± 0.25) × δ18O + (2.39 ± 2.43) and sulphates stable sulphur (δ34S(SO4) 0.3–5.4‰) and oxygen (δ18O(SO4) 4.7–19.1‰) isotope composition in precipitation. The stable sulphur isotope results confirm that sulphates in precipitation primarily originate from high temperature (minimum mean over sampling period 680 °C) combustion of fuels with δ34S signatures ≤4.4‰. The stable oxygen isotope composition of sulphates and precipitation water indicates that the primary sulphate (generated directly by industrial processes) contribution was <49% during the whole study period, with a mean of ∼20% during the non-heating and ∼40% during the heating periods. The δ34S(SO4) value for precipitation displays multi-seasonal oscillations with an amplitude of about 2‰, which has not been previously reported. The mechanism driving the oscillation needs further investigation in order to reveal possible associations between this phenomenon and climatic patterns or changes in fossil fuel use. This new evidence from 5-year-long records needs to be taken into consideration when analysing trends from shorter-term observations.