Sulfur Isotope Analysis in Atmospheric Aerosols

Sulfur isotope analysis has emerged as a powerful tool for tracing the sources, transformation pathways and climatic impacts of atmospheric sulfate aerosols. By measuring the relative abundances of stable sulfur isotopes (notably 32S, 33S and 34S) and, in specialised studies, radionuclides such as 35S, researchers can distinguish between natural emissions (volcanic, biogenic and marine) and anthropogenic inputs (fossil‐fuel combustion, industrial processes and biomass burning). Fractionation processes during gas‐phase and aqueous‐phase oxidation impart unique isotopic signatures to the resulting sulfate, enabling quantification of oxidation pathways mediated by hydroxyl radicals, ozone, hydrogen peroxide, transition‐metal catalysts or halogen species. Mass‐independent isotope anomalies (Δ33S, Δ36S) offer further insight into rare photochemical or combustion‐related processes. Together, these measurements inform models of aerosol radiative forcing, human health impacts and acid deposition, and provide palaeoenvironmental records of industrial emissions archived in ice cores and sediments. Recent advances in analytical sensitivity and single‐particle techniques have expanded spatial and temporal resolution, revealing seasonal variations and regional heterogeneity in source contributions and oxidation mechanisms. This body of work underpins efforts to refine climate projections, evaluate air‐quality policies and understand feedbacks between the sulphur cycle and atmospheric chemistry.

Research from Nature Portfolio

Studies leveraging isotopic tracers in an urban megacity have demonstrated the seasonal interplay between coal combustion and biogenic emissions in controlling aerosol sulphate composition. High‐precision measurements of δ34S and δ18O in Beijing revealed a winter enrichment in 34S consistent with desulfurised coal and flue‐gas emissions, contrasted by lower values in summer reflecting increased biogenic and secondary formation. Correlated shifts in oxygen isotopes further clarified the relative importance of gas‐phase versus aqueous oxidation. These findings underscore the effectiveness of emissions controls and establish a template for isotope‐based evaluation of air‐quality interventions in rapidly developing regions.

Sulfur Isotope Analysis in Atmospheric Aerosols publication trend

The graph below shows the total number of articles in sulfur isotope analysis in atmospheric aerosols across all publications each year (not limited to Nature Index journals).

Technical terms

δ34S: The per-mil deviation of the ^34S/^32S ratio in a sample relative to an international standard, used to distinguish sulphur sources and fractionation processes.

Mass‐independent fractionation (MIF): Anomalous isotope fractionation (e.g. Δ33S, Δ36S) not solely predicted by mass differences, often signalling photochemical or combustion‐related reactions.

Keeling plot: A regression of isotopic composition against the inverse concentration of a species to determine the isotopic signature of a source mixture.

Isotopic fractionation factor (α): The ratio of reaction rates or equilibrium partitioning between heavy and light isotopes, quantifying preferential incorporation during chemical transformations.

Secondary sulfate aerosols: Fine particulate sulphate formed in the atmosphere via oxidation of gaseous SO₂, as opposed to directly emitted primary particles.

References

1. Using stable isotopes to trace sources and formation processes of sulfate aerosols from Beijing, China. Scientific Reports (2016).
2. Isotopic Constraints on SO2 Oxidation Rates and Their Potential Relationship with Sulfate Formation Pathways in the Planetary Boundary Layer. ACS Environmental Au (2024).
3. Sulfur isotopes quantify the impact of anthropogenic activities on industrial-era Arctic sulfate in a Greenland ice core. Environmental Research Letters (2023).
4. Tracing the origin of elevated springtime atmospheric sulfate on the southern Himalayan-Tibetan plateau. Environmental Science Advances (2023).
5. Sulfur isotope fractionation during oxidation of sulfur dioxide: gas-phase oxidation by OH radicals and aqueous oxidation by H2O2, O3 and iron catalysis. Atmospheric Chemistry and Physics (2012).
6. Isotopic constraints on the role of hypohalous acids in sulfate aerosol formation in the remote marine boundary layer. Atmospheric Chemistry and Physics (2016).