EA-IRMS: Using isotope fingerprints to track sources of PM2.5 in air pollution

Importance of the Topic

Airborne fine particulate matter (PM2.5) poses significant risks to climate, visibility, and human health. Identifying the emission sources of PM2.5 is critical for designing targeted pollution control strategies and improving air quality. Stable isotope fingerprinting offers a rapid and informative approach to pinpoint contributions from fossil fuels, biomass, and natural processes.

Study Objectives and Overview

This application brief describes the use of carbon (δ13C), nitrogen (δ15N), and sulfur (δ34S) isotope ratios in PM2.5 collected on quartz filters in Seoul, South Korea. By comparing measured isotope signatures with known source ranges, the study aims to trace the origins of particulate pollution during winter haze events from November 2016 through January 2017.

Instrumentation

• High-volume PM2.5 impactor sampler with quartz microfiber filters (254 × 203 mm, 2.2 μm).
• Thermo Scientific™ EA IsoLink™ IRMS System coupled with MAS Plus Autosampler.
• Combustion reactor (oxidation and reduction zones) for simultaneous C, N, and S conversion to CO2, N2, and SO2.
• Helium carrier gas and hot copper for removal of excess O2 and conversion of NOx to N2.

Methodology

Filter sections containing 5–6 mg quartz were weighed into tin capsules and introduced to the EA IsoLink reactor under oxygen. Combustion products passed over hot copper, yielding N2, CO2, and SO2 for IRMS detection. Each sample was analyzed in triplicate, taking ten minutes per run with 1.4 L/min helium. Isotope ratios were calibrated against USGS and IAEA standards: USGS 40 and IAEA N1 for nitrogen, IAEA S1, S2, and USGS 42 for sulfur.

Key Findings and Discussion

The seasonal averages for the analyzed filters were:

• δ13C: –26.8 ± 0.5‰, indicative of fossil fuel combustion (vehicle diesel and coal emissions).
• δ15N: 6.7 ± 1.5‰, reflecting increased coal-derived NOx during winter heating.
• δ34S: 5.8 ± 1.2‰, consistent with terrestrial fossil sulfur rather than marine or biogenic sources.

As PM2.5 concentrations rose, δ15N values increased (4.2‰ to 8.6‰) and δ34S values decreased (7.35‰ to 4.01‰), confirming a stronger influence from coal combustion in northern China and local vehicular emissions. The narrow δ13C range also aligned with road transport signatures reported in prior Seoul studies.

Benefits and Practical Applications

Using EA-IRMS for direct isotope analysis of filter-collected PM2.5 offers:

• Rapid, high-throughput source apportionment without extensive chemical preparation.
• Automated operation reducing labor and consumable costs.
• High data quality comparable with traditional offline methods.

Future Trends and Opportunities

Continued refinement of isotope fingerprint libraries for regional sources will improve apportionment accuracy. Integration with real-time aerosol collection and IRMS could enable near-continuous monitoring. Expanding multi-isotope approaches (e.g., oxygen isotopes) and coupling with receptor models will enhance understanding of secondary formation processes and transboundary pollution dynamics.

Conclusion

Stable isotope analysis of carbon, nitrogen, and sulfur in PM2.5 filters using the EA IsoLink IRMS System provides a fast, reliable method for tracing pollution sources. The case study in Seoul confirms dominant contributions from coal combustion and traffic emissions during winter haze events. This approach supports targeted mitigation efforts and informs air quality management policies.

References

1. Han X. et al. Nature Sci. Rep. 6, 29958 (2016).
2. Beyn F. et al. Atmos. Environ. 107, 281–288 (2015).
3. Dai L. et al. Atmos. Chem. Phys. 15, 3097–3108 (2015).
4. IPCC Climate Change 2007: WG1, Cambridge Univ. Press (2007).
5. Masalaite A., Garbaras A., Remeikis V. Lith. J. Phys. 52, 261–268 (2012).
6. Park Y-M. et al. Environ. Pollut. 233, 733–744 (2018).
7. Xiao H-Y., Liu C-Q. Org. Geochem. 42, 84–93 (2011).
8. Shaheen R. et al. Proc. Natl. Acad. Sci. 111, 11979–11983 (2014).