Characterizing Particulate Organic Carbon Isotopes from Typical Emission Sources and Ambient Air in Beijing

Compound-specific stable carbon isotope analysis is an effective technique for identifying sources of atmospheric organic aerosols, but there are still issues such as low responsiveness to certain organic components and the lack of δ¹³C data for emitted organic components from sources which limit the widespread application. This study optimized the analytical methodologies using compound-specific isotope analysis to construct a stable carbon isotope database for organic components in PM_2.5 from four typical sources in Chinavehicle exhaust, coal burning, biomass burning, and residential emissions. Results show that for n-alkanes, biomass burning is the most ¹³C-enriched source (-26.06‰ ± 1.27‰), while residential emissions are the most depleted (-29.10‰ ± 1.04‰). For PAHs, δ¹³C exhibit a clear gradient across sources, varying in the order. Fatty acids also show distinct source-specific signatures, with biomass burning being the most ¹³C-enriched and the only source containing long-chain components >C₂₂, while residential emissions exhibit a higher proportion of unsaturated acids, indicating a cooking-related origin. Application of a Bayesian mixing model to winter and summer aerosol samples from Beijing revealed that n-alkanes mainly originate from biomass burning (summer: 60.7% ± 4.3%; winter: 62.8% ± 3.9%), with relatively stable source contributions. In contrast, PAH sources showed significant seasonal variation: vehicle emissions dominated in summer (76.3% ± 20.8%), while coal combustion increased to 34.9% ± 21.7% in winter. Fatty acids were primarily derived from biomass burning and residential emissions. This study filled the critical gap in δ¹³C fingerprint data for fatty acids and n-alkanes from emission sources, laying a foundation for precise source apportionment of atmospheric particulate matter. The observed shifts in source profiles reflect the effectiveness of energy structure transitions under coal control policies, providing a scientific basis for targeted air pollution management.