Spatial distribution and Source Apportionment of Organic Nitrogen in PM2.5 over Northeast Asia

Nitrogen-containing compounds constitute up to 77% of the molecular species in organic aerosols (OA), contributing approximately 40% to the total OA mass. Despite this significant abundance, research on characterizing organic nitrogen (ON) in particulate matter with an aerodynamic diameter of 2.5 micrometers or less (PM_2.5) has predominantly focused on water-soluble ON (WSON) or specific subgroups due to the complexity of ON and challenges in identifying its diverse sources. Beyond its abundance, ON plays an essential role in new particle formation, secondary organic aerosol (SOA) formation, and serves as a major atmospheric source of reactive nitrogen, potentially disrupting the global nitrogen cycle.
This study aimed to investigate the spatial distribution and source apportionment of ON in PM_2.5 across four sites in Northeast Asia. PM_2.5 samples were collected daily for one month in the fall of 2023 from Ulaanbaatar (Mongolia), Beijing (China), Seoul, and Seosan (South Korea). ON concentrations were measured using a simultaneous ON and inorganic nitrogen (IN) detection system, consisting of a thermal aerosol carbon analyzer and a chemiluminescence NOx analyzer (Yu et al., 2021). The average concentrations were 0.35 ± 0.17 μgN/m³ in Ulaanbaatar, 0.22 ± 0.12 μgN/m³ in Beijing, 0.20 ± 0.08 μgN/m³ in Seoul, and 0.28 ± 0.10 μgN/m³ in Seosan, corresponding to 39 ± 15%, 21 ± 15%, 23 ± 12%, and 23 ± 11% of total aerosol nitrogen in PM_2.5, respectively. The correlation analysis of water-soluble organic carbon (WSOC) and water-insoluble organic carbon (WISOC) in PM_2.5 with ON showed that in Ulaanbaatar ON correlated well only with WISOC, in Seoul only with WSOC, and in Beijing and Seosan with both WSOC and WISOC. The correlation analysis between IN and ON revealed the strongest relationship in Beijing, followed by Seoul, Seosan, and Ulaanbaatar. Since IN generally originates from secondary formation, the strong ON-IN correlation suggests that they may largely share common formation pathways or precursors, or that IN indirectly facilitates ON formation by providing reactive precursors through photochemical processes. Overall, it can be inferred that primary emissions, such as coal combustion, are the main source of ON in Ulaanbaatar, resulting in water-insoluble, lipid-like characteristics. In Seoul, ON likely originates from a combination of primary emissions and secondary formation. In Beijing, secondary formation, particularly IN-associated chemical reactions, appears to be the dominant source. In Seosan, primary emissions, particularly those linked to WSOC, such as biomass burning, are the primary contributors.

                                    

Acknowledgement

This research was supported by Particulate Matter Management Specialized Graduate Program through the Korea Environmental Industry & Technology Institute (KEITI) funded by the Ministry of Environment (MOE).

 

References

Yu, X., Li, Q., Ge, Y., Li, Y., Liao, K., & Huang, X. H. (2021). Environmental Science & Technology, 55(17), 11579–11589.