Disentangling Nitrate Formation and Sources over East Asia and North America via Computational Quantum...

Atmospheric particulate nitrate (pNO₃^-) is a global pollutant, yet its sources remain poorly constrained and debated. While isotope analysis is a powerful tool for source tracing, its application is hampered by an incomplete understanding of isotopic fractionation, particularly the poorly constrained fractionation during gas-particle partitioning. Here, we integrate isotope with computational quantum chemistry to quantify fractionation during gas-particle partitioning. The results indicate that partitioning process induces ¹⁵N (4.8 to 5.2‰) and ¹⁸O fractionation (-0.8 to -4.9‰), which introduces uncertainties into pNO₃^- pollution causes identification. Isotope-based insights show distinct patterns on a global scale: while the NO₂ + OH pathway dominate pNO₃^- generation overall, formation via N₂O₅ hydrolysis and NO₃ + VOCs pathways is more pronounced in East Asia than others. This highlights the significant roles of higher humid climate and VOCs loads in this region. Furthermore, our analysis indicates an approximately 11.3% underestimation of pNO₃^- from agricultural and biogenic soil, potentially because partitioning processes promotes its formation. It also reveals greater contributions from industrial and combustion sources in East Asia versus North America, underscoring the necessity for reduction targeting these sources. These findings demonstrate that gas-particle partition plays a crucial role in regulating particulate nitrate isotopes.