Characteristics of the atmospheric behavior of particulate Nitro(so) compounds in the urban atmosphere of Seoul during Spring 2019: Role of the oxides of nitrogen to the formation of Nitro(so) compounds

Atmospheric concentrations and formation mechanisms of particulate nitrosamines and nitramines were investigated in Seoul, South Korea during spring 2019. The total concentration of seven particulate nitrosamines was 17.51 ± 16.74 ng/m³, with nitroso-dibutylamine (NDBA, 7.86 ± 8.59 ng/m³) being the predominant species, while the sum of two nitramines was 0.70 ± 0.52 ng/m³. Correlation analysis showed that nitro(so) compounds were correlated with both primary emission markers (CO, PAHs) and factors associated with secondary formation (the ratio of total nitroso compounds to PM_2.5, and liquid water content). Box model simulations estimated that atmospheric reactions contributed 24.4 ± 25.2 % and 55.4 ± 27.0 % to particulate N-nitrosodimethylamine (NDMA) and N-nitrodimethylamine (DMN) formation, respectively. Multilinear regression analysis identified ozone as the strongest predictor for both measured NDMA (β = 1.035, p < 0.01) and DMN (β = 0.893, p < 0.05) concentrations, although this correlation likely reflects the non-linear relationship between NO_x and O₃ due to O₃ titration in NO_x-saturated conditions rather than direct ozonation effects. Sensitivity analyses revealed that both compounds responded positively to NO₂ increases through enhanced N₂O₃ and N₂O₄ formation, while NO increases showed differential effects: promoting NDMA formation while having minimal impact on DMN concentrations due to their distinct formation pathways. These findings demonstrate the complex atmospheric chemistry of nitro(so) compounds in urban environments and highlight the importance of NO_x chemistry in their formation.