Significant N-containing brown carbon emission from heavy-duty diesel vehicles revealed by the molecular and chromophore analysis using ultra-high resolution mass spectrometry

Brown carbon (BrC) holds scientific significance by influencing radiative balance, cloud condensation dynamics, and regional air quality. This study demonstrated that heavy-duty diesel vehicles (HDDVs) emit substantially higher levels of light-absorbing carbonaceous aerosols under aggressive conditions, such as frequent acceleration and high-speed phases, by investigating the emission profiles, formula distribution, and chromophore characteristics under various driving conditions. A non-targeted analysis of BrC was performed using Fourier-transform ion cyclotron resonance mass spectrometry coupled with a soft electrospray ionization source. The light absorption properties were assessed and revealed significantly higher light absorption during frequent acceleration and high-speed phases compared to low-speed phases. Formula distribution analysis highlighted a substantial presence of nitrogen-containing species, constituting 53–65% of the identified peaks, with high O/N ratios ( ≥ 3), double bond equivalent values (DBE > 10), and aromaticity equivalent (Xc ≥ 2.5), which indicated the substantial contribution of aromatic structures, condensed aromatics, and nitrooxy functionalities to BrC chromophores.