Abstract: In order to study the mechanism by which nitrogen-containing organic compounds (NOCs) produced during straw burning affected the formation of secondary aerosols,  a self-built smog-chamber system was used to simulate the aging processes of straw burning aerosol (SBA) under light (UV) and no light (dark) conditions. High-resolution electrospray ionization mass spectrometry (HRESI-MS) combined with Van Krevelen (VK) diagram analysis was used  to characterize the molecular composition and oxidation features of NOCs in SBA. The results show that more than 60% of the organic compounds produced by straw burning are NOCs,  including CHN (compounds containing C,H,N elements, 9.61%—58.63%),  CHON (compounds containing C,H,O,N elements, 22.38%—62.89%),  and CHONS (compounds containing C,H,O，N，S elements, 6.48%—29.90%). The overall oxidation state of the organic compounds under UV light is higher than that under dark conditions. The combination of HRESI-MS and VK diagram can achieve accurate qualitative and oxidation state characterization of NOCs components in SBA, effectively tracking dynamic changes of  molecular composition and elemental ratio parameters  at different aging stages, and  providing a reliable analytical approach for molecular-level research on NOC aging process in biomass burning aerosols.

Key words: straw burning aerosol,  , high resolution electrospray ionization mass spectrometry,  , nitrogen-containing organic compound,  , photochemical aging