Molecular Characterization of Organosulfur and Organonitrogen Compounds in Summer and Winter PM2.5 via UHPLC-Q-Orbitrap MS/MS.

Organosulfur and organonitrogen compounds (OrgSs and OrgNs) notably influence haze formation, reflecting the intricacies of sulfur and nitrogen chemistry in the atmospheric process. Despite this, a comprehensive understanding of OrgSs and OrgNs remains elusive. Here, we conducted molecular analyses of OrgSs and OrgNs in PM_2.5 concurrently during three haze episodes in winter and summer from 2016 to 2019. OrgSs and OrgNs collectively constituted 68.8-73.8% of identified organics, with CHON (35.8%) being the most prevalent followed by CHONS (13.6%), CHN (11.5%), CHOS (5.6%), CHNS (3.2%), and CHS (0.9%). Nitrogen within CHX (CH + CHN + CHS + CHNS) compounds were predominantly present as nitriles or amines, while sulfur existed as alkaline thioethers (ESI+) or acidic mercaptans and thiophenols (ESI-). Oxygen-containing OrgSs and OrgNs exhibited greater structural complexity. Specifically, most CHON were associated with nitric esters and nitro-compounds (ESI-), or basic amino acids (ESI+). CHONS primarily comprised nitrogen heterocyclic substances containing oxygen and sulfur, with some potentially containing organic sulfates (OSs) and organic nitrates if O ≥ 4S + 3N. CHOS with (O-3S)/C ≥ 0 were identified as sulfonic acids or sulfate esters. This comprehensive spectrum of OrgSs and OrgNs enhances the understanding of the physicochemical properties of aerosols, providing insights for future laboratory and air quality model studies.