Novel Discoveries about the Potential Nonsecondary Origins of C ₂ –C ₃ Organosulfates in Ambient Aerosol Particles

Organosulfates (OSs) are significant components of secondary organic aerosol, with extensive research focusing on characterizing precursor-specific molecular signatures in their compositions. However, the origins of the critical class of small-molecule OSs (e.g., C₂-C₃ OSs) in ambient aerosols remain ambiguous. We investigated the abundance and composition of C₂-C₃ OSs in wintertime PM_2.5 across 11 Chinese cities, along with their occurrence in primary aerosols from biomass burning, coal combustion, and vehicle emissions. Total C₂-C₃ OS abundance was higher in northern China than in southern China. The transformation of biogenic volatile organic compounds was a larger source of C₂-C₃ OSs in southern China (∼66%), whereas anthropogenic contributions (including biomass and coal combustion) dominated in the north. All investigated C₂-C₃ OSs were detected in primary combustion aerosols. The emission factor of total C₂-C₃ OSs in fresh PM_2.5 generated from biomass burning was 0.42 ± 0.20 mg kg^-1. The contribution of primary combustion sources likely led to a decrease in the proportion of secondarily formed C₂-C₃ OSs, particularly in northern China. Furthermore, reducing primary emissions caused by clean heating policies can markedly mitigate aerosol C₂-C₃ OS pollution, as exemplified by Beijing. This study provides novel field evidence for the primary emissions of aerosol C₂-C₃ OSs.