Large contribution of fossil-derived components to aqueous secondary organic aerosols in China

Incomplete understanding of secondary organic aerosol (SOA) sources creates significant uncertainty in air quality management and climate change assessment. Aqueous-phase chemical reactions are a major SOA source, but the impact of anthropogenic emissions on aqueous SOA (aqSOA) is poorly understood. This study uses compound-specific dual-carbon isotopic fingerprints (δ¹³C and Δ¹⁴C) of dominant aqSOA molecules (e.g., oxalic acid) to trace precursor sources and formation mechanisms. Significant stable carbon isotope fractionation in aqSOA molecules indicates extensive aqueous-phase processing. Contrary to the assumption that aqSOA is primarily biogenic, radiocarbon analysis reveals that fossil precursors contribute over half of the aqSOA molecules. This large fraction of fossil-derived aqSOA significantly impacts total water-soluble organic aerosol load, affecting air quality and anthropogenic radiative forcing projections. The findings highlight the importance of fossil emissions in aqSOA formation and their climate and air quality implications.

Buqing Xu, Gan Zhang, Örjan Gustafsson, Kimitaka Kawamura, Jun Li, August Andersson, Srinivas Bikkina, Bhagawati Kunwar, Ambarish Pokhrel, Guangcai Zhong, Shizhen Zhao, Jing Li, Chen Huang, Zhineng Cheng, Sanyuan Zhu, Pingan Peng, Guoying Sheng