Haze in Beijing is linked to atmospherically formed secondary organic aerosol (SOA), which has been shown to be particularly harmful to human health. This study quantified the sources of organic aerosol in central Beijing using direct near-molecular observations. In winter, pollution arises mainly from fresh solid-fuel emissions and SOA originating from both solid-fuel combustion and aqueous processes. The most severe haze is linked to SOA from solid-fuel combustion, transported from the Beijing–Tianjing–Hebei Plain and rural areas. In summer, the increased fraction of SOA is dominated by aromatic emissions from the Xi’an–Shanghai–Beijing region. Overall, the main sources of SOA affecting Beijing extend beyond local emissions, suggesting regional targeting of key organic precursor emissions is needed for effective mitigation.

Kaspar R. Daellenbach, Jing Cai, Simo Hakala, Lubna Dada, Chao Yan, Wei Du, Lei Yao, Feixue Zheng, Jialiang Ma, Florian Ungeheuer, Alexander L. Vogel, Dominik Stolzenburg, Yufang Hao, Yongchun Liu, Federico Bianchi, Gaëlle Uzu, Jean-Luc Jaffrezo, Douglas R. Worsnop, Neil M. Donahue, Markku Kulmala