On August 28, 2025, Professor Ru-Jin Huang, Principal Investigator at the Institute of Earth Environment, Chinese Academy of Sciences (IEECAS), published a major review as first and corresponding author in the internationally renowned journal Science.

Title: Secondary organic aerosol in urban China: A distinct chemical regime for air pollution studies

Key Scientific Contributions:

With primary particulate emissions having been effectively controlled since 2013, this study reveals that secondary organic aerosol (SOA) has now become the dominant contributor to urban haze pollution in China. The authors demonstrate that Chinese urban atmospheres feature a unique chemical regime that is rarely observed elsewhere in the world — characterized by high atmospheric oxidizing capacity driven by multiple synergistic pathways, including nitrous acid photolysis, NOₓ-involved ozonolysis of alkenes, halogen radical reactions, and interfacial oxidation/hydrolysis processes.

The study further shows that elevated NOₓ levels promote the formation of nitrogen-containing organic compounds, which extend the lifetime of organic peroxy radicals and exacerbate regional secondary pollution. Rising nitrate fractions also increase aerosol liquid water content, further facilitating aqueous-phase SOA formation. The paper discusses the implications of anthropogenic SOA formation and aging on particle hygroscopicity, optical properties, and health effects, and outlines future research priorities — including the exploration of unknown oxidation pathways and molecular-level characterization of precursors and multi-generation oxidation products.

This work builds upon Professor Huang's landmark 2014 Nature paper, which first identified secondary aerosol formation as the key chemical driver of haze pollution in China.