Tong Shengrui1， Zhang Hailiang1， Yu Shanshan1， Sun Jian， Zhai Mingzhu1，2， Xu Yanyong1，2， Lyu Xiaofan1，2， Li Yuhang1，2， Wang Shuai1，2， Zhu Ling3， Ning Heshan1，2， Lan Tong1，2， Afzaal Ashraf1， Ge Maofa1，2
1.Laboratory for Structural Chemistry of Unstable and Stable Species， Beijing National Laboratory for Molecular Sciences， Institute of Chemistry， Chinese Academy of Sciences， Beijing 100190， China； 2.University of Chinese Academy of Sciences， Beijing 100049， China； 3.College of Environmental Science and Engineering， Beijing University of Technology， Beijing 100124， China
Abstract
Significance The formation and atmospheric evolution of secondary organic aerosol （SOA） are central topics in climate change， regional air quality， and human health. A detailed mechanistic understanding of SOA formation and aging is therefore crucial for quantifying SOA sources， improving atmospheric models， and formulating effective particulate-matter control strategies. Volatile organic compounds （VOCs） are major precursors of SOA. Their oxidation pathways determine the molecular composition， volatility distribution， gas-particle partitioning， and aerosol formation potential of oxidation products. In China， SOA contributes substantially to fine particulate matter （PM2.5）， especially during severe haze episodes， yet SOA precursor sources and formation pathways remain insufficiently constrained. Environmental chambers and oxidation flow reactors are widely used to simulate atmospheric oxidation processes under controlled conditions and to quantify SOA yields， chemical composition， and physicochemical evolution. Early studies mainly focused on the gas-phase oxidation of individual VOC precursors. However， these simplified systems could not fully represent the chemical complexity of the atmosphere. Recent studies have increasingly focused on mixed-precursor systems and multiphase chemistry under atmospherically relevant conditions.
Progress Advances in analytical methods have greatly improved the ability to characterize SOA precursors， oxidation intermediates， and particle-phase products， thereby providing an important basis for mechanistic studies of SOA formation and aging. Proton-transfer-reaction mass spectrometry provides real-time measurements of VOCs and oxygenated VOCs. Orbitrap-based and other high-resolution mass spectrometers are commonly used for the molecular characterization of particle-phase organic compounds. Spectroscopic and mass spectrometric techniques have also been used to investigate Criegee intermediates formed during alkene ozonolysis. Together， these methods have advanced the understanding of SOA formation， atmospheric evolution， and aerosol properties. Hydroxyl radical-initiated oxidation is a dominant daytime pathway for the atmospheric degradation of VOCs. The chemical fate of organic peroxy radicals （RO2） plays an important role in controlling oxidation product distributions， volatility， and SOA yields. Alkene ozonolysis represents another established pathway for SOA formation， whereas nitrate radical-initiated oxidation constitutes an important nighttime transformation pathway for reactive VOCs. These processes are influenced by factors such as precursor molecular structure， oxidant exposure， NOx regimes， temperature， relative humidity， and the abundance and composition of pre-existing particles. Gas-phase mechanisms alone， however， often cannot account for observed organic aerosol mass concentrations， chemical compositions， and temporal evolution. Remaining uncertainties include insufficient characterization of SOA precursors， incomplete understanding of multigenerational oxidation， and limited treatment of interfacial and bulk-phase processes. Chamber artifacts， particularly vapor wall loss and particle deposition， can further affect measured SOA yields and product distributions. These issues complicate the interpretation of chamber experiments and the extrapolation of laboratory results to ambient conditions. Along with continued refinement of gas-phase mechanisms， increasing attention has been given to heterogeneous uptake， particle-phase reactions， and other multiphase processes. These processes can alter both SOA mass and chemical composition through the reactive uptake and condensed-phase transformation of gaseous oxidation products. They may occur at particle surfaces or within liquid and semisolid aerosol phases. Their rates and product distributions depend on aerosol composition， acidity， liquid water content， phase state， and oxidant exposure. Mineral dust， acidic sulfate aerosols， and sea-salt particles have therefore been widely used as seed aerosols to investigate the effects of particle composition on SOA formation and aging. Aqueous-phase chemistry constitutes an additional pathway for SOA production and atmospheric processing. Aerosol liquid water， cloud droplets， and fog water provide condensed-phase environments for the uptake， dissolution， and chemical transformation of water-soluble gases. Reactions in these media can produce aqueous-phase SOA and modify the oxidation state， volatility， hygroscopicity， viscosity， and optical properties of existing particles. The importance of aqueous processing can increase under humid conditions and with increasing aerosol liquid water content， although its contribution varies with precursor composition， aerosol acidity， and oxidation conditions. Multigenerational oxidation and multiphase aging can therefore lead to progressive changes in the chemical and physicochemical properties of SOA. Overall， these advances have deepened the mechanistic understanding of SOA formation and evolution under atmospherically relevant conditions.
Conclusions and Prospects The past decade has witnessed substantial advances in mechanistic research on SOA formation and aging， providing new insights into the chemical processes involved in atmospheric haze formation. Processes such as multigenerational gas-phase oxidation， heterogeneous reactions， and aqueous chemistry mediated by aerosol liquid water have been incorporated into laboratory simulations to elucidate the chemical evolution of organic aerosols. These studies demonstrate that SOA formation is governed by coupled gas-phase， interfacial， and condensed-phase processes rather than by gas-phase oxidation alone. However， most current experiments still rely on simplified conditions and cannot fully capture the complexity of atmospheric chemical processes， particularly in the highly polluted and chemically complex environments associated with severe urban haze in China. Future studies should therefore focus on multicomponent systems that better represent ambient atmospheric conditions， including realistic precursor mixtures， oxidant regimes， NOx levels， seed aerosol composition， aerosol liquid water content， and atmospheric aging timescales. Meanwhile， closer integration and systematic cross-validation among laboratory simulations， field observations， and numerical models are required. Such efforts will facilitate the incorporation of mechanistic knowledge into reduced chemical mechanisms and quantitative model parameterizations， improve the representation of SOA sources， yields， composition， and atmospheric aging in air quality models， and provide a stronger scientific basis for PM2.5 source attribution and the development of effective particulate pollution control strategies in China.
Keywords： secondary organic aerosol； volatile organic compound； gas-phase oxidation； multiphase reaction； smog chamber
Get Citation:Tong Shengrui， Zhang Hailiang， Yu Shanshan， et al. Research progress on formation mechanisms and multiphase chemistry of secondary organic aerosols［J］. China Powder Science and Technology， 2027， 33（2）： 193-208.
Received：2026-07-22， Revised： 2026-09-20， Online： 2026-10-10。
Funding： The research was supported by the National Key Research and Development Program of China (Grant No. 2022YFC3701003) and the National Natural Science Foundation of China (Grant No. 42430606).
DOI：10.13732/j.issn.1008-5548.2027.02.014
CLC No.:TB4； TQ324.8
Type Code：A
Serial No.:1008-5548（2027）02-0193-16
