Atmospheric Semi- and Intermediate-Volatility Organic Compounds: Recent Progress and Future Perspectives

Semi-volatile and intermediate-volatility organic compounds (S/IVOCs) represent a chemically complex class of atmospheric organics that contribute substantially to secondary organic aerosol (SOA) formation and may pose health risks. This review synthesizes recent advances in S/IVOC measurement, ambient concentrations and composition, spatiotemporal variations, SOA formation, and health effects. Online techniques provide high-time-resolution measurements, whereas offline GC–MS and GC×GC–MS offer superior capabilities for compound separation and identification. However, unresolved complex mixtures, sampling artifacts, limited standards, and variable instrumental responses remain major challenges. Field observations reveal pronounced differences in S/IVOC levels and composition among industrial, urban, traffic-influenced, and background environments, while seasonal and diurnal patterns vary across sites. Evidence from field observations, source-emission studies, chamber experiments, and model simulations indicates that S/IVOCs are important SOA precursors, although quantitative estimates remain subject to considerable uncertainties arising from precursor coverage, yield parameters, oxidation conditions, gas–particle partitioning, emission inventories, and model parameterizations. Current health evidence is largely confined to compounds with established toxicity data, particularly polycyclic aromatic hydrocarbons, whereas unresolved components and oxidation products remain poorly characterized. Overall, our synthesis suggests that the key challenge in current S/IVOC research is to reduce uncertainties across measurement, ambient characterization, SOA contribution, and health-risk assessment through standardized measurements, coordinated long-term observations, improved emission and aging representations, and broader toxicological characterization.