## 8 Conclusions and Implications  
### Conclusions  
This study systematically reviews the latest research progress on IVOCs, both domestically and internationally, summarizes the research advancements in terms of source emission characteristics, ambient concentration levels, and contributions to SOA formation of IVOCs, and conducts a health risk assessment of typical IVOC species, revealing their key roles in regard to atmospheric chemistry and public health.  
The sources of IVOCs are diverse, and their chemical composition shows significant source-dependent characteristics. In recent years, although the overall emission of IVOCs has shown a downward trend, the emissions and emission factors associated with certain sources (e.g., VCPs) have increased. The concentration of IVOCs exhibits significant spatiotemporal heterogeneity and phase distribution characteristics. Urban areas generally show higher IVOC concentrations, with indoor concentrations being significantly higher than outdoor levels. In China, the concentration of long-chain alkanes shows a carbon number-dependent decreasing trend, which is not observed in European and American cities. Marine concentrations of IVOCs are relatively lower compared to terrestrial environments.  
As important precursors of SOAs, IVOCs make a significant contribution to their formation and yield that far exceeds that of traditional VOCs, especially in traffic-dense areas and high-emission urban zones. SOA tracers for species such as \(\beta\)-carophyllene and naphthalene have been identified. The SOA yields of IVOCs are generally high and are regulated by environmental variables, such as oxidation pathways, NOx concentrations, seeds, temperature and humidity, and coexisting inorganic gases. The main pathways for IVOCs to generate SOAs are through oxidation by OH:, NO\({}_{3}\):, and Cl atoms. The oxidation pathways of long-chain alkanes are mainly regulated by NOx concentrations; PAHs generate epoxide, nitro, and chlorinated products through radical addition; and sesquiterpenes react with O\({}_{3}\) or NO\({}_{3}\) to form epoxides and nitro compounds. Owing to the above key role in SOA formation, integrating IVOC emission inventories has significantly improved the SOA simulation accuracy of regional air quality models.  
Health risk assessments indicate that the carcinogenic risk of Nap should be prioritized for control purposes, while its non-carcinogenic risk management priority can be moderately reduced. In contrast, BaP requires combined risk assessment and tiered management of both its carcinogenic and non-carcinogenic effects. The carcinogenic and non-carcinogenic risks of Nap and BaP show significant spatial differentiation, with high-risk hotspots concentrated in dense urban areas and industrial clusters.  
This review integrates the research findings along the entire chain of \"emission-exposure-transformation-risk\" to systematically analyze the pollution characteristics and environmental impact of IVOCs, filling some gaps in the understanding of IVOCs. Future research is expected to focus on the development of high-resolution online detection technologies, in-depth analysis of multiphase reaction mechanisms, and comprehensive assessment of human health risks.