## 5 Contribution to SOA Formation  
IVOCs make a significant contribution to the amount of SOA formation in the atmospheric environment, far exceeding that of traditional VOCs [78; 79]. The experiment in the Pearl River Tunnel in October 2019 showed that SOAs generated from IVOCs emitted by vehicles were seven times that of VOCs [49]. Studies on vehicle emissions in California in the USA found that SOAs generated from IVOCs in gasoline and diesel vehicles accounted for 50% and over 95% of total SOAs, respectively [55; 56]. From September to November 2018, high concentrations of long-chain alkanes were observed in the suburban Baoding area of the North China Plain and in urban Guangzhou in the Pearl River Delta. Their contributions to SOAs reached 9.4 \(\pm\) 9.1% and 7 \(\pm\) 8%, respectively, which were comparable to or higher than those of monocyclic aromatics and Nap to SOAs [69]. In July 2017, [PERSON] et al. conducted field observations on a large cargo ship in Chinese waters and found that the estimated SOA formation from fuel emissions from the cargo ship was 546.5 \(\pm\) 284.1 mg\(\cdot\)kg\({}^{-1}\) of fuel, with IVOC emissions from the ship contributing 98.9 \(\pm\) 0.9%  
Figure 3: Atmospheric concentrations (ppV) of (**a**) gas-phase and (**b**) particulate-phase IVOCs at different observation sites [11; 32; 36; 68; 69; 70; 71; 72; 73; 74]. PRD refers to the Pearl River Delta region in China, and NCP refers to the North China Plain (NCP) region in China. to the SOA formation [50]. In 2014, [PERSON] et al. conducted field observations in Pasadena in the USA, and found that although the concentration of IVOCs (6.3 \(\pm\) 1.9 \(\upmu\)g\(\cdot\)m\({}^{-3}\)) accounted for only 7.4 \(\pm\) 1.2% of the identified VOCs, their contribution to SOAs was as high as 57%, which was 4.75 times that of VOCs [11]. From 7 to 8 November 2014, [PERSON] et al. conducted observations in Beijing, China, and found that the contribution of IVOCs to SOAs was as high as 82% of the total SOA concentration [80]. IVOCs not only significantly contribute to the formation of SOAs, but existing studies have also confirmed that SOA tracers can be used to effectively indicate IVOC species and their sources. This is of great significance for a deeper understanding of the behavior patterns of IVOCs in the atmosphere. However, corresponding research is still relatively limited, and available information is scarce. Current studies mainly focus on using SOAs as tracers to reveal information about IVOC sources. Specifically, levoglucosan, a major product of cellulose pyrolysis, has been widely recognized as a typical tracer for biomass burning; vanillic acid, derived from the pyrolysis of lignin in coniferous trees (e.g., pine), is a specific tracer for conifer combustion; syringic acid, originating from the pyrolysis of lignin in broadleaf trees (e.g., oak), accordingly serves as a tracer for broadleaf tree combustion [39]. In addition, four- and five-ring polycyclic aromatic hydrocarbons (PAHs) are considered tracers for light-duty gasoline vehicle exhausts, while three-ring PAHs are regarded as tracers for diesel vehicle emissions [81]. Although direct studies on SOAs indicating IVOC species are relatively lacking, it is now possible to clearly identify SOA tracers for naphthalene and other PAHs, as well as for sesquiterpen, such as \(\upbeta\)-caryophyllene [82] (Table 2). IVOCs exhibit significantly higher SOA yields compared to traditional VOCs, as shown in Figure 4. Laboratory studies have shown that the SOA yields of IVOCs are not only regulated by the baseline concentration, but are also closely related to multiple environmental variables. Key environmental regulatory factors include the oxidation pathways, the competitive mechanisms of nitrogen oxides (NOx), the surface catalytic effects of seed aerosols, temperature and humidity parameters, and the interfacial reaction mechanisms of coexisting inorganic gases.