## 3 Source Characteristics
### Emission Characteristics  
Currently, the research on IVOC emissions mainly focuses on fossil fuel combustion sources, biomass burning sources, cooking sources, and VCP usage sources. [PERSON] and [PERSON] et al. used the primary organic aerosol (POA) emission inventory in the GEOS-Chem model, employing Nap as a surrogate for IVOCs, and estimated that the IVOC emissions from anthropogenic sources, biomass burning, and biofuel combustion in the year 2000 totaled 15 million tons of carbon per year [46]. In recent years, the overall emission of IVOCs in countries such as China and the United States has shown a downward trend, mainly attributed to the control of vehicle emissions [40; 47]. Nevertheless, the emission of IVOCs from fossil fuel combustion remains significant. Vehicle exhausts are also an important source of IVOC emissions. The IVOCs emitted from gasoline and diesel vehicles account for a considerable proportion of VOCs, with diesel vehicles emitting much higher amounts of IVOCs than gasoline vehicles [35; 48; 49]. Trucks account for more than 70% of the total IVOC emissions. The IVOCs from global shipping emissions account for one-fourth of the IVOC emissions from land transportation and have already surpassed the total emissions from gasoline vehicles [50]. [PERSON] et al. measured the IVOC concentration in Shanghai Yangshan Port before and after the G20 Summit in Hangzhou and found that the concentration of IVOCs decreased by 8% as a result of ship control measures, indicating that ships are also one of the most important sources of IVOC emissions [51]. From 2006 to 2020, the total IVOC emissions from motorcycles in China decreased from 197.19 Gg to 12.66 Gg [52]. However, IVOC emissions from certain specific sources, such as VCPs and cooking sources, have increased in recent years. [PERSON] et al. established a full VOC emission inventory, revealing that industrial processes were the main contributors of IVOCs in the central China region in 2020, accounting for as much as 31.7% of the total IVOC emissions [53]. From 2015 to 2021, the emission of IVOCs from cooking sources in China increased, rising from a low level to 241,000 (135-374) tons per year. Commercial cooking is the main source of IVOC emissions, accounting for 66.2% of the total IVOC emissions, with Sichuan and Hunan cuisines contributing the most to the total cooking emissions [54]. Similarly, the emission factors (EFs) of IVOCs in countries such as China and the United States have generally decreased in recent years. There are many factors that affect the EFs of IVOCs from vehicles, including fuels, engines, driving conditions, vehicle age, accumulated mileage, and post-treatment technologies [55; 56; 57; 58]. The fuel type and fuel quality directly affect the EFs of IVOCs, likely because a significant portion of IVOCs originate from incomplete fuel combustion [56]. For example, the EFs of IVOCs from large ships using heavy fuel oil are much higher than those from gasoline vehicles and are comparable to those from diesel vehicles [50]. Comparing the impacts of different engine types, it has been found that the EFs of IVOCs from two-stroke non-road mobile machinery are 4-5 times higher than those from four-stroke non-road mobile machinery. [PERSON] et al. conducted field measurements of IVOCs emitted by non-road construction machinery in working, traveling, and idling conditions and found that the EFs of IVOCs ranged from 245.85 to 1802.19 mg kg\({}^{-1}\) of fuel. Different operating modes significantly affect the EFs of IVOCs, with the EFs associated with the idling mode being 1.24 and 3.28 times higher than those associated with traveling and working modes, respectively [59]. Cycling conditions and post-treatment measures also influence the emission of IVOCs. In regard to low-speed cycling, the EFs of IVOCs are 6-23 times higher than those associated with high-speed cycling.