## 3 Source Characteristics
### Emission Characteristics
In the same driving conditions, the EFs of IVOCs from diesel vehicles without post-treatment devices are 28 times higher than those from diesel vehicles equipped with diesel particulate filters (DPFs) [55]. The EFs of IVOCs also differ at different driving speeds. For example, only 7% of diesel fuel is consumed, but 30% of IVOCs are emitted during low-speed driving. The emission of IVOCs is much higher during hot starts than during cold starts [56]. Fuel quality can also affect the distribution of IVOC emissions. Based on the content of aromatic hydrocarbons, diesel fuel is divided into low, medium, and high aromatic diesel. Low aromatic diesel contains 9% aromatic hydrocarbons, medium aromatic diesel contains 12%, and high aromatic diesel contains 28%. The emission of PAHs via the exhaust of high aromatic diesel vehicles increases with the increase in the content of aromatic hydrocarbons, while the content of unresolved cyclic hydrocarbons decreases [11; 55]. In addition, it has been found that the EFs of IVOCs from ships are related to the engine load, with the lowest emissions occurring at 75% load [60]. Although the EFs of motorcycles have decreased, their average EFs are still 7.78 times higher than those of China V-VI light-duty gasoline vehicles. It should be noted that the uncertainty in the IVOC emission data stems from the strong local characteristics and significant dynamic characteristics of the emission factors, the values of which change significantly depending on variable parameters, such as the fuel type and working conditions. For biomass burning sources, the impact of different biofuels on IVOC emissions differ significantly. [PERSON] et al. conducted field observations on IVOCs from 166 rural household solid fuels in eastern China and found that the average EFs of IVOCs from crop residues, firewood, and coal were 550.7 \(\pm\) 397.9, 416.1 \(\pm\) 249.5, and 361.9 \(\pm\) 308.0 mg kg\({}^{-1}\), respectively [61]. This indicates that the EFs of IVOCs from crop residue combustion are the highest, followed by firewood, while coal has relatively lower EFs. The combustion temperature and duration are also important factors affecting EFs. Higher combustion temperatures and longer durations promote more complete combustion, reducing the EFs of IVOCs; however, the high moisture content in biomass can reduce the combustion efficiency, leading to higher EFs for particulate matter and VOCs [39]. Due to the increased use of VCPs in recent years, the EFs of VCPs have significantly increased [47]. It has been reported that the EFs of VCPs are 1-2 orders of magnitude higher than those of gasoline vehicle exhausts [22]. Regional differences and variations in estimation methods contribute to uncertainties in emission estimates. For instance, the uncertainty range for IVOC emissions from biomass burning in the Pearl River Delta in China, calculated using the IVOCs/POA proportionality coefficient method, spans from \(-\)100% to 336%, while in the Yangtze River Delta in China, it ranges from \(-\)99% to 68%. For mobile sources in Guangdong Province in China, the overall uncertainty in IVOC emissions is between \(-\)54.7% and 144.9%. On a national scale in China, the estimated uncertainty for IVOC emissions falls within the range of \(-\)66% to 153% [31; 62; 63]. Despite existing reports on the emission characteristics of IVOCs, differences in emission characteristics and gas-particle partitioning have not yet been clearly distinguished and fully investigated. The simultaneous identification of gas-phase and particle-phase characteristics is a prerequisite for exploring the main sources and formation processes of IVOCs and is also of great significance for the development of IVOC control strategies. Moreover, understanding the trends in emissions and EFs overall and from specific sources of IVOCs is crucial to assess the air quality and climate impacts. Future research should focus on further identifying the EFs of IVOCs from different sources to improve the accuracy of emission inventories.