###### Abstract
For instance, the maximum mass fraction of aromatics in SAFs such as Fischer-Tropsch hydroprocessed synthesized paraffinic kerosene (FT-SPK), synthesized paraffin kerosene hydroprocessed esters and fatty acids (HEFA SPK), synthesized iso-paraffins (SIP), alcohol-to-jet synthetic paraffinic kerosene (ATJ-SPK), and hydroprocessed hydrocarbons, esters, and fatty acids (HC-HEFAs) cannot exceed 0.5%, while the sulfur content must be less than 15 ppm [10]. In contrast, according to ASTM D1655, Jet A or Jet A-1 fuel allows for maximum aromatic volume fractions and total sulfur mass fractions of 26.5% and 0.3%, respectively [11]. The composition of the fuel not only closely correlates with combustion performance within the combustion chamber but also influences engine exhaust emissions [12; 13; 14]. This is a critical concern for engine manufacturers [15]. The low aromatic and sulfur content of SAF will reduce particulate matter and sulfur dioxide emissions, promoting cleaner combustion behavior in aviation engines [16]. In addition to compositional differences, SAFs and conventional aviation fuels exhibit some differences in physical and chemical properties. For example, according to ASTM D7566, the final boiling points of Jet A or Jet A-1 fuel and SIP fuel are limited to 300 \({}^{\circ}\)C and 255 \({}^{\circ}\)C, respectively. The viscosity ranges at 15 \({}^{\circ}\)C for Jet A or Jet A-1 fuel and FT-SPK fuel are 775-840 kg/m\({}^{3}\) and 730-770 kg/m\({}^{3}\), respectively. Differences in volatility, thermal stability, and viscosity result in SAFs exhibiting different atomization and combustion performance in existing aircraft engines compared with conventional aviation fuels. This can affect pollutant emissions such as CO, NO\({}_{\rm x}\), and unburnt hydrocarbons (UHC) to some extent, although engine operating conditions have a greater influence. Current research on SAF emissions has some shortcomings. Firstly, due to the high fuel consumption and costs during engine testing, there is limited research on fuel emissions performance at the engine level [17] and even at aircraft levels and reviews on engine-level pollutant emissions remain scarce. Secondly, compared with traditional aviation fuels, SAFs demonstrate significant advantages in emissions performance regarding SO\({}_{2}\) and PM, which is widely acknowledged. However, there is controversy regarding the differences in emissions performance for CO and NO\({}_{\rm x}\) between sustainable and petroleum-based aviation fuels. As CO and NO\({}_{\rm x}\) emissions are partially attributed to engine properties rather than solely to fuel [18], it is necessary to conduct synthesis and analysis. Thirdly, the effects of various aviation pollutants on human health are less addressed and should be given significant attention. Air pollution, while contributing to climate change, is also the greatest environmental threat to global public health, causing an estimated 7 million premature deaths annually, with 20% of global newborn deaths attributed to air pollution exposure. Air pollution exposure is linked to many major global diseases; for instance, it is associated with 20% of global ischemic heart disease deaths, and PM\({}_{2.5}\) air pollution can lead to stroke, heart disease, lung disease,lower respiratory diseases (e.g., pneumonia), and cancer [19]. Transportation is one of the largest sources of air pollution, with fossil fuel air pollution responsible for 18-21.5% of global deaths annually [20]. Studies indicate that excess mortality due to aviation emissions will be significantly higher in 2050 compared with 2006. However, considering improved fuel policies (widespread use of SAFs and technological and operational improvements), the number of deaths among adults aged 25 and older is projected to decrease by 72% in 2050 compared with a scenario with no fuel improvements [21].