## 1 Introduction
### Health Effects of Ultrafine Particles  
Exposure to UFPs generally occurs through inhalation, making respiratory complications like asthma one of the key health risks. A 2021 computational fluid dynamics (CFD) study by [PERSON] et al. (2016) found that for particles of less than 10 nm, Brownian diffusion remains the dominant particle deposition mechanism. Those researchers employed two respiratory tract models, the Kitaoka (KG model) and a computed tomography-based patient-specific airway, while UFP deposition efficiency was calculated utilizing data published by The International Commission on Radiological Protection. [PERSON] et al. 's findings showed that the respiratory deposition of particles <10 nm was significantly higher when compared with >10 nm particles, highlighting the health implications of UFP exposure. On the other hand, [PERSON] et al. used a high-mass-resolution single-particle aerosol mass spectrometer to assess the respiratory deposition of UFPs among residents of urban Shenzhen, China, during the summer (2017). These researchers found that particles consisting primarily of elemental carbon (0.05-0.1 \(\upmu\)m) were the dominant components of UFP emissions, a factor that significantly increases deposition and respiratory health complications. Compared with general particulate matter, [PERSON] et al. found that residents are exposed to 0.1 \(\upmu\)m particles with a daily dose of \(\sim\)2.08 \(\pm\) 0.67 billion particles, which significantly increases the risk of such particles being deposited into deeper sections of the respiratory tract due to their small size. Elemental carbon particles, which are significantly small, were also found to account for approximately 85.7% of the UFPs inhaled by residents of the region, further demonstrating the potential deposition of such particles into deeper sections of the respiratory tract. Research indicates that UFPs can penetrate deep into the lungs, including the alveolar region, where they can cause inflammation and oxidative stress (2017). A review study by [PERSON] et al. investigated the toxicity and health effects of ultrafine particles and found that, compared with larger particles of >2.5 \(\upmu\)m, exposure to UFPs was associated with increased pulmonary inflammation ([PERSON] et al., 2017). [PERSON] et al. examined the risk of UFP exposure among urban school children using a sample of 8-11-year-old schoolchildren attending 25 elementary schools in Queensland, Australia (2017). Increased exposure to UFPs in this group was associated with lung inflammation and a diminished capacity, as characterized by greater lung stiffness. A common health implication is asthma, which, according to [PERSON] et al., is a chronic respiratory condition that affects airways in the lungs (2017). Exposure to UFPs can cause asthma by triggering inflammation and the narrowing of the airways, which, according to [PERSON] et al., will result in difficulty breathing and sensitivity of the airways over time (2017). [PERSON] and colleagues, for instance, conducted a one-week sampling campaign using a sample of adolescents with and without asthma (2017). The measurements of lung function by these investigators using the ATS/ERS criteria revealed a significant decline in lung function and an exacerbation of asthma symptoms among those with preexisting diagnoses. [PERSON] et al. also explored the potential effects of ambient UFP exposure among infants and found that prenatal UFP exposure led to an increased risk of asthma development in children [26]. [PERSON] and [PERSON] exposed Female Wistar rats to particulate matter for 21 days and found that the specimens developed a wide range of cardiovascular complications, including heart muscle hypertrophy, vascular calcification, and alterations in cardiac electrophysiology [27]. A meta-analysis of several studies by [PERSON] and [PERSON] also concluded that exposure to UFPs was associated with a higher risk of cardiovascular events, such as heart attacks and strokes [28].