# Combating Pathogens Using Carbon-Fiber Ionizers (CFIs) for Air Purification: A Narrative Review
## 4 Discussion
### Air Ionization and Microorganisms--A Familiar Interplay? The control of pathogenic organisms in indoor environments is a pivotal aspect of public health, particularly because individuals spend a substantial amount of their time indoors, where air quality directly impacts their health and well-being [68]. Indoor environments often facilitate airborne transmission, serving as a significant route for the spread of various pathogens, including viruses [69]. Ensuring these environments are free from harmful pathogens is crucial, especially in sensitive areas like hospitals, schools, and offices. Traditional approaches for mitigating pathogen spread indoors include mechanical filtration, chemical disinfection, and ultraviolet germicidal irradiation (UVGI). Each method, however, has its limitations. Mechanical filters often fail to capture all microbial contaminants, especially viruses, due to their small size [70; 71]. Chemical methods can leave harmful residues and have variable efficacy depending on the pathogen and the environment [72]. Meanwhile, UVGI, while effective at inactivating pathogens, can pose risks to human health and is limited by the need for direct exposure of the pathogens to UV light [71; 73]. Given these challenges, there is significant interest in exploring more effective and less invasive technologies. Ionization, particularly using carbon fibers, emerges as a promising solution [71; 74]. Ionization technologies work by releasing ions that attach to and deactivate harmful particles in the air, including pathogens, and also increase the rates of natural particle deposition [75; 76]. This method is distinct from HEPA filters, which trap particles through a dense fibrous network and can remove 99.97% of particles down to 0.3 um; however, regular filter maintenance is challenging and involves ongoing costs [73]. Various methods exist for generating air ions, which are used to charge aerosols, facilitating their deposition on different surfaces. Air ions, whether positive (PAI), negative (NAI), or bipolar, can enhance the rate at which particles are removed from the air; however, each type influences this rate differently [4]. Air ionization devices fall into two categories: those that emit only negative ions, known as unipolar ionizers, and those that emit both positive and negative ions, referred to as bipolar ionizers [65]. Common technologies like corona discharge (also sometimes denoted as needlepoint bipolar ionization--NBPI) typically produce similar ions that operate through the same mechanisms [77]. Studies have differentiated the effects of positive and negative ions, with each showing distinct benefits in pathogen control. While the specific processes behind the biocidal effects of positive and negative ions are not yet fully understood, the proposed mechanism suggests that these ions cluster around microorganisms. During exposure, both negative and positive ions trigger oxidative stress in bacteria. This stress leads to cell death due to oxidative damage that affects cellular components, including DNA [18]. Many studies have focused more on the antimicrobial efficacy of NAIs than PAIs, which have been shown to have a lesser bactericidal effect, as evidenced by the results of [PERSON] et al. [37] concerning mycobacteria. [PERSON] et al. [38] demonstrated that NAIs effectively reduced tuberculosis transmission in hospital wards, suggesting potential against other airborne pathogens. Furthermore, [PERSON] et al. [78] suggested that NAIs can effectively reduce the concentration of airborne microorganisms, thereby potentially minimizing the risk of respiratory infections. [PERSON] et al. [76] discussed the importance and functions of NAIs, highlighting their effectiveness in filtering particles, especially ones smaller than 10 um (PM10), making them valuable for air purification purposes. Previous research, such as the study by [PERSON] and [PERSON] in 1994 [58], has demonstrated that NAI generation can effectively reduce Newcastle disease virus transmission in animal models.