# Combating Pathogens Using Carbon-Fiber Ionizers (CFIs) for Air Purification: A Narrative Review
## 4 Discussion
### Carbon-fiber Ionizers: The Pros and Cons  
A carbon-fiber ionizer, which can be carefully positioned in front of an air filter, produces charged particles via corona discharge and traps the pathogens through its electrostatic interaction [4; 95]. It is an efficient measure for removing microorganisms from the air. Carbon-fiber ionizers can emit stable unipolar ions that efficiently charge surrounding air particles, with extraordinarily low or comparably lower ozone levels than standard corona ionizers due to the large number of sharp-edged fibers comprising the ionizer tips [96]. The World Health Organization (WHO) and the National Ambient Air Quality Standards (NAAQS) guidelines set specific margins for ozone concentration: <50 ppb for 8 h (2006) [97] and average 70 ppb for 8 h (2018) [98], respectively. In most studies, the CFI ozone levels fall below the designated threshold values, indicating that CFIs are a reliably safe option as ion-generating sources. The presence of ozone in some experiments underlines the role of controlling the input power to the ionizers, the importance of well-planned experiments, as well as care in the proper utilization of CFIs as powerful technological remedies against air pollution. Carbon-fiber ionizers were recognized to destroy the cell membranes of aerosolized bacteria such as _S. epidermidis_ and _E. coli_[10]. Electrostatic disruption of the procaryotic organisms was described as the leading antibacterial outcome. Interestingly, positive ions exhibited greater antibacterial effectiveness compared to negative ions against both types of microbes, despite the fact that the concentration of negative air ions surpassed that of positive air ions in this study. Cellular membrane disruption was also evidenced after utilizing CFI-generated ions in the work by [PERSON] et al. [14]. It should be noted, however, that although ozone was generated during the experiment, the latter work differentiates between ozone- and ion-mediated cell destruction, with bacterial lysis mainly attributed by the authors to the air ions. Moreover, [PERSON] et al. reported that ozone was not generatedwith CFIs at voltages up to \(-4\) kV [5]. Varying degrees of effectiveness of CFIs were reported in another study, where ions were used to inactivate the MS2 bacteriophage [61]. The success of inactivation showed considerable variation, ranging from 42.9 \(\pm\) 29.1% to 99.9 \(\pm\) 0.2%, and was contingent upon factors such as voltage, material choice, and flow velocity. Consequently, the selection of the most suitable material, voltage, and airflow rate appears pivotal in ensuring effective elimination of microorganisms. The CFIs were employed in another setting to distribute ions onto a filter surface, followed by the assessment of their microbicidal efficacy. Negative ions demonstrated greater effectiveness compared to positive ions, a phenomenon ascribed by the authors to their differing concentrations [19]. Moreover, the inactivation rates showed an increase corresponding to the number of ionizers utilized. The great potential of negative ions to enhance indoor air quality was also described elsewhere against the bacterial pathogens _Serratia marcescens_ and _Staphylococcus epidermidis_[17], with the effect of negative ions described in the case of a virus (\(\Phi 6\) bacteriophage) as well [62]. Further confirmation of the ability of negative ions to impinge on microorganisms is reported in the study of [PERSON] et al. [15], where their effect was investigated on _Staphylococcus epidermidis_, _Escherichia coli_, P22, and \(\Phi 6\) bacteriophages. In another study conducted on _Staphylococcus epidermidis_, positive ions were found to be lacking in their antibacterial effect, while bipolar emissions demonstrated antimicrobial influence [16].