# Multi-Disciplinary Optimization of UV-C Filter for Air Disinfection
## 1 Introduction  
The development of ultraviolet germicidal irradiation (UVGI) originates in 1878, when [PERSON] and [PERSON] found that sunlight, at shorter wavelengths, might restrict microbial growth [1]. As a consequence of this work, [PERSON] identified, in 1885, variations in sunlight sensitivity among different bacterial species [2]. A few years later (1890), [PERSON] demonstrated the lethal effect of sunlight on Mycobacterium tuberculosis, discovering the great potential of UVGI to combat airborne diseases like tuberculosis [3]. The mutagenic effects of UV were first discovered in a 1914 study that observed metabolic changes in _Bacillus anthracis_ when exposed to sublethal doses of UV [4]. In the late 1920s, [PERSON] described the first bactericidal action spectra for _Staphylococcus aureus_ and _Bacillus coli_, noting peak effectiveness at 265 nm [5]. This range corresponds to the absorption spectrum of nucleic acids, revealing DNA damage as the key factor in bacterial inactivation. This theory was consolidated by the 1960s through research demonstrating the ability of UV-C to form thymine dimers, which are responsible for microbial inactivation [6]. The methodic utilization of UVGI for air disinfection began in the mid-1930s. [PERSON] demonstrated in 1935 [7] that airborne infectious organisms, specifically aerosolized _B. coli_ exposed to 254 nm UV, could be rapidly inactivated. Soon, this approach was extendedto several hospitals and infant wards using UVGI \"light curtains\", which were designed to prevent respiratory cross-infections [8]. Despite initial successes, the use of UVGI declined in the second half of the 20 th century due to various reasons, in particular the rise of alternative infection control and prevention methods. However, recent events, like the appearance of drug-resistant bacteria and the COVID-19 pandemic, have renewed interest in UVGI for air disinfection [9]. Various engineering approaches to efficiently mitigating the presence of airborne pathogens inside building environments have therefore recently been investigated. Among these, we want to cite methodologies based on filtration, ultraviolet germicidal irradiation (UVGI) [10], and less common emerging methods, such as photocatalytic oxidation [11; 12] and ionizing radiation [13]. The methodology that we focused on in the present study is the filtration of air within heating, ventilation, and air conditioning (HVAC) systems, supported by established classification and criteria (e.g., ANSI/ASHRAE Standard 52.2-1999, ISO 14644-1 1999) [14; 15]. The particular case of UVGI disinfection that originally motivated our study is represented by dental or medical practices, where the combination of closed and non-aerated rooms with patients that cannot be protected by face masks during the medical operations significantly raises the infection risks for patients and medical operators. In this study, therefore, we focused on a solution that aims to remove the risk at the source by the aspiration of the aerosol generated in the dental practice through a vented UV-C LED filter, which neutralizes the viral and bacterial load, releasing the sterilized air in the environment [16]. To minimize the impact of the solution on the working conditions and ergonomic necessities of the physician, the focus was on a design that is practical to use, that does not interfere with the physician's movements and vision, and that does not require particular attention or care during dental operations. Since the efficiency of the pathogen neutralization is proportional to the intensity and time a microorganism is exposed to UV [17], it is required to perform a geometrical optimization of the filter, which maximizes the time the air flow carrying the bacterial load remains exposed to the UV radiation.