During the recent pandemic, there has been a lot of discussion about the effectiveness of air purifiers towards eliminating SARS-CoV-2. Scientists already know that the virus is transmitted through droplets via coughing and sneezing, but they cannot exclude the possibility that the virus may also exist in the aerosols of breathing, or spread through airborne transmission. Studies show that aerosol transmission is possible as the virus can remain active in the air for up to 16 hours (Fears et al., 2020).
An air purifier will not necessarily offer protection from the coronavirus. However, it could help reduce other pollutants that worsen chronic respiratory illnesses such as asthma, or may worse asthma in case they generate harmful byproducts like acetaldehyde, nitrogen dioxide ozon. Due to the fact that SARS-Cov-2 size ranges from 0.05 to 0.20μm (Chen et al., 2020), it is almost impossible for common air filters to remove it.
Few air purification systems can remove the virus and even less kill it.
Today, there are various air purification technologies available in the market. However, they don’t have equal effectiveness and rarely deliver what they promise. The specific characteristics of the various technologies are discussed below.
DFS technology: DFS (Disinfecting Filtration System), award-winning systems, developed through a United States Military Grant, are effective against airborne transmission of viruses and bacteria, proven to trap particles up to 0.007 μm in size, 40 times smaller than those that can be trapped by HEPA filters. By the first passage of air through the system, each unit captures more than 99.99% of ultrafine particles, bacteria and viruses, including SARS-CoV-2.
The most important is that DFS technology kills bacteria and viruses, through microbiostasis condition, which prohibits the breed through effect, where living organisms captured can grow inside the filter and be released back into the environment. In addition, they remove organic volatile compounds through multiple stages of adsorption filters. Units like the HealthWay Deluxe provide the user with 90% cleaner air in just 30 minutes.
UV lamps: UVGI disinfection systems (both UV-A (long wave: 315–400 nm) and UV-C (short wave: 100–280 nm) can be effective only in the form of ballasts (direct radiation, a strong UV projector in an empty space, absence of humans is needed), as it is required high and prolonged exposure to UV radiation in order to eliminate airborne microorganisms.
According to United States Environmental Protection Agency (EPA).”If properly designed, the UVGI cleaner in a typical airstream disinfection application has the potential to reduce the viability of vegetative bacteria and molds and to provide low to moderate reductions in viruses but little, if any, reduction in bacterial and mold spores. Spores tend to be resistant to UV radiation, and killing them requires a very high dosage”
“There is no specific standard test method to rate and compare the effectiveness of UVGI cleaners installed in either residential HVAC systems or portable air cleaners. Typical UVGI air cleaners designed for use in homes do not deliver sufficient UV doses to effectively kill or deactivate most airborne microorganisms because the exposure period is too short and/ or the intensity is too low. Thus, UVGI does not appear to be effective as a sole control device. When UVGI is used, it should be used in addition to—not as a replacement for—conventional particle filtration systems, because UVGI does not actually capture or remove particles. Dead or deactivated biological particles can still contain irritants, allergens, and/ or toxins.” (EPA, 2018 p 26).
Here it is stressed that air flow systems with UVC technology, have almost no effectiveness against viruses, while at the same time only affect 25%-30% of bacteria. In addition, these systems require on average higher energy costs, meticulous cleaning of the lamps’ surface and in the case of insufficient radiation containment, UV radiation can be a very serious health hazard for humans, especially in the eyes and skin areas. Studies exploring UVC systems’ effectiveness against SARS-CoV-2 (Heilingloh et al., 2020), suggest that while they may be suitable for overnight decontamination of surgery theaters, they are not suited for use within people’s everyday lives as the requirements for SARS-CoV-2 inactivation (minimum of 9 minutes exposure to a UVC intensity of 1048 mJ/cm2 at a distance of 3 cm from the source) do not allow for human presence in the space being decontaminated for prolonged amounts of time.
HEPA filters: Systems with HEPA filters can hold up to 99.97% of particles up to 0.3 μm in size (Lowther et al., 2020). Therefore, they cannot capture ultrafine particles (<0.12μm) such as SARS-CoV-2 (the size of SARS-CoV-2 is 0.05μm – 0.2μm). In addition, there is a risk in endotoxins increase in the air caused by micro-organisms trapped in HEPA filters actually colonizing them and producing harmful waste (Niu et al., 2020). Moreover, HEPA filters need to be replaced more frequently compared to DFS technology produce higher noise levels for the same airflow due to the gradual increase of pressure drop during their operation as the filters accumulate more pollutants.
Hydroxyl technology: This technology has an effect on microbial load ranging from 26% to 62% (V Wong et al., 2011), but with significant time delay (decreasing human exposure to harmful airborne microbes and particles requires swift elimination of new contaminants entering the airflow). This technology has also shown a decrease in hospital flora of up to 82% in 24 hours. However, these systems require significant maintenance costs and frequent hydroxyl cartridge replacement. These systems do not filter fine <2,5μmand ultrafine particles (<0.12μm).
According to the World Health Organization, microparticles are responsible for the premature death of 7 million people annually (Air pollution-WHO), and are associated with almost all serious diseases (cardiovascular, cancer, diabetes mellitus, Alzheimer’s, asthma, etc.), while the EU has identified the danger posed by ultrafine particles and is conducting scientific research with a view of revising relevant EU policy.
The importance of air quality and its impact on human health and wellbeing demonstrates the need for air purification systems that are capable of efficiently removing both pathogens (bacteria, viruses, fungi) and airborne contaminants (fine and ultrafine particle matter).