How efficiently can HEPA purifiers remove priority fine and ultrafine particles from indoor air?

Assessing effectiveness of air purifiers (HEPA) for controlling indoor particulate pollution

“…The filtering efficacy of air purifiers is directly proportional to CADR value, the more the CADR value higher the filtering efficiency of HEPA air purifiers. Ample of international studies linked the use of HEPA air purifiers in indoor spaces to substantial reduction (varied percent) in the concentration of TVOC, CO 2 , and CO (Xu et al, 2010); fungi spores (Hashimoto and Kawakami, 2018); airborne allergy particles (Punsmann et al, 2019); PM (Lowther et al, 2020;Kelly and Fussell, 2019;Barn et al, 2018;Ward et al, 2017), influenza virus particles (Zuraimi et al, 2011) as well as induce some health benefits including a decrease in systematic inflammation, coagulation, vasoconstriction, systolic and diastolic blood pressure and improved lung function (Chen et al, 2015;Kelly and Fussell, 2019). In contrast, study like Karottki et al (2013) found no difference in micro vascular and lung function after usage of air purifiers in old age homes.…”

Indoor air quality improvement in COVID-19 pandemic: Review

“…HEPA filters lack self-cleaning or disinfecting properties, resulting in the possibility of transmission of activated pathogens through the air during disposal or replacement of filter ( Miaskiewicz-Peska & Lebkowska, 2012 ). An experimental study examining the efficiency of HEPA purifiers resulted in the fact that particles having 200−250 nm size range were least efficiently removed though this size range has the highest concentration in the ambient air ( Lowther et al, 2020 ). The outcome concluded that the ambient air particles can be removed efficiently and at a similar rate or greater than the Association of home appliance manufacturers' standard particle size, but HEPA air purifiers are not beneficial for removing particles of size 200−250 nm range.…”

A review of strategies and their effectiveness in reducing indoor airborne transmission and improving indoor air quality

“…Natural ventilation faces critical challenges mostly in urban areas for various reasons, such as outdoor air pollution. The intake air can be filtered using air filters to remove the contaminants and then can be supplied into the indoor spaces in such cases ( ASHRAE, 2020c ; Azimi and Stephens, 2013 ; Elsaid and Ahmed, 2021 ; Fermo et al, 2021 ; Lowther et al, 2020 ; Nwanaji-enwerem et al, 2020 ; REHVA, 2020a ). Various researchers indicated that air filtration or purification systems could be provided in the ducts of air conditioning systems (retrofitting), inside the room, and for the occupant zones to functionally minimize the risk of the virus transmission through aerosols ( Mousavi et al, 2021 ; Noorimotlagh et al, 2021 ; Shen et al, 2021 ).…”

“…Incoming outdoor air can be screened with High-Efficiency Particulate Air (HEPA) filters to remove infectious agents and contaminants ( Kumar and Morawska, 2019 ; Nazarenko, 2021 ). HEPA filters effectively reduce bio-aerosols since they remove at least 99.95% of the particles with a diameter of 0.3 μm and larger fractions while only causing low-pressure drops ( Blocken et al, 2020 ; Lowther et al, 2020 ). All-day use of HEPA filters has been found effective in reducing the PM 2.5 concentrations (31%–72% reduction) in indoor spaces, and all-day use of air filters can result in an 8–37% reduction in mortality associated with indoor air pollution ( Liao et al, 2019 ).…”

“…The capital cost of the HEPA filter is low, but it has high operational and energy costs. A reduction in efficiency was reported with a 200–250 nm particle size range when HEPA filter-based air purifiers were tested in a laboratory setting in China, and this is critical as the particles with these size ranges are present in megacities and can penetrate the building envelope and remain suspended in the air ( Lowther et al, 2020 ) and can be a virus carrier.…”