HEPA filters for airliner cabins: State of the art and future development

Composite electrospun membranes from cellulose nanocrystals, castor oil, and poly(ethylene terephthalate): Air permeability, thermal stability, and other relevant properties

The study examined the use of cellulose nanocrystals (CNCs) in poly(ethylene terephthalate) (PET)/castor oil (CO) electrospun membranes, focusing on how CNCs influenced membrane properties for aerosol filtration applications. PET membranes were fabricated using 5 wt% and 10 wt% of CNCs and 2.5 wt% CO to assess its effectiveness as a compatibilizing agent, under a solution flow rate of 25.5 μL/min, a voltage of 25 kV, and a needle-collector distance of 8 cm. Nonaligned fiber membranes featured a network of ultrafine and nanofibers, while aligned fibers had an average diameter of over 300 nm (ultrafine fibers). The PET membranes permeability parameters were applied to Forchheimer's equation. All membranes presented values of Darcian (k1)/non-Darcian (k2) permeability coefficients in the order of 10-13 m2/10-8 m, respectively, near the range reported for commercial high-efficiency particulate air filters. CNCs acted as reinforcing agents, while CO was a compatibilizing agent, improving the material's mechanical behavior. Nonaligned PET/CO/10 wt% CNC presented a storage modulus (E') 2-fold higher/tensile strength 3-fold higher than pristine PET. Aligned PET/CO/5 wt% CNC, characterized in the preferential direction of fiber alignment, had approximately an E' 42-fold higher/tensile strength 6-fold higher than the same membrane, but tested in the perpendicular alignment direction. The glass transition temperature (Tg) values of PET (90-110 °C) did not exhibit any significant impact from membrane composition or fiber alignment. This study demonstrated the promising capability of PET-CNC bio-based electrospun membranes to be used in aerosol filtration or gas-solid and liquid-solid separations.

Experimental investigation of interpersonal particle transport in an aircraft cabin mockup with nanofiber air filters

Improving aircraft environmental control systems could reduce the risk of airborne infectious disease transmission in aircraft cabins. The high-efficiency particulate air (HEPA) filters used in the existing systems exhibit high pressure drop, which results in high consumption of energy and fuel. Nanofiber air filters fabricated by electrospinning can reduce pressure drop, but their performance in aircraft cabins is unknown. Therefore, this study experimentally investigated the interpersonal particle transport in an aircraft cabin mockup with nanofiber air filters. First, a full-scale, fully occupied, 7-row, single-aisle aircraft cabin mockup was constructed. Nanofiber filtration units were fabricated using the electrospinning technique. Under the well-sealed laboratory testing conditions, both the small-scale nanofiber and HEPA filter media exhibited a particle removal efficiency of around 99 %. The performance of nanofiber and HEPA filtration units installed in the environmental control system of the mockup was then measured. Finally, the interpersonal particle transport in the cabin was measured. The results show that the particle removal efficiency of the nanofiber filtration units installed in the environmental control system ranged from 64 to 72 % when the particle size was 0.3-0.4 μm, which primarily reflected the large air leakages associated with the filter installation. At the filter media level, the pressure drop across the nanofiber units in the mockup was 61-67 % lower than that across the HEPA units under the same airflow rate, which however may not necessarily translate into lower pressure drop for actual filters in aircraft due to the potentially different design in terms of media face area. The average normalized particle concentration in the breathing zones of fellow passengers in the cabin mockup with the nanofiber filtration units was by 0.23, 0.29, and 0.32, respectively, when the index passenger was seated at the window, middle, and aisle.

A PM2.5 pollution-level adaptive air filtration system based on elastic filters for reducing energy consumption

Exacerbated by human activities and natural events, air pollution poses severe health risks, requiring effective control measures to ensure healthy living environments. Traditional filtration systems that employ high-efficiency particulate air (HEPA) filters are capable of effectively removing particulate matter (PM) in indoor environments. However, these systems often work without considering the fluctuations in air pollution levels, leading to high energy consumption. This study proposed a novel PM2.5 pollution-level adaptive air filtration system that combined elastic thermoplastic polyurethane (TPU) filters and an Internet of Things (IoT) system. The developed system can effectively adjust its filtration performance (i.e., pressure drop and PM2.5 filtration efficiency) in response to real-time air quality conditions by mechanically altering the structures of TPU filters. Furthermore, while operating in varied pollution conditions, the proposed system demonstrated remarkable reductions in pressure drop without notably compromising the pollution control capability. Finally, the energy consumption of the pollution-level adaptive air filtration system was estimated when applied in mechanical ventilation systems in different cities (Hong Kong, Beijing, and Xi'an) with various pollution conditions. The results revealed that, compared to a traditional fixed system, the annual energy consumption could be reduced by up to ∼26.4 % in Hong Kong.

Investigating the filtration performance and service life of vehicle cabin air filters in China

To protect occupants in vehicle cabin environments from the health risks of high concentrations of particulate matter (PM), it is important to install vehicle cabin air filter (VCAF) to eliminate PM. In this study, we investigated the filtration performance of 22 VCAFs. Results showed that the minimum average filtration efficiency was 56.1 % for particles with a diameter of 0.1-0.3 μm, a pressure drop of 33.2-250 Pa at air velocity of 2.5 m/s, and the dust-holding capacity ranged from 5.8 to 19.4 g. In addition, as the filter area increased from 0.23 m2 to 0.50 m2, the filtration efficiency for particles with a diameter of 0.1-0.3 μm increased from 56.7 % to 77.5 %, the pressure drop decreased from 96.1 to 62.5 Pa, and the dust holding capacity increased 2.7 times. Furthermore, we compared the service life of VCAF from 31 major Chinese cities and found that the service life varied greatly from maximum of 1730 h for Haikou to minimum of 352 h for Shijiazhuang. Considering occupant health risks, Beijing requires that VCAFs have PM2.5 filtration efficiency at least 88.1 %, and Liaoning requires minimum of 97.5 %. Hence, choosing the appropriate VCAF based on the atmospheric environment of different cities deserves our attention.

The role of nanoparticles in bleed air in the etiology of Aerotoxic Syndrome: A review of cabin air-quality studies of 2003-2023

Aerotoxic Syndrome may develop as a result of chronic, low-level exposure to organophosphates (OPs) and volatile organic compounds in the airplane cabin air, caused by engine oil leaking past wet seals. Additionally, acute high-level exposures, so-called "fume events," may occur. However, air quality monitoring studies concluded that levels of inhaled chemicals might be too low to cause adverse effects. The presence of aerosols of nanoparticles (NPs) in bleed air has often been described. The specific hypothesis is a relation between NPs acting as a vector for toxic compounds in the etiology of the Aerotoxic Syndrome. These NPs function as carriers for toxic engine oil compounds leaking into the cabin air. Inhaled by aircrew NPs carrying soluble and insoluble components deposit in the alveolar region, where they are absorbed into the bloodstream. Subsequently, they may cross the blood-brain barrier and release their toxic compounds in the central nervous system. Olfactory absorption is another route for NPs with access to the brain. To study the hypothesis, all published in-flight measurement studies (2003-2023) of airborne volatile (and low-volatile) organic pollutants in cabin air were reviewed, including NPs (10-100 nm). Twelve studies providing data for a total of 387 flights in 16 different large-passenger jet aircraft types were selected. Maximum particle number concentrations (PNC) varied from 104 to 2.8 × 106 #/cm3 and maximum mass concentrations from 9 to 29 μg/m3. NP-peaks occurred after full-power take-off, in tailwind condition, after auxiliary power unit (APU) bleed air introduction, and after air conditioning pack failure. Chemical characterization of the NPs showed aliphatic hydrocarbons, black carbon, and metallic core particles. An aerosol mass-spectrometry pattern was consistent with aircraft engine oil. It is concluded that chronic exposure of aircrew to NP-aerosols, carrying oil derivatives, maybe a significant feature in the etiology of Aerotoxic Syndrome. Mobile NP measuring equipment should be made available in the cockpit for long-term monitoring of bleed air. Consequently, risk assessment of bleed air should include monitoring and analysis of NPs, studied in a prospective cohort design.