key: cord-0742532-dm8gv7sv authors: Wang, Feng; You, Ruoyu; Zhang, Tengfei; Chen, Qingyan title: Recent progress on studies of airborne infectious disease transmission, air quality, and thermal comfort in the airliner cabin air environment date: 2022-04-28 journal: Indoor Air DOI: 10.1111/ina.13032 sha: 0401ca8b432ef633113893cb0e8ec3ae2ee3a163 doc_id: 742532 cord_uid: dm8gv7sv Airborne transmission of infectious diseases through air travel has become a major concern, especially during the COVID‐19 pandemic. The flying public and crew members have long demanded better air quality and thermal comfort in commercial airliner cabins. This paper reviewed studies related to the airliner cabin air environment that have been published in scientific journals since 2000, to understand the state‐of‐the‐art in cabin air environment design and the efforts made to improve this environment. In this critical review, this paper discusses the challenges and opportunities in studying the cabin air environment. The literature review concluded that current environmental control systems for airliner cabins have done little to stop the airborne transmission of infectious diseases. There were no reports of significant air quality problems in cabins, although passengers and crew members have complained of some health‐related issues. The air temperature in cabins needs to be better controlled, and therefore, better thermal comfort models for airliners should be developed. Low humidity is a major complaint from passengers and crew members. Gaspers are used by passengers to adjust thermal comfort, but they do not improve air quality. Various personalized and displacement ventilation systems have been developed to improve air quality and thermal comfort. Air cleaning technologies need to be further developed. Good tools are available for designing a better cabin air environment. environment and the health of passengers and crew members. The study concluded that although cabin air quality may not be very low, passengers have complained of dry eyes, sore throat, dizziness, headaches, and other symptoms. However, the causes of these symptoms remain unclear. 7 In addition, thermal comfort is a very important aspect of the cabin air environment. According to Fanger, 8 thermal comfort is a function of the air temperature, relative humidity, air velocity, and radiant temperature of the environment,clothing level; and metabolic rate. The first four parameters are related to the cabin air environment. Meanwhile, measurements and surveys conducted by Cui et al. 9 found that the spatial distributions of comfort parameters in cabins were not uniform, and almost 30% of passengers complained that they were too warm. To solve problems related to infectious disease transmission, cabin air quality, and thermal comfort, government agencies have 11 They studied cabin air distribution, thermal comfort, air quality, design parameters, inverse design methods, and environmental control systems. The research, however, did not find major issues related to health or thermal comfort. The "ideal cabin envi- reviewed models used to predict thermal comfort in airliner cabins. They found large differences between the cabin air environment and buildings on the ground, such that the models for buildings cannot be used for airliner cabins. Chen et al. 14 examined nearly 50 flights on commercial aircraft in terms of volatile organic compounds (VOCs). They found that the concentrations of VOCs were below the permissible levels, with the exception of benzene. Hayes et al. 15 reviewed literature on the occupational risks of chemical and radiative exposure in aircraft cabins. They found that the potential for such risks cannot be ruled out. A review of the impact of cabin air quality on the well-being of crew members and passengers by Zubair et al. 16 discussed the prevalence of dizziness, fatigue, headaches, sinus and ear problems, dry eyes, and sore throats during and after travel and concerns about infectious diseases before the COVID-19 pandemic. Zhao et al. 17 reviewed the role of interior surfaces in the formation of potentially hazardous microorganisms, which could pose health risks by causing infectious diseases. The objective of a review conducted by Conceição et al. 18 was to evaluate airborne dispersion of contaminants, especially expiratory droplets, inside aircraft cabins. Leitmeyer and Adlhoch 19 reviewed influenza virus transmission aboard aircraft and found evidence of such transmission and found that the major limiting factor was the comparability of the studies. Elmaghraby et al. 20 reviewed different ventilation strategies used in commercial aircraft and the common airborne contaminants encountered in cabins. All the reviews provided very useful information for stakeholders in the aircraft cabin air environment. However, most of the reviews were on one of the subjects of infectious disease transmissions, air quality, thermal comfort, or air distribution. Air quality and thermal comfort are inter-related,so, they should be considered simultaneously, while air distribution is the fundamental behind. The COVID-19 pandemic brought additional challenges to the flying public, commercial airliner manufacturers, and public officials. The literature reviews have not been conducted for COVID -19 transmissions. One of the authors of the present review, Qingyan Chen Council 6 published a very good book of overview on cabin environment. By using Google Scholar, this investigation found hundreds of articles concern cabin air environment. The 150 papers were selected because they are representative, have high citations, and/or seem to be of high quality. The cabin air environment is created by By reviewing the most important publications concerning the air environment in commercial airliner cabins, this paper provided a summary of the state-of-the-art on cabin air environment studies. The review also recommended further research needed to improve the cabin air environment. environmental control systems through air distribution. The air distribution is fundamental to airborne infectious disease transmission, air quality, and thermal comfort in airliner cabins. After reviewing the state-of-the-art in these areas, this paper presents recent efforts to improve the cabin air environment. Finally, this paper describes the research efforts that are still needed for the airliner cabin air environment. The air environment inside airliner cabins includes air quality, thermal comfort, and air pressure. Due to the COVID-19 pandemic, the flying public has significant concerns about airborne infectious disease transmission. Since few studies have been published on air pressure, we did not review this topic specifically. On the contrary, air distribution is fundamental to airborne infectious disease transmission, air quality, and thermal comfort. This review began with air distribution systems in airliner cabins. When an airliner is flying at a cruising height of around 35 000 ft (10 000 m) above sea level, the outside air pressure is about 25 kPa, which is too low to sustain human life. Therefore, airliner cabins must be pressurized to an equivalent height of 8000 ft (2450 m) or lower, so that pressure is not lower than 75 kPa, thus, ensuring the safety of crew members and passengers. 21 The air used to pressurize airliner cabins is conditioned for the thermal comfort of the passengers and crew members. The pressurized air or the bleed air is normally from aircraft engine, except B-787 that uses a separated compressor, as shown in Figure 1 (a). Typically, airliners use a mixture of 50% outdoor air and 50% filtered return air to reduce energy costs while maintaining acceptable air quality inside cabins. 22 The supply air should be clean to create a healthy environment inside the cabin. Thus, the return air is filtered by a HEPA filter, while assuming the bleed air is clean at cruising height. At ground level, the outside air is either from an air-conditioning system at jet bridge or from auxiliary power unit. Since thermal comfort is related to air temperature, relative humidity, air velocity, and radiant temperature, airplane manufacturers use mixing ventilation as shown in Figure 1 Since actual measurements of in-flight air distribution are difficult, the studies of cabin air distribution in airliner cabins in the past two decades can be classified as experimental measurements on the ground using airplanes or cabin mock-ups, and computer simulations. Liu et al. 23 and Liu and Chen 24 provided overviews of the research F I G U R E 1 (A) Sketch of environmental control system for an aircraft cabin, (B) air distribution at a cross section in a singleaisle cabin, and (C) air distribution at a cross section in a twin-aisle cabin 26 The investigation compared the airflow simulated by CFD with experimental data measured by ultrasonic anemometers. Liu et al. 23 used an MD-82 aircraft to measure air distribution with ultrasonic anemometers. They obtained high-quality data for validating CFD models. They also found that the flow fields were of low speed and high turbulence intensity and that the flow in the cross 36 found that the thermal plumes from manikins used to simulate passengers were greatly influenced by the cabin geometry. Their results than RANS models, RANS modeling is less expensive and faster. Among different RANS models, their performance is case dependent. As illustrated by Figures 1 and 2 , air in both single-and twin-aisle cabins in a cross-section is well mixed. The design of the cabins was intended to provide better thermal comfort, but it may facilitate the transmission of airborne infectious diseases. Figure 3 shows that droplets generated by a passenger can be transmitted to the entire cross section and several rows before and after an index patient in a cabin 26,50 . According to simulation results reported by Lei et al., 51 that "COVID-19 is spread in three main ways: • Breathing in air when close to an infected person who is exhaling small droplets and particles that contain the virus. • Having these small droplets and particles that contain virus land on the eyes, nose, or mouth, especially through splashes and sprays like a cough or sneeze. • Touching eyes, nose, or mouth with hands that have the virus on them." The first bullet point indicates airborne transmission. The World Health Organization 56 has given similar reasons for COVID-10 spread. Mahmoud et al. 57 showed that the airflow pattern plays a major role in gaseous contaminant concentration level. The concentration level at some seats may be higher than at the source seat. Although the airflow in a cross section of a cabin may be well mixed, Yan et al. 58 found that particles from a coughing passenger at a window seat travel much further than at other seats. However, Khatib et al. 59 found that proximity to an index patient was more important than seat type or location. Gupta et al. 60 studied influenza transmission in an airliner cabin by using deterministic and probabilistic approaches to quantify the risks based on the number of inhaled influenza virus RNA particles and quanta, respectively. They found that influenza can be easily spread in the cabin. In regard to air distribution in existing airplanes, Yan et al. 61 found spectively, according to a study by Han et al. 63 Their results indicate that passenger movement may increase the average infection risk in the cabin, especially for the passengers seated three rows in front of and one row behind the index patient. Yang et al. 64 studied several flights with COVID-19 cases in the early days of the pandemic. They concluded that there was potential COVID-19 transmission in airplane cabins. Toyokawa et al. 5 studied passengers and flight attendants exposed to COVID-19 during a flight on March 23, 2020. By using whole-genome sequencing of SARS-CoV-2 to identify the infectious linkage, they found a secondary attack rate of 9.7%. They asserted that the lack of face-mask usage in the airplane was a risk factor for contracting COVID-19. Very similarly, Choi et al. 65 studied air quality data from 177 flights, including B-787 flights. They concluded that "smell events" classified as oil leakage with odor perception were false positives, and that VOC and tricresyl phosphate concentrations presented no threat to human health. Giaconia et al. 76 level was significantly lower than the limit specified in the relevant air-worthiness standard (100 ppb). However, ozone by-products such as nonanal were still at relatively high levels (averaging 11 μg/ m 3 ), and their effect on passengers' perception must not be ignored. Bekö et al. 82 concluded that exposure to ozone during a flight may lead to discomfort and associated symptoms related to the eyes and upper respiratory system. They measured ozone concentrations on 83 US domestic and international flights at cruising altitude and found that the average concentrations were relatively low (median: 9.5 ppb). Bagshaw and Illig 83 found that passengers and crew members were the primary sources of microorganisms in aircraft cabins and were also the reservoirs of infectious agents on aircraft. Tamás et al. 84 The researchers concluded that textile seats were much more contaminated by pet allergens and fungal DNA than leather seats. and crew members. Crew members experienced more health symptoms than other workers. Several studies attempted to link the symptoms to chemicals in air cabins. Many chemical data obtained from cabins were available and their reactions in cabins were also studied. The data were within the thresholds of standards and regulations and was comparable with that in buildings. Thus, more studies are needed to identify the causes of the health symptoms. As mentioned in the previous section, the environmental control systems of airliners supply air to cabins to create a well mixed condition in a cross-section and to minimize airflow in the longitudinal direction. Figure 4 shows the air temperature distributions computed by CFD in a cross-section and a longitudinal section (see section locations in Figure 2 ). The air temperature distributions were fairly uniform, although thermal plumes were generated by the heated manikins that were used to simulate passengers. In the longitudinal direction, the amount of air supplied to and returned from each row was the same, and the thermal load in each row was also the same. One would expect uniform air temperature as well. The mixing air distribution system should also generate a uniform distribution of relative humidity. However, as shown in Figure 2 , the air velocity was not uniform. In some seats, passengers might experience a draft. In addition, the surface temperatures of the walls, ceiling, and floor of the cabin during cruising were different from the temperatures of the air and passenger clothing. Therefore, radiant temperature asymmetry exists in airliner cabins. Chen et al. 81 measured air temperature in 46 flights and found that the air temperature during the flights ranged from 21 to 30°C. Higher cabin temperatures were usually found on Chinese domestic flights, and lower temperatures on international flights. Apparently, the flight crew did not set a comfortable temperature for some of the flights. The relative humidity on international flights was maintained at a relatively low level (10%-25%), except for the first 2 h of the flights. The average relative humidity on domestic flights was slightly higher (averaging 28%). More than 90% of the passengers reported that the cabin air quality and thermal environment were acceptable, while the most frequent complaints according to the subjective perception were odor (more than 50% of passengers perceived an intensity above "slight"), irritation (more than 25% of passengers perceived an intensity above "slight"), and dryness (more than 25% of passengers perceived the cabin air as "very dry"). According to experimental measurements during 14 short-haul domestic flights in Italy by Giaconia et al. 76 Relative humidity is important not only to thermal comfort but also to health. An overview by Wolkoff 101 perception of "dry air." Lindgren and Norbäck 102 found that the most common symptoms among airline crew were fatigue (21%), nasal symptoms (15%), eye irritation (11%), dry or flushed facial skin (12%), and dry/itchy skin on hands (12%). The most common complaint was dry air (53%). Tesón et al. 103 Relative humidity in air cabins was usually very low, especially in intercontinental long-haul flights. Many health-related symptoms seem to be related to relative humidity. Humidification technology is being applied to some of the airplanes. According to the above review of the state-of-the-art in the airliner cabin air environment, the environmental control systems in airliner cabins are effective in maintaining a reasonable thermal comfort level. However, the rate of dissatisfaction with thermal comfort remains high. 9, 92, 98 The systems also seem to provide adequate amount of outside air to maintain reasonable air quality. Although the measured chemical levels seem to be acceptable, passengers and crew members experience symptoms that cannot be explained. In particular, the relative humidity in cabins is low, which may cause some health-related issues. The environmental control system cannot provide adequate protection to passengers and crew members from airborne infectious diseases such as COVID-19. The low infection rate in airplane cabins seems to be attributable to mask wearing by passengers and crew. Since these problems are not new, what has the research community done to improve the cabin air environment in the last two decades? This section provides a critical review of their efforts. In commercial airplanes, a system of gaspers, which are small, circular, and adjustable vents above the seats, provides personalized ventilation for the thermal comfort of each passenger. Although the gasper system has been used for decades, very few assessments of its performance were conducted before 2000. Cui et al. 156 The airflow from a gasper is complex. Tang et al. 113 measured gasper flow with a high-frequency hot-wire anemometer and found that the mean velocity, velocity gradient, and energy spectra in the near fields of jet flows depended on nozzle geometry, and beyond the attachment point the flow exhibited self-similarity. On the contrary, it is not easy to predict airflow from a gasper. Studies by Shi et al. 114 and You et al. 115 show that the SST kω turbulence model could predict gasper-induced jet flows better than the RNG kε model. In other regions, the RNG kε model was better. Thus, it is necessary to use the two models together for predicting cabin airflow with gaspers on. 111 Because the gasper has an extremely small geometry, the prediction would require tens of millions of grid cells. Therefore, You et al. 116 proposed an approach to accurately predict airflow from a gasper with a limited number of grid cells in CFD. A half of the passengers would turn on gaspers to improve thermal comfort. Since gasper provides local cooling, corresponding thermal comfort models were developed. However, the air quality at the breathing zone did not improve with gaspers on, because the entrainment from the jet introduced contaminants as well. To accurately study the gasper flow would need specific RANS turbulence model. Compared with other advanced systems, the personalized ventilation system provided the best air quality without a draft risk. Gao and Niu 119 proposed a system to deliver clean air directly to the breathing zone. According to their results, the system can prevent inhalation of up to 60% of air pollutants by a passenger. Zítek et al. 120 proposed a similar When proposing personalized system, Zhang and Chen 118 also developed an underfloor displacement ventilation system that supplied air at floor level along the aisles. The latter system provided much better air quality than mixing ventilation and was easy to install. Bosbach et al. 124 were the first to test a displacement ventilation system with air supply from the side walls under flight conditions in an A-320 passenger aircraft cabin. They found that the system provided low air velocity and turbulence. They also tested a hybrid system that used both lower and upper side-wall supplies. Both systems provided acceptable thermal comfort. Recently, Liu et al. 125 proposed a modified mixing ventilation system that supplied air at shoulder level. A portion of the air was supplied upward and the other downward. They found that the system provided the lowest age of air, compared with other systems they studied. The system was even more effective than underfloor displacement ventilation. In order to develop more innovative ventilation systems, Chen et al. 128 Air cleaning is another important technology for improving air quality and reducing airborne infectious disease transmission in airliner cabins. Wang et al. 133 found that VOCs in cabin air can be removed by means of photocatalytic oxidation (PCO) and that TiO 2 is the most popular photocatalyst; this approach is efficient and cost-effective. However, the reactions produce intermediates that can be more toxic to human health and should be removed or further oxidized to CO 2 . Sun et al. 134 140 found that aerosols with initial sizes under 28 μm in diameter can stay airborne for a long time. Using influenza data as an example, they estimated that the risk of infection through inhalation of the airborne virus was at least two orders of magnitude higher than the risk of infection through contact. Therefore, many investigations focused on airborne aerosols, particles, or droplets. Sze To et al. 141 experimentally studied dispersion and deposition of expiratory aerosols in aircraft cabins. Their results indicate that 60%-70% of expiratory aerosols by mass were deposited in close proximity to the source, but airborne transmission is possible. A study by Powell et al. 142 determined that particle deposition on a horizontal surface in a cabin mock-up was 10 times higher than on a vertical surface. Wang et al. 27 found that the droplets from a cough in a cabin deposited mainly on the seat and seatback of the seat in front. Meanwhile, particle deposition onto surfaces depends on particle size, particle release mode, and the airflow pattern in an airliner cabin, according to Wang et al. 143 They found that 35% of small (0.7 μm) particles, 55% of medium (10 μm) particles, and 100% of large (100 μm) particles from breathing deposited onto the cabin surfaces, and the rest were removed by the cabin ventilation. The proportions of small, medium, and large deposited particles changed to 48%, 69%, and 100%, respectively, in the case of coughing. You and Zhao 144 discovered that the passenger occupancy rate in a cabin did not greatly influence the particle deposition rate. There may be concerns that particles deposited on a surface could be resuspended due to airflow, but Zhai et al. 145 found that resuspension is not an important factor, especially as time elapses. Although large particles can be easily deposited on various surfaces in a cabin, small particles that are not heavy but are very large in number can be airborne. Many viruses, including SARS, H1N1A influenza, and SARS-CoV-2, are smaller than 0.3 μm in diameter. The fine droplets produced by breathing, speaking, coughing, and sneezing can cause people who inhale them to become sick through air transport, even though modern airplanes were designed not to have flow in the longitudinal direction. Beneke et al. 146 measured a roughly 37% decrease in particle concentration with each successive row in the longitudinal direction from the source in a cabin mock-up. In a cross-section with very strong mixing, experimental measurements by Li et al. 147 in a cabin mockup found that the particle exposure for the passenger in the window seat was always the lowest, regardless of the particle source location. The researchers also found that particles from a passenger can be transported across at least four rows of seats in the longitudinal direction, which was much farther than the distance of two to three rows stated in earlier literature. Since experimental studies are expensive and time consuming, many more investigations have used CFD modeling to predict particle dispersion and transportation in airliner cabins. Particle transport can be predicted by the Lagrangian method, which tracks the motion of individual particles, or by the Eulerian method, which treats particles as a continuum in CFD simulations. Chen and Zhang 148 found that the two methods yielded nearly identical results. Zhang et al. 149 determined that sub-micron-sized heavy particles behaved like a passive gas contaminant in a cabin mock-up. Li et al. 150 measured very similar distributions of 3 μm-diameter particles and a tracer gas released in the same location in a first-class cabin. Meanwhile, Zhang et al. 149 demonstrated that the RNG kε model can predict particle transmission in a cabin mock-up with reasonable accuracy. For better accuracy and simulation of transient particle transport, a hybrid DES-Lagrangian and RANS-Eulerian model should be used. 151 To reduce the computing costs of DES and RANS modeling, Chen et al. 152 introduced the Markov chain method, which can provide faster-than-real-time information about particle transport in a cabin. Human respiration activities, such as coughing, talking, breathing, and sneezing, can generate many droplets in different sizes with virus. Large particles would deposit to different cabin surfaces due to inertial force and gravity. While fine droplets can remain airborne and be transferred to different parts of air cabin. Since the air cabin has limited longitudinal flow, the virus would still be confined in the proximity of the source. CFD with Lagrangian method was most popular, while other methods were also available to improve accuracy or to reduce computing costs. Airflow in an airliner cabin is very complex. The main driving forces for the air motion are jets from the environmental control system and thermal plumes from passengers and crew. The inertial forces from the jets and the buoyancy forces from thermal plumes are comparable. As a result, the flow in the cabin is unstable. Yao et al. 153 proved theoretically that the topological structure of flow in a cabin is absolutely unstable and is low on anti-jamming. Correct prediction of cabin airflow by CFD is difficult. To simulate the flow in a sevenrow cabin that did not have gaspers, Yao et al. 153 On the contrary, it may not be necessary to simulate the flow in a whole cabin with many gaspers on. Whether the simulation is conducted for design purposes or for evaluating airborne infectious disease transmission, air quality and thermal comfort, one can study the flow characteristics in a row or two with no more than 100 million grid cells. This is affordable with a computer cluster if LES or DES is employed. If an understanding of global flow in a whole cabin is needed, the cabin can still be divided into several zones, such as the first-class cabin, business-class cabin, economy-class cabin, and service areas. This would require prescribing the flow and thermal conditions between zones. One solution is to use a zonal model to estimate the conditions, as demonstrated by Chao et al. 154 . In addition, not all simulations need to be highly accurate. For example, during the conceptual design of a cabin flow, the designer may only need to know the general flow features. In that case, RANS modeling is appropriate. Even adaptive coarse-grid-generation methods together with fast fluid dynamics 155 may be sufficient. Traditional airplane design has not taken airborne infectious disease transmission into account. The past two decades have taught us that such transmission occurs from time to time. The airplane manufacturing industry cannot continue to ignore the issue. During the COVID-19 pandemic, some manufacturers and top airline executives released misleading information. For example, they claimed that because commercial airplanes used HEPA filters, the cabins were very clean. It is true that HEPA filters can filter out the majority of viruses. Unfortunately, our literature review identified infection by means of passenger-topassenger transfer within a cabin, before the air was filtered by the environmental control system. The CDC 55 and WHO 56 asserted that transmission mainly occurred in close proximity to an index patient. The supply of clean air on airplanes is essential. Our literature review did not find evidence that air-conditioning systems can transport SARS-CoV-2 in buildings or airplanes. In addition, the airplane manufacturers and airliner executives claimed that the high air exchange rate in airplanes made the air quality in a cabin is better than that in an office. If it is the number of viruses inhaled that determines whether or not a person becomes sick, the number can be calculated as The air exchange rate, which is not in the above two equations, is defined as Thus, the smaller the air cabin volume, the higher the air exchange rate. Since the volume of space occupied by a passenger is much smaller than that occupied by an office worker, the air exchange rate in a cabin should be much higher than that in an office. Instead, the air supply rate to an office for each worker is much higher than that to a cabin for each passenger, and thus, the virus concentration in an office is lower than that in a cabin. At present, the low infection rate found on airplanes seems to be attributable to the wearing of Our review has shown that cabin crew members experience worse gastrointestinal, sound perception, and common cold symptoms than nurses and teachers. Passengers and crew exhibited numerous health symptoms during air travel. However, the review did not find concrete evidence that the symptoms are linked to chemical exposure in air cabins. Is the low outdoor flow rate of 5 L/s per passenger a problem? The CO 2 concentration in many cabins was well above the 1000 ppm that is specified for buildings, but well below the 5000 ppm set by air-worthiness regulations. Is the high CO 2 level a problem? So far, no one has answered this question with scientific evidence. Guan et al. 89 found a total of 346 VOCs on 107 flights. Many VOCs and other chemicals have not been measured. The list of chemicals present on flights may not have been exhausted. The PCO technology used to convert VOC-generated secondary products and their toxicity has not been well studied. Studies on the link between exposure to VOCs and other chemicals and health issues require considerable resources as well as research teams with multidisciplinary knowledge. At present, only dryness is an obvious factor in passenger and crew complaints, and some studies have attempted to rule out a link between complaints and health issues. Therefore, it is necessary to continue the efforts to determine whether the health issues and complaints of passengers and crew are linked to cabin air quality. The air pressure in an airliner cabin at cruising height is lower than the atmospheric pressure at sea level. Cui et al. 156 found that the respiratory flow rate decreased as pressure dropped, while the O 2 consumption and CO 2 production increased. They also observed a significant increase in the respiratory quotient. The widely used model for predicting PMV does not apply to air cabins. In addition, Wu et al. 109 found that the draft model cannot be employed in air cabins, especially with the use of gaspers. The special thermal environment in airliner cabins poses a unique thermal comfort problem that requires further study and development of suitable comfort and draft models. To completely solve the problems related to airborne disease transmission, air quality, and thermal comfort in airliner cabins, designers of environmental control systems need to think outside the box. Many efforts have focused on personalized ventilation, displacement ventilation, and underfloor air distribution, which are traditionally used in buildings. The airliner cabin is a distinct environment with specialized geometry, high occupant density, low pressure, low relative humidity, use of specific materials for seats and cabin walls, limited outside airflow rate, high outdoor ozone level, and increased thermal load from electronics. In addition, the visual environment, vibration, turbulence, high noise level, jet lag, and other factors make the situation even worse. The available inverse modeling methods 128 are interesting, as they can set PMV and local age of air as design objectives. If additional design objectives were included, the computing efforts for most of the methods would increase exponentially. Wearable technologies, artificial intelligence, and big data analytics may be introduced in the design process, although this literature review did not find any research on these subjects for the airliner cabin air environment. • Studies on the transmission of airborne infectious diseases, especially SARS-CoV-2, in airliner cabins have been inconclusive because there were too few well-defined cases in which infection was proven to occur in the cabin rather than elsewhere in the travel process. At the same time, it has been difficult to prove that airliner cabins are safe for passengers. The low infection rate observed at the present time may be due to the wearing of masks by passengers and crew members. • Comprehensive experiments have been conducted to measure the concentrations of inorganic and organic chemical compounds on hundreds of flights with very detailed results. The ozone level was found to be low, and there has been no evidence of contaminated bleed air. In general, few of the chemicals are considered a threat to health. The review did find numerous papers reporting health-related issues among passengers and crew members during air travel. However, no concrete evidence has been published that would establish a link between the health issues and the detected chemicals. • The air temperature distribution in airliner cabins was found to be uniform. Air temperature varied greatly, which led to some complaints. Low relative humidity was a major complaint of passengers and crew, but several studies indicated that it was not a problem. Due to low cabin pressure, the thermal comfort models used in buildings may not be suitable for air cabins. • The use of gaspers can improve thermal comfort, as many passengers have found, but the flow from gaspers cannot improve air quality in the breathing zone due to high entrainment. The development of personalized and displacement ventilation systems for airliner cabins has yielded some promising results in improving air quality and preventing infections. However, none of these ventilation systems has been used in practice. Meanwhile, air cleaning with the use of PCO technology may generate secondary products that could have an adverse impact on health; therefore, more studies are needed. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Feng Wang involved in literature search and analysis and paper draft. Ruoyu You and Tengfei Zhang involved in conceptualization, further analysis, and paper editing. Qingyan Chen involved in project administration, paper structure design, supervision, review, and final editing of the manuscript. The peer review history for this article is available at https://publo ns.com/publo n/10.1111/ina.13032. 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