Development of a new photocatalytic oxidation air filter for aircraft cabin

A new photocatalytic oxidation air filter (PCO unit) has been designed for aircraft cabin applications. The PCO unit is designed as a regenerable VOC removal system in order to improve the quality of the recirculated air entering the aircraft cabin. The PCO was designed to be a modular unit, with four UV lamps sandwiched between two interchangeable titanium dioxide coated panels. Performances of the PCO unit has been measured in a single pass mode test rig in order to show the ability of the unit to decrease the amount of VOCs (toluene, ethanol, and acetone) entering it (VOCs are fed separately), and in a multipass mode test rig in order to measure the ability of the unit to clean the air of an experimental room polluted with the same VOCs (fed separately). Triangular cell panels have been chosen instead of the wire mesh panels because they have higher efficiency. The efficiency of the PCO unit depends on the type of VOCs that challenges it, toluene being the most difficult one to oxidise. The efficiency of the PCO unit decreases when the air flow rate increases. The multipass mode test results show that the VOCs are oxidized but additional testing time would be necessary in order to show if they can be fully oxidized. The intermediate reaction products are mainly acetaldehyde and formaldehyde whose amount depends on the challenge VOC. The intermediate reaction products are also oxidized and additional testing time would be necessary in order to show if they can be fully oxidized. The development of this new photocatalytic air filter is still going on. PRACTICAL IMPLICATIONS: The VOC/odor removing adsorbers are available for only a small proportion of aircraft currently in service. The photocatalytic oxidation (PCO) technique has appeared to be a promising solution to odors problems met in aircraft. This article reports the test results of a new photocatalytic oxidation air filter (PCO unit) designed for aircraft cabin applications. The overall efficiency of the PCO unit is function of the compound (toluene, ethanol, and acetone) that challenges the unit and toluene appears to be the most difficult compound to oxidize. Test results have shown the influence of the design of the PCO unit, the air flow rate and the type of UV on the efficiency of the PCO unit. The results obtained in this study represent a first attempt on the way to design a filter for VOC removal in cabin aircraft applications. The PCO technique used by the tested prototype unit is able to partially oxidized the challenge VOCs but one has to be aware that some harmful intermediate reaction products (mainly formaldehyde and acetaldehyde) are produced during the oxidation process before being partially oxidized too.     

An under-aisle air distribution system facilitating humidification of commercial aircraft cabins

Air environment in aircraft cabins has long been criticized especially for the dryness of the air within. Low moisture content in cabins is known to be responsible for headache, tiredness and many other non-specific symptoms. In addition, current widely used air distribution systems on airplanes dilute internally generated pollutants by promoting air mixing and thus impose risks of infectious airborne disease transmission. To boost air humidity level while simultaneously restricting air mixing, this investigation uses a validated computational fluid dynamics (CFD) program to design a new under-aisle air distribution system for wide-body aircraft cabins. The new system supplies fully outside, dry air at low momentum through a narrow channel passage along both side cabin walls to middle height of the cabin just beneath the stowage bins, while simultaneously humidified air is supplied through both perforated under aisles. By comparing with the current mixing air distribution system in terms of distribution of relative humidity, CO₂ concentration, velocity, temperature and draught risk, the new system is found being able to improve the relative humidity from the existent 10% to the new level of 20% and lessen the inhaled CO₂ concentration by 30%, without causing moisture condensation on cabin interior and inducing draught risks for passengers. The water consumption rate in air humidification is only around 0.05 kg/h per person, which should be affordable by airliners.     

A critical review of reported air concentrations of organic compounds in aircraft cabins

This paper presents a review and assessment of aircraft cabin air quality studies with measured levels of volatile and semivolatile organic compounds (VOCs and SVOCs). VOC and SVOC concentrations reported for aircraft cabins are compared with those reported for residential and office buildings and for passenger compartments of other types of transportation. An assessment of measurement technologies and quality assurance procedures is included. The six studies reviewed in the paper range in coverage from two to about 30 flights per study. None of the monitored flights included any unusual or episodic events that could affect cabin air quality. Most studies have used scientifically sound methods for measurements. Study results indicate that under routine aircraft operations, contaminant levels in aircraft cabins are similar to those in residential and office buildings, with two exceptions: (1). levels of ethanol and acetone, indicators of bioeffluents and chemicals from consumer products are higher in aircraft than in home or office environments, and (2). levels of certain chlorinated hydrocarbons and fuel-related contaminants are higher in residential/office buildings than in aircraft. Similarly, ethanol and acetone levels are higher in aircraft than in other transportation modes but the levels of some pollutants, such as m-/p-xylenes, tend to be lower in aircraft.     

Novel insight into VOC removal performance of photocatalytic oxidation reactors

A general model has been developed for analyzing the removal of volatile organic compounds (VOCs) by photocatalytic oxidation (PCO) reactors, taking into consideration of the photocatalytic (surface) reaction and the convective mass transfer coefficients including allowance for their spatial dependence. On this basis, a novel insight into VOC removal performance of PCO reactors is presented. The key parameter for evaluating PCO reactor VOC removal performance is the number of the mass transfer unit (NTU(m)), which is shown to be a simple linear product of three dimensionless parameters: the ratio of the reaction area to the cross-sectional area of the flow channel (A*), the Stanton number of mass transfer (St(m)), and the reaction effectiveness (eta). The A* represents the geometric and structural characteristic of a PCO reactor. The St(m) shows the synergistic degree of alignment between the fluid and mass flow fields, and reflects the convective mass transfer rate of the reactor. The eta, describes the relative intensity between the PCO reaction rate and the mass transfer rate. By using the relationship and the parameters, the influence of various factors on the VOC removal performance, the bottleneck for improving the performance and design of a PCO reactor can be determined. Three examples are used to illustrate the application of our proposed model. It is found that the VOC removal bottleneck is the reaction rate for honeycomb type reactor, while mass transfer rate for light-in-tube type reactor. With six fins the fractional conversion of a light-in-tube reactor increases about 70% relative to the one without any fins. PRACTICAL IMPLICATIONS: Indoor air quality problem caused by volatile organic compounds (VOCs) have annoyed people for many years. Photocatalytic oxidation (PCO) appears to be a promising technique for destroying VOCs in indoor air. With the model and the novel insight presented in this paper, the influence of various factors on the VOC removal performance can be determined. And the bottleneck for improving the performance of a PCO reactor can be easily identified. These are helpful for designing high performance PCO reactors and optimizing their operative performance.     

Comparison of strategies to improve indoor air quality at the pre-occupancy stage in new apartment buildings

Indoor air quality of new apartment buildings, which is known to cause Sick Housing Syndrome, has become a major concern among apartment residents as well as construction companies in Korea. Recently, the Indoor Air Quality Management Act, a regulation that limits concentration levels of formaldehyde and five volatile organic compounds in new apartment buildings, has been implemented. In this study, the effects of ventilation and decomposing agents were investigated and compared, which could be used at the pre-occupancy stage as solutions to high VOCs concentration levels in new apartment buildings. Six housing units were investigated under different conditions to assess the extent of the improvement in indoor air quality. The results demonstrate that ventilation is an effective way to control indoor air pollution caused by VOCs emissions, and the effect of decomposing agents on improving indoor air quality depends on the types of VOCs.     

Novel air distribution systems for commercial aircraft cabins

Air distribution systems in commercial aircraft cabins are important for providing a healthy and comfortable environment for passengers and crew. The mixing air distribution systems used in existing aircraft cabins create a uniform air temperature distribution and dilute contaminants in the cabins. The mixing air distribution systems could spread infectious airborne diseases. To improve the air distribution system design for aircraft cabins, this investigation proposed an under-floor displacement air distribution system and a personalized air distribution system. This study first validated a computational fluid dynamics (CFD) program with the experimental data of airflow, air temperature, and tracer-gas concentration from an environmental chamber. Then the validated CFD program was used to calculate the distributions of the air velocity, air temperature, and CO₂ concentration in a section of Boeing 767 aircraft cabin with the mixing, under-floor displacement, and personalized air distribution systems, respectively. By comparing the air and contaminant distributions in the cabin, this study concluded that the personalized air distribution system provided the best air quality without draft risk.     

Experimental study of ventilation effectiveness and air velocity distribution in an aircraft cabin mockup

Ventilation effectiveness in aircraft cabins is a critical factor for minimizing the cross-contamination of airborne pathogens exhaled by the passengers. In this study, a full-scale section of a Boeing 767 aircraft cabin containing thirty five mannequins was used for evaluating the ventilation effectiveness and characterizing the air distribution. Each mannequin was attached with a body heater and an outlet of carbon dioxide to simulate breathing. A set of experiment trials was conducted to measure the local mean age of air and the ventilation effectiveness factor (VEF) at the breathing level of the passengers. Carbon dioxide was used as the trace gas to determine the local mean age of air and the VEF. The air velocity profiles measured using a volumetric particle tracking velocimetry (VPTV) system was used to generate the airflow patterns and investigate the underlying mechanism affecting the local mean age of air and the VEF. In addition, measurements were conducted at different air supply rates to examine its effect on the ventilation performance.     

Modeling and physical interpretation of photocatalytic oxidation efficiency in indoor air applications

Volatile organic compounds (VOCs) are the major pollutants in indoor air, which significantly impact indoor air quality (IAQ). As a promising technique to remove VOCs, photocatalytic oxidation (PCO) takes the advantages of oxidation of a large range of VOCs with low energy consumption. In this study, the mass transports and reaction mechanism involved in the PCO process have been studied. In addition, the kinetic models of PCO on the different conditions of elementary reactions have been critically reviewed. Moreover, the factors that may affect the efficiency of PCO were interpreted based on the established fundamental mechanism of PCO. Some recommendations were made for future work to improve the efficiency of PCO system for building applications.     

The effect of a photocatalytic air purifier on indoor air quality quantified using different measuring methods

The effect on indoor air quality of an air purifier based on photocatalytic oxidation (PCO) was determined by different measuring techniques: sensory assessments of air quality made by human subjects, Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) and chromatographic methods (Gas Chromatography/Mass Spectrometry and High-Pressure Liquid Chromatography with UV detection). The experiment was conducted in a simulated office, ventilated with 0.6 h⁻¹, 2.5 h⁻¹ and 6 h⁻¹, in the presence of additional pollution sources (carpet, chipboard and linoleum). At the lowest air change rate, additional measurements were made with no pollution sources present in the office. All conditions were tested with the photocatalytic air purifier turned on and off. The results show that operation of the air purifier in the presence of pollutants emitted by building materials and furniture improves indoor air quality, as documented by sensory assessments made by human subjects. It also reduces concentrations of many chemical compounds present in the air as documented by the PTR-MS technique. For the lowest ventilation, results from measurements using the chromatographic methods have similar tendency, however many of the 50 compounds that were targeted for analysis were not detected at all, independent of whether the purifier was on or off. For the two conditions with higher ventilation the results were inconclusive.     

Experimental and CFD study of unsteady airborne pollutant transport within an aircraft cabin mock-up

It has been documented that diseases can spread within an aircraft cabin from the sneezing, coughing or breathing of a sick passenger. To understand the spreading mechanism it is very important to quantify the airflow and droplet transmission around a sneezing/coughing incident. In this project, tracer gas experiments were carried out in a full-scale Boeing 767-300 mock-up to study the global transport process of contaminated air within the cabin. Computational fluid dynamics (CFD) simulation was also used to provide additional information for understanding the principle. A steady airflow field was simulated first and then it was compared with the experimental data. The global airflow patterns were similar to those observed experimentally. This velocity field was adopted as the initial condition for further unsteady pollutant transport simulation. Experimental and simulated results were compared and discussed to develop a relationship between concentration and airflow pattern, source location, transport direction, and ventilation rate. Finally, the overall picture of concentration evolution by both experimental and simulated approaches was discussed.     

Influence of fins on formaldehyde removal in annular photocatalytic reactors

The influence of fins on formaldehyde removal in annular photocatalytic reactors was theoretically, numerically and experimentally studied. The simulated and experimental results agreed well. It was found that mass transfer tends to be the bottleneck of formaldehyde removal in conventional annular photocatalytic oxidation (PCO) reactors. When using fins coated with titania in a PCO reactor, the reaction area is greatly increased and the convective mass transfer is, therefore, obviously enhanced. The reaction coefficient may, however, be reduced. On the whole, the formaldehyde removal performance in an annular PCO reactor can be obviously improved by adding fins to the reactor. This analysis is helpful for annular PCO reactor design, and for performance optimization.     

Advantages for passengers and cabin crew of operating a gas-phase adsorption air purifier in 11-h simulated flights

Experiments were carried out in a three-row, 21-seat section of a simulated aircraft cabin installed in a climate chamber to evaluate the extent to which passengers' perception of cabin air quality is affected by the operation of a gas-phase adsorption (GPA) purification unit. A total of 68 subjects, divided into four groups of 17 subjects took part in simulated 11-h flights. Each group experienced four conditions in balanced order, defined by two outside air supply rates (2.4 and 3.3 l/s per person), with and without the GPA purification unit installed in the recirculated air system, a total of 2992 subject-hours of exposure. During each flight the subjects completed questionnaires five times to provide subjective assessments of air quality, cabin environment, intensity of symptoms, and thermal comfort. Additionally, the subjects' visual acuity, finger temperature, skin dryness, and nasal peak flow were measured three times during each flight. Analysis of the subjective assessments showed that operating a GPA unit in the recirculated air provided consistent advantages with no apparent disadvantages. PRACTICAL IMPLICATIONS: Operating a gas-phase adsorption (GPA) air purifier unit in the recirculated air in a simulated airplane cabin provided a clear and consistent advantage for passengers and crew that became increasingly apparent at longer flight times. This finding indicates that the expense of undertaking duly blinded field trials on revenue flights would be justified.     

Characterization of the frequency and nature of bleed air contamination events in commercial aircraft

Contamination of the bleed air used to pressurize and ventilate aircraft cabins is of concern due to the potential health and safety hazards for passengers and crew. Databases from the Federal Aviation Administration, NASA, and other sources were examined in detail to determine the frequency of bleed air contamination incidents. The frequency was examined on an aircraft model basis with the intent of identifying aircraft make and models with elevated frequencies of contamination events. The reported results herein may help investigators to focus future studies of bleed air contamination incidents on smaller number of aircrafts. Incident frequency was normalized by the number of aircraft, number of flights, and flight hours for each model to account for the large variations in the number of aircraft of different models. The focus of the study was on aircraft models that are currently in service and are used by major airlines in the United States. Incidents examined in this study include those related to smoke, oil odors, fumes, and any symptom that might be related to exposure to such contamination, reported by crew members, between 2007 and 2012, for US‐based carriers for domestic flights and all international flights that either originated or terminated in the US. In addition to the reported frequency of incidents for different aircraft models, the analysis attempted to identify propulsion engines and auxiliary power units associated with aircrafts that had higher frequencies of incidents. While substantial variations were found in frequency of incidents, it was found that the contamination events were widely distributed across nearly all common models of aircraft.     

Performance of ultraviolet photocatalytic oxidation for indoor air cleaning applications

Ultraviolet photocatalytic oxidation (UVPCO) systems for removal of volatile organic compounds (VOCs) from air are being considered for use in office buildings. Here, we report an experimental evaluation of a UVPCO device with tungsten oxide modified titanium dioxide (TiO2) as the photocatalyst. The device was challenged with complex VOC mixtures. One mixture contained 27 VOCs characteristic of office buildings and another comprised 10 VOCs emitted by cleaning products, in both cases at realistic concentrations (low ppb range). VOC conversion efficiencies varied widely, usually exceeded 20%, and were as high as approximately 80% at about 0.03 s residence time. Conversion efficiency generally diminished with increased airflow rate, and followed the order: alcohols and glycol ethers > aldehydes, ketones, and terpene hydrocarbons > aromatic and alkane hydrocarbons > halogenated aliphatic hydrocarbons. Conversion efficiencies correlated with the Henry's law constant more closely than with other physicochemical parameters. An empirical model based on the Henry's law constant and the gas-phase reaction rate with hydroxyl radical provided reasonable estimates of pseudo-first order photocatalytic reaction rates. Formaldehyde, acetaldehyde, acetone, formic acid and acetic acid were produced by the device due to incomplete mineralization of common VOCs. Formaldehyde outlet/inlet concentration ratios were in the range 1.9-7.2. PRACTICAL IMPLICATIONS: Implementation of air cleaning technologies for both VOCs and particles in office buildings may improve indoor air quality, or enable indoor air quality levels to be maintained with reduced outdoor air supply and concomitant energy savings. One promising air cleaning technology is ultraviolet photocatalytic oxidation (UVPCO) air cleaning. For the prototype device evaluated here with realistic mixtures of VOCs, conversion efficiencies typically exceeded the minimum required to counteract predicted VOC concentration increases from a 50% reduction in ventilation. However, the device resulted in the net generation of formaldehyde and acetaldehyde from the partial oxidation of ubiquitous VOCs. Further development of the technology is needed to eliminate these hazardous air pollutants before such a UVPCO device can be deployed in buildings.     

Field measurements of indoor air pollutant concentrations on two new ships

Indoor air quality (IAQ) on ships is important for the passengers’ comfort and the crew’s work efficiency, despite ships not being as common as vehicles and airplanes. The builders and operators need to be aware of the importance and present status of IAQ, but sufficient data and information are not available. In this study, we measured the pollutant concentrations on two different kinds of newly launched ships: a passenger ship and a chemical cargo ship. Although higher than in the passenger ship, the concentrations of most volatile organic compounds (VOCs) and formaldehyde in the cargo ship were lower than the recommended standards and acceptable with a few exceptions. The high CO and CO₂ concentrations in the kitchen, engine room, and engine control room were generally attributed to combustion sources. Overall, the IAQ of the cargo ship was worse than that of the passenger ship, and the concentrations of some pollutants surpassed the international criteria. For the passenger ship, the variation of IAQ was also investigated after 17 months. The observed data showed some differences in concentration variation according to the types of pollutants. To improve IAQ on ships, more data need to be collected and minimum requirements suggested.     

Mitigation of cross-contamination in an aircraft cabin via localized exhaust

Most aircraft cabin ventilation designs currently use a 50% mix of fresh and recirculated, filtered air and supply approximately 8–10 l/s per person. In order to make the most efficient use of the air supply at hand, the 50% of cabin air that is exhausted from the aircraft should remove with it as much contaminant from within the cabin as possible. This will thereby reduce cross-contamination among passengers and improve overall air quality. This study examines the use of localized suction orifices near and around the source occupant to unobtrusively ingest the individual’s thermal plume and exhaust it from the aircraft cabin before contaminants entrained in the plume can significantly mix with the bulk airflow. Through the use of Computational Fluid Dynamics (CFD), various suction seat designs have been tested for their contaminant removal effectiveness and subsequent cross-contamination reduction. CFD results indicate significant improvements over conventional mixing air ventilation systems with a 40–50% decrease in passenger exposure predicted in a conventional coach-class seating arrangement.     

The effect of environmental and structural factors on indoor air quality of apartments in Korea

The indoor air quality (IAQ) was measured in newly built Korean apartments before and after occupancy in a survey of 158 residences in 24-apartment complexes nationwide. Factors that might affect pollutant concentration, such as temperature, humidity, housing size, and duration of occupancy, were analyzed in relation to the measured concentrations. Average pollutant levels were consistent with the Ministry of the Environment's recommended standards; however, pollutant levels in some apartments exceeded the current standards. We found that the concentrations of formaldehyde and toluene often exceeded the more stringent guidelines that will soon be enacted. Our results suggest that stronger countermeasures are therefore required to control these two chemicals. The results show that the pollution concentration was generally proportional to temperature and humidity, but that, in some cases, the concentration measurements were inversely proportional to these two factors, and in a few others the relationship between these factors was not clear. Indoor air pollution readings were highest in the 30-pyeong apartments, followed by 10-, and 20-pyeong residences. The pollutant concentrations decreased to about half of their initial levels after one year of occupancy, but the concentration of formaldehyde in indoor air persisted for a longer period. The duration of the apartment's occupancy affected indoor air pollutant concentrations more so than other factors such as temperature, humidity, and apartment size.     

Indoor air quality in Michigan schools

Indoor air quality (IAQ) parameters in 64 elementary and middle school classrooms in Michigan were examined for the purposes of assessing ventilation rates, levels of volatile organic compounds (VOCs) and bioaerosols, air quality differences within and between schools, and emission sources. In each classroom, bioaerosols, VOCs, CO(2), relative humidity, and temperature were monitored over one workweek, and a comprehensive walkthough survey was completed. Ventilation rates were derived from CO(2) and occupancy data. Ventilation was poor in many of the tested classrooms, e.g., CO(2) concentrations often exceeded 1000 ppm and sometimes 3000 ppm. Most VOCs had low concentrations (mean of individual species <4.5 microg/m(3)); bioaerosol concentrations were moderate (<6500 count per m(3) indoors, <41,000 count per m(3) outdoors). The variability of CO(2), VOC, and bioaerosol concentrations within schools exceeded the variability between schools. These findings suggest that none of the sampled rooms were contaminated and that no building-wide contamination sources were present. However, localized IAQ problems might remain in spaces where contaminant sources are concentrated and that are poorly ventilated. PRACTICAL IMPLICATIONS: Indoor air quality (IAQ) is a continuing concern for students, parents, teachers, and school staff, leading to many complaints regarding poor IAQ. Investigations of these complaints often include air sampling, which must be carefully conducted if representative data are to be collected. To better understand sampling results, investigators need to account for the variability of contaminants both within and between schools.     

Experimental study of photocatalytic concrete products for air purification

Air quality in inner-city areas is a topic which receives much attention nowadays but in the coming years, the overall interest on this topic will become even bigger. One major concern is caused by the reduction of the limiting values given by the European Council Directive 1999/30/EC [Relating to limit values for sulphur dioxide, nitrogen dioxide and oxides of nitrogen, particulate matter and lead in ambient air. Official Journal of the European Communities 1999, L 163/41–60] and increasing traffic rates especially for diesel powered passenger cars and freight vehicles.A promising approach for solving the problem of nitrogen oxides (NO_x) is the photochemical conversion of nitrogen oxides to low concentrated nitrates due to heterogeneous photocatalytic oxidation (PCO) using titanium dioxide (TiO₂) as photocatalyst. A variety of products containing TiO₂ are already available on the European market and their working mechanism under laboratory conditions is proven. However, there is still a lack of transforming the experimental results obtained under laboratory conditions to practical applications considering real world conditions.This paper presents the research conducted on photocatalytic concrete products with respect to the evaluation of air-purifying properties. The degradation process of nitric oxide (NO) under laboratory conditions is studied using a test setup for measuring the performance of photocatalytic active concrete products. The test setup uses the UV-A induced degradation of NO and is oriented on the ISO standard ISO 22197-1:2007. Besides the introduction of the test setup, a uniform measuring procedure is presented to the reader which allows for an evaluation and direct comparison of the performance of photocatalytic active concrete products. This kind of direct comparison was not possible so far. Furthermore, the results of a comparative study on varying photocatalytic concrete products of the European market will be discussed.     

Characterization of endotoxin and 3-hydroxy fatty acid levels in air and settled dust from commercial aircraft cabins

Endotoxin was measured in air and dust samples collected during four commercial aircraft flights. Samples were analyzed for endotoxin biological activity using the Limulus assay. 3-hydroxy fatty acids (3-OH FA) of carbon chain lengths C10:0-C18:0 were determined in dust by gas chromatography-ion trap tandem mass spectrometry. The geometric mean (geometric standard deviation) endotoxin air level was 1.5 EU/m3 (1.9, n = 28); however, significant differences were found by flight within aircraft type. Mean endotoxin levels were significantly higher in carpet dust than in seat dust (140 +/- 81 vs. 51 +/- 25 EU/mg dust, n = 32 each, P < 0.001). Airborne endotoxin levels were not significantly related to either carpet or seat dust endotoxin levels. Mean 3-OH FA levels were significantly higher in carpet dust than in seat dust for C10:2, C12:0, and C14:0 (P < 0.001 for each), while the mean level of C16:0 was significantly higher in seat dust than in carpet dust (P < 0.01). Carpet dust endotoxin was significantly, but moderately, correlated with 3-OH-C12:0 and 3-OH-C14:0 (Pearson r = 0.52 and 0.48, respectively), while correlation of seat dust endotoxin with individual 3-OH FAs depended on the test statistic used. Mean endotoxin potency was significantly higher for carpet dust than for seat dust (6.3 +/- 3.0 vs. 3.0 +/- 1.4 EU/pmol LPS, P < 0.0001). Mean endotoxin levels in the air and dust of commercial aircraft cabins were generally higher than mean levels reported in homes and office buildings. These results suggest that exposure route and dust source are important considerations when relating endotoxin exposure to specific health outcomes.