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As concerns about indoor air quality increase, air purifiers and fresh air systems are increasingly being used in conjunction with air conditioners in office buildings. To study the synergistic effects of multisystem joint operation on indoor air quality, this study used a combination of experimental and simulation methods to study the indoor particulate matter with a diameter of less than 2.5 µm (PM2.5) and carbon dioxide (CO2) concentrations under different operation conditions. The purification time and the PM2.5 concentration distribution under different conditions were compared with the condition in which the purifier was used alone. The results showed that the purification time required for the condition that the air conditioner runs together with the purifier was shortened by 15.2%. When the fresh air system is running together with the purifier, the purification time can be reduced by 30.4%. It was reduced by 32.6% when the three systems were operating at the same time. The PM2.5 concentration distribution under the joint operating condition was much more even than that under the condition in which the purifier was running alone. To analyze the impact on the CO2 distribution, the CO2 distributions under different joint operations were compared. The results show that the fresh air system can effectively dilute CO2 below 1000 ppm in 30 min. The air conditioner and purifier could help to mix the indoor air to provide a much more uniform indoor CO2 distribution. [ABSTRACT FROM AUTHOR]

In indoor spaces without mechanical ventilation systems, a common approach involves using a ceiling-mounted 4-way fan coil unit (4WFCU) to regulate indoor temperature and placing floor-level air purifiers (APs) to remove indoor pollutants. This study introduces a differentiated displacement ventilation system (DVS) that connects multiple APs to the 4WFCU using ductwork. The age of air was compared between the case where the newly designed DVS was implemented and the reference case where 4WFCU and APs operated independently. When there were no obstacles in the office central area, the reference system exhibited a lower age of air. Conversely, when obstacles such as desks and partitions were present in the central area, the proposed DVS was found to improve indoor air quality. The DVS resulted in minimal interference among pathlines of the air discharged from multiple floor-level APs and their efficient suction through the ceiling-mounted 4WFCU and diffusers, significantly reducing stagnant air zones, while pathlines of the air discharged from the 4WFCU and APs interfered significantly when they operated independently, leading to larger stagnant areas in the air distribution. Therefore, modifying office spaces with ceiling-mounted 4WFCUs using the proposed DVS is anticipated to substantially enhance indoor air quality through a straightforward installation process. [ABSTRACT FROM AUTHOR]

As concerns about indoor air quality increase, air purifiers and fresh air systems are increasingly being used in conjunction with air conditioners in office buildings. To study the synergistic effects of multisystem joint operation on indoor air quality, this study used a combination of experimental and simulation methods to study the indoor particulate matter with a diameter of less than 2.5 µm (PM2.5) and carbon dioxide (CO2) concentrations under different operation conditions. The purification time and the PM2.5 concentration distribution under different conditions were compared with the condition in which the purifier was used alone. The results showed that the purification time required for the condition that the air conditioner runs together with the purifier was shortened by 15.2%. When the fresh air system is running together with the purifier, the purification time can be reduced by 30.4%. It was reduced by 32.6% when the three systems were operating at the same time. The PM2.5 concentration distribution under the joint operating condition was much more even than that under the condition in which the purifier was running alone. To analyze the impact on the CO2 distribution, the CO2 distributions under different joint operations were compared. The results show that the fresh air system can effectively dilute CO2 below 1000 ppm in 30 min. The air conditioner and purifier could help to mix the indoor air to provide a much more uniform indoor CO2 distribution.

Household air purifiers are widely used to enhance indoor air quality. However, limited information exists regarding the factors that influence their long-term performance. This study investigates the impact of various residential environments on the long-term efficacy of air purifiers. We deployed household air purifiers in three distinct environments: oily fumes (Group A), non-oily fumes (Group C), and a mixture of oily and non-oily fumes (Groups B-I and B-II). The selected air filter consisted of melt-blown polypropylene and activated carbon, materials commonly employed in commercial applications. The results demonstrated that the control efficiency of air purifiers in non-oily fume environments surpassed that in oily fume environments. After 12 months of operation, particulate matter (PM) concentrations rose by 92.7% and 76.5% in oily and non-oily fume environments, respectively. This increase was primarily attributed to the loss of electrostatic attraction in the polypropylene material due to the organic matter in oily particulate matter. After operating for 1000 h, the clean air delivery rate (CADR) attenuation rates for particulate matter were 70.6%, 19.9%, 16.7%, and 12.5% in Groups A, B-I, B-II, and C, respectively. The CADR attenuation rates for formaldehyde were 80.6%, 48.4%, 38.9%, and 37.3% in the same groups. Additionally, we developed a real-time prediction model for the service life of air purifiers using data from online sensors. When operated for 12 h daily at varying PM concentrations, the filters had an expected service life of 29–97 days in non-oily fume environments and 66–220 days in oily fume environments. [Display omitted] • Long-term performances of air purifier in different residential environments were performed. • Decay rate of performance over time in different residential environments was determined. • Oily particles loading on electret filters will significantly reduce efficiency. • A real-time prediction model for service life of air purifiers was developed. [ABSTRACT FROM AUTHOR]

Indoor PM2.5 in apartments must be effectively managed to minimize adverse impacts on human health. Cooking is the one of the main PM2.5 sources in apartments, and indoor air quality (IAQ) management methods (natural ventilation, mechanical ventilations, range hoods, and air purifiers) are typically used to reduce PM2.5 generated during cooking. For effective control of indoor PM2.5, prediction of PM2.5 reduction for various IAQ management methods is necessary. This study carefully predicted indoor PM2.5 concentrations in an apartment when IAQ management methods were applied separately and/or in combination during cooking. The infiltration and exfiltration were verified by comparing the experimental results of CO2 concentration with those predicted with or without mechanical ventilation. The deposition rate for PM2.5 generated by cooking was also derived by comparing the experimental PM2.5 changes with the predicted values for PM2.5 natural decay. Through this method, effective PM2.5 control ways during cooking in apartments can be proposed, such as natural ventilation with a range hood for 30 min and then the operation of an air purifier for 30 min. Additionally, if this prediction is combined with energy consumption, it will be possible to propose the most energy‐efficient indoor PM2.5 control methods for various seasons and outdoor conditions. [ABSTRACT FROM AUTHOR]

During wildfire smoke events public health agencies release advisories to stay indoors, close doors and windows, and operate a portable air cleaner (PAC). The do‐it‐yourself (DIY) air cleaner consisting of a box fan and a furnace filter is a widely used low‐cost alternative to commercial PACs because of its increased accessibility. In this study, we evaluate the clean air delivery rate (CADR) of different DIY air cleaner designs for reducing simulated wildfire smoke and identify operating parameters that may impact their performance and use. The simplest formulation of a DIY air cleaner (box fan with taped on minimum effectiveness reporting value – [MERV] 13 furnace filter) had a CADR of 111.2 ± 1.3 ft3/min (CFM). Increasing the fan flow by changing the fan type, increasing the fan setting, or reducing the pressure drop across the filtering surface increased the CADR. Large increases in CADR could be obtained by using a shroud (40%), using a 4″ thick filter (123%) using two filters in a wedge shape (137%), or using four filters in a Corsi‐Rosenthal (CR) box design (261%). The CADR was greatly reduced with filters heavily loaded with smoke, pointing to the need for frequent filter changes during smoke events. [ABSTRACT FROM AUTHOR]

Indoor PM2.5 must be effectively controlled to minimize adverse impacts on public health. Cooking is one of the main sources of PM2.5 in residential areas, and indoor air quality (IAQ) management methods such as natural and mechanical ventilation, range hood, and air purifier are typically used to reduce cooking-generated PM2.5 concentrations. However, studies on the combined effects of various IAQ management methods on indoor PM2.5 reduction and energy consumption are limited. In this study, a theoretical model was established to estimate the performance of various IAQ management methods for controlling indoor PM2.5 concentrations and energy consumption. The model was verified by comparative experiments in which, various IAQ management methods were operated individually or combined. Seasonal energy consumption was calculated through the verified model, and energy consumption saving scenarios were derived for maintaining indoor PM2.5 concentrations less than 10 μg/m3, a World Health Organization annual guideline, under fair and poor outdoor PM2.5 concentrations of 15 and 50 μg/m3, respectively. Based on our results, we found that energy consumption could be reduced significantly by applying natural ventilation in spring, autumn, and summer and mechanical ventilation in winter. Our study identified efficient energy saving PM2.5 management scenarios using various IAQ management methods by predicting indoor PM2.5 concentration and energy consumption according to the annual life patterns of typical residents in South Korea. [ABSTRACT FROM AUTHOR]

Mass COVID-19 infection cases in indoor spaces have been continuously reported since its global outbreak, generating increasing public interest in reducing the spread of the virus. This study considered a situation in which an infected individual continuously releases the virus into the air in a classroom, simulated by continuous injection of NaCl particles ≤ 5 μm, with heater operation during winter. The effects of applying natural ventilation and operating one or two air purifiers on the removal of virus-containing aerosols were experimentally compared and analyzed based on the spatiotemporal changes in NaCl concentration within the classroom. When a heater was operated with all windows shut, operating one and two air purifiers reduced the amount of the aerosol in indoor air by approximately 50 and 60%, respectively, compared to the case with no air purifier. Additionally, when the heater was operated with one or two air purifiers under natural ventilation, the amount of virus-containing aerosol in the air was reduced by 86–88% compared to the case with neither natural ventilation nor air purifier. Because natural ventilation significantly varies with weather conditions and particulate matter concentrations, combining natural ventilation with air purifiers in classrooms during winter needs to be adjusted appropriately. [ABSTRACT FROM AUTHOR]

We sought to investigate the impact of air purifiers in the removal of particular matter (PM)10, PM2.5, PM1, and particle number concentration (PNC) in the indoor air of dormitories located at Iran's largest medical university, Tehran University of Medical Sciences. Twelve rooms were selected and randomly assigned to two rooms: sham air purifier system deployed room (SR) and true air purifier system deployed room (TR). All study samples were drawn simultaneously from assigned rooms using portable GRIMM dust monitors for 24 h. The PM monitors of air were positioned in the middle of each room next to the air purifier at the height of the breathing zone (1.5 m in height). The mean PM10, PM2.5, PM1, and PNC removal efficiency in rooms with and without a smoker were measured to be 40.7 vs 83.8%, 31.2 vs 78.4%, 29.9 vs 72.3%, and 44.3 vs 75.6%, respectively. The results showed that smoking is an important influencing factor on the indoor air quality; smoking lowered the removal efficiency of PM10, PM2.5, PM1, and PNC by 43%, 47%, 43%, and 31%, respectively. An air purifier could decline the PM10 and PM2.5 even lower than the WHO 24-h guideline level in non-smoker rooms. This study revealed that using household air purifiers in rooms with smokers and non-smokers significantly reduces the non-carcinogenic risks of exposure to PM10 and PM2.5. [ABSTRACT FROM AUTHOR]

Indoor exposure to PM2.5 (particulate matter with aerodynamic diameter less than 2.5 μm) has a substantial negative impact on people's health. However, indoor PM2.5 can be controlled through effective ventilation and filtration. This study aimed to develop a smart control framework that (1) combines a portable home air purifier (HAP) and window control system to reduce indoor PM2.5 concentrations whilst maintaining thermal comfort; (2) evaluates the associated health impacts and additional energy use. The proposed framework was demonstrated through a simulation-based case study of a low-energy apartment. The simulation results showed that joint control of HAP and window openings has great potential to not only maintain thermal comfort but also achieve effective PM2.5 removal which, consequently, can lead to considerable health benefits at a low additional energy cost. Compared to similar previous studies, the strength of the proposed control framework lies in combining window operations and HAPs in the same system and including both thermal comfort and indoor PM2.5 as the control targets. This work also introduces a novel concept of linking a building control system with a health impact assessment, an important and innovative step in the creation of holistic and responsive building controls. Practical application: This study proposes a novel control framework that jointly controls portable home air purifiers (HAPs) and windows to maintain thermal comfort and achieve effective PM2.5 removal. The simulation results suggest that such a hybrid control strategy can result in considerable health benefits at low additional energy costs. [ABSTRACT FROM AUTHOR]

A prototype air purifier (AP) module has been constructed using bismuth-doped titanium dioxide (Bi x -P25: x(%) as Bi/Ti molar ratios of 1.1, 2.1, 3.3, 5.3, and 8.7). The reactive adsorption property of Bi x -P25 materials is evaluated against H 2 S gas at a recirculation rate of 160 L min−1 in a 17 L closed chamber. The AP (Bi 5.3 -P25) exhibits superior performance against 10 ppm H 2 S in dry air under dark conditions (i.e., without light irradiation), with a removal efficiency (X H2S)= 99% in 5 mins, reaction kinetic rate (r (at X = 10%))= 7.3 mmol h−1g−1, and partition coefficient= 0.18 mol kg−1 Pa−1. As such, its superiority is evident over the reference AP (P25) filter with X H2S < 10%. The clean air delivery rate (CADR) of AP (Bi 5.3 -P25) increases noticeably from 9.9 to 17.8 L min−1 with increasing relative humidity (RH) from 0 to 80%, respectively. In contrast, the CADR decreases from 9.9 to 5.8 L min−1 as the H 2 S increases from 10 to 20 ppm. According to density functional theory (DFT), the presence of H 2 O vapor enhances the hydroxylation of Bi x -P25 surface to promote H 2 S mineralization through the formation of TiS 3 (i.e., thermodynamic reaction of S atom with the catalytic surface). Complete removal of H 2 S on the Bi 5.3 -P25 surface is also confirmed consistently through gas chromatography-mass spectrometry (GC-MS), in-situ diffuse reflection infrared spectroscopy (in-situ DRIFTS), and elemental analysis (EA). This work represents the first utilization of Bi x -P25 materials fabricated on an AP platform toward the desulfurization of H 2 S at room temperature (RT). The practical utility of Bi x -P25 is overall validated by its eminent role in reactive adsorption and catalytic oxidation (RACO) of H 2 S from the air. [Display omitted] • Air purifiers (AP) are useful to improve indoor air quality, health safety, and life quality. • The utility of AP (Bi x -P25) is validated for reactive adsorption and catalytic oxidation (RACO) of H 2 S under varying conditions. • The combination of Bi and P25 synergistically improves Bi x -P25 surface reactivity against H 2 S. • H 2 O vapor enhances the RACO of H 2 S onto AP (Bi x -P25) by hydroxylating the surface and facilitating the dispersion of Bi active sites for catalysis. [ABSTRACT FROM AUTHOR]

An air curtain machine is used in the entrances and exits of public places where air conditioners are used. The high-speed centrifugal or axial fan blows out the air, creating an airflow barrier to prevent air convection inside and outside, reducing air conditioning losses, and maintaining the indoor air quality by preventing dust, insects, and harmful gases from entering the room. Observation of the airflow behavior was conducted using CFD simulation, to explore whether it has a blocking effect, and the air curtain principle was applied to the air purification equipment. It is mainly composed of several rows of arrayed hole air outlets to form a multi-composite air wall. The airflow on the two sides, or below, can be blocked by the composite air wall and integrated into the main airflow, so that the air walls will not affect each other, and form a barrier effect to prevent infection. This research includes the measurement of impedance characteristics for three layers of filters made of different materials. These filters are used as the input characteristic parameters in the simulation analysis. Four scenarios are discussed, including the consultation room, hospital ward, quarantine station, and conference room. From the simulation results, it is known that when there are many people, the equipment can be set to high speed to increase the volume of air, forming a wind wall to effectively block airflow from the people in the chairs, reducing the risk of infection. Note that the rotation speed should not be too high. The air outlet equipment is susceptible to turbulent flow, which will make the airflow deviate from the expected direction and increase the possibility of mutual infection between adjacent people. Partitions can be used to block airflow to reduce the risk of infection. [ABSTRACT FROM AUTHOR]

One of the most widely available technologies to clean the air in homes of particulate matter of less than 2.5 µm in diameter (PM2.5), known to have negative health impacts, are portable home air purifiers (HAPs). This paper presents research which (1) explored the effectiveness of HAPs in real-world conditions in 57 homes in three European cities; (2) examined if HAPs affect users' perceptions of the indoor air quality (IAQ) at home; and (3) considered the motivations for occupants' operation of HAPs. Results from this study found that PM2.5 concentrations in bedrooms were reduced by 45% to 69%; perceptions of IAQ were not correlated with measured high PM2.5 levels; occupants reported the HAPs to have a 'cooling' effect, which may explain why the predominant driver of HAP use was thermal comfort, rather than IAQ, in all three cities. The latter finding was supported by a statistically significant increase in the probability of HAP use with increasing indoor temperatures. If the operation of HAPs can be managed, or fully automated, to reflect indoor air pollution levels rather than thermal conditions, better pollutant reduction would be feasible and their use to reduce PM2.5 may help mitigate the negative health effects of exposure whilst at home. [ABSTRACT FROM AUTHOR]

Indoor PM2.5 must be effectively controlled to minimize adverse impacts on public health. Cooking is one of the main sources of PM2.5 in residential areas, and indoor air quality (IAQ) management methods such as natural and mechanical ventilation, range hood, and air purifier are typically used to reduce cooking-generated PM2.5 concentrations. However, studies on the combined effects of various IAQ management methods on indoor PM2.5 reduction and energy consumption are limited. In this study, a theoretical model was established to estimate the performance of various IAQ management methods for controlling indoor PM2.5 concentrations and energy consumption. The model was verified by comparative experiments in which, various IAQ management methods were operated individually or combined. Seasonal energy consumption was calculated through the verified model, and energy consumption saving scenarios were derived for maintaining indoor PM2.5 concentrations less than 10 μg/m3, a World Health Organization annual guideline, under fair and poor outdoor PM2.5 concentrations of 15 and 50 μg/m3, respectively. Based on our results, we found that energy consumption could be reduced significantly by applying natural ventilation in spring, autumn, and summer and mechanical ventilation in winter. Our study identified efficient energy saving PM2.5 management scenarios using various IAQ management methods by predicting indoor PM2.5 concentration and energy consumption according to the annual life patterns of typical residents in South Korea.

The indoor air quality in public transport systems is a major concern in South Korea. Within this context, we investigated the effect of air purification systems on the indoor air quality of intercity buses, one of the most popular transport options in South Korea. Air purifiers were custom designed and equipped with high-efficiency particulate air (HEPA) filters to remove particulate matter and ultraviolet light-emitting diodes (UV-LEDs) to remove airborne bacteria. To investigate the effectiveness of the air purification systems, we compared concentrations of particulate matter (PM2.5 and PM10), airborne bacteria, and carbon dioxide (CO2) in six buses (three with air purification systems and three without) along three bus routes (BUS1, BUS2, BUS3) in Gyeonggi Province, South Korea, between 6 April and 4 May 2021. Compared to the buses without air purification, those with air purification systems showed 34–60% and 25–61% lower average concentrations of PM2.5 and PM10, respectively. In addition, buses with air purification systems had 24–78% lower average airborne bacteria concentrations compared to those without air purification systems (when measured after 30 min of initial purification).

The most recent research confirms that airborne transmission may be the dominant mode of SARS-CoV-2 virus spread in the interior spaces of buildings. Consequently, based on some prescriptions that implemented natural ventilation during face-to-face lessons in a university centre, an experimental characterization of several complementary options aimed at reinforcing the prevention and safety of the occupants was carried out. The action protocol adopted was based on the combination of mandatory natural ventilation, a maximum contribution of outdoor air supply in the air conditioning system, and the use of filtering devices located inside the classroom. All the strategies were incorporated concomitantly with necessary compliance with the basic conditions of social distance, occupation, use of masks and guidelines for use and cleaning within educational buildings. The suitability of this protocol was further evaluated throughout the teaching day with students and teachers by measuring the CO2 concentration. The results showed that the measures implemented successfully removed the possible pollutants generated inside.

An innovative vacuum ultraviolet photocatalytic oxidation (VUV-PCO) air purifier, consisting of a photocatalytic unit bearing nanoporous TiO 2 film, an ozone removal unit bearing Mn-Fe catalyst and a radial fan, was designed and constructed. The performance of the VUV-PCO air purifier in simultaneous elimination of VOCs and O 3 by-product was, for the first time, evaluated in a sealed actual room. The evaluation was conducted in both intermittent on/off and continuous operations. The results illustrated that the air purifier had high efficiency in removing formaldehyde and moderate efficiency in removing benzene, toluene, ofm-xylene, ortho-xylene, pentanal, octanal and nonanal, which were released from particleboard into the sealed room. During the removal of formaldehyde decomposition and TVOC in intermittent three-time on/off operation, the air purifier exhibited good stability. During the operation without heating, the air purifier had high formaldehyde and TVOC removal efficiencies, reaching values of about 48.00% and 78.71%, respectively after 90 min. During the continuous operation, the air purifier was able to continuously and effectively remove formaldehyde, benzene homologues, aldehyde and ketone compounds, while the ozone removal unit was able to effectively eliminate ozone generated during VUV photocatalysis. The removal of TVOC by 38.25% was reached after 240 min. In addition, heating the ozone removal unit was found to not only accelerate the release of VOCs from particleboard, but also promote the decomposition of ozone. The ozone removal unit operated with heating was able to reduce ozone content from 250 to 75 ppb. [ABSTRACT FROM AUTHOR]

Many indoor air pollutants have been demonstrated to have a negative impact on occupants and due to physiological and behavioural differences, young children are more vulnerable to these effects than adults. Millions of children in the UK spend large parts of the day in nurseries, where occupant density is high, and indoor air quality can be poor. Therefore, it is imperative to understand the quality of indoor air in nurseries and how to improve it. The aims of the research presented here were to explore the indoor air quality (IAQ) in nurseries and the impact of both the use of air purifiers and window operations on IAQ. Three nurseries in London were selected and monitored via both continuous air quality sensors and passive sampling covering a total of 21 pollutants. Key findings include that mean reduction rate of PM 2.5 by using air purifier was 63% with window closed, and 46% with window open. The results also highlight the impacts of operational changes implemented during the Covid-19 pandemic. Windows were operated more frequently for ventilation needs rather than being driven by temperature alone. The increased ventilation in the monitored nurseries in London led to low levels of VOCs and aldehydes (except for formaldehyde and 2-ethylhexanol) but could bring thermal discomfort to occupants. Both temperature and noise levels were shown to be relevant factors impacting the operation of air purifiers. Air purifiers can be effective at reducing PM 2.5 when combined with proper window operation and have potential to bring substantial health benefits. • Mean reduction rate of PM 2.5 by using air purifier was 63% with window closed, and 46% with window open. • Windows were operated more frequently for ventilation needs rather than being driven by temperature during COVID-19. • The increased ventilation led to low levels of VOCs and aldehydes but could bring thermal discomfort in some circumstance. • Both temperature and noise levels were shown to be relevant factors impacting the operation of air purifiers. • Air purifiers can be effective at reducing PM 2.5 indoors when combined with proper window operation. [ABSTRACT FROM AUTHOR]

PM2.5 has negative impact on human health. Although air purifiers can remove indoor PM2.5 effectively, occupants do not use them well to achieve best performance. It is important to develop automatic control strategy for air purifiers to achieve both indoor air quality and energy efficiency. As traditional air purifier control strategy cannot adapt to the stochastic behavior of residents such as PM2.5 emissions and occupants' window behavior and result in superfluous energy consumption, this study uses the deep reinforcement learning (DeepRL) approach to automatically control the air purifier, which provide better indoor air quality with lower energy consumption. To make the DeepRL applicable in real daily life, we first develop a stochastic model based on measured indoor air quality data, which is able to simulate the indoor PM2.5 process in real time. To improve the energy efficiency of air purifier under this condition, we further trained DeepRL approach to control the air purifier under the simulated PM2.5 process. By virtue of adaption to the stochastic environmental parameters, RL strategy can make the best fit decision in advance to achieve more stable control effect. Comparing to the baseline strategy, both RL-1 and RL-2 show significant improvement in energy efficiency. In specific, RL-1 strategy could reduce 43.7% energy consumption with basically the same indoor PM2.5 concentration level in the best-IAQ scenario, and RL-2 strategy could reduce 40.6% energy consumption and 25.6% frequency of indoor PM2.5 concentration exceed WHO air quality guideline. Thus, it has better comprehensive control performance in the general-IAQ scenario. • We developed a stochastic room model to describe indoor IAQ process. • RL-1 saves air purifier energy by 43% with the same indoor PM2.5 concentration level. • RL-2 saves energy by 40.6% and reduces average indoor PM2.5 concentration by 3.7%. • RL adapts to the stochastic environmental parameters and achieve a better control effect. [ABSTRACT FROM AUTHOR]

Exposure to diesel combustion particles is known to cause and exacerbate respiratory conditions, including asthma. High efficiency particulate air (HEPA) purifiers can provide health benefits by reducing concentrations of these particles. National standards call for air purifiers to be tested using tobacco smoke, as well as aerosolized dust, pollen, and potassium chloride (KCl) particles. Little is known about the efficiency of HEPA air purifiers against diesel particles. Previous studies performed with respirator filters have shown higher penetration of combustion generated particles compared to standard test particles. Within a controlled laboratory setting, we compared the Clean Air Delivery Rate (CADR) of six models of air purifiers with diesel and KCl particles, and measured noise during operation. CADR was determined for total concentration and size-selectively for particles of 0.03–1 μm. Lowest CADRs were consistently found for particles <0.1 μm. Results showed significant differences between CADRs obtained with diesel and KCl aerosols. This was found for CADRs calculated from total concentration data as well as from size-selective data. Unexpectedly, CADR for diesel exceeded the one for KCl particles indicating lower penetration of diesel particles through the HEPA filter. It was concluded that KCl particles may underestimate the actual CADR against diesel particles. The measurements of noise levels produced by the tested air purifiers revealed a low positive association between noise and CADR (r 2 = 0.55). Thus, both noise and CADR should be considered when selecting an air cleaner. [ABSTRACT FROM AUTHOR]

This work assessed the potential impact on mortality and life expectancy that would occur due to reductions of indoor PM 2.5 in dwellings in the UK using portable air purifiers. Reductions in indoor PM 2.5 concentrations from air purifier use were modelled using findings from the literature for mean air purifier efficiency, mean indoor PM 2.5 concentrations associated with air purifier use, and the relative risks associated with exposure. Life-table models were used to estimate changes to mortality from the following PM 2.5 -associated diseases: lung cancer, lower respiratory infection (LRI), chronic obstructive pulmonary disease (COPD), ischemic heart disease (IHD), and stroke. Different scenarios were modelled to represent a range of daily use patterns, the starting age of use and the duration of the intervention. The overall impact of the central scenario, in which air purifiers were used during all hours whilst at home (15.6 h) for the entirety of the modelled period (birth to 97 years), was to increase life expectancy in the birth cohort by, on average, 138 and 120 days for males and females, respectively, and to add more than 23 million years of life (YLG) to the UK population. When used at home, air purifiers reduced indoor PM 2.5 concentrations and prolonged life expectancy, but questions regarding feasibility of the intervention, occupant behaviour and social inequities remain. The estimation of the impact of use by the whole population is, however, important for informing policy and designing interventions. • Portable air purifiers reduce indoor PM 2.5 by approximately 50%. • Reductions in indoor PM 2.5 from air purifiers could add as much as 6 months of life expectancy in the UK. • In residences with inadequate ventilation, air purifiers can be an effective strategy to improve health. [ABSTRACT FROM AUTHOR]

Particulate matter (PM) samples were collected from inside ten childcare centers, and from their adjacent outdoor environments in Seoul, Korea during the summer, autumn and winter seasons. The concentrations and distribution of microbial size of the airborne bacteria and fungi in bio-aerosols were also investigated. The average indoor concentrations of fine particles less than 2.5 μm (PM 2.5 ) in the residential areas ranged from 37.1 μg/m 3 (±5.8 μg/m 3 ) to 45.2 μg/m 3 (±5.3 μg/m 3 ), while indoor PM 2.5 concentrations in centers with roadways nearby ranged from 48.9 μg/m 3 (±9.5 μg/m 3 ) to 52.9 μg/m 3 (±7.7 μg/m 3 ), and up to 51.1 μg/m 3 (±6.4 μg/m 3 ) in residential areas located near construction sites. The concentrations of particulate matter indoor in childcare centers were correlated with the corresponding outdoor locations, in residential areas ( R 2 of 0.64 for PM 10 and 0.66 for PM 2.5 ), near roadways ( R 2 of 0.72 for PM 10 and 0.76 for PM 2.5 ), and near construction areas ( R 2 of 0.45 for PM 10 and 0.62 for PM 2.5 ). The distribution of bio-aerosols showed that 69.4% to 78.1% of the airborne bacteria in the outdoor environments existed in stages 1–3 (over 3.3 μm), while from 59.2% to 78.6% existed in stages 2–4 (2.1–7.0 μm) inside the childcare centers. When the efficiency of air purifiers was compared with the location and characteristics of the indoor of child care centers, the removal efficiency of particulate matter with new data that may characterize indoor air quality. [ABSTRACT FROM AUTHOR]

Nitrogen dioxide ( NO2), a by-product of combustion produced by indoor gas appliances such as cooking stoves, is associated with respiratory symptoms in those with obstructive airways disease. We conducted a three-armed randomized trial to evaluate the efficacy of interventions aimed at reducing indoor NO2 concentrations in homes with unvented gas stoves: (i) replacement of existing gas stove with electric stove; (ii) installation of ventilation hood over existing gas stove; and (iii) placement of air purifiers with high-efficiency particulate air ( HEPA) and carbon filters. Home inspection and NO2 monitoring were conducted at 1 week pre-intervention and at 1 week and 3 months post-intervention. Stove replacement resulted in a 51% and 42% decrease in median NO2 concentration at 3 months of follow-up in the kitchen and bedroom, respectively ( P = 0.01, P = 0.01); air purifier placement resulted in an immediate decrease in median NO2 concentration in the kitchen (27%, P < 0.01) and bedroom (22%, P = 0.02), but at 3 months, a significant reduction was seen only in the kitchen (20%, P = 0.05). NO2 concentrations in the kitchen and bedroom did not significantly change following ventilation hood installation. Replacing unvented gas stoves with electric stoves or placement of air purifiers with HEPA and carbon filters can decrease indoor NO2 concentrations in urban homes. [ABSTRACT FROM AUTHOR]