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Formaldehyde, a common indoor air pollutant emitted from building decoration materials, poses a significant health hazard, potentially leading to cancer. Therefore, developing a gas sensor capable of real-time monitoring of indoor formaldehyde concentration is essential. Herein, a metal oxide semiconductor gas sensor with SnO 2 /Zn 2 SnO 4 hybrid structure as the sensitive material has been successfully fabricated. The sensor exhibits the ability to detect formaldehyde down to 50 ppb, meeting the safety concentration limit proposed by the World Health Organization (WHO). Additionally, it displays rapid response characteristics, with a response time of 84 s and a recovery time of 46 s for 50 ppb of formaldehyde at 200 °C, respectively. Moreover, the sensor demonstrates good selectivity and long-term stability, making it promising for real-time monitoring of indoor air pollutants. Furthermore, the evolution process of intermediates in the sensing reaction was investigated by in-situ diffuse reflaxions infrared fourier transformations spectroscopy, providing a comprehensive understanding of the surface chemistry. This in-depth comprehension offers valuable insights into the mechanisms underlying formaldehyde sensing. • SnO 2 /Zn 2 SnO 4 hybrid structure was prepared by a simple hydrothermal method. • The gas sensor showed high response and fast detection of formaldehyde. • The gas sensor exhibits the ability to detect formaldehyde down to 50 ppb. • Evolution process of intermediates was investigated by in-situ DRIFTs. [ABSTRACT FROM AUTHOR]

As a climate-responsive building, the building integrated heat pipes (BIHP) can greatly improve the indoor thermal environment during the local heating season, utilizing the thermal diode characteristic and ultrahigh equivalent thermal conductivity of the L-shaped flat gravity heat pipe. The thermophysical properties of the internal envelope greatly influence the heating effect, and the utilization potentiality of BIHP varies in locations with diverse climate resources. In this paper, the utilization effects of BIHP at 61 locations in severe cold and cold regions of China are investigated. Improved backtracking search and particle swarm optimization are used to obtain the optimal heating effect and the corresponding thermophysical properties of the internal envelope at zero-carbon heating locations and non-zero-carbon heating locations, respectively. The relationship between the improvement degree of thermal discomfort and the solar radiation over temperature difference is studied, and the utilization potentiality map and zoning of BIHP are obtained. This study is of great significance for promoting the application of climate-responsive BIHP to effectively and efficiently utilize solar energy to reach zero-carbon heating. • Proposes improved backtracking search for zero-carbon heating solution set of BIHP. • Obtains zero-carbon heating solution set of interior envelope thermal properties. • Obtains relationship between RRTD and IDTD for heating effect pre-evaluation. • Obtains application potential map of BIHP in severe cold and cold regions of China. • Proposes three zones of application effect of BIHP based on RRTD. [ABSTRACT FROM AUTHOR]

The techniques capable of accurately and effectively detecting low-concentration volatile organic compounds (VOCs) are promising for environmental contaminant monitoring and non-invasive disease diagnosis. However, low-concentration measurement and selective quantification of multiple components are two major challenges for VOC detection. This work proposes the idea of a sensing system that incorporates preconcentration and multiple sensor arrays to address the two challenges. The design principles and strategies of the sensing system were discussed, as well as the key requirements and challenges of each step of the design process. We further developed a goal-oriented, sequential, inverse design method for an accurate sensing system of indoor VOCs, enabling the realization of high cross-selectivity detection. We also demonstrate the potential and feasibility of the sensing system with a preconcentrator through illustrative examples. The proposed system is expected to be scalable and intermittent, moving it closer to reliable, commercial, and portable near real-time determinations of specific VOC concentrations. It would promote the effectiveness of indoor air quality (IAQ) assessments and interventions. [Display omitted] • Sensing system incorporating a preconcentrator and a sensor array is proposed. • Characteristics and challenges of key steps in the sensing system are summarized. • A goal-oriented, sequential, inverse design method is developed for the sensing system. • Examples demonstrate that the proposed system has great potential in VOC detection. [ABSTRACT FROM AUTHOR]

In order to investigate the key factors resulting in the large deviations of the literature-reported PAE partition coefficients on particles, a direct particle sampling and DEHP partition coefficient-detecting method was developed to analyze realistic indoor airborne particles (AirP), Arizona test dust (ATD) and Beijing road dust (BJD). Mechanistic models were developed to determine the partition coefficients. Our results showed that the AirP partition coefficient (K ap) of DEHP was 4.03 × 104 m3/g, and the DEHP absorption in AirP organic matters dominates the sorption capacity. We found that the realistic AirP organic matter components varied from the traditional hypothesis that assumes organic matter is similar to octanol. In contrast, the DEHP partition coefficients (K dust) for ATD and BJD were two orders of magnitude smaller than that of AirP. DEHP adsorption on the inorganic matter was found to be the main sorption mechanism on the surfaces of ATD and BJD. Following an 8-day DEHP exposure, the adhesion forces increased approximately from 4.0 nN to 11.0 nN for AirP and BJD, indicating the formation of organic films. These films could potentially enrich other organic pollutants to generate more hazardous combined pollution. This study provides a direct particle sorption method and more accurate partition coefficients to correctly evaluate DEHP concentrations in airborne particles and settled dust in indoor environments. [Display omitted] • A particle sampling and DEHP partition coefficient-detecting method was developed. • The K ap was measured as 4.03 × 104 m3/g for the practical indoor airborne particles. • Specific surface areas dominated the DEHP adsorption on inorganic road dust. • Organic films were detected on particles and dust during DEHP sorption. [ABSTRACT FROM AUTHOR]

Effective and reliable uptake rates are crucial for applying passive samplers in monitoring gaseous volatile organic compounds (VOCs). However, there is currently a lack of data regarding the 24-h passive uptake rates of VOCs for workplace and environmental monitoring. This study aims to address this gap by utilizing a Tenax TA-based sampling tube to investigate the 24-h uptake rates of 25 kinds of VOCs in enclosed ship cabin environments. The results reveal that the uptake rate of VOCs ranges from 0.32 to 0.44 mL/min. A relationship between diffusive uptake rates and the boiling point of the compounds is proposed. The variation in uptake rate under different sampling durations was examined. The difference in uptake rate between 24 h and 8 h was smaller than that between 24 h and 6 days, with an average difference of 20%. In addition, the indoor uptake rate obtained in this study was compared with the outdoor uptake rates in the literature, and results showed that the outdoor uptake rate was generally higher than the indoor uptake rate, but the difference decreased when the sampling duration was longer. Field measurement was conducted by utilizing the measured uptake rates to characterize VOC pollution in both living and engine cabins in actual ships. This study contributes to facilitating the evaluation of environmental daily average concentrations in enclosed ship cabins, which will be helpful for assessing the effectiveness of air pollution control systems or epidemiological studies in ships. • 24h uptake rates of 25 kinds of VOCs under vessel environment were estimated. • A relationship between diffusive uptake rates and boiling point is proposed. • The difference in uptake rate under different sampling duration can reach 70%. • A field measurement campaign in a real vessel was conducted for VOC characterization. [ABSTRACT FROM AUTHOR]

Exposure to VOCs causes a variety of adverse health effects, with much of the exposure occurring at home during sleep. The use of an air cleaner maybe an effective and convenient way to reduce associated exposures and health risks. Studies about the impacts of air cleaner on VOCs are limited. The main objective of this paper was to assess the inhalation health risks that toxic VOCs present during nighttime sleep and to estimate the removal effectiveness of an indoor air cleaner on these VOCs. Asthmatic children, who are especially vulnerable to the detrimental effects of air pollutants, were recruited and the VOC concentrations in their bedrooms were measured during two periods - once with a true air cleaner and once with a sham air cleaner. Among the toxic VOCs quantified, formaldehyde, acetaldehyde and toluene had the highest concentrations (median: 18.0, 14.0 and 12.1 μg/m³, respectively) in the bedrooms. Health risk assessments were conducted to identify compounds of greatest concern. During nighttime sleep, 7 VOCs presented inhalation cancer risk above the acceptable risk (1 × 10−6), 4 VOCs exceeded the non-cancer risk threshold (1) in most of the homes tested. The results indicate that the use of an air cleaner in residences may lead to significant reductions in VOC concentrations indoors, but even with this reduction, the associated health risks are still of concern. This study highlights the need for reductions in toxic VOCs at home, points to the imminent need for improvements in control of VOC sources. Image 1 • Indoor and outdoor levels and inhalation health risks of toxic VOCs in 20 asthmatic children's homes were analysed. • The contribution of air cleaners on 13 toxic VOCs in asthmatic children's homes were assessed. • Stressed the need to reduce the exposure to toxic VOCs, especially in formaldehyde, acetaldehyde, 1,2-DCP, benzene and 1,4-DCB. [ABSTRACT FROM AUTHOR]

Abstract Traditionally preferred air filtration systems have a large pressure drop, and consequently use energy in building ventilation systems. This study developed an electrostatically assisted metal foam (EAMF) coarse filter. Comparing with electrostatic precipitator (ESP), in an EAMF coarse filter, charged particles go through rather than in parallel to the collecting electrodes and therefore are more likely to be removed from air flow as they are drawn closer to the collecting electrodes. We investigated the influences of material and pore density of metal foam on fraction filtration efficiency of 0.3–10 μm particles, net ozone production, pressure drop and power dissipation of the EAMF coarse filter. We used ambient aerosol in a ventilation duct to perform our experiments. Using 75 ppi nickel foam, the EAMF coarse filter can remove 0.3–0.5 μm particles from ambient air with 78.9% filtration efficiency and 10.8 Pa pressure drop at 0.5 m/s face air velocity. We defined a structural coefficient N s,E = α 1/3/ d f 2/3 to evaluate the theoretical filtration efficiency of the EAMF coarse filter. We proposed that metal foams whose oxide layers have smaller (h o / ε r,o) are more efficient in EAMF coarse filters. We also presented a comprehensive quality factor (CQF) to evaluate the performance of electrostatic particle removal technologies including our EAMF coarse filter. Graphical abstract Image 1 Highlights • We developed an electrostatically assisted metal foam (EAMF) filter. • EAMF filters have efficient filtration efficiency and small pressure drop. • Metal foam with large structural coefficient N s,E = α 1/3/ d f 2/3 is electrostatically efficient. • Oxide layers on metal foams with large h o / ε r,o sharply reduce efficiency. • We present a comprehensive quality factor for evaluating particle removal devices. [ABSTRACT FROM AUTHOR]

To appropriately assess exposure to indoor semi-volatile organic compounds (SVOCs), an accurate relationship considering the non-equilibrium sorption behavior between their gas-phase concentration ( C g ) and particle-phase concentration ( C sp ) is necessary. The reasons are: (1) the equilibrium model frequently used in previous studies may result in significant errors because the time that particles stay in the indoor air is often much shorter than the critical time for C g - C sp equilibrium; (2) several dynamic models developed previously took the mean residence time of indoor airborne particles as the time duration of the mass transfer between SVOCs and particles in the indoor environments, which may obviously reduce their accuracy because residence time varies among individual particles, and the C g - C sp relationship and residence time are not linearly correlated. Therefore, we present a new concept, indoor particle age (the time that airborne particles have spent since entering the room), and develop a “ η -indoor particle age method”: the C sp / C g value can be obtained by multiplying the equilibrium result by a modification factor, η (which is a function of indoor particle age, particle size distribution and the critical time for C g - C sp equilibrium). The η -indoor particle age method can reduce the relative error of the existing methods by 30% to more than 1000%, which is preliminarily supported by the experimental results in the literature. [ABSTRACT FROM AUTHOR]

Efficient particle removal technology with minimal pressure drop is urgently needed for both air purification and energy conservation. We developed a compact electrostatically assisted air (cEAA) coarse filter, whose particle removal performance is enhanced by the synergistic effect of a corona charging field and a polarizing field. We investigated the influences of charging voltage ( U ), polarizing distance ( d pl ), effect of dielectric and geometric characteristics of the filter material on fraction filtration efficiency of PM 0.01∼5 , net ozone production, pressure drop and power dissipation of the cEAA coarse filter. Our experiments were performed in a ventilation duct using ambient air particulate matter. We found an optimal U between the corona charging onset voltage and the polarizing onset voltage that enhances particle filtration efficiency with nearly no net ozone production and low energy consumption. Single pass filtration efficiency for 0.3 μm particles increased from 4% to 69% with U varying from 0 to +9 kV ( d pl  = 3.5 cm). We found that filter material of larger relative dielectric constant or larger tortuosity yields higher filtration efficiencies. During a 458-h long-term operating period, the single pass filtration efficiency of the cEAA coarse filter did not decrease but increased slightly, and the pressure drop grew from 14.3 Pa to 31.5 Pa. We present a design strategy for a cEAA coarse filter with less than 30 Pa pressure drop at 1 m/s air velocity. [ABSTRACT FROM AUTHOR]

The technology of in-situ thermally regenerated air purifiers (TRAP) can effectively recover adsorbents' adsorption capacity, which is promising for low-concentration uncontinuous waste gas treatments in light pollution industries, such as furniture industries and tire factories. This study aims to provide a design model for the adsorption behaviours of the TRAP module under various practical situations in the furniture industry. We propose a dimensionless parameter (the Number of Mass Transfer Units, NTU m) to predict the one-pass efficiency. A TRAP module consisting of multiple flexible and thin adsorption boards was developed to validate the model experimentally. The polluted air with xylene flows through the module and is adsorbed by the boards. When the adsorption boards are saturated, the heating plate will be electrically heated to about 80 °C, releasing xylene from the boards and regenerating their adsorption performance. The modelling results agree with the experimental results., which indicate that the NTU m is a crucial and helpful parameter in enhancing the efficiency of the TRAP module. • A mathematical model was developed to simulate the performance of the TRAP module. • A TRAP module was designed and implemented to validate the model experimentally. • Experimental results indicated that the maximum error of model prediction is 13.3%. • Thermal regeneration can recover the performance of the TRAP module by 90%. [ABSTRACT FROM AUTHOR]

Exposure to indoor formaldehyde has been reported to be relevant to several adverse health effects, especially in occupational exposure scenarios. In this study, a systematic review and meta-analysis has been conducted for epidemiological studies published between January 1980 and December 2017 in order to summarize available evidence and to obtain concentration-response (C-R) relationships between different health outcomes and formaldehyde exposure in residences, offices or schools. We searched four databases to identify the related studies. Finally, we selected 31 studies through the systematic review, and included 23 studies in the meta-analysis. The results show that the pooled odds ratios (ORs) for asthma in children were 1.27 (95% CI: 1.20–1.35) in eastern countries and 1.03 (95% CI: 1.02–1.04) in western countries per 10 μg/m3 increase in formaldehyde concentration. For asthma in adults, the pooled OR was 1.09 (95% CI: 1.03–1.15) per 10 μg/m3 increase of formaldehyde concentration. We did not obtain significant associations of formaldehyde exposure with dermatitis or rhinitis. Our findings provide robust evidences for C-R relationships of formaldehyde exposure in civil buildings for different adverse health outcomes. The obtained C-R relationships can be helpful to estimate the attributable disease burden of indoor formaldehyde exposure. [Display omitted] [ABSTRACT FROM AUTHOR]

Every year, ambient particulate matter (PM) causes more than one million deaths worldwide. Considering that people spend more than 80% of their time indoors, there is an urgent need for efficient air purification in the built environment. Electrostatic forces have been armed with fibrous filters to promote filtration efficiency and avoid large pressure drops leading to large energy consumption, noise problems, and frequent replacements. Here, we summarise the electrostatic-force-strengthened filtration studies with application potentials for indoor PM removal (studies for masks, industrial processes and pollution control are not included), and divide them into three categories according to whether the PM and fibers are charged. Among them, singly-fiber-charged filtration, especially electret filters fabricated by electrospinning, serves in the simplest structure. Synergistically charging both PM and fibers outperforms the singly particle- or fiber-charged filtration, as the PM-fiber Coulombic force is far beyond the dielectrophoresis force. We introduce the working principle for each technology, compare their initial and long-term performance for non-oily particles, oily particles, and bioaerosols, and provide specific research prospects for improving the performance of these technologies. [Display omitted] • Classified and clarified mechanisms of electrostatic effect on PM filtration. • Summarized studies of electrostatic-force strengthened PM filtration. • Concerned experimental studies tested at large air velocity. • Concerned long-term performance and PM holding amount. • Provided some improvements and challenges for future research. [ABSTRACT FROM AUTHOR]

Decoration and refurbishment in homes is associated with rapid urbanization in China. Its popularity has led to indoor elevated levels of benzene, toluene, and xylenes (BTX), posing adverse health effects to occupants. In this study, concentration levels of BTX and associated health risk were investigated in homes with new renovations in urban and suburban areas in Guangzhou, China. All air samples were collected with passive samplers for 24 h exposure in winter 2012. The average concentrations of benzene, toluene, m/p-xylene and o-xylene were 18.5 μg/m3, 173.2 μg/m3, 58.1 μg/m3 and 40.8 μg/m3 respectively, similar to or higher than those reported in previous studies for new homes or recently renovated homes, but generally greater than those measured in old homes. Higher BTX concentrations were observed in urban homes than in suburban homes. The mean incremental lifetime cancer risk induced by inhalation exposure to benzene in newly renovated homes in Guangzhou was 6.8 × 10−6, higher than the acceptable risk level of 1.0 × 10−6 and those estimated for old homes. Taking into consideration the variation in exposure concentration, potency factor and exposure factors, the incremental risk decreased to 4.7 × 10−6. Monte Carlo simulation provides a clearer picture of cancer risk with a range of 1.0 × 10−6–1.2 × 10−5 for the selected population. Results of sensitivity analysis show that the accuracy of risk assessment could be enhanced by specifying the dose–response characterization and increasing the sample size. This study provides representative statistics regarding the BTX exposures and benzene cancer risk in newly renovated homes. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

In-situ thermally regenerated adsorption is superior for the long-term purification of indoor VOCs. In this study, a concrete mathematical model has been built to predict adsorption behaviors in various practical situations. Parametric analyses, including the influences of adsorption kinetic parameters, face velocity, and geometric parameters, were then conducted to optimize the material coating, improve the module's structure, and predict long-term performance. Experiments were conducted on the board prepared with activated carbon. Results show that the predicted adsorption – regeneration behaviors of the adsorption-board module fit well with the experimental data within an error of 10%. Furthermore, the energy consumption of the adsorption board module was compared with that of the conventional packed-bed module. For formaldehyde and xylene, the heating energy consumption per unit of the dimensionless effective purification volume was reduced by 50.7% and 39.6%, respectively. The model provided a technical incentive for indoor VOC purification by selecting adsorbents and designing in-situ thermally regenerated adsorption modules. • Kinetic parameters of adsorption materials were measured and verified. • A mathematical model was built and experimentally validated within 10% error. • Parametric analyses in a whole cycle were conducted to optimize the module. • Adsorption behaviors and energy saving potential were obtained quantitatively. [ABSTRACT FROM AUTHOR]

Fine particulate matter (PM 2.5) pollution is of national concern in China. Indoor PM 2.5 concentrations may contribute significantly to human exposure because people spend most of their time indoors. In this study, we systematically reviewed the level of indoor PM 2.5 concentrations in residences, offices, and schools in China. We looked for corresponding literature published between 1980 and 2019 in six major literature databases and finally obtained 118 articles. We then summarized the spatial distribution of indoor PM 2.5 concentrations in urban and rural areas, analyzed the indoor PM 2.5 concentrations in residences, offices, and schools in urban areas across three time periods, and compared the indoor PM 2.5 concentration levels in the urban and rural areas. It was found that the urban areas considered are mainly distributed in the middle and eastern part of China, while the rural areas are mainly distributed in northeast, north, and southwest China. Indoor PM 2.5 concentrations have decreased significantly in the past decades. The mean ± SD value of indoor PM 2.5 concentration decreased from 127.5 ± 111.4 μg/m³ prior to 2010 to 70.1 ± 35.2 μg/m³ following 2015. The indoor PM 2.5 concentration in rural areas was much higher than that in urban areas. The mean ± SD value of indoor PM 2.5 concentrations in rural residences was up to 275.7 ± 326.4 μg/m³, while that in urban residences was 95.4 ± 71.0 μg/m³. A long-term national indoor PM 2.5 concentration measurement is suggested to obtain a more comprehensive and accurate indoor PM 2.5 concentration level. • 118 articles with measured indoor PM 2.5 concentrations in China were reviewed. • The indoor PM 2.5 concentrations in rural areas exceeded those in urban areas. • Harbin and Lhasa showed the highest and lowest urban concentrations in 2010–2015. • The highest and lowest urban concentrations were in Taian and Changchun after 2015. • Lhasa and Wuwei had the highest and lowest rural concentrations. [ABSTRACT FROM AUTHOR]

Electrostatically assisted air (EAA) coarse filter can improve the particle filtration performance of low efficiency filters without increasing their pressure drop. In this study, we investigated the long-term single pass filtration efficiency for 0.3–10 μm ambient particles, pressure drop, PM 2.5 collecting amount, and energy consumption of an EAA coarse filter during a 51-day operation period. We found that the efficiency of EAA coarse filter varied with average values of 87.6%–97.1% for 0.3–10 μm particles, respectively, while the pressure drop increased from 14.6 Pa to 63.1 Pa at face air velocity of 1 m/s. Using K-means clustering and principal components analysis methods, we discovered that before 33 days, the significant influencing factors of the efficiency for 0.3–0.5 μm particles included air temperature, air moisture content, 3–10 μm particle number concentration, and PM 2.5 collecting amount. While after 33 days, only PM 2.5 mass collecting amount has a significant negative correlation with the efficiency for 0.3–0.5 μm particles. The efficiency became relatively unsteady and the PM 2.5 collecting amount reached 131 g/m2 after 33 days. The total energy consumption of EAA coarse filter rose more slowly as PM 2.5 collecting amount increased when compared with that of a conventional electret filter (KAFPO78A4, Daikin Inc., Japan). We suggest the high efficiency EAA coarse filtration as an energy efficient method for ambient particle removal in the view of its long-term performance. Image 1 • We examined the performance of an EAA coarse filter in a 51-day continuous operation. • PM 0.3~0.5 average efficiency was 87.6% with air resistance of 34.3 Pa at v air of 1 m/s. • Filtration efficiency became unsteady along daytime after 33 days. • T air , d air , C n,up (3–10), and CA acc (PM 2.5) have positive correlations with η (0.3–0.5). • EAA coarse filter is more energy efficient than a conventional electret filter in long-term test. [ABSTRACT FROM AUTHOR]