Major Indoor Air Pollutant Research Articles

Portable temperature-controlled permeation device for the generation of formaldehyde gas standard

Formaldehyde is a major indoor air pollutant. Accurate analysis of airborne formaldehyde is essential for effective monitoring and risk assessment. For many formaldehyde analysis techniques, the accuracy of the results depends on the calibration system. Existing formaldehyde calibration methods often face limitations, such as instability over time or limited concentration range. They also lack practicality for on-field calibration either because of bulkiness or because of high gas consumption. To address these challenges, a device using a paraformaldehyde permeation tube within a custom-built, temperature-controlled system was designed and evaluated.The device weighs less than 3 kg and operates using a nitrogen source. Its low gas consumption (30–100 mL min−1) enables the use of a portable gas cylinder of pure nitrogen (<2 kg) as gas supply. Formaldehyde concentrations ranging from 8.3 to 464 µg/m−3 were successfully generated, demonstrating the device’s versatility. A custom-built high-emission permeation tube could generate concentrations from 5 940 to 49 471 µg/m−3 using the same system. Additionally, the emission rate is independent of the flow rate and follows Antoine’s law with respect to temperature, enabling accurate prediction of concentration in various conditions over the evaluated range and beyond. Furthermore, the study confirms the long-term stability (1 year) of the low-emission paraformaldehyde permeation tube, with emission rates remaining mostly within ± 5 % of the average value for each temperature.The temperature-controlled permeation system approach enabled rapid stabilisation of formaldehyde generation at various concentrations and low flow rates, eliminating the need for additional dilution equipment and facilitating on-site instrument calibration at various gas concentrations. This reliable and efficient portable formaldehyde generator offers a valuable solution for field calibration, providing accurate and stable reference gas for diverse analytical needs.

Exposure to Volatile Organic Compounds May Contribute to Atopic Dermatitis in Adults.

Volatile organic compounds (VOC) are major indoor air pollutants. Previous studies reported an association between VOC exposure and allergic diseases. Here, we aimed to explore the relationship between VOC exposure and atopic dermatitis (AD) in adults. We prospectively enrolled 31 adult AD patients and 11 healthy subjects as controls. Urine metabolite levels of VOCs, including 1.3-butadiene, acrylamide, benzene, toluene, and xylene, were all determined with liquid chromatography-mass spectrometry. The relationship between AD and log-transformed urine levels of VOC metabolites were examined using a multivariate linear regression model adjusted for age and sex. We also treated mouse bone marrow-derived cells (BMMCs) with 1,3-butadiene and toluene and measured the release of β-hexosaminidase. Our results demonstrated that creatinine-corrected urine levels of N-Acetyl-S- (3,4-dihydroxybutyl)-L-cysteine (DHBMA), N-Acetyl-S-(2-carbamoyl-2-hydroxyethyl)-L-cysteine (GAMA), and N-Acetyl-S-(benzyl)-L-cysteine (BMA) were all elevated in AD patients compared with controls. In a multivariate linear regression model, creatinine-corrected urine levels of BMA (a toluene metabolite) and DHBMA (a 1,3-butadiene metabolite) appeared elevated in AD patients, although statistical significance was not reached after correction for multiple comparisons. In addition, 1,3-butadiene and toluene could stimulate BMMCs to degranulate as much as compound 48/80. Some VOCs, such as 1,3-butadiene and toluene, might be associated with AD pathogenesis in adults.

Experimental study of adsorption characteristic of novel pyrazole-based metal-organic frameworks for volatile organic compounds

Volatile organic compounds (VOCs) are the major indoor air pollutants that affect human health, comfort, and working performance. Sorbent material and adsorption technology are considered to be one of the most effective and economical ways to remove VOCs from indoor air. Among many sorbent materials, metal-organic frameworks (MOFs) have received more and more attention because of their superior performance in capturing a variety of compounds. In this work, the adsorption characteristic of a newly synthesized pyrazole-based metal-organic framework (Al-pda) for different VOCs was investigated. First, the single-pass VOC adsorption rates of Al-pda and activated carbon were tested under different low-concentration VOCs mixture, which is in line with the practical application in the indoor environment. The results showed that Al-pda had an especially high adsorption ability for formaldehyde. The single-pass efficiency of formaldehyde adsorption was up to 89% at the beginning of the test and gradually stabilized at 66%. Compared with activated carbon, Al-pda had significantly higher selectivity and adsorption efficiency for the capture of formaldehyde. Then the effect of relative humidity on formaldehyde adsorption was investigated. After increasing the relative humidity from 15% to 65%, Al-pda’s formaldehyde single-pass adsorption rate almost remained at a similar level. Preliminary research showed that Al-pda is a promising material for the selective adsorption of indoor formaldehyde under humid conditions. More work is needed to probe this new MOF’s adsorption mechanism and application method.

A psycho-social-environmental lens on radon air pollutant: authorities', mitigation contractors', and residents' perceptions of barriers and facilitators to domestic radon mitigation.

Radon is a major indoor air pollutant that poses a significant risk of lung cancer to those exposed in their homes. While mitigation of high radon levels in homes has been shown to be effective, home mitigation rates remain low. This study examines the barriers and facilitators to radon mitigation in homes from the perspectives of authorities responsible for radon risk management, the mitigation industry (contractors), and residents in four European countries (Belgium, Ireland, Slovenia, and the UK) with high radon risks and low mitigation rates. A multi-method approach was used to gather data from various stakeholders, including online surveys, content analysis of legal documents, group interviews, workshops, and focus groups. Authorities, contractors, and residents identified various facilitators to radon mitigation, including legal requirements for mitigation, awareness campaigns, low mitigation costs, availability of financial support, accreditation of mitigation contractors, and a perception of radon as a health threat. However, barriers to mitigation were also identified, such as a lack of awareness, fragmented mitigation processes, and inadequate communication between stakeholders. The study highlights the complexity of the radon mitigation process and suggests that interventions aimed at increasing mitigation rates should target stakeholders beyond just residents, such as constructors, health professionals, and policy makers. An integrated approach to radon mitigation, from policy to provision, is necessary to effectively lower levels of this indoor air pollutant.

Performance and Mechanism of Chlorine Dioxide on BTEX Removal in Liquid and Indoor Air.

With the development of the chemical industry, benzene, toluene, ethylbenzene, and xylene (BTEX) have gradually become the major indoor air pollutants. Various gas treatment techniques are widely used to prevent the physical and mental health hazards of BTEX in semi-enclosed spaces. Chlorine dioxide (ClO2) is an alternative to chlorine as a secondary disinfectant with a strong oxidation ability, a wide range of action, and no carcinogenic effects. In addition, ClO2 has a unique permeability which allows it to eliminate volatile contaminants from the source. However, little attention has been paid to the removal of BTEX by ClO2, due to the difficulty of removing BTEX in semi-enclosed areas and the lack of testing methods for the reaction intermediates. Therefore, this study explored the performance of ClO2 advanced oxidation technology on both liquid and gaseous benzene, toluene, o-xylene, and m-xylene. The results showed that ClO2 was efficient in the removal of BTEX. The byproducts were detected by gas chromatography-mass spectrometry (GC-MS) and the reaction mechanism was speculated using the ab initio molecular orbital calculations method. The results demonstrated that ClO2 could remove the BTEX from the water and the air without causing secondary pollution.

Indoor Volatile Organic Compounds: Concentration Characteristics and Health Risk Analysis on a University Campus.

Volatile organic compounds (VOCs) are major indoor air pollutants that contain several toxic substances. However, there are few studies on health risk assessments of indoor VOCs in China. This study aimed to determine the concentration characteristics of VOCs on college campuses by collecting VOC samples from different locations on campus during different seasons combined with the exposure times of college students in each location obtained from a questionnaire survey to assess the possible health risks. The highest total VOC concentration (254 ± 101 µg/m3) was in the dormitory. The seasonal variation of TVOC concentrations was related to the variation of emission sources in addition to temperature. Health risk assessments of VOCs were evaluated using non-carcinogenic and carcinogenic risk values, represented by hazard quotient (HQ) and lifetime cancer risk (LCR), respectively. The non-carcinogenic risks at all sampling sites were within the safe range (HQ < 1). Dormitories had the highest carcinogenic risk, whereas the carcinogenic risk in the other three places was low (with LCR < 1.0 × 10-6). Moreover, 1,2-dichloroethane was identified as a possible carcinogenic risk substance in the dormitory due to its high LCR (1.95 × 10-6). This study provides basic data on health risks in different locations on campus and a basis for formulating measures to improve people's living environments.

Overexpression of CcFALDH from spider plant (Chlorophytum comosum) enhances the formaldehyde removing capacity of transgenic gloxinia (Sinningia speciosa)1

Formaldehyde can cause leukemia and nasopharyngeal cancer in humans, and is a major indoor air pollutant. In this study, to improve the ability of flowering plants to purify formaldehyde, we cloned the CcFALDH gene encoding formaldehyde dehydrogenase (FALDH) from the spider plant (Chlorophytum comosum), which encodes 379 amino acids with the alcohol dehydrogenase (ADH) structural domain, and used it to transform the flowering plant gloxinia (Sinningia speciosa). The FALDH activity of transgenic gloxinia was 1.8–2.7 times that of wild-type (WT) with a considerable increase in formaldehyde stress tolerance. The activities of the antioxidant enzymes SOD, POD, and CAT of transgenic gloxinia were 1.5–2.0 times those of the WT under formaldehyde stress; H2O2, O2−, and MDA contents were markedly lower than those in WT. Liquid formaldehyde and gaseous formaldehyde were metabolized at 2.1–2.8 and 2.1–2.7 times higher rates in transgenic gloxinia than in WT. Our findings indicate that overexpression of CcFALDH can enhance the capacity of flowering plants to metabolize formaldehyde, which provides a new strategy to tackle the indoor formaldehyde pollution problem.

Toxicokinetics of Major Anthropogenic Indoor Air Pollutants and Their Effects on Human Health: A Review of Literature

Research studies have shown that about 90% of the time is spent in indoor environments (homes, hospitals, schools, offices, restaurants and subways). During the past decade, many studies have been conducted to assess indoor air quality in school environments. A large number of indoor air pollutants have been measured including volatile organic compounds, nitrogen oxides, sulphur dioxide, carbon dioxide, carbon monoxide, bioaerosols and particulate matters. In most low and medium-income countries, biomass fuel-based cooking and heating is considered to be a significant source of the household as well as ambient air pollution formaldehyde from clipboard and hydrocarbons from paints, cleaners and furnishings (anthropogenic sources). A wide range of acute and chronic diseases are now associated with exposure to air pollution, starting from diabetes mellitus, declining cognitive functions, and obstructive pulmonary diseases, haematopoietic diseases, to cardiovascular disease.

Adsorption of gaseous formaldehyde on Y zeolites and on metal-organic frameworks

Formaldehyde is a known carcinogen and a major indoor air pollutant, which has led the authorities to regulate its levels in the air. To reduce indoor airborne concentrations, several strategies can be adopted, namely the reduction of emissions or the elimination of this pollutant by different depollution processes. Among them, adsorption on highly porous solid materials remains one of the most efficient strategy.This study aims to provide experimental data on formaldehyde adsorption capacity over different microporous materials at realistic levels (∼164 ppb), being representative of the performance of the investigated materials in a real environment. For that purpose, gaseous formaldehyde breakthrough experiments were performed under laboratory-controlled conditions over several porous solids: focusing on cation-exchanged zeolites and metal-organic frameworks (MOFs). These materials were fully characterized in terms of textural and structural properties.Cu-based MOFs acted as more promising HCHO adsorbents than zeolites, exhibiting at least one order of magnitude higher adsorption capacity under realistic indoor conditions. Among MOFs, SUM-102 (Strasbourg University Material) exhibited the highest surfacic adsorption capacity (0.52 μg HCHO m−2), yielding more than 1 kg HCHO adsorbed per m3sorbent being superior to the zeolite family by at least one order of magnitude.

Potential Sources, Formation Routes, and Health Effects of Nitrogen Dioxide (NO2) on Indoor Air Quality, Human Health, Safety, and the Environment: A Review

Since human beings spend 80-90% of the day inside houses, educational and recreation centers, office blocks, or automobiles, the quality of air within these buildings or structures is crucial for human health and safety. Hence, indoor air quality (IAQ) highlights the general characteristics of indoor air that affect the state of health, thermal comfort, and well-being of humans. Despite numerous regulatory standards, framework policies, and monitoring plans proposed for IAQ, the occurrence of indoor pollutants including radon (Rn), ozone (O3), and oxides of carbon, sulfur, and nitrogen have become common. Many studies contend that nitrogen dioxide (NO2) is a major indoor air pollutant and one of the most poisonous on Earth. It is a reddish-brown gas generated from the oxidation of nitrogen oxides (NOx) and molecular oxygen or O3 or the high-temperature combustion of solid fuels. This paper presents an overview of the potential sources, formation routes, and health effects of NO2. According to reviewed literature, the occurrence, concentrations, and ratios of NO2 in the indoor environment are affected by residential factors, weather/climate, and proximity to NO2 sources indoors, such as burners, ovens, and stoves. Furthermore, long-term exposure to NO2 causes diabetes, heart, cardiovascular, hypertension diseases, severe cough, hemoptysis, pediatric lung edema and, more recently, fatalities arising from COVID-19. Therefore, the overdependence on polluting fuels that generate NO2 must be minimized or eliminated to improve IAQ and protect human health, safety, and the environment. Future design plans for constructing kitchens, homes, offices, automobiles, factories, and power plants must incorporate smart sensors or ventilation systems for detecting, monitoring, or removal of exhaust gases, including NO2.

Synergetic Molecular Oxygen Activation and Catalytic Oxidation of Formaldehyde over Defective MIL-88B(Fe) Nanorods at Room Temperature.

Defective MIL-88B(Fe) nanorods are exploited as exemplary iron-bearing metal-organic framework (MOF) catalyst for molecular oxygen (O2) activation at ambient temperature, triggering effective catalytic oxidation of formaldehyde (HCHO), one of the major indoor air pollutants. Defective MIL-88B(Fe) nanorods, growing along the [001] direction, expose abundant coordinatively unsaturated Fe-sites (Fe-CUSs) along extended hexagonal channels with a diameter of ca. 5 Å, larger enough for the diffusion of O2 (3.46 Å) and HCHO (2.7 Å). The Lewis acid-base interaction between Fe-CUSs and accessible HCHO accelerates the FeIII/FeII cycle, catalyzing Fenton-like O2 activation to produce reactive oxidative species (ROSs), including superoxide radicals (•O2-), hydroxyl radicals (•OH), and singlet oxygen (1O2). Consequently, adsorbed HCHO can be oxidized into CO2 with a considerable mineralization efficiency (over 80%) and exceptional recyclability (4 runs, 48 h). Dioxymethylene (CH2OO), formate (HCOO-) species, and formyl radicals (•CHO) are recorded as the main reaction intermediates during HCHO oxidation. HCHO, H2O, and O2 are captured and activated by abundant FeIII/FeII-CUSs as acid/base and redox sites, triggering synergetic ROS generation and HCHO oxidation, involving cooperative acid-base and redox catalysis processes. This study will bring new insights into exploiting novel MOF catalysts for efficient O2 activation and reliable indoor air purification at ambient temperature.

(Invited) Development of Pulse-Heated Diaphragm Type MEMS Gas Sensors for Indoor Air Quality Measurement

IntroductionAmid growing concern about indoor air quality (IAQ), MOS type gas sensors for the detection of volatile organic compounds (VOC) are widely used in household appliances such as air purifiers for on-demand control of the appliances depending on VOC concentration in surrounding air. There are also potential demands for gas sensors to be used for mobile applications, with which people can monitor environmental conditions in dwelling or workplaces. However, detection accuracy, power consumption and cost of conventional MOS type gas sensors have not yet reached the level generally required for VOC concentration monitoring by mobile applications. To solve these issues, we have developed a new diaphragm type MEMS gas sensor, and studied their appropriate pulsed heating conditions. This optimized MEMS sensor chip was integrated with an ASIC with built-in temperature and humidity sensors in a SMD package, and its practical performance and mechanical durability were evaluated.Sensor structuresTwo types of MEMS structures were used for this study as shown in Fig.1. Air-bridge type MEMS structure [1] [2] which is being produced on a commercial basis has a square-shaped micro hot plate (MHP) with dimensions of 0.1 x 0.1 mm. Materials of the sensor electrodes and heater are Platinum, and the gas sensing material is Palladium doped Tin dioxide, which is turned into a paste using terpineol as a solvent. The gas sensing material was applied onto the MHP by micro dispenser, and then was calcined at 450°C for 3 hours in an electric furnace. The newly developed diaphragm type MEMS structure has a round shape MHP with 270m diameter which can avoid stress concentration of SiN/SiO2 membrane. Thickness of each layer stacked on the MHP was also optimized to achieve uniform dispersion of internal stress. The same sensing material as above mentioned was applied onto the MHP of the diaphragm type MEMS by screen printing method so that the gas sensing layers are formed in one printing pass on a wafer that produces 74K chips of MHP.MethodIn order to determine the appropriate pulsed heating conditions and thickness of the sensing material, sensor resistances in air (Ra) and in various concentrations of gases (Rg) were measured by using the air-bridge type MEMS sensor. The sensing material was intermittently heated for 100 msec. at several different temperature conditions in a range from 300 ~ 450 °C, and at different heating intervals ranging from 1 ~ 60 seconds. The thickness of gas sensing layer was varied in a range from 20 ~ 50 micro meters. For the diaphragm type MEMS sensor, the sensing material was heated at 430°C for 100 msec. at 1 second intervals.Results and ConclusionsSensing characteristics of the air-bridge type MEMS sensor to toluene and ethanol were investigated at different working temperature as shown in Fig. 2. Response to toluene increased as the working temperature decreased within the range between 350°C and 450°C, suggesting the capability for detecting low concentration toluene below 1 ppm. On the other hand, Response to ethanol within the same temperature range remained largely the same. Toluene and ethanol sensitivities both drastically dropped at 300°C. There were significant differences in toluene response depending on the heating intervals as shown in Fig.3. Response to toluene became smaller as the heating interval was longer. This result implies that a reaction of the gas sensing material with gas was inhibited by water vapor which had adsorbed on the surface of the sensing element during the heater OFF period. As for the effect of sensing material thickness on sensitivity, ethanol sensitivity was relatively more affected by the thickness than toluene. The sensor with the thinnest sensing layer showed the highest ethanol response, especially at a short heating interval.Taking these results into consideration, driving conditions of the diaphragm type MEMS sensor were determined as described above. Its sensing characteristics to various gases were examined as shown in Fig. 4. This sensor showed a particularly large response to m-xylene and hydrogen sulfide which are both among the major indoor air pollutants, and very small response to hydrogen and methane, both of which would work as an interference gas in IAQ measurement if present in ambient air. It was confirmed in parallel that the diaphragm type MEMS sensor with the determined driving conditions has a sufficient mechanical durability under the heater ON/OFF cycle test equivalent to 10 years operation, and the drop test which is required for mobile applications. The diaphragm type MEMS sensor produced by high-efficiency screen printing method was expected to have a capability as a practical solution for mobile IAQ monitoring. In addition, user-friendliness of the sensor was much improved by integrating with ASIC in comparison with conventional type single sensor.

Indoor air quality of 5,000 households and its determinants. Part B: Volatile organic compounds and inorganic gaseous pollutants in the Japan Environment and Children's study

Volatile organic compounds (VOCs) are major indoor air pollutants. Quantification of indoor concentrations of VOCs and identification of factors associated with these concentrations can help manage indoor air quality. This study measured the concentrations of VOCs and inorganic gaseous pollutants in around 5000 households in Japan and utilised a random forest model to estimate these concentrations and identify important determinants. The homes of 5017 randomly selected participants in the Japan Environment and Children's Study (JECS) were visited twice, when the children were aged 1.5 and 3 years. Twelve VOCs and inorganic gaseous pollutants were measured during 7 days by passive samplers. Various factors in these households, including household appliances, building characteristics, cooking styles, use of consumer products, renovation, pets, personal behaviours and ventilation were recorded. A random forest model with recursive feature elimination was utilised to identify factors predictive of VOCs and inorganic gaseous pollutants. Toluene, formaldehyde and acetaldehyde were the dominant indoor VOCs. The 95th percentiles of indoor p-dichlorobenzene concentrations at 1.5 and 3 years were 67 μg/m3 and 71 μg/m3, respectively. Random forest models with coefficients of determination ranging from 0.34 to 0.76 outperformed the traditional linear regression models. Factors associated with indoor VOC and inorganic gaseous pollutant concentrations included their outdoor concentrations, indoor and outdoor temperature and relative humidity, month of the year, hours windows were open, kerosene heater use and times of operation and building age. The results provided basic descriptions of indoor VOCs and inorganic gaseous pollutants in Japan and identified several determinants of these concentrations. These determinants should be considered to maintain indoor air quality. These results can be used in epidemiological assessments of the effects of VOCs and inorganic gaseous pollutants on health in children.

Ambient gamma dose rate as an indicator of geogenic radon potential

Radon is the second cause of lung cancer after smoking, therefore is acknowledged as a major indoor air pollutant. Geogenic radon potential indicates regions where for natural reasons elevated indoor radon levels or elevated probability of their occurrence can be expected. The most common procedure for establishing geogenic radon potential includes measurements of soil permeability and soil gas radon concentrations. These measurements are time-consuming and expensive therefore a limited number of measurements is carried out and their results are extrapolated to the specific area. Our research aimed to analyse the usefulness of ambient gamma dose rate survey to assess radon concentration in the environment and therefore geogenic radon potential. The measurements were carried out on two granite massifs with higher (Karkonosze) and lower (Strzelin) radioactive elements contents. Seasonal variations of atmospheric radon concentrations and ambient gamma dose rates were registered with higher values during warmer and lower during colder seasons. The opposite seasonal variations were observed for soil gas radon concentrations. No distinctive seasonal variations were recorded in results of uranium, thorium and potassium contents in soil measured in situ by the gamma-ray spectrometer. The correlation coefficients were calculated on the base of annual average data. The correlations between ambient gamma dose rate and radon concentration in soil and in the atmosphere were 0.83 and 0.62 respectively, which may suggest that ambient gamma dose rate can be a useful parameter to indicate geogenic radon potential.

Combined exposure to formaldehyde and PM2.5: Hematopoietic toxicity and molecular mechanism in mice

PM2.5 and formaldehyde (FA) are major outdoor and indoor air pollutants in China, respectively, and both are known to be harmful to human health and to be carcinogenic. Of all the known chronic health effects, leukaemia is one of the most serious health risks associated with these two pollutants. To explore the influence and underlying mechanisms of exposure to formaldehyde and PM2.5 on hematopoietic toxicity, we systematically studied the toxicity induced in hematopoietic organs: bone marrow (BM); spleen; and myeloid progenitor cells (MPCs). Male Balb/c mice were exposed to: PM2.5 (20, 160 μg/kg·d) at a dose of 40 μL per mouse or formaldehyde (0.5, 3.0 mg/m3) for 8 h per day for 2 weeks or co-exposed to formaldehyde and PM2.5 (20 μg/kg·d PM2.5 + 0.5 mg/m3 FA, 20 μg/kg·d PM2.5 + 3 mg/m3 FA, 160 μg/kg·d PM2.5 + 0.5 mg/m3 FA, 160 μg/kg·d PM2.5 + 3 mg/m3 FA) for 2 weeks. Similar toxic effects were found in the formaldehyde-only and PM2.5-only groups, including significant decrease of blood cells and MPCs, along with decreased expression of hematopoietic growth factors. In addition, individual exposure of formaldehyde or PM2.5 increased oxidative stress, DNA damage and immune system disorder by destroying the balance of Th1/Th2, and Treg/Th17. DNA repair was markedly inhibited by deregulating the mammalian target of rapamycin (mTOR) pathway. Combined exposure to PM2.5 and formaldehyde led to more severe effects. Administration of Vitamin E (VE) was shown to attenuate these effects. In conclusion, our findings suggested that PM2.5 and formaldehyde may induce hematopoietic toxicity by reducing the expression of hematopoietic growth factors, increasing oxidative stress and DNA damage, activating the ‘immune imbalance’ pathway and suppressing the DNA-repair related mTOR pathway. The hematopoietic toxicity induced by combined exposure of PM2.5 and formaldehyde might provide further insights into the increased incidence of hematological diseases, including human myeloid leukaemia.

Impact of indoor air pollution in nursery and primary schools on childhood asthma

Poor indoor air quality in scholar environments have been frequently reported, but its impact on respiratory health in schoolchildren has not been sufficiently explored. Thus, this study aimed to evaluate the associations between children's exposure to indoor air pollution (IAP) in nursery and primary schools and childhood asthma. Multivariate models (independent and multipollutant) quantified the associations of children's exposure with asthma-related health outcomes: reported active wheezing, reported and diagnosed asthma, and lung function (reduced FEV1/FVC and reduced FEV1). A microenvironmental modelling approach estimated individual inhaled exposure to major indoor air pollutants (CO2, CO, formaldehyde, NO2, O3, TVOC, PM2.5 and PM10) in nursery and primary schools from both urban and rural sites in northern Portugal. Questionnaires and medical tests (spirometry pre- and post-bronchodilator) were used to obtain information on health outcomes and to diagnose asthma following the newest international clinical guidelines. After testing children for aeroallergen sensitisation, multinomial models estimated the effect of exposure to particulate matter on asthma in sensitised individuals. The study population were 1530 children attending nursery and primary schools, respectively 648 pre-schoolers (3–5 years old) and 882 primary school children (6–10 years old). This study found no evidence of a significant association between IAP in nursery and primary schools and the prevalence of childhood asthma. However, reported active wheezing was associated with higher NO2, and reduced FEV1 was associated with higher O3 and PM2.5, despite NO2 and O3 in schools were always below the 200 μg m−3 threshold from WHO and National legislation, respectively. Moreover, sensitised children to common aeroallergens were more likely to have asthma during childhood when exposed to particulate matter in schools. These findings support the urgent need for mitigation measures to reduce IAP in schools, reducing its burden to children's health.

In vivo respiratory toxicology of cooking oil fumes: Evidence, mechanisms and prevention

BackgroundAs cooking is an essential part of people’s daily life, cooking oil fumes (COF) has been recognized as one of the major indoor air pollutant. Mounting epidemiological evidence has indicated that COF exposure is significantly associated with an increased risk of various health effects including lung cancer, but toxicological studies are very limited. ObjectivesWe conduct a systematic study to provide toxicological evidence of COF exposure on the lungs, to examine the underlying toxicological mechanism, and to suggest intervention measures to mitigate this toxicity. MethodsA total 96 female rats were randomly divided into control groups, COF exposure groups (0.2, 2, 20 mg/kg) and vitamin E protection groups, receiving appropriate treatment for 30 days. First we measured airway hyperresponsiveness (AHR) followed by a lung histological analysis to investigate the toxicological effects of COF. We next analyzed the biomarkers of oxidative stress, inflammation, and apoptosis to examine the underlying toxicological mechanism, and finally we investigated the protective effects of vitamin E against the toxicity of COF. ResultsAHR measurement indicated that the airway resistance increased with the COF dose and the lung histological assay showed narrowing of the airway lumen, which provided evidence of the toxicological effects of COF. The biomarkers of oxidative stress (ROS and MDA), pro-inflammation (TNF-α and IL-1β), and apoptosis (NF-κB and Caspase-3) were all significantly increased with COF dose. We observed that above toxicological effects and biomarker levels induced by COF were significantly ameliorated after administration of VE. ConclusionThe toxicity of cooking oil fumes on the lungs is clear from the evidence and mechanism, and can be ameliorated by vitamin E. We suggested that oxidative stress may be primarily responsible for the observed cooking oil fumes-induced toxicity.

On the capture of ultralow-level benzene in indoor environments: Experiments, modeling and molecular simulation

Benzene is one of the major indoor air pollutants, according to the World Health Organization (WHO), and understanding its adsorption and the difference between the adsorption behavior of benzene and water are essential in developing high-performance, water-resistant adsorbents. This paper presents a comprehensive study of benzene adsorption in carbon nano-porous materials by combining high-resolution measurement, modeling and molecular simulation. High-resolution isotherms and isosteric heats of benzene adsorption in two materials, microporous activated carbon fiber (ACF) and micro-mesoporous CMK-3 were provided. It is found that CMK-3 has higher specific adsorption capacity than ACF at very low pressures (<10−3 P/P0), making it a promising adsorbent for benzene capture in indoor environments. The Dubinin – Radushkevich model were used to fit the isotherms over the low-pressure regions. Furthermore, the experimental isotherm and the isosteric heat were analyzed with molecular simulation results, and the emphasis is placed on the behavior at ultralow pressures of benzene, typically found in indoor environments. Suggestion on the evaluation and management of adsorbents in terms of minimizing the impacts of ambient moisture were provided.

(Invited) Development of Pulse-Heated Diaphragm Type MEMS Gas Sensors for Indoor Air Quality Measurement

Introduction Amid growing concern about indoor air quality (IAQ), MOS type gas sensors for the detection of volatile organic compounds (VOC) are widely used in household appliances such as air purifiers for on-demand control of the appliances depending on VOC concentration in surrounding air. There are also potential demands for gas sensors to be used for mobile applications, with which people can monitor environmental conditions in dwelling or workplaces. However, detection accuracy, power consumption and cost of conventional MOS type gas sensors have not yet reached the level generally required for VOC concentration monitoring by mobile applications. To solve these issues, we have developed a new diaphragm type MEMS gas sensor, and studied their appropriate pulsed heating conditions. This optimized MEMS sensor chip was integrated with an ASIC with built-in temperature and humidity sensors in a SMD package, and its practical performance and mechanical durability were evaluated. Sensor structures Two types of MEMS structures were used for this study as shown in Fig.1. Air-bridge type MEMS structure [1] [2] which is being produced on a commercial basis has a square-shaped micro hot plate (MHP) with dimensions of 0.1 x 0.1 mm. Materials of the sensor electrodes and heater are Platinum, and the gas sensing material is Palladium doped Tin dioxide, which is turned into a paste using terpineol as a solvent. The gas sensing material was applied onto the MHP by micro dispenser, and then was calcined at 450°C for 3 hours in an electric furnace. The newly developed diaphragm type MEMS structure has a round shape MHP with 270mm diameter which can avoid stress concentration of SiN/SiO2 membrane. Thickness of each layer stacked on the MHP was also optimized to achieve uniform dispersion of internal stress. The same sensing material as above mentioned was applied onto the MHP of the diaphragm type MEMS by screen printing method so that the gas sensing layers are formed in one printing pass on a wafer that produces 74K chips of MHP. Method In order to determine the appropriate pulsed heating conditions and thickness of the sensing material, sensor resistances in air (Ra) and in various concentrations of gases (Rg) were measured by using the air-bridge type MEMS sensor. The sensing material was intermittently heated for 100 ms at several different temperature conditions in a range from 300 ∼ 450 °C, and at different heating intervals ranging from 1 ∼ 60 seconds. The thickness of gas sensing layer was varied in a range from 20 ∼ 50 μm. For the diaphragm type MEMS sensor, the sensing material was heated at 430 °C for 100 ms at 1 second intervals. Results and Conclusions Sensing characteristics of the air-bridge type MEMS sensor to toluene and ethanol were investigated at different working temperature as shown in Fig. 2. Response to toluene increased as the working temperature decreased within the range between 350 °C and 450 °C, suggesting the capability for detecting low concentration toluene below 1 ppm. On the other hand, response to ethanol within the same temperature range remained largely the same. Toluene and ethanol sensitivities both drastically dropped at 300 °C. There were significant differences in toluene response depending on the heating intervals as shown in Fig.3. Response to toluene became smaller as the heating interval was longer. This result implies that a reaction of the gas sensing material with gas was inhibited by water vapor which had adsorbed on the surface of the sensing element during the heater OFF period. As for the effect of sensing material thickness on sensitivity, ethanol sensitivity was relatively more affected by the thickness than toluene. The sensor with the thinnest sensing layer showed the highest ethanol response, especially at a short heating interval. Taking these results into consideration, driving conditions of the diaphragm type MEMS sensor were determined as described above. Its sensing characteristics to various gases were examined as shown in Fig. 4. This sensor showed a particularly large response to m-xylene and hydrogen sulfide which are both among the major indoor air pollutants, and very small response to hydrogen and methane, both of which would work as an interference gas in IAQ measurement if present in ambient air. It was confirmed in parallel that the diaphragm type MEMS sensor with the determined driving conditions has a sufficient mechanical durability under the heater ON/OFF cycle test equivalent to 10 years operation, and the drop test which is required for mobile applications. The diaphragm type MEMS sensor produced by high-efficiency screen printing method was expected to have a capability as a practical solution for mobile IAQ monitoring. In addition, user-friendliness of the sensor was much improved by integrating with ASIC in comparison with conventional type single sensor.

Differences in purifying and resistance tolerance ability of Scindapsus and Chlorophytum to formaldehyde pollution

Formaldehyde is a major indoor air pollutant, and its removal decreases the health risk of urban inhabitants. Scindapsus and Chlorophytum are indoor plants that have been reported to remove formaldehyde. However, their ability to absorb formaldehyde, their resistance, and their morphological changes in response to formaldehyde absorption have not been reported to date. In this study, both Scindapsus and Chlorophytum were used as test materials and their phenotype, microscopic change, enzyme activity, gene expression, and ability to absorb formaldehyde were investigated in response to formaldehyde stress. The results showed that the ability of Chlorophytum to absorb formaldehyde was stronger than that of Scindapsus; moreover, the expression level of the ADH2 gene in Chlorophytum was significantly higher than in Scindapsus. However, Chlorophytum suffered more severe damage of the leaves than Scindapsus. The superoxide dismutase, peroxidase, and catalase enzyme activities of Chlorophytum were lower than those of Scindapsus in response to formaldehyde absorption. This showed that compared with Scindapsus, Chlorophytum had a strong ability to absorb formaldehyde but a weaker ability to tolerate formaldehyde. Based on these results, to purify formaldehyde pollution from indoor air, it is recommended to use the Chlorophytum. However, regular replacement of these damaged Chlorophytum plants should be implemented to retain a beautiful indoor environment.