Indoor Formaldehyde Concentrations Research Articles

Highly sensitive formaldehyde detection using biomass hydrogel with core-shell structure

The indoor formaldehyde concentration is in trace quantities; however, it considerably deteriorates indoor air quality and poses a serious threat to human health and ecosystems. Since current formaldehyde analyzers are only suitable for high-concentration detection or are expensive, there is a pressing need for an easy-to-use, storable, and highly sensitive formaldehyde detector. In this study, we developed a colorimetric sensing sphere using affordable and eco-friendly sodium alginate as a porous matrix. Polyethyleneimine, a molecule rich in amino groups, and an indicator are embedded in the matrix to create a core-shell structured, responsive porous hydrogel colorimetric sensor for indoor formaldehyde detection. The sensing sphere exhibits high sensitivity and excellent detection limits at a polyethyleneimine to pH agent mass ratio of 23:1, reaching a sensitivity of 0.02 mg/m3 and a detection limit of 0.06 mg/m3. The sensing sphere demonstrates superior selectivity among common indoor pollutants and remains unaffected by temperature (up to 70 ℃) or humidity (20–80 %) changes. Moreover, the core-shell structure of the colorimetric sensor ball addresses the poor stability and storage issues. The core-shell structure resists interference from external environmental changes, offering remarkable stability for 6 months and longer, hence, facilitating easy transportation and storage. The colorimetric sensing sphere is simple, cost-effective, and reliable for ordinary households, thus maintaining the indoor air quality and health of residents.

Performance analysis on a wood-color thermal catalytic Trombe wall in wood buildings

The wood buildings had huge advantages such as high thermal insulation performance and carbon fixation. While the indoor air pollution caused by the release from volatile organic compounds (VOCs) from the artificial boards in wood buildings creates huge threat on human health. Considering architectural aesthetics and solar building-integration principles, this article proposed a novel thermal catalytic Trombe wall with wood-color thermal catalysts that realized heating and air purification. Firstly, the color difference between thermal catalysts and wood board was analyzed. Secondly, the heat and mass transfer model of the wood building with Trombe wall was developed and verified. Thirdly, the thermal and purification performance under different occupancy ratios of Trombe wall to whole wall (RT) and wood species were discussed. The main results were: (1) The color difference between thermal catalysts and wood was 0.97, which was similar and acceptable to meet architectural aesthetics; (2) Compared to ordinary wood building, the indoor temperature increased by 18 ℃ when combined with Trombe wall. The average thermal efficiency, purification efficiency and generated clean air were 26.91 %, 94.34 % and 385.58 m3, respectively. (3) With the increase of RT, the formaldehyde degradation performance and indoor air temperature increased from 73.52 % to 94.34 %, 25 to 38 ℃, respectively. (4) When considering natural running in daytime and forced running in nighttime, more than 90 % of indoor formaldehyde was degraded for five wood boards with different formaldehyde emission rates. The indoor formaldehyde concentration would be below 80 ppb for the release rate of 0.98 and 1.40 mg/L.

Health Risk Assessment of Indoor Formaldehyde Exposure in Facilities for Medically Vulnerable People

A health risk assessment was conducted using indoor formaldehyde concentrations measured during a four-year period from 2019 to 2022 for 322 facilities within Busan Metropolitan City. In the facilities, the average concentration of formaldehyde was 26.7 <i>μg</i>/m3 for general hospitals, 27.4 <i>μg</i>/m3 for nursing hospitals, 17.8 <i>μg</i>/m3for daycare centers, 42.9 <i>μg</i>/m3 for postpartum care centers, and 14.1 <i>μg</i>/m3 for elderly care facilities. As for the health risk of formaldehyde, workers in hospitals, daycare centers, postpartum care centers, and elderly care facilities had ECR (excess cancer risk) values of 3.54 × 10-5, 2.84 × 10-5, 6.84 × 10-5, and 1.86 × 10-5 for CTE (central tendency exposure), respectively. Based on the Busan City ordinance seven out of 322 facilities in this study were found to be non-compliant. When the risk was calculated for individual data according to the exposure of workers in each facility, 303 ECR values (94%) exceeded 1.0 × 10-5. If excess cancer risk is calculated by assuming a gradual change in formaldehyde concentration, the current maintenance standard (70 <i>μg</i>/m3) is insufficient to provide appropriate safety for workers, patients and residents. Therefore, higher stringent values than 50 <i>μg</i>/m3 are required to obtain indoor air quality standards for formaldehyde that meet an ECR of 1.0 × 10-4.

Flushing newly built residential buildings with outdoor air for reducing formaldehyde and VOCs concentrations

ABSTRACT New building construction is often counted as a source of indoor air pollution because of formaldehyde and volatile organic compounds (VOCs) emitted from new building materials, such as furnishings, wood, and finishings. The high levels of formaldehyde and VOCs in the early stage of new buildings could be linked to the negative health effects on occupants. The aim of this study is to examine the impacts of flush-out air flow rate and flush period in reducing formaldehyde and VOCs produced by building materials or furnishing of newly built residential buildings. Field measurements were conducted from September 2016 to August 2018 in nineteen newly built apartments to verify the effectiveness of the flush-out procedure. The field measurements showed that after the flush-out, the indoor concentrations of formaldehyde and VOCs in the newly built samples significantly decreased. The indoor concentrations of formaldehyde and TVOCs were reduced to about 61% and 41% of the initial concentration when the samples were flushed at 0.7ACH for nine days. The results of this study showed that the flush-out for a short term of below two weeks was more effective reducing the emission potential of VOCs than of formaldehyde. When the samples were flushed for more than seven days, the air change rates of the flushing did not significantly influence the reduction of indoor pollutants.

Refinement and predicting formaldehyde concentrations of indoor fabric: Effects of temperature and humidity

Indoor air pollution resulting from volatile organic compounds (VOCs) is a significant health concern, especially formaldehyde. Therefore, predicting indoor formaldehyde concentration is essential for environmental control. In this research, the authors develop a thermal and wet coupling calculation model of porous fabric that considers the influence of different phases of wet components and the coupling effect of heat and humidity on formaldehyde migration. We propose a modified calculation method of the formaldehyde mass transfer characteristic parameters of fabric to obtain the diffusion coefficient D and partition coefficient K. The heat and humidity coupling model and formaldehyde mass transfer model of fabric are simultaneously solved, and the authors analyze the influence mechanism of fabric loading rate, fabric type, temperature, and humidity on indoor formaldehyde mass transfer characteristics. We study the variation trend of fabric formaldehyde mass transfer characteristics coefficient and the temporal and spatial distribution of indoor formaldehyde concentration. The theoretical model is applied to practical problems by pre-evaluating the indoor formaldehyde concentration of decorated residential buildings in typical climate areas of China before occupancy. The authors obtain the variation rule of indoor formaldehyde concentration of residential buildings under typical hot and humid climate conditions, building materials, furniture, and fabrics. To provide theoretical support for indoor environmental control and human health protection.

Au-functionalized MoO3 nanoribbons towards rapid and selective formaldehyde gas sensing at room temperature

The detection of indoor formaldehyde concentration attracted great attention owing to its serious harm to human bodies. Traditional semiconductor formaldehyde sensors are still suffering from high working temperature and slow response and recovery performance. In this work, a room-temperature semiconductor formaldehyde gas sensor with fast response and high selectivity were developed by exploiting the synergistic effect of Au decoration on MoO3 nanoribbons. The metallic Au nanocrystals with size lower than 10 nm were prepared by a chemical reduction method and uniformly distributed on the surface of the [1 0 0] -oriented orthorhombic MoO3 nanoribbons after the surface decoration. The results show that the surface decoration by Au nanoparticles could greatly fasten the response and recovery speed of the sensors at room temperature. Under an optimal composition with Au/Mo atomic ratio of 0.10%, the response and recovery time towards 100 ppm HCHO could be decreased to 4.5 and 3 s. The sample also exhibited high sensitivity and low limit of detection of 1 ppm. Meanwhile, the sensor exhibited highly selective HCHO response with 1–2 magnitude higher sensor response against toluene, ethanal, methanol and acetone. The performance enhancement should be attributed to synergistic effect induced by the surface Au decoration, which not only serves as the catalysts improving the gas adsorption and desorption efficiency, but also introduced additional contribution to the formaldehyde response by forming the metal–semiconductor interface states.

Simulation of Formaldehyde Distribution Characteristics under Different Indoor Conditions and Optimization of Monitoring Methods

The distribution of indoor formaldehyde concentration is affected by many factors, which makes the concentration distribution of formaldehyde in different indoor positions uneven, which has a negative impact on the monitoring accuracy. Firstly, through orthogonal experiment and numerical simulation, it is determined that the airflow organization and the location of pollution source have a great influence on the monitoring accuracy. Further research found that the relative position of the air supply airflow and the pollution source affected the diffusion of formaldehyde in the room. Through Computational Fluid Dynamics(CFD) simulation, the error and correction basis of the monitoring data caused by different monitoring conditions were obtained. Finally, the accurate optimal monitoring position is given by genetic algorithm optimization. In the optimization process of 17 working conditions, 76% of the working conditions only need one sensor and correction, which can make the monitoring effective coefficient λ reach more than 80%, and 24% of the working conditions need two sensors.

Development of a Prediction Model for Subjective Physical Symptoms Induced During Systematic Anatomy Practice Among Medical Students.

To prevent unpleasant symptoms in medical students during systematic anatomy practice, we aimed to develop and validate a model that predicts the likelihood of these symptoms occurring during practice based on risk factors prior to the start of practice. A total of 452 medical students enrolled from 2014 to 2018 were surveyed before and during practice, with questions regarding their sex, psychological status, subjective symptoms, and allergies. The sum of the scores concerning three subjective symptoms related to the eyes and three subjective symptoms related to the nose and fatigue were defined as the "eye-score" and "mask-score," respectively, and a total score of 7 or more was considered symptomatic. A prediction model was developed based on a generalized linear mixed model; the outcome variable in the model was symptoms during practice, and the explanatory variables were indoor formaldehyde concentration during practice, sex, and pre-practice status, such as the students' psychological state, eye-score, mask-score, and the presence of allergies. Five-fold cross-validation was used to assess internal validity and the prediction model was applied to 110 medical students enrolled in 2021 to assess external validity. The sensitivity and specificity by five-fold cross-validation were 0.843 and 0.314 for eye symptoms and 0.847 and 0.432 for mask symptoms. In the external validity assessment, the sensitivity and specificity were 0.889 and 0.207 for eye symptoms and 0.879 and 0.532 for mask symptoms. The prediction model developed in this study can be used in future measures aimed at preventing symptoms in students.

The performance analysis of a novel photocatalytic-thermal-catalytic-photovoltaic-Trombe wall system integrated with compound parabolic concentrator

This paper proposes a novel photocatalytic-thermal-catalytic-photovoltaic-Trombe wall system integrated with compound parabolic concentrator (CPC/PTCPV-TW), which can make full use of outdoor solar radiation and make the system have multiple functions of heating, purification and photovoltaic power generation. The experimental detection platform of CPC/PTCPV-TW system was built and then turbulent natural convection model and indoor formaldehyde diffusion and transfer model were established to study the performance of CPC/PTCPV-TW system. The results were: (1) In the photocatalytic flow channel, the average daily thermal efficiency and the single pass rate of formaldehyde were 0.36 and 0.25–0.56, respectively. In the thermal catalytic flow channel, the average daily thermal efficiency and the single pass rate of formaldehyde were 0.26 and 0.18–0.38, respectively. The average daily photoelectric conversion efficiency of CPCPTCPV-TW system was 6.68%; (2) The greater the solar irradiation intensity and the lower the air inlet temperature, the higher the instantaneous thermal efficiencies of the photocatalytic channel and thermal catalytic channel and the photoelectric conversion efficiency of the system. The lower the formaldehyde inlet concentration, the greater the amount of clean air delivery rate (CADR) and the smaller ventilation times, the better the degradation effect of formaldehyde in the room equipped with CPC/PTCPV-TW system, and the lower the indoor formaldehyde concentration in a stable state.

Enhanced ppb-level formaldehyde sensing performance over Pt deposited SnO2 nanospheres

Formaldehyde is one of the most serious threats to human health in modern interior decoration. Thereby, online detection of indoor formaldehyde concentration has become an urgent problem. In this work, the Pt deposited porous SnO2 nanospheres were synthesized as the formaldehyde sensing materials, which were prepared by hydrothermal and chemical reduction methods. The diameter of as-synthesized Pt-SnO2 were centered in the range of 30–50 nm, with the dominant pore size of ~10 nm and the specific surface area of 89.79 m2 g−1, which provided a raft of passages and active sites for gas molecules to diffuse and interact mutually. Moreover, the experimental results demonstrated that the 1 wt.% Pt-SnO2 exhibited higher response (16.03), high-speed response time (9 s) and outstanding selectivity with exposure to low-concentration formaldehyde compared with original SnO2. The porous structures and catalytic effect of Pt nanoparticles were jointly responsible for the enhancement of SnO2 on sensing performance towards formaldehyde.

Seasonal and diurnal patterns of outdoor formaldehyde and impacts on indoor environments and health

Formaldehyde is concerned as an important indoor carcinogen. While contribution of outdoor formaldehyde to indoor concentration is recognized, long-term measurement about its impact on indoor environments remain missing. We measured both outdoor and indoor formaldehyde concentrations for over one year in Nanjing (east-central China) and calculated the outdoor/indoor (O/I) ratios. 64.8% of the measured outdoor concentration have exceeded the chronic reference exposure criteria of 0.009 mg/m3 set by Office of Environmental Health Hazard Assessment (OEHHA). The outdoor concentration was highest in summer with median value of 0.020 mg/m3 and lowest in spring with median value of 0.009 mg/m3. Diurnally, outdoor formaldehyde concentration was highest at noon with median value of 0.013 mg/m3 and lowest at night with median value of 0.01 mg/m3. Health analysis revealed that cancer risk by exposure to this concentration level is 1.6 × 10−4, higher than threshold limit of 10−6. In addition, the median O/I ratios are 0.18 and 0.27 in two offices, indicating that outdoor formaldehyde contributes to indoor concentrations by about one quarter. The change of O/I ratio also shows a similar seasonal and diurnal trend as outdoor concentrations (highest in the summer in a year and at noon in a day). Outdoor formaldehyde concentration is therefore not negligible as a contributor to indoor concentration, especially as indoor concentration limit gets continuously lowered. This factor should be taken into account in indoor air quality design and maintenance.

Diurnal variation and potential sources of indoor formaldehyde at elementary school, high school and university in the Centre Val de Loire region of France

Formaldehyde (HCHO) is one of the abundant indoor pollutants and has been classified as a human carcinogen by the International Agency for Research on Cancer (IARC). Indoor HCHO at schools is particularly important due to the high occupancy density and the health effects on children. In this study, high time resolved measurement of formaldehyde concentration was conducted in the classrooms at elementary school, high school and university under normal students' activities in three different locations in the Region Centre Val de Loire-France. Indoor average formaldehyde concentrations at those three educational institutions were observed to be in the range 10.96–17.95 μg/m3, not exceeding the World Health Organization (WHO) guideline value of 100 μg/m3. As expected, ventilation was found playing an important role in the control of indoor formaldehyde concentration. After opening windows for 30 min, formaldehyde level decreased by ~25% and 38% in the classroom at the elementary school and the high school, respectively. In addition to the primary sources, the objective of this study was also to determine potential secondary sources of indoor formaldehyde in these schools by measuring the other volatile organic compounds (VOCs) present in the classrooms by a Proton Transfer Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS). The measurements suggest that the release of residue from tobacco smokers is one of the major sources of indoor HCHO at the high school, which increases HCHO by ~55% averagely within 1 h. Moreover, the control experiments conducted in the university suggests that VOCs such as that released from cleaning products like terpenes, can contribute to the increase of indoor formaldehyde levels through chemical reactions with ozone. This study confirms simple recommendations to reduce the indoors HCHO concentration in schools: use ventilation systems, limit the emissions like cigarette smoke or cleaning products. It also points out that the secondary sources of formaldehyde must be also considered in the classroom.

Long-term indoor formaldehyde variations and health risk assessment in Chinese urban residences following renovation

Formaldehyde is a ubiquitous indoor gaseous pollutant classified as a human carcinogen. Indoor formaldehyde concentrations tend to change over time in newly renovated buildings. However, this variation is not typically considered in inhalation cancer risk assessments. In this study, long-term indoor formaldehyde concentrations in newly renovated residences in China were collected from related literature. A total of 66 data sets collected from 42 different studies in 38 cities were analyzed. An exponential model was used to describe the variation patterns of indoor concentrations. The distribution of initial indoor formaldehyde concentrations immediately after renovation (Ca0) and the decay constant (k) were then obtained. The mean values of Ca0 and k were 0.376 mg/m3 and 1.98 × 10−4 h−1, respectively. Exposure model was revised by considering the long-term variation characteristics. The inhalation health risks related to formaldehyde exposure were then estimated. The median cancer risk was 3.41 × 10−5, and the probability of exceeding the acceptable risk was 99%. The median cancer risk decreased by 40% and 60% if the start time of room occupancy was increased to 0.5 y and 1 y after renovation, respectively. k (>1 y) contributed the most to the variation in cancer risk, followed by Ca0 (>1 y). Ignoring the decay of indoor formaldehyde concentrations overestimates the health risks related to exposure to formaldehyde in newly renovated residences. Our results present a more accurate method for determining human health risks related to indoor formaldehyde that can also be applied to other volatile organic compounds.

Indoor formaldehyde concentrations and the influencing factors in urban China

Indoor formaldehyde concentrations and the influencing factors in urban China

Development of a physics-based model for analyzing formaldehyde emissions from building material under coupling effects of temperature and humidity

Material emission characteristics constitute significant information for indoor formaldehyde control, exposure estimation, and health risk assessment. Based on observations over 29 months in a designed experimental room, we identified and reported seasonal variations in formaldehyde emitted by a medium-density fiberboard (MDF) in a previously published paper. Temperature and absolute humidity (AH) were confirmed to prominently contribute to the variations. In the current study, we further developed a physics-based model to analyze the formaldehyde emissions of the MDF under the coupling effects of temperature and AH. Indoor formaldehyde concentration and emission rate were solved numerically according to the emission history and key emission parameters. The key parameters at different temperatures and AH conditions were obtained independently through short-term (80 h) emission tests using an environmental chamber. The model predicted that indoor formaldehyde concentration varied with cyclical seasonal features, which is consistent with field observations. The slope of the regression line between the simulated and measured concentrations was 0.83 with a correlation coefficient of 0.94, indicating good quantitative consistency between the simulations and the long-term data. The model demonstrated potential for application in predicting long-term formaldehyde emissions in buildings under varying environmental conditions.

Chitosan-dosed adsorptive filter media for removal of formaldehyde from indoor air – Performance and cancer risk assessment

It is firmly established that contemporary building materials and indoor furnishings are associated with elevated concentrations of formaldehyde in indoor air, representing a hazard to human health. To mitigate this issue, formaldehyde and other pollutants in indoor air are removed via air conditioning systems fitted with appropriate filters. Based on positive results from earlier, relevant research, this study investigates the use of air conditioning filters treated with chitosan as potential eco-friendly absorbents for removal of formaldehyde, a significant indoor air pollutant.The filter is sprayed with different dosages of chitosan, in accordance with our previous work [8]. Removal rate and adsorption of formaldehyde are calculated for the health risk assessment. After twenty-four hours testing, the results showed the averaged concentration of formaldehyde is 1.146 ppm, 0.714 ppm, and 0.084 ppm with chitosan dosage of 2.6 mg m−2, 5.3 mg m−2, 8.0 mg m−2, respectively. The averaged reduction of formaldehyde concentration is 64.9%, 80.0%, and 96.0%; the averaged absorption of chitosan on formaldehyde is 0.167 mg, 0.204 mg and 0.271 mg for chitosan dosage of 2.6 mg m−2, 5.3 mg m−2, 8.0 mg m−2, respectively. The risk characterization figures without spaying chitosan are 2.94, 2.65 and 7.07 times higher when compared with the same figures associated with filters treated with 2.6 mg m−2, 5.3 mg m−2, and 8.0 mg m−2 of chitosan. This study finds that chitosan has strong potential as a commercial adsorbent. Increasing the amount of chitosan applied to the filter substrate improves the efficacy of the absorbent and further reduces the indoor formaldehyde concentration and the associated carcinogenic risk.

Residential building ventilation in situations with outdoor PM2.5 pollution

Affordable ventilation of residential buildings in situations with outdoor PM2.5 pollution is a challenge. This investigation used the validated EnergyPlus software program to model ventilation performance in a newly constructed residential apartment in five different climate zones in China. The evaluated ventilation modes were natural ventilation, balanced mechanical ventilation, and hybrid ventilation, together with indoor particle filtration. Both indoor-generated particles due to cooking and ventilation-drawn particles from the outdoor environment were considered. Different heat recovery modes for mechanical ventilation were also compared. The evaluated parameters included indoor CO2 (carbon dioxide), PM2.5 (fine particulate matter), formaldehyde, and TVOC (total volatile organic compound) concentrations, energy consumption, and operating costs. The natural ventilation mode was found to be the cheapest, but it may provide an insufficient ventilation rate for 27%–79% of the occupied time. Mechanical ventilation can ensure good indoor air quality continuously, but the associated utility cost may be more than twice that for natural ventilation. Indoor particulate filtration should be utilized in situations with severe outdoor PM2.5 pollution. Heat recovery is not recommended in residential buildings due to the high initial investment cost at present. The least energy-consuming ventilation mode for residential buildings with maximum potential to use natural ventilation is recommended.

Identifying the K-12 classrooms' indoor air quality factors that affect student academic performance

The objective of this study was to investigate associations between indoor air quality (IAQ) in K-12 classrooms and student academic performance. During the academic years 2015–2017, various IAQ factors in 220 classrooms in the US were measured seasonally, excluding summer. Measurements were taken during occupied and unoccupied times in several classrooms within each school. Occupied measurements included indoor carbon dioxide (CO2) and formaldehyde concentrations, and fine and coarse particle counts. Unoccupied measurements consisted of ozone (O3), carbon monoxide (CO), nitrogen dioxide (NO2), and total volatile organic compounds (TVOCs) concentrations. Ventilation rates of classrooms were estimated using measured CO2 concentrations. In addition to IAQ data, classroom aggregated student achievement scores and demographic information were collected from participating school districts. Demographic data included percentage rates of free and reduced lunch recipients (PFRL), high-performance students (PGIF), and special education students (PSPED). A multivariate linear regression analysis was used to investigate the associations between IAQ factors and student scores using demographic data as controls. The results revealed associations between student scores and ventilation system type, ventilation rates, fine particle counts, and O3 and CO concentrations. This research provides valuable information to school districts and design engineers, enabling them to design school environments for improved student performance.

Development of formaldehyde flux sampler using a commercial DNPH cartridge

Building materials and consumer products are main sources of formaldehyde emitted in non-smoking environments. Identifying major emitters in existing buildings is difficult since the emission factors (EFs) are typically determined in a chamber test that is not suitable for on-site measurement. In this study, a new passive flux sampler (PFS) was developed for on-site measurement of formaldehyde EFs from building materials. The PFS is non-invasive and suitable for a long-term test (4–7 days) that is based on a commercially available 2,4-dinitrophenylhydrazine (DNPH) cartridge.Five designs of PFS with different diffusion lengths and diameters were tested with 8 composite wood products (CWPs). The PFS with a diffusion length of 20 mm and a diameter of 10 mm (PFS-D1) was shown to have the EFs comparable to those from conventional chamber tests. Laboratory tests showed that the PFS-D1 has acceptable variability (<21% of relative standard deviation) and sensitivity that can collect mass above detection limit for 4–7 day sampling. The PFS-D1 was used to determine EFs of 5–9 CWPs in a research house at 3 and 8 months after construction. The EFs were used to predict the indoor formaldehyde concentration, which led to good agreement (±25%) with the measured concentration. The major emitters were determined to be CWPs such as floor and door, indicating that PFS-D1 is a useful tool to identify and prioritize formaldehyde sources in existing buildings.

Formaldehyde Emissions from Wooden Toys: Comparison of Different Measurement Methods and Assessment of Exposure.

Formaldehyde is considered as carcinogenic and is emitted from particleboards and plywood used in toy manufacturing. Currently, the flask method is frequently used in Europe for market surveillance purposes to assess formaldehyde release from toys, but its concordance to levels measured in emission test chambers is poor. Surveillance laboratories are unable to afford laborious and expensive emission chamber testing to comply with a new amendment of the European Toy Directive; they need an alternative method that can provide reliable results. Therefore, the application of miniaturised emission test chambers was tested. Comparisons between a 1 m3 emission test chamber and 44 mL microchambers with two particleboards over 28 days and between a 24 L desiccator chamber and the microchambers with three puzzle samples over 10 days resulted in a correlation coefficient r2 of 0.834 for formaldehyde at steady state. The correlation between the results obtained in microchambers vs. flask showed a high variability over 10 samples (r2: 0.145), thereby demonstrating the error-proneness of the flask method in comparison to methods carried out under ambient parameters. An exposure assessment was also performed for three toy puzzles: indoor formaldehyde concentrations caused by puzzles were not negligible (up to 8 µg/m3), especially when more conservative exposure scenarios were considered.