After nearly twenty years of rapid modernization and urbanization in China, huge achievements hav... more After nearly twenty years of rapid modernization and urbanization in China, huge achievements have transformed the daily lives of the Chinese people. However, unprecedented environmental consequences in both indoor and outdoor environments have accompanied this progress and have triggered public awareness and demands for improved living standards, especially in residential environments. Indoor pollution data measured for N7000 dwellings (approximately 1/3 were newly decorated and were tested for volatile organic compound (VOC) measurements, while the rest were tested for particles, phthalates and other semi-volatile organic compounds (SVOCs), moisture/mold, inorganic gases and radon) in China within the last ten years were reviewed, summarized and compared with indoor concentration recommendations based on sensory or health end-points. Ubiquitous pollutants that exceed the concentration recommendations, including particulate matter, formalde-hyde, benzene and other VOCs, moisture/mold, inorganic gases and radon, were found, indicating a common indoor air quality (IAQ) issue in Chinese dwellings. With very little prevention, oral, inhalation and dermal exposure to those pollutants at unhealthy concentration levels is almost inevitable. CO 2 , VOCs, humidity and radon can serve as ventilation determinants, each with different ventilation demands and strategies, at typical occupant densities in China; and particle reduction should be a prerequisite for determining ventilation requirements. Two directional ventilation modes would have profound impacts on improving IAQ for Chinese residences are: 1) natural (or window) ventilation with an air cleaner and 2) mechanical ventilation with an air filtration unit, these two modes were reviewed and compared for their applicability and advantages and disadvantages for reducing human exposure to indoor air pollutants. In general, mode 2 can more reliably ensure good IAQ for occupants; while mode 1 is more applicable due to its low cost and low energy consumption. However, j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / s c i t o t e n v besides a roadmap, substantial efforts are still needed to develop affordable, applicable and general ventilation solutions to improve the IAQ of residential buildings in China.
Indoor air pollutants in offices can be attributed to various sources, including building materia... more Indoor air pollutants in offices can be attributed to various sources, including building materials, consumer products, and exhalation from occupants. The required ventilation rate for offices can be determined by estimating the majority of emissions originated from building materials, as an additional determinant factor for ventilation rate, with the assumption of constant ventilation with 100% outdoor air, uniform indoor mixing, and no chemical reactions. In this paper, the validity of these assumptions was investigated by incorporating the effects of various physical and chemical factors in determining material emissions and ventilation rates. Three physical factors investigated were recirculation ventilation, intermittent ventilation and pollutant distribution. Simplified methods using correction factors were proposed to revise the ventilation rate and validated by emission modeling and CFD method. In addition, three chemical factors were discussed. First, 28 building materials were selected from the NRC database and each was subject to determining the ventilation rate. As a result, 28 leading pollutants that are likely to determine the ventilation rate were obtained. Because most of the leading pollutants are reactants rather than products of indoor air reactions, it was concluded that the current ventilation rate determining methods should still be applicable. Additionally, a correction method was proposed for a reaction product such as formaldehyde. Second, the methods to revise ventilation rate based on temperature variation and pollutant concentration in outdoor air were proposed. This study showed that ventilation rate for offices could be determined based on building material emissions in more realistic ventilation and environmental conditions.
Knowing the value of the key mass-transfer model parameters is a critical requirement for evaluat... more Knowing the value of the key mass-transfer model parameters is a critical requirement for evaluating volatile organic compound (VOC) emissions from indoor materials. The key parameters are diffusion coefficient (D), partition coefficient (K), and initial material-phase emittable concentration (C0). Although these parameters can be individually measured in the laboratory, the required time and expense are substantial. A simple method of determining D and C0 using data from ventilated chamber tests and dimensionless analysis is proposed and then validated using VOC emission data from the material emissions database developed by National Research Council Canada (NRC). The primary application of this method is to provide a rapid screening-level estimate of inhalation exposure to VOCs in building materials. Two standard scenarios using the NRC database are employed to demonstrate the value of the approach to indoor air quality assessment. The method could be a useful screening tool for assessing material emissions or environmental exposures.
Ventilation is commonly used as a basic means to supply outdoor air to indoor environment to achi... more Ventilation is commonly used as a basic means to supply outdoor air to indoor environment to achieve better indoor air quality. To reduce harmful effect due to indoor pollutants such as formaldehyde and VOCs emitted from building materials, proper ventilation should be maintained to meet a minimum ventilation rate at least. Two new methods, i.e., characteristic and two-stage ventilation rate method, were proposed to predict ventilation rate based on building material emissions. Scenarios involving four standard rooms and different material loadings were analyzed to study adequate ventilation rates for residential buildings and offices. The study followed the IAQ procedure recommended by ASHRAE. The emission source data were from the National Research Council Canada (NRC) database. The building material emissions and consequent VOC concentrations were predicted by using two approaches called the characteristic emission rate method and the two-stage emission rate method. The ventilation rates were calculated for ten scenarios to meet the thresholds given by seven indoor air quality references. The results showed that the ventilation rate depended on the selection of reference standard, material and emission area. The dominating chemical substance in determining ventilation rate in various cases was not unique. The time to take for the emission to complete was 2.5–5 years for all cases. Due to the inherent nature of the characteristic emission rate method for over-estimating long-term emissions, replacing the characteristic ventilation rate with steady-state ventilation rate could lead to the ventilation rate requirement reduced by approximately half.
Due to its environmental ubiquity and concern over its potential toxicity, the mass-transfer char... more Due to its environmental ubiquity and concern over its potential toxicity, the mass-transfer characteristics of formaldehyde are of critical importance to indoor air quality research. Previous studies have suggested that formaldehyde mass transfer in polymer is partially irreversible. In this study, mechanisms that could cause the observed irreversibility were investigated. Polycarbonate and four other polymeric matrices were selected and subjected to formaldehyde sorption/desorption cycles. Mass transfer of formaldehyde was partially irreversible in all cases, and three potential mechanisms were evaluated. First, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) analysis was used to investigate possible formaldehyde polymerization on polymer surfaces. ATR-FTIR showed no detectable paraformaldehyde or formaldehyde on the film surfaces that had been exposed to formaldehyde and air. ATR-FTIR did detect aliphatic acids suggesting oxidation had occurred on film surfaces as a result of exposure to formaldehyde. However, additional study suggested that air is not the primary cause for irreversibility. Second, statistical physics theory was tested as a possible explanation. According to this theory, reversible and irreversible sorption could be taking place simultaneously. The irreversible fraction should be constant during sorption and the fraction could be determined by performing a complete sorption/desorption test. The sorption/desorption data was consistent with this theory. Third, chemisorption was considered as another possible cause for irreversibility. Extraction/fluorimetry testing of post-sorption and post-desorption films showed measurable quantities of formaldehyde suggesting that some of the chemisorbed formaldehyde was reversible at the higher extraction temperature. Further quantitative study on chemical reaction products is needed.
Chamber testing is a common method to evaluate VOC emissions from building materials. Empirical ... more Chamber testing is a common method to evaluate VOC emissions from building materials. Empirical models based on short-term testing (typically less than 28 days) are frequently used to estimate long-term emissions (up to years). However, the applicability of the empirical models for long-term prediction remains unclear in practice. Four empirical models, i.e., two constant models with and without a prerequisite (M1 and M2), a power-law model (M3), and an exponential model (M4), were used to test the applicability of predicting year-long emissions using emission data that were less than one month. The diffusion-based mass-transfer model was used to generate reference emission data with random variations involved to represent measurement errors, etc. For M1 and M2, the discrepancy ratios between the constant emissions and the characteristic average emissions are quantified. For M3 and M4, an additional measure, i.e., normalized mean square error (NMSE), was adopted to statistically study the applicability of using empirical models to predict long-term emissions. The results shown that, first, the NMSE values indicate that M3 prefers slow emissions and generally performs better than M4. However, M4 performs better for predicting year-long emissions for cases with characteristic emission time of one year. Second, both M3 and M4 predict the average life-long emissions reasonably well for most scenarios. Third, while the effects of test duration are less significant for M3 than M4, the early-stage sampling points are more important for better long-term predictions. Additionally, experimental data by National Research Council Canada (NRC) were used to validate the applicability of the empirical models in year-long emission predictions, with the results similar to those from the simulated data. This paper can be used as a reference to select appropriate empirical model(s), as well as the testing duration, to simulate long-term VOC emissions from building materials using short-term testing data.
Volatile organic compounds emissions from building materials can be a major pollution source in l... more Volatile organic compounds emissions from building materials can be a major pollution source in low-occupant-density spaces. Composite-style indoor air quality references, which reflect the combined effects of multiple volatile organic compounds, can be used to determine ventilation rate requirements based on building material emissions. The lowest concentration of interest concept was adopted to implement the idea. Twenty-eight building materials selected from the National Research Council of Canada database were subjected to emission modelling, resulting in 101 volatile organic compounds as a starting volatile organic compound pool. A method was proposed to generate a volatile organic compound priority list that determines ventilation rate requirements while considering ozone-initiated reactions. Three priority lists were obtained based on three lowest concentration of interest schemes, i.e., AFSSET, AgBB and EU-LCI, with each consisting of 17–21 volatile organic compounds that were most likely to attribute to large ventilation rate requirements. Also, analyses of selected volatile organic compounds showed that the changes in the composition of the priority lists due to ozone-initiated reactions could be ignored at a typical indoor ozone concentration level. The application of priority lists was discussed for source control and air cleaning device testing. This paper provides a method to prioritize the chemicals based on ventilation rate requirements with a goal of developing volatile organic compound control strategies at building design stage.
After nearly twenty years of rapid modernization and urbanization in China, huge achievements hav... more After nearly twenty years of rapid modernization and urbanization in China, huge achievements have transformed the daily lives of the Chinese people. However, unprecedented environmental consequences in both indoor and outdoor environments have accompanied this progress and have triggered public awareness and demands for improved living standards, especially in residential environments. Indoor pollution data measured for N7000 dwellings (approximately 1/3 were newly decorated and were tested for volatile organic compound (VOC) measurements, while the rest were tested for particles, phthalates and other semi-volatile organic compounds (SVOCs), moisture/mold, inorganic gases and radon) in China within the last ten years were reviewed, summarized and compared with indoor concentration recommendations based on sensory or health end-points. Ubiquitous pollutants that exceed the concentration recommendations, including particulate matter, formalde-hyde, benzene and other VOCs, moisture/mold, inorganic gases and radon, were found, indicating a common indoor air quality (IAQ) issue in Chinese dwellings. With very little prevention, oral, inhalation and dermal exposure to those pollutants at unhealthy concentration levels is almost inevitable. CO 2 , VOCs, humidity and radon can serve as ventilation determinants, each with different ventilation demands and strategies, at typical occupant densities in China; and particle reduction should be a prerequisite for determining ventilation requirements. Two directional ventilation modes would have profound impacts on improving IAQ for Chinese residences are: 1) natural (or window) ventilation with an air cleaner and 2) mechanical ventilation with an air filtration unit, these two modes were reviewed and compared for their applicability and advantages and disadvantages for reducing human exposure to indoor air pollutants. In general, mode 2 can more reliably ensure good IAQ for occupants; while mode 1 is more applicable due to its low cost and low energy consumption. However, j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / s c i t o t e n v besides a roadmap, substantial efforts are still needed to develop affordable, applicable and general ventilation solutions to improve the IAQ of residential buildings in China.
Indoor air pollutants in offices can be attributed to various sources, including building materia... more Indoor air pollutants in offices can be attributed to various sources, including building materials, consumer products, and exhalation from occupants. The required ventilation rate for offices can be determined by estimating the majority of emissions originated from building materials, as an additional determinant factor for ventilation rate, with the assumption of constant ventilation with 100% outdoor air, uniform indoor mixing, and no chemical reactions. In this paper, the validity of these assumptions was investigated by incorporating the effects of various physical and chemical factors in determining material emissions and ventilation rates. Three physical factors investigated were recirculation ventilation, intermittent ventilation and pollutant distribution. Simplified methods using correction factors were proposed to revise the ventilation rate and validated by emission modeling and CFD method. In addition, three chemical factors were discussed. First, 28 building materials were selected from the NRC database and each was subject to determining the ventilation rate. As a result, 28 leading pollutants that are likely to determine the ventilation rate were obtained. Because most of the leading pollutants are reactants rather than products of indoor air reactions, it was concluded that the current ventilation rate determining methods should still be applicable. Additionally, a correction method was proposed for a reaction product such as formaldehyde. Second, the methods to revise ventilation rate based on temperature variation and pollutant concentration in outdoor air were proposed. This study showed that ventilation rate for offices could be determined based on building material emissions in more realistic ventilation and environmental conditions.
Knowing the value of the key mass-transfer model parameters is a critical requirement for evaluat... more Knowing the value of the key mass-transfer model parameters is a critical requirement for evaluating volatile organic compound (VOC) emissions from indoor materials. The key parameters are diffusion coefficient (D), partition coefficient (K), and initial material-phase emittable concentration (C0). Although these parameters can be individually measured in the laboratory, the required time and expense are substantial. A simple method of determining D and C0 using data from ventilated chamber tests and dimensionless analysis is proposed and then validated using VOC emission data from the material emissions database developed by National Research Council Canada (NRC). The primary application of this method is to provide a rapid screening-level estimate of inhalation exposure to VOCs in building materials. Two standard scenarios using the NRC database are employed to demonstrate the value of the approach to indoor air quality assessment. The method could be a useful screening tool for assessing material emissions or environmental exposures.
Ventilation is commonly used as a basic means to supply outdoor air to indoor environment to achi... more Ventilation is commonly used as a basic means to supply outdoor air to indoor environment to achieve better indoor air quality. To reduce harmful effect due to indoor pollutants such as formaldehyde and VOCs emitted from building materials, proper ventilation should be maintained to meet a minimum ventilation rate at least. Two new methods, i.e., characteristic and two-stage ventilation rate method, were proposed to predict ventilation rate based on building material emissions. Scenarios involving four standard rooms and different material loadings were analyzed to study adequate ventilation rates for residential buildings and offices. The study followed the IAQ procedure recommended by ASHRAE. The emission source data were from the National Research Council Canada (NRC) database. The building material emissions and consequent VOC concentrations were predicted by using two approaches called the characteristic emission rate method and the two-stage emission rate method. The ventilation rates were calculated for ten scenarios to meet the thresholds given by seven indoor air quality references. The results showed that the ventilation rate depended on the selection of reference standard, material and emission area. The dominating chemical substance in determining ventilation rate in various cases was not unique. The time to take for the emission to complete was 2.5–5 years for all cases. Due to the inherent nature of the characteristic emission rate method for over-estimating long-term emissions, replacing the characteristic ventilation rate with steady-state ventilation rate could lead to the ventilation rate requirement reduced by approximately half.
Due to its environmental ubiquity and concern over its potential toxicity, the mass-transfer char... more Due to its environmental ubiquity and concern over its potential toxicity, the mass-transfer characteristics of formaldehyde are of critical importance to indoor air quality research. Previous studies have suggested that formaldehyde mass transfer in polymer is partially irreversible. In this study, mechanisms that could cause the observed irreversibility were investigated. Polycarbonate and four other polymeric matrices were selected and subjected to formaldehyde sorption/desorption cycles. Mass transfer of formaldehyde was partially irreversible in all cases, and three potential mechanisms were evaluated. First, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) analysis was used to investigate possible formaldehyde polymerization on polymer surfaces. ATR-FTIR showed no detectable paraformaldehyde or formaldehyde on the film surfaces that had been exposed to formaldehyde and air. ATR-FTIR did detect aliphatic acids suggesting oxidation had occurred on film surfaces as a result of exposure to formaldehyde. However, additional study suggested that air is not the primary cause for irreversibility. Second, statistical physics theory was tested as a possible explanation. According to this theory, reversible and irreversible sorption could be taking place simultaneously. The irreversible fraction should be constant during sorption and the fraction could be determined by performing a complete sorption/desorption test. The sorption/desorption data was consistent with this theory. Third, chemisorption was considered as another possible cause for irreversibility. Extraction/fluorimetry testing of post-sorption and post-desorption films showed measurable quantities of formaldehyde suggesting that some of the chemisorbed formaldehyde was reversible at the higher extraction temperature. Further quantitative study on chemical reaction products is needed.
Chamber testing is a common method to evaluate VOC emissions from building materials. Empirical ... more Chamber testing is a common method to evaluate VOC emissions from building materials. Empirical models based on short-term testing (typically less than 28 days) are frequently used to estimate long-term emissions (up to years). However, the applicability of the empirical models for long-term prediction remains unclear in practice. Four empirical models, i.e., two constant models with and without a prerequisite (M1 and M2), a power-law model (M3), and an exponential model (M4), were used to test the applicability of predicting year-long emissions using emission data that were less than one month. The diffusion-based mass-transfer model was used to generate reference emission data with random variations involved to represent measurement errors, etc. For M1 and M2, the discrepancy ratios between the constant emissions and the characteristic average emissions are quantified. For M3 and M4, an additional measure, i.e., normalized mean square error (NMSE), was adopted to statistically study the applicability of using empirical models to predict long-term emissions. The results shown that, first, the NMSE values indicate that M3 prefers slow emissions and generally performs better than M4. However, M4 performs better for predicting year-long emissions for cases with characteristic emission time of one year. Second, both M3 and M4 predict the average life-long emissions reasonably well for most scenarios. Third, while the effects of test duration are less significant for M3 than M4, the early-stage sampling points are more important for better long-term predictions. Additionally, experimental data by National Research Council Canada (NRC) were used to validate the applicability of the empirical models in year-long emission predictions, with the results similar to those from the simulated data. This paper can be used as a reference to select appropriate empirical model(s), as well as the testing duration, to simulate long-term VOC emissions from building materials using short-term testing data.
Volatile organic compounds emissions from building materials can be a major pollution source in l... more Volatile organic compounds emissions from building materials can be a major pollution source in low-occupant-density spaces. Composite-style indoor air quality references, which reflect the combined effects of multiple volatile organic compounds, can be used to determine ventilation rate requirements based on building material emissions. The lowest concentration of interest concept was adopted to implement the idea. Twenty-eight building materials selected from the National Research Council of Canada database were subjected to emission modelling, resulting in 101 volatile organic compounds as a starting volatile organic compound pool. A method was proposed to generate a volatile organic compound priority list that determines ventilation rate requirements while considering ozone-initiated reactions. Three priority lists were obtained based on three lowest concentration of interest schemes, i.e., AFSSET, AgBB and EU-LCI, with each consisting of 17–21 volatile organic compounds that were most likely to attribute to large ventilation rate requirements. Also, analyses of selected volatile organic compounds showed that the changes in the composition of the priority lists due to ozone-initiated reactions could be ignored at a typical indoor ozone concentration level. The application of priority lists was discussed for source control and air cleaning device testing. This paper provides a method to prioritize the chemicals based on ventilation rate requirements with a goal of developing volatile organic compound control strategies at building design stage.
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