Loss of NO(g) to painted surfaces and its re-emission with indoor illumination

Heterogeneous surface reactions play a key role in the chemistry of the indoor environment because of the large indoor surface-to-volume ratio. The presence of photocatalytic material in indoor paints may allow photochemical reactions to occur at wavelengths of light that are present indoors. One such potential reaction is the heterogeneous photooxidation of NO to HONO. NO(g) is commonly found indoors, originating from combustion sources, ventilation and infiltration of outdoor air. We studied the interaction of NO(g) with painted surfaces illuminated with indoor fluorescent and incandescent lighting. There is a loss of NO(g) to painted surfaces in the dark at both 0 and 50% RH. At 50% RH, there is a re-release of some of that NO(g) under illumination. The same behavior is observed for illumination of different colored paints. This is in contrast to what is seen with TiO₂ as the substrate, where photoenhanced uptake of NO(g) and formation of NO₂(g) are observed. We hypothesize that the loss of NO(g) is due to adsorption and diffusion into the paint. The re-release of NO under illumination is thought to be due to photooxidation of NO to HONO on the painted surface at higher relative humidities and subsequent HONO photolysis.     

Nitrous Acid Formation in an Experimental Exposure Chamber

Reactive indoor chemistry has seldom been considered in investigations of the health effects of exposure to indoor contaminants although improved understanding may help to reduce exposure misclassification as well as identify previously unknown exposures. Nitrous acid (HONO), formed from the heterogeneous reaction of NO₂ with water on indoor surfaces, may be a neglected and important confounder in studies of nitrogen dioxide (NO₂) health effects. The understanding of HONO – NO₂ relationships is important since conventional measurements of NO₂ actually measure a number of nitrogen oxides including HONO. Accordingly, we examined the effects of relative humidity, chamber residence time, the presence of carpeted sufaces and the presence of human subjects on the production of HONO following the injection of NO₂ into a chamber. Increasing chamber relative humidity led to greater HONO concentrations at a given NO₂ level. At 80% relative humidity, HONO concentrations were 11% of the NO₂ concentration. Increased residence time in the chamber increased HONO levels, with a five-fold increase in HONO levels between 20 minute and 120 minute residence times. The presence of wool carpets in the chamber was not found to affect significantly the HONO production rates, although NO₂ decay rates were increased. When human subjects were present in the chamber, HONO concentrations decreased by as much as 50% of the levels present under similar conditions with no subjects in the chamber. In light of our results we argue that future investigations of NO₂ health effects and indoor air quality must recognize the importance of indoor chemistry, and in particular, the likelihood of elevated concentrations of HONO which will interfere with NO₂ measurements and potentially confound the investigation of concentration-effect relationships. Similarly, previous studies demonstrating a relationship between health endpoints and NO₂ exposure should be viewed with caution until the presence and importance of other potentially toxic nitrogenous compounds in the exposure environment are evaluated.     

Indoor heterogeneous photochemistry of furfural drives emissions of nitrous acid

People spend approximately 80% of their time indoor, making the understanding of the indoor chemistry an important task for safety. The high surface-area-to-volume ratio characteristic of indoor environments leads the semi-volatile organic compounds (sVOCs) to deposit on the surfaces. Using a long path absorption photometer (LOPAP), this work investigates the formation of nitrous acid (HONO) through the photochemistry of adsorbed nitrate anions and its enhancement by the presence of furfural. Using a high-resolution proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS), this work also investigates the surface emissions of VOCs from irradiated films of furfural and a mix of furfural and nitrate anions. Among the emitted VOCs, 2(5H)-furanone/2-Butenedial was observed at high concentrations, leading to maleic anhydride formation after UV irradiation. Moreover, the addition of potassium nitrate to the film formed NO_x and HONO concentrations up to 10 ppb, which scales to ca. 4 ppb for realistic indoor conditions. This work helps to understand the high levels of HONO and NO_x measured indoors.     

Nitrous acid interference with passive NO2 measurement methods and the impact on indoor NO2 data

Recent research has demonstrated that nitrous acid (HONO) is produced in indoor environments by NO2 reacting with interior surfaces, and is also emitted directly by some combustion sources. We have recently characterized the interference by HONO to NO2 measurements made by several commonly used continuous NO2 monitors. This paper reports on the effect of HONO on NO2 measurements made by passive sampling devices. The objective of this study was to evaluate this interference, and the accuracy and precision of passive samplers used for indoor NO2 measurements. We report that HONO interferes quantitatively with three of the four NO2 passive samplers tested.     

Indoor acids and bases

Numerous acids and bases influence indoor air quality. The most abundant of these species are CO₂ (acidic) and NH₃ (basic), both emitted by building occupants. Other prominent inorganic acids are HNO₃, HONO, SO₂, H₂SO₄, HCl, and HOCl. Prominent organic acids include formic, acetic, and lactic; nicotine is a noteworthy organic base. Sources of N-, S-, and Cl-containing acids can include ventilation from outdoors, indoor combustion, consumer product use, and chemical reactions. Organic acids are commonly more abundant indoors than outdoors, with indoor sources including occupants, wood, and cooking. Beyond NH₃ and nicotine, other noteworthy bases include inorganic and organic amines. Acids and bases partition indoors among the gas-phase, airborne particles, bulk water, and surfaces; relevant thermodynamic parameters governing the partitioning are the acid-dissociation constant (K_a), Henry's law constant (K_H), and the octanol-air partition coefficient (K_oa). Condensed-phase water strongly influences the fate of indoor acids and bases and is also a medium for chemical interactions. Indoor surfaces can be large reservoirs of acids and bases. This extensive review of the state of knowledge establishes a foundation for future inquiry to better understand how acids and bases influence the suitability of indoor environments for occupants, cultural artifacts, and sensitive equipment.     

Measurements and computations of ventilation efficiency and temperature efficiency in a ventilated room

In order to improve the indoor air quality in a room and to save energy, the air movement and contamination distributions in the room with ventilation have been studied experimentally and numerically. The experiment is carried out in a full-scale climate room with different air supply systems, heat gains from the venetian blinds and ventilation rates. The measurements concern room airflow patterns and air temperature, velocity and contamination concentration fields, etc. The airflow computer program PHOENICS and the cooling load program ACCURACY have been applied for the numerical simulations. PHOENICS solves the conservation equations of air mass, momentum, energy, concentration, kinetic energy and dissipation rate of kinetic energy. ACCURACY, which considers the influence of room air temperature distributions, is employed for the determination of cooling load, wall surface temperatures and convective heat transfer on room enclosure surfaces. These are the boundary conditions required by PHOENICS.The agreements between the computations and the measurements are good. The ventilation efficiency and temperature efficiency which are used for evaluation of indoor air quality and energy consumption are reported for each case. Additional application of these computations to annual energy analysis is also discussed.     

Continuous measurement of reactive oxygen species inside and outside of a residential house during summer

Reactive oxygen species (ROS) are an important contributor to adverse health effects associated with ambient air pollution. Despite infiltration of ROS from outdoors, and possible indoor sources (eg, combustion), there are limited data available on indoor ROS. In this study, part of the second phase of Air Composition and Reactivity from Outdoor aNd Indoor Mixing campaign (ACRONIM-2), we constructed and deployed an online, continuous, system to measure extracellular gas- and particle-phase ROS during summer in an unoccupied residence in St. Louis, MO, USA. Over a period of one week, we observed that the non-denuded outdoor ROS (representing particle-phase ROS and some gas-phase ROS) concentration ranged from 1 to 4 nmol/m³ (as H₂O₂). Outdoor concentrations were highest in the afternoon, coincident with peak photochemistry periods. The indoor concentrations of particle-phase ROS were nearly equal to outdoor concentrations, regardless of window-opening status or air exchange rates. The indoor/outdoor ratio of non-denuded ROS (I/O_ROS) was significantly less than 1 with windows open and even lower with windows closed. Combined, these observations suggest that gas-phase ROS are efficiently removed by interior building surfaces and that there may be an indoor source of particle-phase ROS.     

Factors affecting wavelength-resolved ultraviolet irradiance indoors and their impacts on indoor photochemistry

We measured wavelength-resolved ultraviolet (UV) irradiance in multiple indoor environments and quantified the effects of variables such as light source, solar angles, cloud cover, window type, and electric light color temperature on indoor photon fluxes. The majority of the 77 windows and window samples investigated completely attenuated sunlight at wavelengths shorter than 320 nm; despite variations among individual windows leading to differences in indoor HONO photolysis rate constants (J_HONO) and local hydroxyl radical (OH) concentrations of up to a factor of 50, wavelength-resolved transmittance was similar between windows in residential and non-residential buildings. We report mathematical relationships that predict indoor solar UV irradiance as a function of solar zenith angle, incident angle of sunlight on windows, and distance from windows and surfaces for direct and diffuse sunlight. Using these relationships, we predict elevated indoor steady-state OH concentrations (0.80–7.4 × 10⁶ molec cm⁻³) under illumination by direct and diffuse sunlight and fluorescent tubes near windows or light sources. However, elevated OH concentrations at 1 m from the source are only predicted under direct sunlight. We predict that reflections from indoor surfaces will have minor contributions to room-averaged indoor UV irradiance. These results may improve parameterization of indoor chemistry models.     

Impact of surface ozone interactions on indoor air chemistry: A modeling study

An INdoor air Detailed Chemical Model was developed to investigate the impact of ozone reactions with indoor surfaces (including occupants), on indoor air chemistry in simulated apartments subject to ambient air pollution. The results are consistent with experimental studies showing that approximately 80% of ozone indoors is lost through deposition to surfaces. The human body removes ozone most effectively from indoor air per square meter of surface, but the most significant surfaces for C₆‐C₁₀ aldehyde formation are soft furniture and painted walls owing to their large internal surfaces. Mixing ratios of between 8 and 11 ppb of C₆‐C₁₀ aldehydes are predicted to form in apartments in various locations in summer, the highest values are when ozone concentrations are enhanced outdoors. The most important aldehyde formed indoors is predicted to be nonanal (5‐7 ppb), driven by oxidation‐derived emissions from painted walls. In addition, ozone‐derived emissions from human skin were estimated for a small bedroom at nighttime with concentrations of nonanal, decanal, and 4‐oxopentanal predicted to be 0.5, 0.7, and 0.7 ppb, respectively. A detailed chemical analysis shows that ozone‐derived surface aldehyde emissions from materials and people change chemical processing indoors, through enhanced formation of nitrated organic compounds and decreased levels of oxidants.     

Identification of the major HOx radical pathways in an indoor air environment

OH and HO₂ profiles measured in a real environment have been compared to the results of the INCA‐Indoor model to improve our understanding of indoor chemistry. Significant levels of both radicals have been measured and their profiles display similar diurnal behavior, reaching peak concentrations during direct sunlight (up to 1.6×10⁶ and 4.0×10⁷ cm^?3 for OH and HO₂, respectively). Concentrations of O₃, NO_x, volatile organic compounds (VOCs), HONO, and photolysis frequencies were constrained to the observed values. The HO_x profiles are well simulated in terms of variation for both species (Pearson's coefficients: p_OH=0.55, p_HO2=0.76) and concentration for OH (mean normalized bias error: MNBE_OH=?30%), HO₂ concentration being always underestimated (MNBE_HO2=?62%). Production and loss pathways analysis confirmed HONO photolysis role as an OH precursor (here up to 50% of the production rate). HO₂ formation is linked to OH‐initiated VOC oxidation. A sensitivity analysis was conducted by varying HONO, VOCs, and NO concentrations. OH, HO₂, and formaldehyde concentrations increase with HONO concentrations; OH and formaldehyde concentrations are weakly dependent on NO, whereas HO₂ concentrations are strongly reduced with increasing NO. Increasing VOC concentrations decreases OH by consumption and enhances HO₂ and formaldehyde.     

Machine learning and statistical models for predicting indoor air quality

Indoor air quality (IAQ), as determined by the concentrations of indoor air pollutants, can be predicted using either physically based mechanistic models or statistical models that are driven by measured data. In comparison with mechanistic models mostly used in unoccupied or scenario‐based environments, statistical models have great potential to explore IAQ captured in large measurement campaigns or in real occupied environments. The present study carried out the first literature review of the use of statistical models to predict IAQ. The most commonly used statistical modeling methods were reviewed and their strengths and weaknesses discussed. Thirty‐seven publications, in which statistical models were applied to predict IAQ, were identified. These studies were all published in the past decade, indicating the emergence of the awareness and application of machine learning and statistical modeling in the field of IAQ. The concentrations of indoor particulate matter (PM_2.5 and PM₁₀) were the most frequently studied parameters, followed by carbon dioxide and radon. The most popular statistical models applied to IAQ were artificial neural networks, multiple linear regression, partial least squares, and decision trees.     

Computational fluid dynamics modelling of the air movement in an environmental test chamber with a respiring manikin

In recent years, computational fluid dynamics (CFD) has been widely used as a method of simulating airflow and addressing indoor environment problems. The complexity of airflows within the indoor environment would make experimental investigation difficult to undertake and also imposes significant challenges on turbulence modelling for flow prediction. This research examines through CFD visualization how air is distributed within a room. Measurements of air temperature and air velocity have been performed at a number of points in an environmental test chamber with a human occupant. To complement the experimental results, CFD simulations were carried out and the results enabled detailed analysis and visualization of spatial distribution of airflow patterns and the effect of different parameters to be predicted. The results demonstrate the complexity of modelling human exhalation within a ventilated enclosure and shed some light into how to achieve more realistic predictions of the airflow within an occupied enclosure.     

Case study of window opening behavior using field measurement results

Window opening behavior has significant influences on indoor environment and energy consumption in residential buildings. As a response to indoor environment, the control mechanism (window and interior door open/closed) should be studied first by comprehensive understanding of the variation of indoor environmental conditions. For this reason, a field measurement of environmental conditions was carried out in five representative apartments in Beijing from April to May in 2010. By comparison analyses of the field measurement results, major findings are as follows: (1) the concentration of room CO₂ can be the best predictor of occupant behavior, also window opening behavior, in residential buildings; (2) the variation in indoor air quality mainly results from large variation in window opening behavior; (3) apart from indoor and outdoor thermal environment, indoor air quality as well as occupants’ presence at room have also considerable effect on window opening behavior; (4) while defining window opening behavior for one room in residential building, it is necessary to take the window adjustment of its connecting room and the adjustment of the connecting door into consideration due to air diffusion between the two connecting rooms.     

A general mechanistic model for predicting the fate and transport of phthalates in indoor environments

A mechanistic model that considers particle dynamics and their effects on surface emissions and sorptions was developed to predict the fate and transport of phthalates in indoor environments. A controlled case study was conducted in a test house to evaluate the model. The model‐predicted evolving concentrations of benzyl butyl phthalate in indoor air and settled dust and on interior surfaces are in good agreement with measurements. Sensitivity analysis was performed to quantify the effects of parameter uncertainties on model predictions. The model was then applied to a typical residential environment to investigate the fate of di‐2‐ethylhexyl phthalate (DEHP) and the factors that affect its transport. The predicted steady‐state DEHP concentrations were 0.14 μg/m³ in indoor air and ranged from 80 to 46 000 μg/g in settled dust on various surfaces, which are generally consistent with the measurements of previous studies in homes in different countries. An increase in the mass concentration of indoor particles may significantly enhance DEHP emission and its concentrations in air and on surfaces, whereas increasing ventilation has only a limited effect in reducing DEHP in indoor air. The influence of cleaning activities on reducing DEHP concentration in indoor air and on interior surfaces was quantified, and the results showed that DEHP exposure can be reduced by frequent and effective cleaning activities and the removal of existing sources, though it may take a relatively long period of time for the levels to drop significantly. Finally, the model was adjusted to identify the relative contributions of gaseous sorption and particulate‐bound deposition to the overall uptake of semi‐volatile organic compounds (SVOCs) by indoor surfaces as functions of time and the octanol‐air partition coefficient (K_oa) of the chemical. Overall, the model clarifies the mechanisms that govern the emission of phthalates and the subsequent interactions among air, suspended particles, settled dust, and interior surfaces. This model can be easily extended to incorporate additional indoor source materials/products, sorption surfaces, particle sources, and room spaces. It can also be modified to predict the fate and transport of other SVOCs, such as phthalate‐alternative plasticizers, flame retardants, and biocides, and serves to improve our understanding of human exposure to SVOCs in indoor environments.     

Source term models for fine particle resuspension from indoor surfaces

Understanding the dispersion of contaminants inside buildings is important for improving indoor air quality (IAQ). Detailed information on the dispersion profile within a room is required to design active protection systems and to develop countermeasure strategies against potential threats from particulate based agents. A number of computational fluid dynamics (CFD) codes in the public and commercial domain can simulate contaminant dispersion inside a building. One of the critical boundary conditions required by these CFD codes is a resuspension source term model. This paper develops general source term models for particle resuspension from indoor surfaces based on dimensional analysis. First, the physical mechanisms responsible for fine particle resuspension from indoor surfaces are investigated and relevant parameters are identified. Then, three different models are developed using dimensional analysis and published resuspension data in the literature. Finally, the models are evaluated against independent experimental data that were not used to determine the model coefficients.     

公共建筑室内空气品质与人体舒适性关系研究

对北京市的部分公共建筑进行了大量的现场调查,测试了室内的温度、相对湿度、甲醛、CO、TVOC和PM10等室内环境参数,同时对室内人员进行了问卷调查,了解了建筑使用者对空气品质的满意度,从主客观两方面对室内空气品质进行评价。研究了环境参数与人体满意度之间的关系,建立了室内空气品质预评价模型,对研究室内环境和进行建筑室内环...     

Analysis of thermal comfort and indoor air quality in a mechanically ventilated theatre

Theatres are the most complex of all auditorium structures environmentally. They usually have high heat loads, which are of a transient nature as audiences come and go, and from lighting which changes from scene to scene, and they generally have full or nearly full occupancy. Theatres also need to perform well acoustically, both for the spoken word and for music, and as sound amplification is less used than in other auditoria, background noise control is critically important. All these factors place constraints on the ventilation design, and if this is poor, it can lead to the deterioration of indoor air quality and thermal comfort. To analyse the level of indoor air quality and thermal comfort in a typical medium-sized mechanically ventilated theatre, and to identify where improvements could typically be made, a comprehensive post-occupancy evaluation study was carried out on a theatre in Belgrade. The evaluation, based on the results of monitoring (temperature, relative humidity, CO₂, air speed and heat flux) and modelling (CFD), as well as the assessment of comfort and health as perceived by occupants, has shown that for most of the monitored period the environmental parameters were within the standard limits of thermal comfort and IAQ. However, two important issues were identified, which should be borne in mind by theatre designers in the future. First, the calculated ventilation rates showed that the theatre was over-ventilated, which will have serious consequences for its energy consumption, and secondly, the displacement ventilation arrangement employed led to higher than expected complaints of cold discomfort, probably due to cold draughts around the occupants’ feet.     

Entwicklung und Validierung einer hygrothermischen Raumklima‐Simulationssoftware WUFI®‐Plus

Development and validation of the hygrothermal indoor climate simulation software WUFI®‐Plus. Well‐balanced conditions of thermal, moisture and air quality are very important in buildings because an imbalance of these factors could have significant influences on the construction and the inhabitants. The focus of this paper is the influence of different materials on the fluctuation of relative humidity specifically humidity peaks. In lieu of complicated and expensive laboratory testing several different software tools have been developed to estimate the indoor environmental conditions of buildings. The Fraunhofer‐Institute for Building Physics (IBP) developed a hygrothermal simulation tool. With this software the temperature and moisture conditions of the walls, ceiling and floor constructions, of the indoor air and the energy consumption for the building can be calculated. In the context of the IEA‐Annex 41 project “Moist‐Eng“ a common exercise has been carried out for the validation of such software tools. For the common exercise at the free field investigation area in Holzkirchen (Germany) two identical rooms were used to measure the moisture buffering capacity of several interior finish systems. To address the questions of buffering capacity the IBP developed a hygrothermal simulation tool, WUFI®‐Plus [1]. Using the measurement data from the common exercise calculations were carried out with several software tools for the validation of it. In this paper the results of the laboratory tests and simulation results are described.     

Experimental and numerical study of room airflow under stratum ventilation

This paper investigates the air movement, air temperature profile and gaseous contaminant transportation in an individual office with stratum ventilation. The room temperature is elevated compared with conventional standards. The experimental investigation is carried out in an environmental chamber with the presence of heat generating rectangles used to simulate an occupant and a computer. Measurements of temperature, velocity, and CO₂ concentration are carried out for nine plumb lines in the chamber. Up to sixteen points are measured along each plumb line. The experimental data of the aforesaid three parameters of the individual office in warm condition under stratum ventilation are presented. The experimental data collected are used to validate a re-normalization group (RNG) k–? turbulence model used for the warm condition. The agreements between the predicted values and experimental results are acceptable, which demonstrates the feasibility of simulating indoor airflows at elevated room temperature under stratum ventilation by the RNG k–? turbulence model.     

Floor-supply displacement ventilation for workshops

This paper reported the investigation of the performance of floor-supply displacement ventilation with swirl diffusers or perforated panels under a high cooling load (nearly 90 W/m²). The experiment was carried out in a full-scale environmental chamber to obtain reliable data on the floor-supply displacement ventilation for the validation of a computational-fluid-dynamics (CFD) program. Numerical simulations using CFD program were to evaluate the performance of the system for a large workshop. The impacts of several parameters, such as the air change rate, number of diffusers, diffuser location, occupant location, furniture arrangement, partition location, and arrangement of exhausts, on the indoor environment were investigated based on the thermal comfort level and indoor air quality. This study ranked the impacts of these parameters on indoor environment.