Characterization of indoor air quality using multiple measurements of nitrogen dioxide

Indoor air quality can be affected by indoor sources, ventilation, decay and outdoor levels. Although technologies exist to measure these factors, direct measurements are often difficult. The purpose of this study was to develop an alternative method to characterize indoor environmental factors by multiple indoor and outdoor measurements. Daily indoor and outdoor NO2 concentrations were measured for 30 consecutive days in 28 houses in Brisbane, Australia, and for 21 consecutive days in 37 houses in Seoul, Korea. Using a mass balance model and regression analysis, penetration factor (ventilation rate divided by the sum of ventilation rate and deposition constant) and source strength factor (source strength divided by the sum of ventilation rate and deposition constant) were calculated using multiple indoor and outdoor measurements. Subsequently, the ventilation rate and NO2 source strength were estimated. Geometric means of ventilation rate were 1.44 air change per hour (ACH) in Brisbane, assuming a residential NO2 deposition constant of 1.05/h, and 1.36 ACH in Seoul, with the measured residential NO2 deposition constant of 0.94/h. Source strengths of NO2 were 15.8 +/- 18.2 and 44.7 +/- 38.1 microg/m3/h in Brisbane and Seoul, respectively. In conclusion, indoor environmental factors were effectively characterized by this method using multiple indoor and outdoor measurements.     

Effect of ventilation and filtration on submicrometer particles in an indoor environment

The effect of filtration and ventilation on reduction of submicrometer particle concentration indoors was investigated in an office building. The air-handling system consisting of dry media filters and an air-conditioning unit, reduced particle concentration levels by 34%. The characteristics of indoor airborne particles were dominated by, and followed the pattern of, outdoor air, with vehicle combustion aerosols as the main pollutant. The ratio indoor/outdoor particle concentration varied between 14 and 26% for different sub-zones. The presence of significant source of particles indoors was not observed. A simple mathematical model predicting evolution of particles indoors is presented. The model, based on a particle number balance equation, was validated with experimental data and showed very good agreement between predicted and measured parameters.     

Control strategies for sub-micrometer particles indoors: model study of air filtration and ventilation

The effects of air filtration and ventilation on indoor particles were investigated using a single-zone mathematical model. Particle concentration indoors was predicted for several I/O conditions representing scenarios likely to occur in naturally and mechanically ventilated buildings. The effects were studied for static and dynamic conditions in a hypothetical office building. The input parameters were based on real-world data. For conditions with high particle concentrations outdoors, it is recommended to reduce the amount of outdoor air delivered indoors and the necessary reduction level can be quantified by the model simulation. Consideration should also be given to the thermal comfort and minimum outdoor air required for occupants. For conditions dominated by an indoor source, it is recommended to increase the amount of outdoor air delivered indoors and to reduce the amount of return air. Air filtration and ventilation reduce particle concentrations indoors, with the overall effect depending on efficiency, location and the number of filters applied. The assessment of indoor air quality for specific conditions could be easily calculated by the model using user-defined input parameters.     

A review of ventilation and the quality of ventilation air

Ventilation is pivotal in terms of securing optimum indoor air quality. In addition, it also has a major impact on energy use in buildings. It is important, therefore, that the role and impact of ventilation is fully understood and that ventilation is employed efficiently. The purpose of this paper is to review these aspects with particular reference to recent research and developments. Key aspects are concerned with identifying the role of ventilation and reviewing this role in the context of the other measures that must be taken to secure a healthy indoor environment. References are particularly made to the development of standards and recent related research. Although good progress is being made, areas that still need to be addressed include maintaining good outdoor air quality and preventing contaminated outdoor air from entering buildings. The outcome of recent research must also be disseminated in practical ways to policy makers, building occupiers and practitioners. Good indoor climate can be achieved, not so much by introducing expensive concepts, but by developing a rationale approach to identifying needs and applying the necessary tools to deal with each need.     

Relationship between outdoor and indoor air quality in eight French schools

In the frame of the French national research program PRIMEQUAL (inter-ministry program for better air quality in urban environments), measurements of outdoor and indoor pollution have been carried out in eight schools in La Rochelle (France) and its suburbs. The buildings were naturally ventilated by opening the windows, or mechanically ventilated, and showed various air permeabilities. Ozone, nitrogen oxides (NO and NO(2)), and airborne particle (particle counts within 15 size intervals ranging from 0.3 to 15 mum) concentrations were continuously monitored indoors and outdoors for two 2-week periods. The indoor humidity, temperature, CO(2) concentration (an indicator of occupancy), window openings and building permeability were also measured. The temporal profiles of indoor and outdoor concentrations show ozone and nitrogen oxides behave differently: NO and NO(2) indoor/outdoor concentration ratios (I/O) were found to vary in a range from 0.5 to 1, and from 0.88 to 1, respectively, but no correlation with building permeability was observed. On the contrary, I/O ratios of ozone vary in a range from 0 to 0.45 and seem to be strongly influenced by the building air-tightness: the more airtight the building envelope, the lower the ratio. Occupancy, through re-suspension of previously deposited particles and possible particle generation, strongly influences the indoor concentration level of airborne particles. However, this influence decreases with particle size, reflecting the way deposition velocities vary as a function of size. The influence of particle size on deposition and penetration across the building envelope is also discussed by analyzing the I/O ratios measured when the buildings were unoccupied, by comparing the indoor concentrations measured when the buildings were occupied and when they were not (O/U ratios), and by referring to previously published studies focussing on this topic. Except one case, I/O were found to vary in the range from 0.03 to 1.79. All O/U are greater than one and increase up to 100 with particle size. PRACTICAL IMPLICATIONS: Assessing children's total exposure requires the knowledge of outdoor and indoor air contaminant concentrations. The study presented here provides data on compared outdoor and indoor concentration levels in school buildings, as well as information on the parameters influencing the relationship between outdoor and indoor air quality. It may be used as a basis for estimating indoor concentrations from outdoor concentrations data, or as a first step in designing buildings sheltering children against atmospheric pollution.     

Ventilation effectiveness as an indicator of occupant exposure to particles from indoor sources

Ventilation effectiveness is an indicator of the quality of supply air distribution in ventilated rooms. It is a representation of how well a considered space is ventilated compared to a perfect air mixing condition. Depending on pollutant properties and source position relative to the airflow, ventilation effectiveness can more or less successfully be used as an indicator of air quality and human exposure. This paper presents an experimentally and numerically based study that examines the relationship between ventilation effectiveness and particle concentration in typical indoor environments. The results show that the relationship varies predominantly with airflow pattern and particle properties. Fine particles (1 μm) follow the airflow pattern more strictly than coarse particles (7 μm), and the high ventilation effectiveness indicates better removal of fine particles than coarse particles. When a ventilation system provides high mixing in the space and ventilation effectiveness is close to one, particle sizes and source location have a relatively small effect on particle concentration in the breathing zone. However, when the supply air is short circuited and large stagnation zones exist within the space, the particle concentration in the breathing zone varies with particle size, source location, and airflow pattern. Generally, the results show that for fine particles (1 μm), increase of ventilation effectiveness reduces occupant exposure; while for coarser particles (7 μm), source location and airflow around the pollutant source are the major variables that affect human exposure.     

Indoor air quality in Portuguese schools: levels and sources of pollutants

Indoor air quality (IAQ) parameters in 73 primary classrooms in Porto were examined for the purpose of assessing levels of volatile organic compounds (VOCs), aldehydes, particulate matter, ventilation rates and bioaerosols within and between schools, and potential sources. Levels of VOCs, aldehydes, PM_2.5, PM₁₀, bacteria and fungi, carbon dioxide (CO₂), carbon monoxide, temperature and relative humidity were measured indoors and outdoors and a walkthrough survey was performed concurrently. Ventilation rates were derived from CO₂ and occupancy data. Concentrations of CO₂ exceeding 1000 ppm were often encountered, indicating poor ventilation. Most VOCs had low concentrations (median of individual species <5 μg/m³) and were below the respective WHO guidelines. Concentrations of particulate matter and culturable bacteria were frequently higher than guidelines/reference values. The variability of VOCs, aldehydes, bioaerosol concentrations, and CO₂ levels between schools exceeded the variability within schools. These findings indicate that IAQ problems may persist in classrooms where pollutant sources exist and classrooms are poorly ventilated; source control strategies (related to building location, occupant behavior, maintenance/cleaning activities) are deemed to be the most reliable for the prevention of adverse health consequences in children in schools.     

Ventilation in public housing: implications for indoor nitrogen dioxide concentrations

Although elevated nitrogen dioxide (NO2) exposures may exacerbate asthma, few studies have examined indoor NO2 levels in low-income, urban neighborhoods, where asthma prevalence is high. As part of the Healthy Public Housing Initiative, NO2 was measured in 77 homes within three Boston public housing developments, using Palmes tubes placed in the kitchen, living room, and outdoors. Air exchange rates (AERs) were assessed using a perfluorocarbon tracer technique. Overall NO2 levels were [mean (ppb)+/-s.d.]: kitchen (43+/-20, n=100), living room (36+/-17, n=102), outdoor (19+/-6, n=91). Indoor NO2 levels were significantly higher in the heating season (living room: 43 ppb vs. 26 ppb, kitchen: 50 ppb vs. 33 ppb), while AERs were significantly lower in the heating season (medians 0.49/h vs. 0.85/h). Significant univariate predictors of indoor concentrations include: outdoor NO2 levels, AERs, and occupancy. AERs and outdoor NO2 remained significant in multivariate models (P<0.05). A dummy variable for supplemental heating with gas stove was not significant (P=0.14), but had a large, positive coefficient. Indoor NO2 levels in this cohort are higher than those generally reported in residential US settings, associated in part with increased gas stove usage and decreased AERs during the heating season. PRACTICAL IMPLICATIONS: Indoor air quality is mainly a function of outdoor concentrations, indoor sources, ventilation, and residential behavior. Indoor exposures to nitrogen dioxide and other combustion pollutants may be elevated within low-income housing developments due to the presence of multiple sources, poor ventilation, small apartment size, and behavioral responses to apartment conditions (e.g. supplemental heating with gas stove). This information may be used by housing authorities and other landlords to decrease potential environmental stressors, through interventions such as source substitution and improved ventilation, particularly for sensitive sub-populations such as asthmatics.     

Estimation of odour intensity of indoor air pollutants from building materials with a multi-gas sensor system

This study shows an approach to estimate odour intensity in an indoor environment with a multi-gas sensor system. The sensor system uses 38 non-specific gas sensors, each of which responds to a wide range of different volatile compounds. Due to the complexity of indoor air pollution, the study focuses on emissions of building products as one of the major contributors to indoor air quality. The system has been calibrated and tested, combining measurements from gas sensor systems and assessments of odour intensity by a human panel. To find a relation between the sensor signal and the odour intensity, a data processing model has been developed comprising a classification and a class-specific regression method. The model is able to map the odour intensity to the sensor signal pattern in order to predict the odour intensity caused by the investigated building products. Investigations with varying relative humidity have shown a significant influence by the humidity level, which will be considered for future measurements.     

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.     

Comparison of mold concentrations quantified by MSQPCR in indoor and outdoor air sampled simultaneously

Mold specific quantitative PCR (MSQPCR) was used to measure the concentrations of the 36 mold species in indoor and outdoor air samples that were taken simultaneously for 48 h in and around 17 homes in Cincinnati, Ohio. The total spore concentrations of 353 per m(3) of indoor air and 827 per m(3) of outdoor air samples were significantly different (por=0.5). These results suggest that interpretation of the meaning of short-term (<48 h) mold measurements in indoor and outdoor air samples must be made with caution.     

Relationship of indoor and outdoor air pollutants in a naturally ventilated historical building envelope

Concentrations of NO₂, O₃, SO₂, acetic and formic acids, HNO₃ and NH₃ were measured inside and outside a historical building, the Baroque Library Hall (BLH) in the National Library in Prague (Czech Republic). The naturally ventilated system of the building, the restriction of personnel access, reduced groups of visitors and absence of activities which could influence indoor pollutant concentrations are characteristics that make the Baroque Library Hall a suitable location to study the influence of outdoor environment on the indoor air quality. The relationship between indoor and outdoor (I/O) concentration was investigated to assess the infiltration of outdoor generated pollutants. Outdoor and indoor pollution sources were determined and, infiltration of ammonium nitrate and a shift of the equilibrium to the gas phase were the reason for the high concentration of ammonia measured inside the BLH. A significant seasonal variation was observed and interpreted as a consequence of different infiltration regime associated with indoor–outdoor temperature differences, which in addition drives dilution processes of indoor generated pollutants. Based on the indoor air quality assessment performed in the BLH with regard to human and material exposure, there is reason for concern about material preservation and in particular paper at the BLH.     

Preventing the entry of outdoor particles with the indoor positive pressure control method: Analysis of influencing factors and cost

Maintaining positive pressure indoors with a mechanical ventilation system is a popular control method for preventing the entry of outdoor airborne particles. This paper analyzes the factors which affect the satisfied superfluous airflow rates of positive pressure control. Through modeling a large amount of cases with a validated model, the factors, e.g. temperature difference, outdoor wind velocity, effective air leakage gaps in the envelopes, the area of the air leakage and the room, were analyzed. Based on the theoretical model, a correlating equation to calculate the satisfied superfluous airflow rate was established by multiple full quadratic regressions. The correlating equation is simple for engineers or designers to use to determine the satisfied superfluous airflow rate. This paper also aims to find which method, pressure control or indoor air cleaning, costs less to prevent the same amount of outdoor-originated particles from entering indoor environments. Generally speaking, indoor air cleaning control method requires less supply airflow rate than positive pressure control method for reducing the concentration of indoor particles with outdoor origin. An exception for this is a situation with a very low indoor/outdoor particle concentration (I/O ratio) requirement.     

Inhalation intake fraction of pollutants from episodic indoor emissions

The intake fraction is the attributable pollutant mass inhaled by an exposed population per unit mass released from a source. In this paper, mathematical models are combined with empirical data to explore how intake fraction varies with governing parameters for episodic indoor pollutant releases, such as those from cleaning, cooking, or smoking. Broadly, the intake fraction depends on building-related factors (e.g., ventilation rate), occupant factors (e.g., occupancy), and pollutant dynamic factors (e.g., sorption). In the simple case of the episodic release of a nonreactive pollutant into a well-mixed indoor space with steady occupancy and constant ventilation and breathing rates, the intake fraction is the ratio of the occupants’ volumetric breathing rate to the building's ventilation flow rate. Factors such as incomplete mixing, time-varying occupancy, and sorptive interactions modify this basic relationship.     

The impact of particle filtration on indoor air quality in a classroom near a highway

A pilot study was performed to investigate whether the application of a new mechanical ventilation system with a fine F8 (MERV14) filter could improve indoor air quality in a high school near the Amsterdam ring road. PM10, PM2.5, and black carbon (BC) concentrations were measured continuously inside an occupied intervention classroom and outside the school during three sampling periods in the winter of 2013/2014. Initially, 3 weeks of baseline measurements were performed, with the existing ventilation system and normal ventilation habits. Next, an intervention study was performed. A new ventilation system was installed in the classroom, and measurements were performed during 8 school weeks, in alternating 2‐week periods with and without the filter in the ventilation system under otherwise identical ventilation conditions. Indoor/outdoor ratios measured during the weeks with filter were compared with those measured without filter to evaluate the ability of the F8 filter to improve indoor air quality. During teaching hours, the filter reduced BC exposure by, on average, 36%. For PM10 and PM2.5, a reduction of 34% and 30% was found, respectively. This implies that application of a fine filter can reduce the exposure of schoolchildren to traffic exhaust at hot spot locations by about one‐third.     

Characterizing ultrafine particles and other air pollutants at five schools in South Texas

This study examined five schools with different ventilation systems in both urban and rural areas in South Texas. Total particle number concentration, ultrafine particle (UFP, diameter < 100 nm) size distribution, PM(2.5) , and CO(2) were measured simultaneously inside and outside of various school microenvironments. Human activities, ventilation settings, and occupancy were recorded. The study found a greater variation of indoor particle number concentration (0.6 × 10(3) -29.3 × 10(3) #/cm(3) ) than of outdoor (1.6 × 10(3) -16.0 × 10(3) #/cm(3) ). The most important factors affecting indoor UFP levels were related to various indoor sources. Gas fan heaters increased the indoor-to-outdoor ratio (I/O ratio) of total particle number concentrations to 30.0. Food-related activities, cleaning, and painting also contributed to the increased indoor particle number concentration with I/O ratios larger than 1.0. Without indoor sources, the I/O ratios for total particles varied from 0.12 to 0.66 for the five ventilation systems studied. The I/O ratio decreased when the outdoor total particle number concentration increased. Particles with diameters <60 nm were less likely to penetrate and stay airborne in indoor environments than larger particles and were measured with smaller I/O ratios. PRACTICAL IMPLICATIONS: From an exposure assessment perspective, schools are important and little-studied microenvironments where students congregate and spend a large proportion of their active time. This study provides information for indoor and outdoor ultrafine particle concentrations at different types of school microenvironments. These data may allow future epidemiological studies to better estimate exposure and assess ultrafine particles health effects among students.     

Uncertainty in indoor air quality and grey system method

Based on analysis of uncertainty, this paper presents grey system theory to handle the “grey” characteristic of IAQ. Grey comprehensive analysis of indoor air quality reveals that we should pay more attention to the air purification and humidity control in the design and maintenance of HVAC. In order to represent grey characteristic of IAQ system, the educed grey IAQ models can identify the variation intervals of key IAQ model parameters that are lack of directly measurable messages in practical situations. Furthermore, grey assessment is an effective multifactor comprehensive assessment method that can express the integrative influence of contamination indexes on indoor air quality. We can determine the IAQ grade and make comparison according to the grey incidence matrix R.     

Comparison of strategies to improve indoor air quality at the pre-occupancy stage in new apartment buildings

Indoor air quality of new apartment buildings, which is known to cause Sick Housing Syndrome, has become a major concern among apartment residents as well as construction companies in Korea. Recently, the Indoor Air Quality Management Act, a regulation that limits concentration levels of formaldehyde and five volatile organic compounds in new apartment buildings, has been implemented. In this study, the effects of ventilation and decomposing agents were investigated and compared, which could be used at the pre-occupancy stage as solutions to high VOCs concentration levels in new apartment buildings. Six housing units were investigated under different conditions to assess the extent of the improvement in indoor air quality. The results demonstrate that ventilation is an effective way to control indoor air pollution caused by VOCs emissions, and the effect of decomposing agents on improving indoor air quality depends on the types of VOCs.     

Effect of mechanically induced ventilation on the indoor air quality of building envelopes

Experiments were conducted to study the effect of mechanically induced fresh-air ventilation on the indoor air quality (IAQ) of the Tuskegee Healthy House (THH), selecting the outdoor weather conditions almost identical during the “fan OFF” and “fan ON” periods. Measurements of outdoor and indoor temperature and relative humidity (RH), in addition to the indoor dust particle concentration levels and interior wall moisture content, were systematically carried out during the summer month of August 2008. Results show that the effect of mechanically induced ventilation (“fan ON” period) is to raise the indoor RH, interior wall moisture content, and indoor dust particle concentration values significantly above those measured during the “fan OFF” period. The indoor temperature increases only slightly during the “fan ON” period.     

Improving energy performance of school buildings while ensuring indoor air quality ventilation

Energy conscious design of school buildings, as well as deemed-to-satisfy provisions in a Performance Based Energy Code, should address the problem known as the energy efficiency—thermal comfort—indoor air quality dilemma (EE-TC-IAQ Dilemma). In warm and moderate climates, the large internal heat sources usually found in school buildings prevent achieving thermal comfort without active cooling in summer, but are not sufficient to eliminate the need for heating in winter. Commonly used air-conditioners do not improve air quality, while natural ventilation induces uncontrolled energy losses. In this study, a step by step process was used for the development of deemed-to-satisfy design solutions, which cope with the EE-TC-IAQ Dilemma, for a performance based code. A distinction is made between improving building design variables and improving ventilation schemes. Results indicate that implementation of improved ventilation schemes in an otherwise well designed energy-conscious building result in savings of 28–30% and 17–18% for northern and southern classroom orientations, respectively.