Sensory evaluation of emissions from selected building products exposed to ozone

The interaction of ozone with eight different building products was studied in test chambers. The products were plasterboard, two types of paints on plasterboard, two types of carpet, linoleum, pinewood, and melamine-covered particleboard. Four months of conditioning prior to the experiment had left the products with a low emission. The products' ability to remove ozone from the air covered a wide range. For three of the products (plasterboard with paint, carpet, and pinewood), it was shown that the removal was primarily due to interactions in the products' surfaces and only to a minor extent due to gas-phase reactions. Sensory evaluations were carried out for five of the products, with different ozone-removal potentials. A sensory panel assessed the emissions from sets of two specimens of each product; one specimen was exposed to a high, but realistic, ozone concentration (10 or 80 ppb) and one specimen was exposed to no ozone (background level < 3 ppb). The panel assessed odor intensity and was asked to choose which odor of the two specimens they preferred. The perceivable changes in emissions due to exposure of the products to ozone depended on the type of product. The greatest effect was seen for carpet. Carpet was the only product that showed significantly higher odor intensity when exposed to ozone. Besides, the effect of ozone on preference was strongest for carpet and resulted in a clear negative sensory evaluation. A similar but less pronounced effect was seen for pinewood and plasterboard with paint. No clear preference was seen for melamine and linoleum.     

Health in occupants of energy efficient new homes

A prospective telephone-administered questionnaire study in new home occupants compared general and respiratory health at occupancy and 1 year later in two groups. The test group or cases, was 52 R-2000(TM) homes (128 occupants) built to preset and certified criteria for energy efficient ventilation and construction practices. The control group were 53 new homes (149 occupants) built in the same year in the same geographic area and price range. Analyzed by household, case occupants' summative symptom scores improved significantly over the year of occupancy (Wilcoxon rank sum test, P < 0.006). Analysis of variance of individuals' total symptom scores showed a significant effect of the type of house (P < 0.0001), with lower change of scores in case buildings, but not of age or sex. In comparison with control homes, occupants of case homes reported more improvement in throat irritation (P < 0.004), cough (P < 0.002), fatigue (P < 0.009) and irritability (P < 0.002) with the main change in symptom category being from 'sometimes' to 'never'. Further extension of this pilot study is required to determine if these perceived health benefits are reproducible and/or relate to objective indoor air quality measures. PRACTICAL IMPLICATIONS: New occupants of energy efficient homes with heat recovery ventilators report improvement over 1 year in the symptoms of throat irritation, cough, fatigue, and irritability in comparison with control new home occupants. If this pilot study is reproducible and shown to relate to indoor air quality, prospective new home buyers may be interested in obtaining this health information prior to decision making.     

Interaction between ozone and airborne particulate matter in office air

This study investigated the hypotheses that humans are affected by air pollution caused by ozone and house dust, that the effect of simultaneous exposure to ozone and dust in the air is larger than the effect of these two pollutants individually, and that the effects can be measured as release of cytokines and changes of the respiratory function. Experimental exposures of eight atopic but otherwise healthy subjects were performed in a climate chamber under controlled conditions. The three controlled exposures were about 75 microg/m3 total suspended particulate matter, 0.3 p.p.m. ozone, and the combination of these. The exposure duration was 3 h. The outcome measures were interleukins and cells in nasal lavages (NAL), respiratory function, bronchial metacholine responsiveness, rhinometry symptoms and general well-being in a questionnaire and time course of general irritation on a visual analogue scale. Indications of interactions between exposure types were demonstrated for peak expiratory flow (PEF) (P<0.05) and for discomfort symptoms (P<0.03). Non-significant interactions were found for the concentration of interleukin-8 in NAL. The combined exposure was found to cause significantly more effects than either ozone exposures or dust exposures. This is interpreted as indications of a potentiation caused by the combined exposures to dust and ozone. The findings in this study are based on a limited number of subjects and thus should not be over-interpreted. However, they support the hypothesis that ozone at relatively high concentrations interacts with dust exposures to cause decrements in PEF and increase in discomfort measures. PRACTICAL IMPLICATIONS: If confirmed at lower ozone and dust concentrations this finding could help to explain many problems with indoor air quality reported in offices throughout the world.     

Heterogeneous reactions of ozone and D-limonene on activated carbon

If released in significant amounts, products formed by reactions between ozone (O3) and volatile organic compounds (VOCs) sorbed on activated carbon (AC) filters could degrade indoor air quality (IAQ). Heterogeneous reactions were investigated in laboratory experiments aimed at characterizing reaction products. Effluent air of AC loaded with limonene and exposed to O3 (5.8 ppm) yielded unreacted limonene (501+/-197 microg/m3), low levels of 4-acetyl-1-methylcyclohexene (AMCH) (20+/-2 microg/m3), and limonene oxides (25+/-7 microg/m3). Most of the O3-limonene products remained on the AC, and most (58%) of the limonene remained unreacted on the AC after exposure to a stoichiometric excess of O3 for 48 h. Thus, in addition to known homogenous reactions, O3-limonene reactions occur heterogeneously on AC but to a much lesser extent. However, the fate of 95% of the depleted limonene was not determined; much of the missing portion was attributed to desorption from the AC, but the formation of other secondary indoor air pollutants is possible. VOC-loaded AC air filters exposed to O3 seem unlikely, however, to constitute a significant emission source of reaction products. More studies are necessary to investigate other pollutants, effects of environmental conditions, and VOC releases from AC that may be enhanced by O3 exposure. PRACTICAL IMPLICATIONS: Reactions between ozone and certain volatile organic compounds such as limonene (a common ingredient of many consumer products) occurring on the surface of ventilation filters could impact indoor air quality if products are released in significant amounts. This study suggests that although very small amounts of limonene adsorbed on a filter will react with O3, ventilation filters are not likely to be significant sources of ozone oxidation products. More studies are needed to investigate whether ozone exposure enhances desorption of pollutants from ventilation filters and to measure the formation of formaldehyde and other products that are not easily retained by charcoal filters.     

Ozone in indoor environments: concentration and chemistry

The concentration of indoor ozone depends on a number of factors, including the outdoor ozone concentration, air exchange rates, indoor emission rates, surface removal rates, and reactions between ozone and other chemicals in the air. Outdoor ozone concentrations often display strong diurnal variations, and this adds a dynamic excitation to the transport and chemical mechanisms at play. Hence, indoor ozone concentrations can vary significantly from hour-to-hour, day-to-day, and season-to-season, as well as from room-to-room and structure-to-structure. Under normal conditions, the half-life of ozone indoors is between 7 and 10 min and is determined primarily by surface removal and air exchange. Although reactions between ozone and most other indoor pollutants are thermodynamically favorable, in the majority of cases they are quite slow. Rate constants for reactions of ozone with the more commonly identified indoor pollutants are summarized in this article. They show that only a small fraction of the reactions occur at a rate fast enough to compete with air exchange, assuming typical indoor ozone concentrations. In the case of organic compounds, the "fast" reactions involve compounds with unsaturated carbon-carbon bonds. Although such compounds typically comprise less than 10% of indoor pollutants, their reactions with ozone have the potential to be quite significant as sources of indoor free radicals and multifunctional (-C=O, -COOH, -OH) stable compounds that are often quite odorous. The stable compounds are present as both gas phase and condensed phase species, with the latter contributing to the overall concentration of indoor submicron particles. Indeed, ozone/alkene reactions provide a link between outdoor ozone, outdoor particles and indoor particles. Indoor ozone and the products derived from reactions initiated by indoor ozone are potentially damaging to both human health and materials; more detailed explication of these impacts is an area of active investigation.     

Surface ozone concentrations and ecosystem health: past trends and a guide to future projections

This paper reviews current understanding of the sources and sinks of ozone in the troposphere, recent studies of long-term trends, and the factors which have to be taken into consideration when constructing and interpreting future models of ozone concentration. The factors controlling surface O₃ concentrations are discussed initially to provide a basis for the ensuing discussion, followed by a summary of the evidence for recent trends in ground-level ozone concentrations, i.e. over the past 3 decades, which have shown a significant increase in the annual average in ‘background’ air typical of the unpolluted northern hemisphere. Closer to precursor sources, although urban winter concentrations have increased, rural peak spring and summer concentrations during ozone ‘episodes’ have decreased markedly in response to emissions reductions. In order to determine whether such trends are meaningful, the statistical techniques for determining temporal trends are reviewed. The possible causes of long-term trends in ozone are then discussed, with particular reference to the use of chemistry-transport models to interpret past trends. Such models are also used to make predictions of future trends in surface ozone concentrations, but few are comprehensive in integrating future climate changes with changes in land use and in emissions of ozone precursors. Guidance is given on the likely effects of climate/precursor/chemistry interactions so that model predictions can be judged.     

Ozone in Residential Air: Concentrations,I/O Ratios,Indoor Chemistry,and Exposures

Ozone concentrations were measured in indoor and outdoor residential air during the summer of 1992. Six homes located in a New Jersey suburban area were chosen for analysis, and each home was monitored for 6 days under different ventilation and indoor combustion conditions. The 5-hour average ozone concentration outdoors over the monitoring period was 95 ± 36 ppbv. One third of the days exceeded the National Ambient Air Quality Standard (NAAQS), one-hour maximum concentration of 120 ppb. The mean indoor to outdoor (I/O) ratios of ozone concentration ranged from 0.22 ± 0.09 to 0.62 ± 0.11, depending upon ventilation rate and indoor gas combustion. The presence of indoor gas combustion can significantly decrease the I/O ratio. Because of the great amount of time that people spend indoors, the indoor residential exposures were estimated to account for 57% of the total residential exposures. One type of the possible gas-phase reactions for indoor ozone, the reaction of ozone with a volatile organic compound containing unsaturated carbon-carbon bonds, is discussed with some supporting evidence provided in the study.     

The effect of an ion generator on indoor air quality in a residential room

Ion generators charge particles with a corona prior to their removal on collector plates or indoor surfaces and also emit ozone, which can react with terpenes to yield secondary organic aerosol, carbonyls, carboxylic acids, and free radicals. This study characterized the indoor air quality implications of operating an ion generator in a 27 m(3) residential room, with four different test room configurations. Two room configurations had carpet overlaying the original flooring of stained/sealed concrete, and for one configuration with and without carpet, a plug-in air freshener was used as a terpene source. Measurements included airborne sampling of particulate matter (0.015-20 μm), terpenes and C(1) -C(4) and C(6) -C(10) aldehydes, ozone concentrations, and air exchange rates. When the heating, ventilating, and air-conditioning system was not operating (room air exchange rate = ～0.5/h), the use of the ion generator in the presence of the air freshener led to a net increase in ultrafine particles (<0.1 μm). Also, increased concentrations of ozone were observed regardless of air freshener presence, as well as increases in formaldehyde and nonanal, albeit within measurement uncertainty in some cases. Thus, it may be prudent to limit ion generator use indoors until evidence of safety can be ascertained. PRACTICAL IMPLICATIONS: Portable ion generators are intended to clean the air of particles, but they may emit ozone as a byproduct of their operation, which has the potential to degrade indoor air quality. This study showed that under certain conditions in a residential room, the use of a portable ion generator can increase concentrations of ozone and, to a lesser degree, potentially aldehydes. Also, if operated in the presence of a plug-in air freshener that emits terpenes, its use can increase concentrations of secondary organic aerosol in the ultrafine size range.     

Outdoor ozone and building-related symptoms in the BASE study

Reactions between ozone and indoor contaminants may influence human health and indoor air quality. The U.S. EPA Building Assessment Survey and Evaluation (BASE) study data were analyzed for associations between ambient ozone concentrations and building-related symptom (BRS) prevalence. Multiple logistic regression (MLR) models, adjusted for personal, workplace, and environmental variables, revealed positive relationships (P < 0.05) between ambient ozone concentrations and upper respiratory (UR), dry eyes, neurological and headache BRS (odds ratios ranged from 1.03 to 1.04 per 10 mug/m(3) increase in ambient ozone concentrations). Other BRS had marginally significant relationships with ambient ozone (P < 0.10). A linear dose-response in UR symptoms was observed with increasing ambient ozone (P = 0.03); most other symptoms showed similar but not statistically significant trends. Ambient ozone correlated with indoor concentrations of some aldehydes, a pattern suggesting the occurrence of indoor ozone chemistry. Coupled with the MLR ambient ozone-BRS analysis, this correlation is consistent with the hypothesis that ozone-initiated indoor reactions play an important role in indoor air quality and building occupant health. Replication with increased statistical power and with longitudinal data is needed. If the observed associations are confirmed as causal, ventilation system ozone removal technologies could reduce UR BRS prevalence when higher ambient ozone levels are present. PRACTICAL IMPLICATIONS: This paper provides strong statistical evidence that supports (but does not prove) the hypothesis that ozone entrained into buildings from the outdoor air is involved in increasing the frequency that occupants experience and a range of upper and lower respiratory, mucosal and neurological symptoms by as much as a factor of 2 when ambient ozone levels increase from those found in low-ozone regions to those typical of high-ozone regions. Although replication is needed, the implication is that reducing the amount of ozone entrained into building ventilation systems, either by ambient pollution reduction or engineered gas-phase filtration, may substantially reduce the prevalence of these symptoms experienced by occupants.     

Assessment of airborne bacteria and fungi in food courts

A study was undertaken to determine the effect of variations in temperature, relative humidity, occupancy density and location (indoor/outdoor) on the concentrations of viable airborne bacterial and fungal spores at an air-conditioned and a non air-conditioned food stall in Singapore. Typically, bioaerosols consisted of 50.5% bacteria and 49.5% fungi in the indoor environment. In contrast, for the outdoor environment, bacteria on an average only accounted for 20.6% of culturable airborne microorganisms whereas fungal concentrations were 79.4%. Results on bioaerosol size distributions revealed that 67% of indoor bacteria and 68% of outdoor bacteria, 85% of indoor fungi and 68% of outdoor fungi were associated with fine mode particulates (<3.3 μm). Occupant density was the key factor that affected indoor airborne bacteria concentrations while concentrations of outdoor airborne bacteria depended strongly on ambient temperature. Indoor fungal concentration was positively correlated to relative humidity whereas outdoor fungal concentration was positively correlated to relative humidity and negatively correlated to temperature. The study also compared the biological air quality between a non air-conditioned food stall (Stall A) and an air-conditioned food stall (Stall B). The dining area of the former had lower bacterial concentrations as compared to the latter, while fungal spore’s concentrations showed a reverse trend. The dominant airborne bacteria genera were Staphylococcus, Pseudomonas, Alcaligens, and Corynebacterium whereas Penicillium, Aspergillus and Cladosporium were the most common fungal genera and groups in both food stalls.     

Transport of airborne particles within a room

The objective of this study is to test a technique used to analyze contaminant transport in the wake of a bluff body under controlled experimental conditions for application to aerosol transport in a complex furnished room. Specifically, the hypothesis tested by our work is that the dispersion of contaminants in a room is related to the turbulence kinetic energy and length scale. This turbulence is, in turn, determined by the size and shape of furnishings within the room and by the ventilation characteristics. This approach was tested for indoor dispersion through computational fluid dynamics simulations and laboratory experiments. In each, 3 mum aerosols were released in a furnished room with varied contaminant release locations (at the inlet vent or under a desk). The realizable k approximately epsilon model was employed in the simulations, followed by a Lagrangian particle trajectory simulation used as input for an in-house FORTRAN code to compute aerosol concentration. For the experiments, concentrations were measured simultaneously at seven locations by laser photometry, and air velocity was measured using laser Doppler velocimetry. The results suggest that turbulent diffusion is a significant factor in contaminant residence time in a furnished room. This procedure was then expanded to develop a simplified correlation between contaminant residence time and the number of enclosing surfaces around a point containing the contaminant. Practical Implications The work presented here provides a methodology for relating local aerosol residence time to properties of room ventilation and furniture arrangement. This technique may be used to assess probable locations of high concentration by knowing only the particle release location, furniture configuration, inlet and outlet locations, and air speeds, which are all observable features. Applications of this method include development of 'rules of thumb' for first responders entering a room where an agent has been released and selection of sampler locations to monitor conditions in sensitive areas.     

Exposure of children to airborne particulate matter of different size fractions during indoor physical education at school

Although moderate regular aerobic exercise is recommended for good health, adverse health consequences may be incurred by people who exercise in areas with high ambient pollution, such as in the centres of large cities with dense traffic. The exposure of children during exercise is of special concern because of their higher sensitivity to air pollutants. The size-segregated mass concentration of particulate matter was measured in a naturally ventilated elementary school gym during eight campaigns, seven to ten days long, from November 2005 through August 2006 in a central part of Prague (Czech Republic). The air was sampled using a five-stage cascade impactor. The indoor concentrations of PM_2.5 recorded in the gym exceeded the WHO recommended 24-hour limit of 25 μg m⁻³ in 50% of the days measured. The average 24-h concentrations of PM_2.5 (24.03 μg m⁻³) in the studied school room did not differ much from those obtained from the nearest fixed site monitor (25.47 μg m⁻³) and the indoor and ambient concentrations were closely correlated (correlation coefficient 0.91), suggesting a high outdoor-to-indoor penetration rate. The coarse indoor fraction concentration (PM_2.5–10) was associated with the number of exercising pupils (correlation coefficient 0.77), indicating that human activity is its main source. Considering the high pulmonary ventilation rate of exercising children and high outdoor particulate matter concentrations, the levels of both coarse and fine aerosols may represent a potential health risk for sensitive individuals during their physical education performed in naturally ventilated gyms in urban areas with high traffic intensity.     

A comparison of airborne ergosterol, glucan and Air-O-Cell data in relation to physical assessments of mold damage and some other parameters

We report here a comparison of long duration air samples in 110 homes where the material collected on open faced filter cassettes was analyzed for beta 1,3-d glucan, ergosterol, cholesterol and endotoxin. These data were then compared to careful estimates of visible mold and Air-O-Cell data. All the values found except cholesterol were of a similar magnitude to values reported in the limited number of studies available. Glucan was measured with a factor G based assay of the Limulus Amebocyte Lysate followed by size exclusion chromatography. This showed that the majority of airborne glucan found in these houses was fungal in origin arising from both yeasts and intact spores, as well as hyphal and spore fragments. Hyphal and spore fragments together represented 16% of the intact spore counts but over a broad range. Correlations between airborne glucan were strong for ergosterol and visible mold. However, airborne ergosterol was more highly correlated to visible mold than glucan. Endotoxin and Air-O-Cell measurements were poorly or not related to the other measures in the study. This study provides confidence that long duration air samples of the toxin glucan and ergosterol are related to building damage. PRACTICAL IMPLICATIONS: Some studies of damp buildings have shown a relationship between extent of water/mold damage and symptoms. This study compared long duration air samples for glucan and ergosterol to extent of visible mold in houses measuring also the nature of the glucans present. Both measures were highly correlated to extent of visible mold damage in the houses; ergosterol was somewhat superior. Spore counts or prevalence of Asp/Pen in Air-O-Cell samples was not related to extent of visible mold damage but the observation of hyphal fragments was more likely when mold damage was present. This indicates that rigorous assessment of mold damage is a useful measure.     

Exposure to the mixtures of organic compounds in homes in Japan

The aim of the study reported herein was to characterize occupants' simultaneous exposure to mixtures of organic compounds in homes. Statistical distributions for concentrations of 28 organic compounds (17 VOCs and 11 aldehydes) measured in 1417 homes were generated to analyze concentration distributions. Three candidate distributions were identified for fitting the measured data: log-normal, exponential and gamma distributions. It appears from the results of fitting tests that gamma distributions are capable of representing 28 compound concentrations. Probability distributions show that formaldehyde and acetaldehyde ranged from 25 to 220 microg/m3 at 90% probabilities and most VOCs ranged from 3 to 80 microg/m3 at 90% probabilities. In order to characterize the occupant's exposure to the mixtures, the joint probability distributions of organic compounds were generated from the best-fitted distributions of individual compounds under the assumption that concentrations of organic compounds are mutually independent in homes. These joint distributions provided the statistical data for characterizing the occupant's exposure to the mixtures of organic compounds in homes. PRACTICAL IMPLICATIONS: Occupants often encounter not just one compound in indoor environments, but many compounds due to their concurrent emissions from several sources. This paper describes characteristics of statistical distributions for concentrations of 17 VOCs and 11 aldehydes in homes in Japan. After applying a probability model to the occupants' simultaneous exposure to mixtures of organic compounds, the authors interpret the current state of the occupant's exposure to the mixtures within homes using joint probability distributions of 28 organic compounds.     

Characterization of winter airborne particles at Emperor Qin's Terra-cotta Museum, China

Daytime and nighttime total suspended particulate matters (TSP) were collected inside and outside Emperor Qin's Terra-cotta Museum, the most popular on-site museum in China, in winter 2008. The purpose of this study was to investigate the contribution of visitors to indoor airborne particles in two display halls with different architectural and ventilating conditions, including Exhibition Hall and Pit No.1. Morphological and elemental analyses of 7-day individual particle samples were performed with scanning electron microscopy and energy dispersive X-ray spectrometer (SEM-EDX). Particle mass concentrations in Exhibition Hall and Pit No.1 were in a range of 54.7–291.7 μg m^− 3 and 95.3–285.4 μg m^− 3 with maximum diameters of 17.5 μm and 26.0 μm, respectively. In most sampling days, daytime/nighttime particle mass ratios in Exhibition Hall (1.30–3.12) were higher than those in Pit No.1 (0.96–2.59), indicating more contribution of the tourist flow in Exhibition Hall than in Pit No. 1. The maximum of particle size distributions were in a range of 0.5–1.0 μm, with the highest abundance (43.4%) occurred in Exhibition Hall at night. The majority of airborne particles at the Museum was composed of soil dust, S-containing particles, and low-Z particles like soot aggregate and biogenic particles. Both size distributions and particle types were found to be associated with visitor numbers in Exhibition Hall and with natural ventilation in Pit No.1. No significant influence of visitors on indoor temperature and relative humidity (RH) was found in either display halls. Those baseline data on the nature of the airborne particles inside the Museum can be incorporated into the maintenance criteria, display management, and ventilation strategy by conservators of the museum.