A critical review of reported air concentrations of organic compounds in aircraft cabins

This paper presents a review and assessment of aircraft cabin air quality studies with measured levels of volatile and semivolatile organic compounds (VOCs and SVOCs). VOC and SVOC concentrations reported for aircraft cabins are compared with those reported for residential and office buildings and for passenger compartments of other types of transportation. An assessment of measurement technologies and quality assurance procedures is included. The six studies reviewed in the paper range in coverage from two to about 30 flights per study. None of the monitored flights included any unusual or episodic events that could affect cabin air quality. Most studies have used scientifically sound methods for measurements. Study results indicate that under routine aircraft operations, contaminant levels in aircraft cabins are similar to those in residential and office buildings, with two exceptions: (1). levels of ethanol and acetone, indicators of bioeffluents and chemicals from consumer products are higher in aircraft than in home or office environments, and (2). levels of certain chlorinated hydrocarbons and fuel-related contaminants are higher in residential/office buildings than in aircraft. Similarly, ethanol and acetone levels are higher in aircraft than in other transportation modes but the levels of some pollutants, such as m-/p-xylenes, tend to be lower in aircraft.     

Application of proton‐transfer‐reaction‐mass‐spectrometry for Indoor Air Quality research

In the field of Indoor Air Quality research, the measurement of volatile organic compounds (VOCs) demands instruments that are rapid, mobile, robust, highly sensitive and allow for simultaneous monitoring of multiple compounds. These instruments should also compensate for possible interferences from permanent gases and air humidity. Proton‐transfer‐reaction‐mass‐spectrometry (PTR‐MS) has proved to be a valuable and promising technique that fits the mentioned requirements for a suitable online measuring device. In this study, five exemplary applications of PTR‐MS are described: (i) release of paint additives during drying process, (ii) emission of VOCs from active hardcopy devices, (iii) reference material evaluation, (iv) diffusion studies, and (v) emission testing of building products. The examples are selected to illustrate possibilities and limitations of the PTR technique in this field of research. The quadruple‐based PTR‐QMS was able to determine the emission characteristics during the experiments, especially in case of depleting emission sources (e.g., reference material). This allows for chemometrical analysis of the measured release patterns and detection of underlying processes. However, PTR‐QMS reaches a functional limit in case of compound identification. If identification of VOCs is necessary, the measurements need to be accompanied by GC/MS analytics or a PTR instrument with higher mass‐resolution (e.g., PTR‐TOF‐MS).     

Organic compounds in office environments - sensory irritation, odor, measurements and the role of reactive chemistry

Abstract Sensory irritation and odor effects of organic compounds in indoor environments are reviewed. It is proposed to subdivide volatile organic compounds (VOCs) into four categories: (i) chemically non-reactive, (ii) chemically 'reactive', (iii) biologically reactive (i.e. form chemical bonds to receptor sites in mucous membranes) and (iv) toxic compounds. Chemically non-reactive VOCs are considered non-irritants at typical indoor air levels. However, compounds with low odor thresholds contribute to the overall perception of the indoor air quality. Reported sensory irritation may be the result of odor annoyance. It appears that odor thresholds for many VOCs probably are considerably lower than previously reported. This explains why many building materials persistently are perceived as odorous, although the concentrations of the detected organic compounds are close to or below their reported odor thresholds. Ozone reacts with certain alkenes to form a gas and aerosol phase of oxidation products, some of which are sensory irritants. However, all of the sensory irritating species have not yet been identified and whether the secondary aerosols (ultrafine and fine particles) contribute to sensory irritation requires investigation. Low relative humidity may exacerbate the sensory irritation impact. Practical Implications Certain odors, in addition to odor annoyance, may result in psychological effects and distraction from work. Some building materials continually cause perceivable odors, because the odor thresholds of the emitted compounds are low. Some oxidation products of alkenes (e.g. terpenes) may contribute to eye and airway symptoms under certain conditions and low relative humidity.     

Effects of exposure to carbon dioxide and bioeffluents on perceived air quality,self‐assessed acute health symptoms,and cognitive performance

The purpose of this study was to examine the effects on humans of exposure to carbon dioxide (CO₂) and bioeffluents. In three of the five exposures, the outdoor air supply rate was high enough to remove bioeffluents, resulting in a CO₂ level of 500 ppm. Chemically pure CO₂ was added to this reference condition to create exposure conditions with CO₂ at 1000 or 3000 ppm. In two further conditions, the outdoor air supply rate was restricted so that the bioeffluent CO₂ reached 1000 or 3000 ppm. The same 25 subjects were exposed for 255 min to each condition. Subjective ratings, physiological responses, and cognitive performance were measured. No statistically significant effects on perceived air quality, acute health symptoms, or cognitive performance were seen during exposures when CO₂ was added. Exposures to bioeffluents with CO₂ at 3000 ppm reduced perceived air quality; increased the intensity of reported headache, fatigue, sleepiness, and difficulty in thinking clearly; and reduced speed of addition, the response time in a redirection task, and the number of correct links made in the cue‐utilization test. This suggests that moderate concentrations of bioeffluents, but not pure CO₂, will result in deleterious effects on occupants during typical indoor exposures.     

Influencing factors of carbonyl compounds and other VOCs in commercial airliner cabins: On-board investigation of 56 flights

Volatile organic compounds (VOCs) as a non-negligible aircraft cabin air quality (CAQ) factor influence the health and comfort of passengers and crew members. On-board measurements of carbonyls (short-chain (C₁-C₆)) and other volatile organic compounds (VOCs, long-chain (C₆-C₁₆)) with a total of 350 samples were conducted in 56 commercial airliner cabins covering 8 aircraft models in this study. The mean concentration for each individual carbonyl compound was between 0.3 and 8.3 μg/m³ (except for acrolein & acetone, average = 20.7 μg/m³) similar to the mean concentrations of other highly detected VOCs (long-chain (C₆-C₁₆), 97% of which ranged in 0–10 μg/m³) in aircraft cabins. Formaldehyde concentrations in flights were significantly lower than in residential buildings, where construction materials are known formaldehyde sources. Acetone is a VOC emitted by humans, and its concentration in flights was similar to that in other high-occupant density transportation vehicles. The variation of VOC concentrations in different flight phases of long-haul flights was the same as that of CO₂ concentration except for the meal phase, which indicates the importance of cabin ventilation in diluting the gaseous contaminants, while the sustained and slow growth of the VOC concentrations during the cruising phase in short-haul flights indicated that the ventilation could not adequately dilute the emission of VOCs. For the different categories of VOCs, the mean concentration during the cruising phase of benzene series, aldehydes, alkanes, other VOCs (detection rate > 50%), and carbonyls in long-haul flights was 44.2 µg/m³, 17.9 µg/m³, 18.6 µg/m³, 31.5 µg/m³, and 20.4 µg/m³ lower than those in short-haul flights, respectively. Carbonyls and d-limonene showed a significant correlation with meal service (p < 0.05). Unlike the newly decorated rooms or new vehicles, the inner materials were not the major emission sources in aircraft cabins. Practical Implications.

• The on-board measurements of 56 flights enrich the VOC database of cabin environment, especially for carbonyls. The literature review of carbonyls in the past 20 years contributes to the understanding the current status of cabin air quality (CAQ).
• The analysis of VOC concentration variation for different flight phases, flight duration, and aircraft age lays a foundation for exploring effective control methods, including ventilation and purification for cabin VOC pollution.
• The enriched VOC data is helpful to explore the key VOCs of aircraft cabin environment and to evaluate the acute/chronic health exposure risk of pollutants for passengers and crew members.

     

Real‐world volatile organic compound emission rates from seated adults and children for use in indoor air studies

Human beings emit many volatile organic compounds (VOCs) of both endogenous (internally produced) and exogenous (external source) origin. Here we present real‐world emission rates of volatile organic compounds from cinema audiences (50‐230 people) as a function of time in multiple screenings of three films. The cinema location and film selection allowed high‐frequency measurement of human‐emitted VOCs within a room flushed at a known rate so that emissions rates could be calculated for both adults and children. Gas‐phase emission rates are analyzed as a function of time of day, variability during the film, and age of viewer. The average emission rates of CO₂, acetone, and isoprene were lower (by a factor of ~1.2‐1.4) for children under twelve compared to adults while for acetaldehyde emission rates were equivalent. Molecules influenced by exogenous sources such as decamethylcyclopentasiloxanes and methanol tended to decrease over the course of day and then rise for late evening screenings. These results represent average emission rates of people under real‐world conditions and can be used in indoor air quality assessments and building design. Averaging over a large number of people generates emission rates that are less susceptible to individual behaviors.     

Characterizing sources and emissions of volatile organic compounds in a northern California residence using space‐ and time‐resolved measurements

We investigate source characteristics and emission dynamics of volatile organic compounds (VOCs) in a single‐family house in California utilizing time‐ and space‐resolved measurements. About 200 VOC signals, corresponding to more than 200 species, were measured during 8 weeks in summer and five in winter. Spatially resolved measurements, along with tracer data, reveal that VOCs in the living space were mainly emitted directly into that space, with minor contributions from the crawlspace, attic, or outdoors. Time‐resolved measurements in the living space exhibited baseline levels far above outdoor levels for most VOCs; many compounds also displayed patterns of intermittent short‐term enhancements (spikes) well above the indoor baseline. Compounds were categorized as “high‐baseline” or “spike‐dominated” based on indoor‐to‐outdoor concentration ratio and indoor mean‐to‐median ratio. Short‐term spikes were associated with occupants and their activities, especially cooking. High‐baseline compounds indicate continuous indoor emissions from building materials and furnishings. Indoor emission rates for high‐baseline species, quantified with 2‐hour resolution, exhibited strong temperature dependence and were affected by air‐change rates. Decomposition of wooden building materials is suggested as a major source for acetic acid, formic acid, and methanol, which together accounted for ~75% of the total continuous indoor emissions of high‐baseline species.     

Indoor air quality,ventilation and health symptoms in schools: an analysis of existing information

We reviewed the literature on Indoor Air Quality (IAQ), ventilation, and building-related health problems in schools and identified commonly reported building-related health symptoms involving schools until 1999. We collected existing data on ventilation rates, carbon dioxide (CO2) concentrations and symptom-relevant indoor air contaminants, and evaluated information on causal relationships between pollutant exposures and health symptoms. Reported ventilation and CO2 data strongly indicate that ventilation is inadequate in many classrooms, possibly leading to health symptoms. Adequate ventilation should be a major focus of design or remediation efforts. Total volatile organic compounds, formaldehyde (HCHO) and microbiological contaminants are reported. Low HCHO concentrations were unlikely to cause acute irritant symptoms (<0.05 ppm), but possibly increased risks for allergen sensitivities, chronic irritation, and cancer. Reported microbiological contaminants included allergens in deposited dust, fungi, and bacteria. Levels of specific allergens were sufficient to cause symptoms in allergic occupants. Measurements of airborne bacteria and airborne and surface fungal spores were reported in schoolrooms. Asthma and 'sick building syndrome' symptoms are commonly reported. The few studies investigating causal relationships between health symptoms and exposures to specific pollutants suggest that such symptoms in schools are related to exposures to volatile organic compounds (VOCs), molds and microbial VOCs, and allergens.     

Cabin air quality on non-smoking commercial flights: A review of published data on airborne pollutants

We reviewed 47 documents published 1967–2019 that reported measurements of volatile organic compounds (VOCs) on commercial aircraft. We compared the measurements with the air quality standards and guidelines for aircraft cabins and in some cases buildings. Average levels of VOCs for which limits exist were lower than the permissible levels except for benzene with average concentration at 5.9 ± 5.5 μg/m³. Toluene, benzene, ethylbenzene, formaldehyde, acetaldehyde, limonene, nonanal, hexanal, decanal, octanal, acetic acid, acetone, ethanol, butanal, acrolein, isoprene and menthol were the most frequently measured compounds. The concentrations of semi-volatile organic compounds (SVOCs) and other contaminants did not exceed standards and guidelines in buildings except for the average NO₂ concentration at 12 ppb. Although the focus was on VOCs, we also retrieved the data on other parameters characterizing cabin environment. Ozone concentration averaged 38 ppb below the upper limit recommended for aircraft. The outdoor air supply rate ranged from 1.7 to 39.5 L/s per person and averaged 6.0 ± 0.8 L/s/p (median 5.8 L/s/p), higher than the minimum level recommended for commercial aircraft. Carbon dioxide concentration averaged 1315 ± 232 ppm, lower than what is permitted in aircraft and close to what is permitted in buildings. Measured temperatures averaged 23.5 ± 0.8°C and were generally within the ranges recommended for avoiding thermal discomfort. Relative humidity averaged 16% ± 5%, lower than what is recommended in buildings.     

The effect of low ventilation rate with elevated bioeffluent concentration on work performance,perceived indoor air quality,and health symptoms

The aim of this laboratory experiment was to study the effects of ventilation rate, and related changes in air quality, predominantly bioeffluents, on work performance, perceived indoor air quality, and health symptoms in a typical conditions of modern open‐plan office with low material and equipment emissions. In Condition A, outdoor air flow rate of 28.2 l/s person (CO₂ level 540 ppm) was applied and in Condition B, outdoor air flow rate was 2.3 l/s person (CO₂ level 2260 ppm). CO₂ concentration level was used as an indicator of bioeffluents. Performance was measured with seven different tasks which measure different cognitive processes. Thirty‐six subjects participated in the experiment. The exposure time was 4 hours. Condition B had a weak negative effect on performance only in the information retrieval tasks. Condition B increased slightly subjective workload and perceived fatigue. No effects on health symptoms were found. The intensity of symptoms was low in both conditions. The experimental condition had an effect on perceived air quality and observed odor intensity only in the beginning of the session. Although the room temperature was controlled in both conditions, the heat was perceived to impair the performance more in Condition B.     

Emissions of DEHP‐free PVC flooring

Degrading 2‐ethylhexyl‐containing PVC floorings (eg DEHP‐PVC floorings) and adhesives emit 2‐ethylhexanol (2‐EH) in the indoor air. The danger of flooring degradation comes from exposing occupants to harmful phthalates plasticisers (eg DEHP), but not from 2‐EH as such. Since the EU banned the use of phthalates in sensitive applications, the market is shifting to use DEHP‐free and alternative types of plasticisers in PVC products. However, data on emissions from DEHP‐free PVC floorings are scarce. This study aimed at assessing the surface and bulk emissions of two DEHP‐free PVC floorings over three years. The floorings were glued on the screed layer of concrete casts at 75%, 85%, and 95% RH. The volatile organic compounds (VOCs) were actively sampled using FLEC (surface emissions) and micro‐chamber/thermal extractor (µ‐CTE, bulk emissions) onto Tenax TA adsorbents and analyzed with TD‐GC‐MS. 2‐EH, C9‐alcohols, and total volatile organic compound (TVOC) emissions are reported. Emissions at 75% and 85% RH were similar. As expected, the highest emissions occurred at 95% RH. 2‐EH emissions originated from the adhesive. Because the two DEHP‐free floorings tested emitted C9‐alcohols at all tested RH, it makes the detection of flooring degradation harder, particularly if the adhesive used does not emit 2‐EH.     

Factors controlling volatile organic compounds in dwellings in Melbourne,Australia

This study characterized indoor volatile organic compounds (VOCs) and investigated the effects of the dwelling characteristics, building materials, occupant activities, and environmental conditions on indoor VOC concentrations in 40 dwellings located in Melbourne, Australia, in 2008 and 2009. A total of 97 VOCs were identified. Nine VOCs, n‐butane, 2‐methylbutane, toluene, formaldehyde, acetaldehyde, d‐limonene, ethanol, 2‐propanol, and acetic acid, accounted for 68% of the sum of all VOCs. The median indoor concentrations of all VOCs were greater than those measured outdoors. The occupant density was positively associated with indoor VOC concentrations via occupant activities, including respiration and combustion. Terpenes were associated with the use of household cleaning and laundry products. A petroleum‐like indoor VOC signature of alkanes and aromatics was associated with the proximity of major roads. The indoor VOC concentrations were negatively correlated (P < 0.05) with ventilation. Levels of VOCs in these Australian dwellings were lower than those from previous studies in North America and Europe, probably due to a combination of an ongoing temporal decrease in indoor VOC concentrations and the leakier nature of Australian dwellings.     

Association of subjective health symptoms with indoor air quality in European office buildings: The OFFICAIR project

The aim of this study was to explore the association between the building-related occupants’ reported health symptoms and the indoor pollutant concentrations in a sample of 148 office rooms, within the framework of the European OFFICAIR research project. A large field campaign was performed in 37 office buildings among eight countries, which included (a) 5-day air sampling of volatile organic compounds (VOCs), aldehydes, ozone, and NO₂ (b) collection of information from 1299 participants regarding their personal characteristics and health perception at workplace using online questionnaires. Stepwise and multilevel logistic regressions were applied to investigate associations between health symptoms and pollutant concentrations considering personal characteristics as confounders. Occupants of offices with higher pollutant concentrations were more likely to report health symptoms. Among the studied VOCs, xylenes were associated with general (such as headache and tiredness) and skin symptoms, ethylbenzene with eye irritation and respiratory symptoms, a-pinene with respiratory and heart symptoms, d-limonene with general symptoms, and styrene with skin symptoms. Among aldehydes, formaldehyde was associated with respiratory and general symptoms, acrolein with respiratory symptoms, propionaldehyde with respiratory, general, and heart symptoms, and hexanal with general SBS. Ozone was associated with almost all symptom groups.     

Ozone reaction with clothing and its initiated VOC emissions in an environmental chamber

Human health is adversely affected by ozone and the volatile organic compounds (VOCs) produced from its reactions in the indoor environment. Hence, it is important to characterize the ozone‐initiated reactive chemistry under indoor conditions and study the influence of different factors on these reactions. This investigation studied the ozone reactions with clothing through a series of experiments conducted in an environmental chamber under various conditions. The study found that the ozone reactions with a soiled (human‐worn) T‐shirt consumed ozone and generated VOCs. The ozone removal rate and deposition velocity for the T‐shirt increased with the increasing soiling level and air change rate, decreased at high ozone concentrations, and were relatively unaffected by the humidity. The deposition velocity for the soiled T‐shirt ranged from 0.15 to 0.29 cm/s. The ozone‐initiated VOC emissions included C6–C10 straight‐chain saturated aldehydes, acetone, and 4‐OPA (4‐oxopentanal). The VOC emissions were generally higher at higher ozone, humidity, soiling of T‐shirt, and air change rate. The total molar yield was approximately 0.5 in most cases, which means that for every two moles of ozone removed by the T‐shirt surface, one mole of VOCs was produced.     

Sensory evaluation and chemical analysis of exhaled and dermally emitted bioeffluents

Conditions in which exhaled and dermally emitted bioeffluents could be sampled separately or together (whole‐body emission) were created. Five lightly dressed males exhaled the air through a mask to another, identical chamber or without a mask to the chamber in which they were sitting; the outdoor air supply rate was the same in both chambers. The carbon dioxide concentration in the chamber with exhaled air was 2000 ppm. Chamber temperatures were 23°C or 28°C, and ozone was present or absent in the supply airflow. When dermally emitted bioeffluents were present, the perceived air quality (PAQ) was less acceptable, and the odor intensity was higher than when only exhaled bioeffluents were present. The presence or absence of exhaled bioeffluents in the unoccupied chamber made no significant difference to sensory assessments. At 28°C and with ozone present, the odor intensity increased and the PAQ was less acceptable in the chambers with whole‐body bioeffluents. The concentrations of nonanal, decanal, geranylacetone, and 6‐MHO were higher when dermally emitted bioeffluents were present; they increased further when ozone was present. The concentration of squalene then decreased and increased again at 28°C. Dermally emitted bioeffluents seem to play a major role in the sensory nuisance experienced when occupied volumes are inadequately ventilated.     

Development of New Volatile Organic Compound (VOC) Exposure Metrics and their Relationship to “Sick Building Syndrome” Symptoms

Abstract Occupants of office buildings are exposed to low concentrations of complex mixtures of volatile organic compounds (VOCs) that encompass a number of chemical classes and a broad range of irritancies. “Sick building syndrome” (SBS) is suspected to be related to these exposures. Using data from 22 office areas in 12 California buildings, seven VOC exposure metrics were developed and their ability to predict self-reported SBS irritant symptoms of office workers was tested. The VOC metrics were each evaluated in a multivariate logistic regression analysis model adjusted for other risk factors or confounders. Total VOCs and most of the other metrics were not statistically significant predictors of symptoms in crude or adjusted analyses. Two metrics were developed using principal components (PC) analysis on subsets of the 39 VOCs. The Irritancy/PC metric was the most statistically significant predictor of adjusted irritant symptoms. The irritant potencies of individual compounds, highly correlated nature of indoor VOC mixtures, and probable presence of potent, but unmeasured, VOCs were variously factored into this metric. These results, which for the first time show a link between low level VOC exposures from specific types of indoor sources to SBS symptoms, require confirmation using data sets from other buildings.     

Volatile organic compound (VOC) adsorption on material: influence of gas phase concentration, relative humidity and VOC type

This paper presents the results of a factorial experiment design analysis to investigate volatile organic compounds (VOC) adsorption on a ceiling tile. The impacts of three factors, VOC gas phase concentration, relative humidity, and VOC type, as single parameters and as a combination, on adsorption have been investigated. Cyclohexane, toluene, ethyl acetate, isopropyl alcohol and methanol were the five VOCs used in this study. A factor significant level was determined through evaluating its F value and comparing it with the critical value of F distribution at 95% confidence level. It was found that: (i) neither the relative humidity and gas phase concentration nor any interaction effect between them had significant impacts on toluene adsorption on the ceiling tile; (ii) the adsorption isotherm appeared to be linear for the non-polar compounds and non-linear for the semi-polar and polar compounds; (iii) no significant impact of relative humidity on adsorption was observed for most VOC compounds except for methanol; and (iv) the ceiling tile had the highest adsorption capacity toward the polar compounds, followed by the aromatic compounds and aliphatic compounds. In addition, the statistical analysis regarding the experimental results of toluene as a single compound or as a part of a mixture showed that toluene adsorption capacity on the ceiling tile as a single compound was higher than as a part of a mixture. PRACTICAL IMPLICATIONS: Building materials and furnishings may act as source and sink of VOCs in the indoor environment. In this study, a factorial experiment design analysis technique was used to show the impact of three factors, VOC gas phase concentration, relative humidity, and VOC type, as single parameters and as a combination, on the adsorption process (sink effect). The aim was to better understand the interaction between these parameters and to verify the common assumptions made in the model development and measurement of indoor air quality.     

Are We Measuring the Relevant Indoor Pollutants?

Abstract Concentrations of volatile organic compounds (VOCs) measured indoors may exceed their odor thresholds, but are usually far below TLV estimates. Even applying additivity to eye and airway irritation effects, it is difficult to rationalize increased sick building syndrome (SBS) symptoms by exposure to generally chemically inert VOCs in the indoor environment. Several studies suggest that chemical reactions in indoor air are linked with SBS symptoms and the examination of these reactions may be necessary in order to understand the role of VOCs as causative agents of SBS symptoms. The usual evaluation of odor annoyance of VOCs based on odor thresholds should be modified, taking into account the large variation of individual human odor thresholds for single substances, and specific additivity phenomena even at subthreshold levels of VOCs. The conclusion of this review is that chemical reactions between oxidizable VOCs and oxidants, such as ozone and possibly nitrogen oxides, can form irritants which may be responsible for the reported symptoms. Compounds adsorbed to particles may also contribute to SBS symptoms. The individual effects of indoor pollutants may act in concert with temperature and relative humidity. New analytical methods are required to measure the oxidative and reactive species or specific markers thereof in indoor air.     

VOC exposures in California early childhood education environments

Little information exists about exposures to volatile organic compounds (VOCs) in early childhood education (ECE) environments. We measured 38 VOCs in single‐day air samples collected in 2010‐2011 from 34 ECE facilities serving California children and evaluated potential health risks. We also examined unknown peaks in the GC/MS chromatographs for indoor samples and identified 119 of these compounds using mass spectral libraries. VOCs found in cleaning and personal care products had the highest indoor concentrations (d‐limonene and decamethylcyclopentasiloxane [D5] medians: 33.1 and 51.4 μg/m³, respectively). If reflective of long‐term averages, child exposures to benzene, chloroform, ethylbenzene, and naphthalene exceeded age‐adjusted “safe harbor levels” based on California's Proposition 65 guidelines (10^?5 lifetime cancer risk) in 71%, 38%, 56%, and 97% of facilities, respectively. For VOCs without health benchmarks, we used information from toxicological databases and quantitative structure–activity relationship models to assess potential health concerns and identified 12 VOCs that warrant additional evaluation, including a number of terpenes and fragrance compounds. While VOC levels in ECE facilities resemble those in school and home environments, mitigation strategies are warranted to reduce exposures. More research is needed to identify sources and health risks of many VOCs and to support outreach to improve air quality in ECE facilities.     

Do time‐averaged,whole‐building,effective volatile organic compound (VOC) emissions depend on the air exchange rate? A statistical analysis of trends for 46 VOCs in U.S. offices

We used existing data to develop distributions of time‐averaged air exchange rates (AER), whole‐building ‘effective’ emission rates of volatile organic compounds (VOC), and other variables for use in Monte Carlo analyses of U.S. offices. With these, we explored whether long‐term VOC emission rates were related to the AER over the sector, as has been observed in the short term for some VOCs in single buildings. We fit and compared two statistical models to the data. In the independent emissions model (IEM), emissions were unaffected by other variables, while in the dependent emissions model (DEM), emissions responded to the AER via coupling through a conceptual boundary layer between the air and a lumped emission source. For 20 of 46 VOCs, the DEM was preferable to the IEM and emission rates, though variable, were higher in buildings with higher AERs. Most oxygenated VOCs and some alkanes were well fit by the DEM, while nearly all aromatics and halocarbons were independent. Trends by vapor pressure suggested multiple mechanisms could be involved. The factors of temperature, relative humidity, and building age were almost never associated with effective emission rates. Our findings suggest that effective emissions in real commercial buildings will be difficult to predict from deterministic experiments or models.