Environmental perceptions,mental performance,and physiological responses of people with respiratory allergies exposed to reduced Indoor Air Quality

To investigate the need of allergic population for indoor environment quality, exposure effects of poor air quality on subjects with respiratory allergies were compared with those on healthy people, including perceptual responses, health symptoms, mental performance, and physiological responses. The experimental intervention was with and without ventilation at thermally neutral rooms, creating two exposure conditions indicated by CO₂ concentration ranges of 502 to 3297 ppm (2438 ± 1527 ppm) and 517 to 5687 ppm (3615 ± 1527 ppm). 63 subjects (32 allergic subjects and 31 non-allergic subjects) were exposed to both conditions for 3 hours. The main results suggested that, compared with healthy people, people with respiratory allergy seem to be more sensitive or less acceptable to reduced air quality polluted by occupants during instantaneous exposure. Besides, the allergic group performed worse in cognitive tests than non-allergic group. After 3 hours of continuous exposure, people with respiratory allergy reported stronger intensity of respiratory irritations and seemed to suffer more inflammation indicated by a higher level of interleukin 1L-1β.     

Symptoms prevalence among office employees and associations to building characteristics

A cross-sectional study was performed in eight companies, comprising 32 buildings without previously recognized indoor air problems. Engineers filled in a technical questionnaire on building characteristics, floor surface materials, ventilation, cleaning procedures, heating and cooling. A total of 3562 employees returned questionnaires on individual factors, workload, perceived physical work environment, allergy and symptoms. Frequent symptoms were feeling of fatigue or heavy-headedness, eye irritation, and dry facial skin. Women reported symptoms more frequently than men. Employees with allergy had a 1.8-2.5 times risk of reporting a high score for general, skin, or mucosal symptoms. The risk of a high symptom score increased with daily visual display unit (VDU) work time. Passive smoking and psychosocial load were also relatively strong predictors of symptoms. Weekly cleaning as compared with a frequency of cleaning two to four times a week increased the risk of symptoms. Adjusted odds ratio for a high general symptoms score from infrequent cleaning was 1.5 (95%CI 1.1-2.0). A high ventilation flow or central ventilation unit filter EU7 vs. EU8 seemed to be associated with an increased risk of general symptoms. Absence of local temperature control increased the risk of mucosal symptoms.     

Health benefits of particle filtration

The evidence of health benefits of particle filtration in homes and commercial buildings is reviewed. Prior reviews of papers published before 2000 are summarized. The results of 16 more recent intervention studies are compiled and analyzed. Also, reviewed are four studies that modeled health benefits of using filtration to reduce indoor exposures to particles from outdoors. Prior reviews generally concluded that particle filtration is, at best, a source of small improvements in allergy and asthma health effects; however, many early studies had weak designs. A majority of recent intervention studies employed strong designs and more of these studies report statistically significant improvements in health symptoms or objective health outcomes, particularly for subjects with allergies or asthma. The percentage improvement in health outcomes is typically modest, for example, 7% to 25%. Delivery of filtered air to the breathing zone of sleeping allergic or asthmatic persons may be more consistently effective in improving health than room air filtration. Notable are two studies that report statistically significant improvements, with filtration, in markers that predict future adverse coronary events. From modeling, the largest potential benefits of indoor particle filtration may be reductions in morbidity and mortality from reducing indoor exposures to particles from outdoor air.     

Nasal hyperreactivity in allergic and non-allergic rhinitis: a potential risk factor for non-specific building-related illness

Self-reported non-allergic nasal symptom triggers in non-allergic ('vasomotor') rhinitis overlap with commonly identified environmental exposures in non-specific building-related illness. These include extremes of temperature and humidity, cleaning products, fragrances, and tobacco smoke. Some individuals with allergic rhinitis also report non-allergic triggers. We wished to explore the phenotypic overlap between allergic and non-allergic rhinitis by ascertaining self-reported non-allergic nasal symptom triggers among allergic rhinitics. Sixty subjects without work-related respiratory exposures or symptoms, aged 19-68 years, stratified by age, gender and (skin test-proven) allergic rhinitis status, were queried with regard to self-reported non-allergic nasal symptom triggers (aggregate score 0-8). In this sample, the number of self-reported non-allergic triggers was bimodal, with peaks at 1 and 5. Forty-two percent of seasonal allergic rhinitic subjects reported more than three non-allergic triggers, compared with only 3% of non-allergic non-rhinitics (P < 0.01). Subjects over 35 years were more likely to report one or more non-allergic triggers, particularly tobacco smoke (P < 0.05). Allergic rhinitics reported more non-allergic symptom triggers than did non-allergic, non-rhinitics. As indexed by self-reported reactivity to non-specific physical and chemical triggers, both non-allergic rhinitics and a subset of allergic rhinitics may constitute susceptible populations for non-specific building-related illness. PRACTICAL IMPLICATIONS: Judging by self-report, a substantial subset of individuals with allergic rhinitis--along with all individuals with nonallergic rhinitis (by definition)--are hyperreactive to non-allergic triggers. There is overlap between these triggers (elicited in the process of obtaining a clinical diagnosis) and environmental characteristics associated with 'problem buildings.' Since individuals with self-identified rhinitis report an excess of symptoms in most epidemiologic studies of problem buildings (even in the absence of unusual aeroallergen levels), rhintics may be acting as a 'sentinel' subgroup when indoor air quality is suboptimal. Together, non-allergic rhinitics plus allergic rhinitics with prominent non-allergic triggers, are thought to constitute approximately one-sixth of the US population.     

Indoor environmental quality in Hellenic hospital operating rooms

Indoor environmental quality (IEQ) in hospital operating rooms (ORs) constitutes a major challenge for the proper design and operation of an energy efficient hospital. A subjective assessment of the indoor environment along with a short monitoring campaign was performed during the audits of 18 ORs at nine major Hellenic hospitals. A total of 557 medical personnel participated in an occupational survey, providing data for a subjective assessment of IEQ in the audited ORs. The OR personnel reported work related health symptoms and an assessment of indoor conditions (thermal, visual and acoustical comfort, and air quality). Overall, personnel reported an average of 2.24 work-related symptoms each, and 67.2% of respondents reported at least one. Women suffer more health symptoms than men. Special dispositions, such as smoking and allergies, increase the number of reported symptoms for male and female personnel. Personnel that perceive satisfactory indoor comfort conditions (temperature, humidity, ventilation, light, and noise) average 1.18 symptoms per person, while for satisfactory indoor air quality the average complaints are 0.99. The perception of satisfactory IEQ (satisfactory comfort conditions and air quality) reduces the average number of health complaints to 0.64 symptoms per person and improves working conditions, even in a demanding OR environment.     

Associations of indoor carbon dioxide concentrations,air temperature,and humidity with perceived air quality and sick building syndrome symptoms in Chinese homes

The indoor environment influences occupants’ health. From March 1, 2018, to February 28, 2019, we continuously monitored indoor temperature (T), relative humidity (RH), and CO₂ concentration in bedrooms via an online system in 165 residences that covered all five climate zones of China. Meanwhile, we asked one specific occupant in each home to complete questionnaires about perceived air quality and sick building syndrome (SBS) symptoms at the end of each month. Higher CO₂ concentration was significantly associated with a higher percentage of perceived stuffy odor and skin SBS symptoms. Higher relative humidity was associated with higher percentage of perceived moldy odor and humid air, while lower RH was associated with a higher percentage of perceived dry air. Occupants who lived in residences with high RH were less likely to have mucosal and skin SBS symptoms (adjusted odds ratio (AOR): 0.73–0.78). However, the benefit of high humidity for perceived dry air and skin dryness symptoms is weaker if there is a high CO₂ concentration level.     

The effect of ventilation strategies of child care centers on indoor air quality and respiratory health of children in Singapore

This paper reports the effects of ventilation strategies on indoor air quality (IAQ) and respiratory health of children within 104 child care centers (CCCs) in a hot and humid climate. The CCCs were categorized by ventilation strategies: natural (NV), air-conditioned and mechanically ventilated (ACMV), air-conditioned using split units (AC), and hybrid (NV and AC operated intermittently). The concentration levels of IAQ parameters in NV CCCs are characterized by the influence of the outdoors and good dilution of indoor pollutants. The lower ventilation rates in air-conditioned CCCs result in higher concentrations of occupant-related pollutants but lower outdoor pollutant ingress. This study also revealed lower prevalence for most asthma and allergy, and respiratory symptoms in children attending NV CCCs. In multivariate analyses controlled for the effects of confounders, the risk of current rhinitis among children is significantly higher if they attend mechanically ventilated CCCs compared to NV CCCs. Air-conditioned CCCs were also associated with higher adjusted prevalence ratio of severe phlegm and cough symptoms and lower respiratory illness. Finally, children attending CCCs with hybrid ventilation are at high risk for almost all the respiratory symptoms studied. PRACTICAL IMPLICATIONS: This large field study indicates that different ventilation strategies employed by child care centers can cause significant variations in the indoor air quality and prevalence of asthma, allergies and respiratory symptoms of attending children. The higher prevalence rates of allergic and respiratory symptoms among young children, whose immune system is still under-developed, in child care centers, whether fully or partially air-conditioned, suggest that ventilation and plausible growth and propagation mechanisms of allergens and infectious agents be further investigated.     

Association between ventilation rates in 390 Swedish homes and allergic symptoms in children

The aim of the study was to test the hypothesis that a low-ventilation rate in homes is associated with an increased prevalence of asthma and allergic symptoms among children. A total of 198 cases (with at least two of three symptoms: wheezing, rhinitis, eczema) and 202 healthy controls, living in 390 homes, were examined by physicians. Ventilation rates were measured by a passive tracer gas method, and inspections were carried out in the homes. About 60% of the multi-family houses and about 80% of the single-family houses did not fulfill the minimum requirement regarding ventilation rate in the Swedish building code (0.5 air changes per hour, ach). Cases had significantly lower ventilation rates than controls and a dose-response relationship was indicated. PRACTICAL IMPLICATIONS: A low-ventilation rate of homes may be a risk factor for allergies among children. Families with allergic children should be given the advice to have good ventilation in the home. In investigations, of associations between environmental factors and allergies, the air change rate in homes has to be considered.     

Onset of mucosal, dermal, and general symptoms in relation to biomarkers and exposures in the dwelling: a cohort study from 1992 to 2002

We examined the associations between biomarkers of allergy and inflammation, indoor environment in dwellings, and incidence and remission of symptoms included in the sick building syndrome (SBS) and changes in the home environment of 452 adults who were followed from 1992 to 2002 within the Uppsala part of the European Community Respiratory Health Survey (ECRHS). The 10-year incidence (onset) of general, mucosal, and dermal symptoms was 8.5%, 12.7%, and 6.8%, respectively. Dampness or indoor molds at baseline was a predictor of incidence of general (relative risk [RR] = 1.98), mucosal (RR = 2.28), and dermal symptoms (RR = 1.91). Women had higher incidence of general (RR = 1.74) and mucosal symptoms (RR = 1.71). Indoor painting increased the incidence of general symptoms (RR = 1.62). Bronchial responsiveness (BR), eosinophil counts in blood, total IgE and eosinophilic cationic protein (ECP) in serum at baseline were predictors of incidence of SBS. At follow-up, BR, total IgE, and C-reactive protein (CRP ) were associated with increased incidence of SBS. Moreover, subjects with doctor-diagnosed asthma at baseline had a higher incidence of general (RR = 1.65) and mucosal symptoms (RR = 1.97). In conclusion, female gender, dampness or indoor molds, indoor painting, and biomarkers of allergy and inflammation were associated with a higher incidence of SBS symptoms, in particular mucosal symptoms. PRACTICAL IMPLICATIONS: The focus in Sweden on indoor environment issues over the last few decades has resulted in improvements in dwellings, and reduced tobacco smoking, which could be beneficial for public health. Reducing dampness and molds in the dwelling place is another important way of reducing occurrence of SBS symptoms in the general adult population. The association between the incidence of SBS symptoms and clinical biomarkers of allergy and inflammation suggests a common etiology between inflammatory diseases, including asthma, rhinitis, and SBS. Lastly, good agreement between self-reported and clinically diagnosed atopy indicates that questionnaire data on atopy can be used in epidemiological studies.     

Effect of classroom air quality on students' concentration: results of a cluster-randomized cross-over experimental study

Abstract To assess the effect of indoor air quality as indicated by the median carbon dioxide (CO(2) ) level in the classroom on the concentration performance (CP) of students, a cross-over cluster-randomized experimental study was conducted in 20 classrooms with mechanical ventilation systems. Test conditions 'worse' (median CO(2) level on average 2115?ppm) and 'better' (median CO(2) level on average 1045?ppm) were established by the regulation of the mechanical ventilation system on two days in one week each in every classroom. Concentration performance was quantified in students of grade three and four by the use of the d2-test and its primary parameter 'CP' and secondary parameters 'total number of characters processed' (TN) and 'total number of errors' (TE). 2366 d2-tests from 417 students could be used in analysis. In hierarchical linear regression accounting for repeated measurements, no significant effect of the experimental condition on CP or TN could be observed. However, TE was increased significantly by 1.65 (95% confidence interval 0.42-2.87) in 'worse' compared to 'better' condition. Thus, low air quality in classrooms as indicated by increased CO(2) levels does not reduce overall short-term CP in students, but appears to increase the error rate. PRACTICAL IMPLICATIONS: This study could not confirm that low air quality in classrooms as indicated by increased CO(2) levels reduces short-term concentration performance (CP) in students; however, it appears to affect processing accuracy negatively. To ensure a high level of accuracy, good air quality characterized, for example, by low CO(2) concentration should be maintained in classrooms.     

The link between symptoms of office building occupants and in-office air pollution: the Indoor Air Pollution Index

The lack of an effective indoor air quality (IAQ) metric causes communication concerns among building tenants (the public), building managers (decision-makers), and IAQ investigators (engineers). The Indoor Air Pollution Index (IAPI) is developed for office buildings to bridge this communication discord. The index, simple and easily understood, employs the range of pollutant concentrations and concentrations in the subject building to estimate a unitless single number, the IAPI, between 0 (lowest pollution level and best IAQ) and ten (highest pollution level and worst IAQ). The index provides a relative measure of indoor air pollution for office buildings and ranks office indoor air pollution relative to the index distribution of the US office building population. Furthermore, the index associates well with occupant symptoms, percentage of occupants with persistent symptoms. A tree-structured method is utilized in conjunction with the arithmetic mean as the aggregation function. The hierarchical structure of the method renders not only one index value, but also several sub-index values that are critical in the study of an office air environment. The use of the IAPI for IAQ management is illustrated with an example. The decomposition of the index leads to the ranking of sampled pollutants by their relative contribution to the index and the identification of dominant pollutant(s). This information can be applied to design an effective strategy for reducing in-office air pollution.     

Estimates of Improved Productivity and Health from Better Indoor Environments

Abstract The existing literature contains strong evidence that characteristics of buildings and indoor environments significantly influence rates of respiratory disease, allergy and asthma symptoms, sick building symptoms, and worker performance. Theoretical considerations, and limited empirical data, suggest that existing technologies and procedures can improve indoor environments in a manner that significantly increases health and productivity. At present, we can develop only crude estimates of the magnitude of productivity gains that may be obtained by providing better indoor environments; however, the projected gains are very large. For the U.S., we estimate potential annual savings and productivity gains of $6 billion to $19 billion from reduced respiratory disease; $1 billion to $4 billion from reduced allergies and asthma, $10 billion to $20 billion from reduced sick building syndrome symptoms, and $12 billion to $125 billion from direct improvements in worker performance that are unrelated to health. Sample calculations indicate that the potential financial benefits of improving indoor environments exceed costs by a factor of 18 to 47. The policy implications of the findings are discussed and include a recommendation for additional research.     

Evidence of inadequate ventilation in portable classrooms: results of a pilot study in Los Angeles County

The prevalence of prefabricated, portable classrooms (portables) for United States public schools has increased; in California, approximately one of three students learn inside portables. Limited research has been conducted on indoor air and environmental quality in American schools, and almost none in portables. Available reports and conference proceedings suggest problems from insufficient ventilation due to poor design, operation, and/or maintenance of heating, ventilation and air conditioning (HVAC) systems; most portables have one mechanical, wall-mounted HVAC system. A pilot assessment was conducted in Los Angeles County, including measurements of integrated ventilation rates based on a perfluorocarbon tracer gas technique and continuous monitoring of temperature (T) and relative humidity (RH). Measured ventilation rates were low [mean school day integrated average 0.8 per hour (range: 0.1-2.9 per hour)]. Compared with relevant standards, results suggested adequate ventilation and associated conditioning of indoor air for occupant comfort were not always provided to these classrooms. Future school studies should include integrated and continuous measurements of T, RH, and ventilation with appropriate tracer gas methods, and other airflow measures. PRACTICAL IMPLICATIONS: Adequate ventilation has the potential to mitigate concentrations of chemical pollutants, particles, carbon dioxide, and odors in portable and traditional classrooms, which should lead to a reduction in reported health outcomes, e.g., symptoms of 'sick building syndrome', allergies, asthma. Investigations of school indoor air and environmental quality should include continuous temperature and relative humidity data with inexpensive instrumentation as indicators of thermal comfort, and techniques to measure ventilation rates.     

A comparative study of asthma, pollen, cat and dog allergy among pupils and allergen levels in schools in Taiyuan city, China, and Uppsala, Sweden

We compared the school environment, asthma and allergy in 10 schools in Taiyuan, China, with eight schools in Uppsala, Sweden. In total 2193 pupils (mean age 13 years) participated. Chinese pupils had more respiratory symptoms, particularly daytime breathlessness after exercise (29.8% vs. 7.1%; P < 0.001), while cat allergy (1.2% vs. 6.6%; P < 0.001) and dog allergy (1.3% vs. 4.0%; P < 0.01) was less common. Cumulative incidence of asthma (1.8% vs. 9.5%; P < 0.001) and doctor's diagnosed asthma (1.2% vs. 9.0%; P < 0.001) were less common in China, indicating an under-diagnosis of asthma. Chinese classrooms were colder (mean 14.7 vs. 21.4 degrees C), more humid (mean 42% vs. 31% RH) and had higher CO2-levels (mean 2211 vs. 761 ppm). Levels of cat (Fel d1), dog (Can f1) allergens were low in settled dust from China (< 200 ng/g dust), but high in airborne dust on Petri-dishes (GM 16.8 ng/m2/day for Fel d1 and 17.7 for Can f1). The Swedish settled dust contained cat, dog and horse allergens in high levels (median 1300 ng/g, 1650 ng/g, 1250 U/g dust, respectively). In conclusion, there were large differences in the school environment, and in respiratory symptom and allergy. Allergen measurements in settled dust only may largely underestimate the classroom exposure. Practical Implications There is a need to improve the school environment, both in China and Sweden. The Swedish schools contained high levels of cat, dog and horse allergens and more amounts of open shelves and textiles that can accumulate dust and allergens. The air measurements indicated that Chinese schools may contain significant amounts of cat and dog allergen, and analysis of settled dust only may not reflect the true allergen exposure. Since the Chinese schools had no mechanical ventilation, they could not fulfill the ventilation standard in winter, and hence there is a need for improving the ventilation. The great discrepancy between respiratory symptoms and reports on asthma, and the high prevalence of attacks of breathlessness without wheeze, may have implication for future questionnaire studies on asthma in China.     

Respiratory allergies on the staff of the police force

The aim of the study was to evaluate respiratory allergies of an occupational nature in the staff of the police force. Five hundred and eighty-five subjects were submitted for lung function tests by dynamic spirometry. Subjects with a history of respiratory symptoms and border line respiratory function underwent bronchial provocation tests with methacholine. If FEV1 was < 80%, a bronchial reversibility test was performed. Allergic tests (skin and RAST) for inhalating allergens (perennial, seasonal and occupational) were performed. The results suggested asthmatic symptoms in 57 subjects, eight of whom were positive to skin and RAST tests for occupational inhalating allergens. Among these eight subjects, three had FEV1 < 80% of the theoretical value without therapy, and five showed obstruction of small caliber airways (MEF 25, MEF 50, FEF 25-75 < 65% of the theoretical value). The analysis showed a low percentage of respiratory occupational allergies. Among 21 subjects positive to Dermatophagoides, seven worked as archivists. In these workers, a concomitant occupational cause for the symptomatological and functional pattern was established.     

Analyzing symptom data in indoor air questionnaires for primary schools

Questionnaires on symptoms and perceived quality of indoor environment are used to assess indoor environment problems, but mainly among adults. The aim of this article was to explore best ways to analyze and report such symptom data, as part of a project to develop a parent‐administered indoor air questionnaire for primary school pupils. Indoor air questionnaire with 25 questions on child's symptoms in the last 4 weeks was sent to parents in five primary schools with indoor air problems and in five control schools. About 83% of parents (N=1470) in case schools and 82% (N=805) in control schools returned the questionnaire. In two schools, 351 (52%) parents answered the questionnaire twice with a 2‐week interval. Based on prevalence of symptoms, their test‐retest repeatability (ICC), and on principal component analysis (PCA), the number of symptoms was reduced to 17 and six symptoms scores were developed. Six variants of these six symptom scores were then formed and their ability to rank schools compared. Four symptom scores (respiratory, lower respiratory, eye, and general symptoms) analyzed dichotomized maintained sufficiently well the diversity of symptom data and captured the between‐school differences in symptom prevalence, when compared to more complex and numerous scores.     

Ventilation and dampness in dorms and their associations with allergy among college students in China: a case-control study

To study the associations between dorm environment and occupants' health, a nested case-control study on 348 college students was carried out in 2006-2007 at Tianjin University, China. Two hundred and twenty-three dorm rooms where the 'cases' and 'controls' resided were inspected. Measured variables were ventilation rate, air temperature, and relative humidity indoors. Allergic symptoms in the last 12 months were self-reported by occupants. Adjusted odds ratios (AORs) of a 'localized moldy smell/moisture indicator' in 'special places' (e.g., in a room corner or close to the radiator under the window) for wheezing was 3.56 [95% Confident Interval (CI): 1.56-8.14] and for rhinitis 2.81 (95% CI: 1.32-5.97). The AOR of a low air change rate (below the median value of 0.7/h) for wheezing was 2.28 (95% CI: 1.38-3.75) and for dry cough 2.26 (95% CI: 1.08-4.75). The prevalence of students with allergic symptoms in dorm rooms decreased with increasing ventilation rate. The combination of a 'localized moldy/moisture indicator' and a low air change rate significantly increased the AOR of case status to 13.35 (95% CI: 3.73-47.83), compared to the reference condition with no-dampness and high ventilation rate (above the median). This supports the hypothesis that ventilation rate is an effect modifier for moisture problems and indoor pollutants.     

Indoor thermal environment and air quality in Chinese-style residential kitchens

This paper reviews the published literature on indoor thermal environment and air quality in Chinese-style residential kitchens (CRKs). The paper first discusses typical characteristics of CRKs, including kitchen layout, cooking methods, and ventilation systems used. Next, the paper describes the current state of the indoor thermal environment and air quality in CRKs. Finally, this paper summarizes measures to control and improve the environment inside CRKs. The results indicate that the indoor environment of CRKs is too hot in summer and exhibits a large vertical temperature difference. No appropriate model was available for accurately evaluating the thermal environment in CRKs. At the same time, CRKs are highly polluted by COx, NOx, TVOC, and particulate matter (PM). Although existing exhaust hoods could improve the indoor environment to some extent, the use of a combined exhaust, make-up air, and air-conditioning system should be considered to provide a comfortable and healthy environment in CRKs.     

建筑环境微生物的危害及其生态特性研究进展

SARS过后,微生物气溶胶对人体造成的危害引起了人们极大的重视。通过文献研究,论述了常见的微生物种类、对人体造成的危害和引起的疾病,以及越来越受到重视的病态建筑综合症;介绍了主要的空气微生物污染物的生态特性;在建筑室内环境中,常见的微生物有尘螨、真菌、细菌和病毒,能够引起传染性疾病、非传染性疾病、非过敏性免疫反应及各种不适症状;指出在实际建筑背景下,对舒适性空调系统中微生物的生态特性、气溶胶化、扩散传播规律及控制方法需要进一步的研究。     

Indoor and outdoor BTX levels in German cities

On the basis of the ongoing study INGA (INdoor exposure and Genetics in Asthma), Germany's most detailed and standardized epidemiological study on indoor exposure to both allergens in house dust and volatile compounds in the air of the home environment has been performed. The purpose of this paper is to describe the spatial and seasonal variability of indoor and outdoor BTX (Benzene, toluene, ethyl benzene, ortho-xylene, meta- and para-xylene) concentrations for the study period from June 1995 to November 1996. Within this framework, air concentrations of volatile organic compounds (BTX) were measured in 204 households in Erfurt (Eastern Germany) and 201 households in Hamburg (Western Germany). BTX sampling was conducted over one week using OVM 3500 passive diffusion sampling devices in the indoor (living room and bedroom) and outdoor environment (outside the window of the living room). Indoor and outdoor median BTX concentrations in Erfurt were slightly, but significantly higher than those in Hamburg. This gap was most pronounced in the levels of indoor toluene (37.3 microg/m3 for Erfurt and 20.5 microg/m3 for Hamburg, P < 0.0001). In both cities, winter indoor and outdoor concentrations for the five compounds exceeded the summer values. Outdoor concentrations of ethyl benzene and ortho-xylene were very low (50% < L.D.). In general, the indoor BTX air concentrations were significantly higher than the outdoor concentra- tions, the lowest I/O ratios were found in the case of benzene. Living room and bedroom values for the five compounds were highly correlated (Spearman coefficient 0.5-0.9). Despite the better insulation of the homes in West Germany, no indication for the expected higher indoor concentrations of BTX in the West could be found. The strong and yet undiscovered indoor source for toluene in East Germany might lead to a further increase in the indoor air load in those homes in the East, which undergo renovations which will lead to improved insulation.