Distribution and determinants of personal exposure to nitrogen dioxide in school children

Indoor Air Pollution, Related Human Diseases, and Recent Trends in the Control and Improvement of Indoor Air Quality

Indoor air pollution (IAP) is a serious threat to human health, causing millions of deaths each year. A plethora of pollutants can result in IAP; therefore, it is very important to identify their main sources and concentrations and to devise strategies for the control and enhancement of indoor air quality (IAQ). Herein, we provide a critical review and evaluation of the major sources of major pollutant emissions, their health effects, and issues related to IAP-based illnesses, including sick building syndrome (SBS) and building-related illness (BRI). In addition, the strategies and approaches for control and reduction of pollutant concentrations are pointed out, and the recent trends in efforts to resolve and improve IAQ, with their respective advantages and potentials, are summarized. It is predicted that the development of novel materials for sensors, IAQ-monitoring systems, and smart homes is a promising strategy for control and enhancement of IAQ in the future.

A cross sectional analysis of behaviors related to operating gas stoves and pneumonia in U.S. children under the age of 5

Background

Poorly ventilated combustion stoves and pollutants emitted from combustion stoves increase the risk of acute lower respiratory illnesses (ALRI) in children living in developing countries but few studies have examined these issues in developed countries. Our objective is to investigate behaviors related to gas stove use, namely using them for heat and without ventilation, on the odds of pneumonia and cough in U.S. children.

Methods

The National Health and Nutrition Examination Survey (1988–1994) was used to identify children < 5 years who lived in homes with a gas stove and whose parents provided information on their behaviors when operating their gas stoves and data on pneumonia (N = 3,289) and cough (N = 3,127). Multivariate logistic regression models were used to examine the association between each respiratory outcome and using a gas stove for heat or without ventilation, as well as, the joint effect of both behaviors.

Results

The adjusted odds of parental-reported pneumonia (adjusted odds ratio [aOR] = 2.08, 95% confidence interval [CI]: 1.08, 4.03) and cough (aOR = 1.66, 95% CI: 1.14, 2.43) were higher among children who lived in homes where gas stoves were used for heat compared to those who lived in homes where gas stoves were only used for cooking. The odds of pneumonia (aOR = 1.76, 95% CI: 1.04, 2.98), but not cough (aOR = 1.23, 95% CI: 0.87, 1.75), was higher among those children whose parents did not report using ventilation when operating gas stoves compared to those who did use ventilation. When considering the joint association of both stove operating conditions, only children whose parents reported using gas stoves for heat without ventilation had significantly higher odds of pneumonia (aOR = 3.06, 95% CI: 1.32, 7.09) and coughing (aOR = 2.07, 95% CI: 1.29, 3.30) after adjusting for other risk factors.

Conclusions

Using gas stoves for heat without ventilation was associated with higher odds of pneumonia and cough among U.S. children less than five years old who live in homes with a gas stove. More research is needed to determine if emissions from gas stoves ventilation infrastructure, or modifiable behaviors contribute to respiratory infections in children.

Outdoor, but not indoor, nitrogen dioxide exposure is associated with persistent cough during the first year of life

BACKGROUND AND AIMS

Because their lungs and immune system are not completely developed, children are more susceptible to respiratory disease and more vulnerable to ambient pollution. We assessed the relation between prenatal and postnatal nitrogen dioxide (NO(2)) levels and the development of lower respiratory tract infections (LRTI), wheezing and persistent cough during the first year of life.

METHODS

The study population consisted of 352 children from a birth cohort in Valencia, Spain. Prenatal exposure to NO(2), a marker of traffic related air pollution was measured at 93 sampling sites spread over the study area during four different sampling periods of 7 days each. It was modeled for each residential address through land use regression using the empirical measurements and data from geographic information systems. Postnatal exposure was measured once inside and outside each home using passive samplers for a period of 14 days. Outcomes studied were any episode of LRTI during the child's first year of life diagnosed by a doctor (bronchitis, bronchiolitis or pneumonia), wheezing (defined as whistling sounds coming from the chest), and persistent cough (more than three consecutive weeks). Outcomes and potential confounders were obtained from structured questionnaires. Multiple logistic regression was used to identify associations.

RESULTS

The cumulative incidence (CI) at first year of life was 30.4% for LRTI (23.0% bronchiolitis, 11.9% bronchitis and 1.4% pneumonia), 26.1% for wheezing and 6.3% for persistent cough. The adjusted odds ratio (95% confidence interval) per 10μg/m(3) increment in postnatal outdoor NO(2) concentration was 1.40 (1.02-1.92) for persistent cough. We also found some pattern of association with LRTI, bronchiolitis, bronchitis, wheezing and persistent cough in different prenatal periods, although it was not statistically significant.

CONCLUSIONS

Our results indicate that exposure to outdoor, but not indoor, NO(2) during the first year of life increases the risk of persistent cough.

Indoor and outdoor concentrations and determinants of NO2 in a cohort of 1-year-old children in Valencia, Spain

Nitrogen dioxide (NO2) is produced from the exhausts of vehicles and gas appliances and is known to pose certain health risks. In this study, we characterize the exposure to this substance during the first year of life, which is an important period of development. To this end, we used passive samplers to measure indoor and outdoor NO2 levels for 2 weeks in the homes of 352 children. To compensate for the fact that NO2 levels were measured only once in each home, a correction factor was calculated to assign each child an outdoor NO2 exposure value for the first year of life. The outdoor NO2 concentrations were 26.1 microg/m(3) while those measured indoors averaged 18.0 microg/m(3). A multivariate linear regression analysis showed that the main determinants of outdoor NO2 levels were the degree of urbanization and the frequency of vehicle traffic at the location of the residence while for indoor NO2 levels the principal determinants were the type of cooking range and water heater present in the home, the season of the year, and both the country of origin and educational level of the mother.

PRACTICAL IMPLICATIONS

Exposure to NO2 has been related to respiratory and other health problems among children. Precise identification of the main sources of both indoor and outdoor NO2 should shed light on appropriate intervention periods and methods. Our results indicate that while population density and traffic-related variables are the main determinants of outdoor NO2 levels, the use of gas appliances have the greatest impact on indoor levels. Strategies should thus be developed to reduce such exposure, especially with regard to reducing emissions from vehicle traffic.

Activity pattern and personal exposure to nitrogen dioxide in indoor and outdoor microenvironments

People are exposed to air pollution from a range of indoor and outdoor sources. Concentrations of nitrogen dioxide (NO(2)), which is hazardous to health, can be significant in both types of environments. This paper reports on the measurement and analysis of indoor and outdoor NO(2) concentrations and their comparison with measured personal exposure in various microenvironments during winter and summer seasons. Furthermore, the relationship between NO(2) personal exposure in various microenvironments and including activities patterns were also studied. Personal, indoor microenvironments and outdoor measurements of NO(2) levels were conducted using Palmes tubes for 60 subjects. The results showed significant differences in indoor and outdoor NO(2) concentrations in winter but not for summer. In winter, indoor NO(2) concentrations were found to be strongly correlated with personal exposure levels. NO(2) concentration in houses using a gas cooker was higher in all rooms than those with an electric cooker during the winter campaign, whereas there was no significant difference noticed in summer. The average NO(2) levels in kitchens with a gas cooker were twice as high as those with an electric cooker, with no significant difference in the summer period. A time-weighted average personal exposure was calculated and compared with measured personal exposures in various indoor microenvironments (e.g. front doors, bedroom, living room and kitchen); including non-smokers, passive smokers and smoker. The estimated results were closely correlated, but showed some underestimation of the measured personal exposures to NO(2) concentrations. Interestingly, for our particular study higher NO(2) personal exposure levels were found during summer (14.0+/-1.5) than winter (9.5+/-2.4).

Predictors of concentrations of nitrogen dioxide, fine particulate matter, and particle constituents inside of lower socioeconomic status urban homes

Air pollution exposure patterns may contribute to known spatial patterning of asthma morbidity within urban areas. While studies have evaluated the relationship between traffic and outdoor concentrations, few have considered indoor exposure patterns within low socioeconomic status (SES) urban communities. In this study, part of a prospective birth cohort study assessing asthma etiology in urban Boston, we collected indoor and outdoor 3-4 day samples of nitrogen dioxide (NO2) and fine particulate matter (PM2.5) in 43 residences across multiple seasons from 2003 to 2005. Homes were chosen to represent low SES households, including both cohort and non-cohort residences in similar neighborhoods, and consisted almost entirely of multiunit residences. Reflectance analysis and X-ray fluorescence spectroscopy were performed on the particle filters to determine elemental carbon (EC) and trace element concentrations, respectively. Additionally, information on home characteristics (e.g. type, age, stove fuel) and occupant behaviors (e.g. smoking, cooking, cleaning) were collected via a standardized questionnaire. The contributions of outdoor and indoor sources to indoor concentrations were quantified with regression analyses using mass balance principles. For NO2 and most particle constituents (except outdoor-dominated constituents like sulfur and vanadium), the addition of selected indoor source terms improved the model's predictive power. Cooking time, gas stove usage, occupant density, and humidifiers were identified as important contributors to indoor levels of various pollutants. A comparison between cohort and non-cohort participants provided another means to determine the influence of occupant activity patterns on indoor-outdoor ratios. Although the groups had similar housing characteristics and were located in similar neighborhoods, cohort members had significantly higher indoor concentrations of PM2.5 and NO2, associated with indoor activities. We conclude that the effect of indoor sources may be more pronounced in high-density multiunit dwellings, and that future epidemiological studies in these populations should explicitly consider these sources in assigning exposures.

Air quality, tobacco smoke, urban crowding and day care: modern menaces and their effects on health

BACKGROUND

The known adverse health effects of outdoor air pollution were reduced in the last century by effective legislation and pollution control. Although combustion of biomass fuels in the indoor environment remains a major hazard in developing countries, there has been a change in the nature of the traffic-generated air pollutants in outdoor air in developed countries. The role of day care and siblings in increasing the risk of infection early in life contrasts with protection from allergic disease later.

METHODS

The mechanisms of how these pollutants exert their effects are poorly understood, but there is emerging evidence that the toxic effects may be related to infection. This synopsis discusses the epidemiologic relationship of the menaces of modern living, including air pollution, urban crowding and infection, and will explore some of the mechanisms of how they act synergistically to cause exacerbations of illnesses in individuals with preexisting respiratory conditions, such as asthma. It will also discuss the roles of day care and siblings in relation to respiratory disease risk.

RESULTS

Current evidence suggests that much of the morbidity and mortality related to sources of both indoor and outdoor pollution occur by causing or interacting with respiratory infection and other acute or chronic health conditions, such as asthma.

CONCLUSION

Improvements in air quality through efforts to tackle environmental problems such as pollution and tobacco smoke will help achieve better health. Day care and siblings increase infectious disease early in life but are associated with protection against development of allergic disease later.

Gas cooking and smoking habits and the risk of childhood and adolescent wheeze

The authors investigated the risk of wheezing illnesses in relation to contemporaneous pollutant exposures (gas cooking, heating, and smoking) in childhood and adolescence in a cohort of 2,289 United Kingdom subjects. Data from two questionnaires assessing wheezing at ages 7-8 and 15-17 years and one questionnaire on current and past pollutant exposures at age 16-18 years were studied (1987-1996). The 1,868 subjects returning all three questionnaires were divided into three groups representing childhood (10.5%), adolescent (10.9%), and persistent (i.e., both; 16.3%) wheezing and compared with 1,165 controls (62.4%) without wheezing. The estimated risks of childhood wheezing were increased by exposure to any gas in childhood (odds ratio (OR) = 1.47, 95% confidence interval (CI): 1.05, 2.04) and exposure to a gas hob in childhood (OR = 1.56, 95% CI: 1.13, 2.16) and were increased further in those persistently exposed. Risk of persistent wheezing in adolescence was paradoxically reduced by exposure to a gas hob (OR = 0.67, 95% CI: 0.50, 0.91), possibly because of selection avoidance. Contemporaneous exposure to combined smoking by both parents was associated with wheezing in all groups (odds ratios ranged from 1.62 (95% CI: 1.06, 2.46) to 1.93 (95% CI: 1.10, 3.38)). Maternal smoking alone was associated with persistent wheezing and with both childhood (OR = 1.90, 95% CI: 1.06, 3.39) and persistent (OR = 2.18, 95% CI: 1.15, 4.14) wheezing if smoking occurred throughout childhood and adolescence. The authors conclude that exposures to gas cooking and smoking in childhood and adolescence increase the overall risk of wheezing.

Concentrations and determinants of NO2 in homes of Ashford, UK and Barcelona and Menorca, Spain

This study examined indoor nitrogen dioxide (NO2) concentrations in Ashford, Kent (UK), Menorca Island and Barcelona city (Spain) and the contribution of their most important indoor determinants (e.g. gas combustion appliances and cigarette smoking). The homes examined (n = 1421) were those from infants recruited for the Asthma Multicentre Infants Cohort Study, which aimed to assess, using a standard protocol, the effects of pre- and post-natal environmental exposures in the inception of atopy and asthma. Indoor NO2 was measured using passive filter badges placed on a living room wall of the homes for between 7 and 15 days. Homes in the three centers had significantly different concentrations of indoor NO2, with those in Barcelona showing the highest levels (median NO2 levels: 5.79, 6.06 and 23.87 p.p.b. in Ashford, Menorca and Barcelona, respectively). Multiple regression analysis showed that the principal indoor determinants of NO2 concentrations in the three cohorts were the heating/cooking fuel used in the house (gas fire increased average NO2 concentrations by 1.27-fold and gas cooker by 2.13 times), parental cigarette smoking and season of measurement. Those variables significantly related to indoor NO(2) accounted for 23, 14 and 39% of the variation in indoor NO2 concentration in Ashford, Barcelona and Menorca, respectively. In all the cohorts combined, 52% of the variation could be explained in this way. Although outdoor NO2 was not measured concurrently, its additional contribution was estimated. In conclusion, despite differences in indoor NO2 mean concentrations probably reflecting different outdoor NO2 level, home factors affecting indoor NO2 values and their specific contributions were constant across the three cohorts.

PRACTICAL IMPLICATIONS

This study found that principal determinants associated to indoor NO2 in three different sites of Europe: Ashford (UK), Barcelona and Menorca (Spain) were the energy source present in the home and cigarette smoking, despite these areas presented different climates, levels of outdoor contamination, housing characteristics and ventilation behavior. It is suggested that interventions in homes of these three centers will need to address principally cigarette smoking and gas combustion appliances. These latter factors require institutional intervention, while cigarette smoking mainly require personal changes.

Residential Exposure to Traffic in California and Childhood Cancer

BACKGROUND

Motor vehicle emissions are a major source of air pollution in California. Past studies have suggested that traffic-related exposures can increase the risk of childhood cancer, particularly leukemia.

METHODS

From California's statewide, population-based cancer registry, we identified cancers diagnosed in children younger than 5 years of age between 1988 and 1997. We matched these cases to California birth certificates. For each case, we randomly selected 2 control birth certificates, matched by birth date and sex. For each mother's residential address at the time of her child's birth, we calculated road density by summing the length of all roads within a 500-foot radius of the residence. Traffic density was based on road lengths and vehicle traffic counts for highways and major roads.

RESULTS

The distributions of road and traffic density values were very similar for the 4369 cases and 8730 matched control subjects. For all cancer sites combined, the odds ratio (OR) for the highest road density exposure category, compared with the lowest, was 0.87 (95% confidence interval [CI] = 0.75-1.00). For all sites combined and for leukemia, the ORs were also below 1.0 for the highest traffic density exposure category (0.92 for both). For central nervous system tumors, the OR was 1.22 (CI = 0.87-1.70).

CONCLUSIONS

In a large study with good power, we found no increased cancer risk among offspring of mothers living in high traffic density areas for all cancer sites or leukemia.

NO2, as a marker of air pollution, and recurrent wheezing in children: a nested case-control study within the BAMSE birth cohort

AIMS

To investigate the association between air pollution, including with NO2, and recurrent wheezing during the first two years of life.

METHODS

A birth cohort (BAMSE) comprised 4089 children, for whom information on exposures, symptoms, and diseases was available from parental questionnaires at ages 2 months, and 1 and 2 years. NO2 was measured during four weeks in and outside the dwellings of children with recurrent wheezing and two age matched controls, in a nested case-control study (540 children).

RESULTS

Conditional logistic regression showed an OR of 1.60 (95% CI 0.78 to 3.26) among children in the highest quartile of outdoor NO2 exposure in relation to those in the lowest quartile, adjusted for potential confounders. The corresponding OR for indoor NO2 was 1.51 (95% CI 0.81 to 2.82). An interaction with environmental tobacco smoke (ETS) was indicated with an OR of 3.10 (95% CI 1.32 to 7.30) among children exposed to the highest quartile of indoor NO2 and ETS. The association between NO2 and recurrent wheezing appeared stronger in children who did not fulfil the criteria for recurrent wheezing until their second year.

CONCLUSIONS

Although the odds of increased recurrent wheezing are not statistically significantly different from one, results suggest that exposure to air pollution including NO2, particularly in combination with exposure to ETS, increases the risk of recurrent wheezing in children.

Personal exposure to nitrogen dioxide (NO2) and the severity of virus-induced asthma in children

BACKGROUND

A link between exposure to the air pollutant nitrogen dioxide (NO2) and respiratory disease has been suggested. Viral infections are the major cause of asthma exacerbations. We aimed to assess whether there is a relation between NO2 exposure and the severity of asthma exacerbations caused by proven respiratory viral infections in children.

METHODS

A cohort of 114 asthmatic children aged between 8 and 11 years recorded daily upper and lower respiratory-tract symptoms, peak expiratory flow (PEF), and measured personal NO2 exposures every week for up to 13 months. We took nasal aspirates during reported episodes of upper respiratory-tract illness and tested for infection by common respiratory viruses and atypical bacteria with RT-PCR assays. We used generalised estimating equations to assess the relation between low (<7.5 microg/m3), medium (7.5-14 microg/m3 ), and high (>14 microg/m3) tertiles of NO2 exposure in the week before or after upper respiratory-tract infection and the severity of asthma exacerbation in the week after the start of an infection.

FINDINGS

One or more viruses were detected in 78% of reported infection episodes, and the medians of NO2 exposure were 5 (IQR 3.6-6.3), 10 (8.7-12.0), and 21 microg/m3 (16.8-42.9) for low, medium, and high tertiles, respectively. There were significant increases in the severity of lower respiratory-tract symptom scores across the three tertiles (0.6 for all viruses [p=0.05] and >2 for respiratory syncytial virus [p=0.01]) and a reduction in PEF of more than 12 L/min for picornavirus (p=0.04) for high compared with low NO2 exposure before the start of the virus-induced exacerbation.

INTERPRETATION

High exposure to NO2 in the week before the start of a respiratory viral infection, and at levels within current air quality standards, is associated with an increase in the severity of a resulting asthma exacerbation.

Air pollution and infection in respiratory illness

The detrimental effects of air pollution on health have been recognized for most of the last century. Effective legislation has led to a change in the nature of the air pollutants in outdoor air in developed countries, while combustion of raw fuels in the indoor environment remains a major health hazard in developing countries. The mechanisms of how these pollutants exert their effects are likely to be different, but there is emerging evidence that the toxic effects of new photochemical pollutants such as nitrogen dioxide are likely to be related to infection. This review discusses the relationship between air pollution and infection and will explore some of the mechanisms of how both could act synergistically to cause respiratory illnesses especially in exacerbating symptoms in individuals with pre-existing respiratory conditions such as asthma and chronic obstructive pulmonary disease.

Factors affecting individual exposure to NO2 in Genoa (northern Italy)

The individual exposure to nitrogen dioxide (NO2) of 89 volunteers living in Genoa, a large port city of northern Italy, was investigated with personal passive diffusion tubes in February-March 2000. The data were related to NO2 concentration in the kitchen and bedroom as measured by static samplers. Volunteers included students, workers and housewives living in three areas of Genoa differing by street traffic and industrial plant location. The kitchen samples showed higher (47.00+/-16.5 microg/m3) NO2 concentrations than those from the bedroom (24.78+/-9.8 microg/m3); overall indoor NO2 concentrations were lower in the Eastern area of Genoa, where outdoor pollution is lower. Students were the volunteer group with the lowest exposure rate (24.9+/-7.8 microg/m3 vs. 44.3+/-10.1 microg/m3 for workers and 40.0+/-13.4 microg/m3 for housewives). This difference is related to the fact that students spend more time indoors, where pollution levels are lower. The main household characteristics which were shown to affect personal NO2 exposure were (a) the presence of a chimney equipped with an active aspiration device in the kitchen and (b) the heating system.

The relationship between low level nitrogen dioxide exposure and child lung function after cold air challenge

BACKGROUND

Nitrogen dioxide (NO(2)) or home gas appliance use has been inconsistently associated with adverse respiratory outcomes in childhood.

OBJECTIVES

(i) To examine the contribution of home gas appliance type and personal NO(2) exposure. (ii) To examine the relationship between NO(2) exposure and child lung function and respiratory history. (iii) To assess whether these relationships vary by house dust mite sensitization status.

METHODS

A cross-sectional survey of 344 children (71% of the eligible group) with a mean age of 9.1 years from four randomly selected schools in the Australian Capital Territory from July to September 1999. Study measurements included a parental questionnaire, NO(2) exposure by passive gas samplers, skin prick testing for 10 aeroallergens and lung function at rest and after cold air challenge.

RESULTS

Total NO(2) exposure was low with a mean concentration of 10.1 ppb. No associations were found between NO(2) exposure or gas appliance use and asthma, wheeze or baseline lung function. Personal NO(2) exposure was associated with a reduction in forced expiratory volume in one second (FEV1)/forced vital capacity (FVC) after cold air challenge (adjusted difference - 0.12% (- 0.23% to - 0.01%) per 1 ppb increase). After exclusion of children who had home heating changed because of asthma, gas heater use was also significantly associated with a reduction in this measure (adjusted difference - 2.0% (- 3.7% to - 0.2%)). There was some evidence that these reductions were greater among the non-mite-sensitized children.

CONCLUSIONS

The effect of low-level NO(2) exposure on these respiratory outcomes was not marked. The possible effect of low-level NO(2) exposure on non-specific bronchial reactivity requires confirmation. Future studies on NO(2) and respiratory health should include measures of house dust mite sensitization and bronchial hyper-responsiveness.

Personal and outdoor nitrogen dioxide concentrations in relation to degree of urbanization and traffic density

To assess differences in exposure to air pollution from traffic in relation to degree of urbanization and traffic density, we measured personal and home outdoor nitrogen dioxide (NO(2)) concentrations for 241 children from six different primary schools in the Netherlands. Three schools were situated in areas with varying degrees of urbanization (very urban, fairly urban, and nonurban) and three other schools were located near highways with varying traffic density (very busy, fairly busy, and not busy). Weekly averaged measurements were conducted during four different seasons. Simultaneously, indoor and outdoor measurements were conducted at the schools. Personal and outdoor NO(2) concentrations differed significantly among children attending schools in areas with different degrees of urbanization and among children attending schools in areas close to highways with different traffic densities. For the children living near highways, personal and outdoor NO(2) concentrations also significantly decreased with increasing distance of the home address to the highway. Differences in personal exposures between children from the different schools remained present and significant after adjusting for indoor sources of NO(2). This study has shown that personal and outdoor NO(2) concentrations are influenced significantly by the degree of urbanization of the city district and by the traffic density of and distance to a nearby highway. Because NO(2) can be considered a marker for air pollution from traffic, the more easily measured variables degree of urbanization, traffic density, and distance to a nearby highway can all be used to estimate exposure to traffic-related air pollution.

Exposures to nitrogen dioxide in EXPOLIS-Helsinki: microenvironment, behavioral and sociodemographic factors

Personal exposures to nitrogen dioxide (NO(2)) were monitored for 176 randomly selected inhabitants (25-55 years old) of Helsinki Metropolitan area as a part of the EXPOLIS (Air Pollution Exposure Distributions Within Adult Urban Populations in Europe) study between October 1996 and December 1997. NO(2) measurements were 48-h averages collected by Palmes passive sampler tubes. Differences in personal exposures to NO(2) were analyzed between sub-populations stratified by microenvironment, behavioral, socioeconomic and demographic factors. Factors significantly associated with differences in exposures to NO(2) were home and work location, housing characteristics, traffic volume near home, season and keeping windows open at home. Exposure to environmental tobacco smoke (ETS) and use of gas stove were also associated with increased personal exposures, although only few participants had a gas stove in Helsinki, and other gas appliances are non-existent. Single adults had higher average exposures to NO(2) than married or cohabiting participants, suggesting differences in living conditions between these two groups. Increased education was associated with decreased exposures to NO(2) and employed men were more exposed than unemployed men. Increased exposures to NO(2) were not associated with age or occupational status in Helsinki. Thus, behavioral and sociodemographic factors may have significant impact on personal exposures to NO(2) and should be considered in addition to environmental determinants in any monitoring program.

Nitrogen dioxide exposure assessment and cough among preschool children

The association between exposure to ambient air nitrogen dioxide and cough was evaluated in a panel study among 162 children aged 3-6 y. The weekly average nitrogen dioxide exposure was assessed with Palmes-tube measurements in three ways: (1) personally, (2) outside day-care centers, and (3) inside day-care centers. Ambient air nitrogen dioxide concentrations were obtained from the local network that monitored air quality. The parents recorded cough episodes daily in a diary. The risk of cough increased significantly (relative risk = 3.63; 95% confidence interval = 1.41, 9.30) in the highest personal nitrogen dioxide exposure category in winter, and a nonsignificant positive trend was noted for the other assessment groups. In spring, risk increased nonsignificantly in all exposure-assessment groups, except for the fixed-site monitoring assessment. It is important that investigators select an exposure-assessment method sufficiently accurate to reflect the effective pollutant dose in subjects.

Outdoor air concentrations of nitrogen dioxide and sulfur dioxide and prevalence of wheezing in school children

We report analysis of data on outdoor air pollution and respiratory symptoms in children collected in the Czech part of the international Small Area Variations in Air pollution and Health (SAVIAH) Project, a methodological study designed to test the use of geographical information systems (GIS) in studies of environmental exposures and health at small area level. We collected the following data in two districts of Prague: (1) individual data on 3,680 children (response rate 88%) by questionnaires; (2) census-based socio-demographic data for small geographical units; (3) concentrations of nitrogen dioxide (NO2) and sulfur dioxide (SO2) measured by passive samplers in three 2-week surveys at 80 and 50 locations, respectively. We integrated all data into a geographical information system. Modeling of NO2 and SO2 allowed estimation of exposure to outdoor NO2 and SO2 at school and at home for each child. We examined the associations between air pollution and prevalence of wheezing or whistling in the chest in the last 12 months by logistic regression at individual level, weighted least squares regression at small area (ecological) level and multilevel modeling. The results varied by the level of analysis and method of exposure estimation. In multilevel analyses using individual data, odds ratios per 10 microg/m3 increase in concentrations were 1.16 (95% CI = 0.95-1.42) for NO2, and 1.08 (95% CI = 0.97-1.21) for SO2. While mapping of spatial distribution of NO2 and SO2 in the study area appeared valid, the interpolation from outdoor to personal exposures requires consideration.

Complex interconvertibility of nitrogen oxides (NOX): impact on occupational and environmental health

Oxides of nitrogen have been implicated in a vast number of environmental and occupational health effects, some of which lack concrete mechanisms. Whereas certain compelling pieces of evidence link a particular nitrogen oxide to a particular adverse health effect, other reports seem to implicate virtually all the oxides in one form of toxic process or the other. Such diversity has probably emerged because each oxide of nitrogen possesses a different oxidation state, in which each form exerts different important levels of biological activity. Most important, each nitrogen oxide readily interconverts into another oxide at a very fast rate. This property of rapid interconvertibility poses problems to researchers in identifying with great confidence the actual oxide of nitrogen that is responsible for a specific occupational and environmental health effect. This paper reviews the complex nature of the nitrogen oxides (represented collectively as NOX) to explore the extent to which their acute or chronic exposure could be associated with toxicity. The nomenclature of the nitrogen oxides is outlined as a necessity for clarity and simplicity in understanding their reactions and interconvertibility and how they affect health. The natural occurrence and sources of occupational and environmental exposures and effects are critically evaluated and analyzed.

Indoor nitrogen dioxide in homes along trunk roads with heavy traffic

OBJECTIVES

To assess the distribution of indoor nitrogen dioxide (NO2) concentrations in homes located in differing environments, and to investigate the influence of factors such as automobile exhaust on the indoor environment.

METHODS

The concentrations of indoor NO2 over 24 hours were measured in both the heating and non-heating periods in homes of pupils from nine elementary schools in Chiba, Japan. Information on factors that could influence indoor environments was collected by questionnaire.

RESULTS

Indoor NO2 concentrations during the heating period were higher in homes with unvented heaters than in homes with vented heaters, although the concentrations varied greatly among homes primarily because of the type of heating device used. During the non-heating period, indoor NO2 concentrations were significantly higher in homes adjacent to trunk roads than in homes located in other areas. Multiple regression analysis showed that indoor NO2 concentrations were associated with atmospheric NO2 in homes with vented heaters during the heating period, and in homes in areas other than on the roadside during the non-heating period. In areas other than the roadside, cigarette smoking in indoor environments also significantly contributed to indoor NO2. The average concentrations of indoor NO2 in the homes of pupils attending each school were significantly related to the atmospheric NO2 in areas other than the roadside. However, the relation between indoor and atmospheric NO2 concentrations was not significant in roadside areas.

CONCLUSIONS

These findings suggest that indoor NO2 concentrations are related to the atmospheric NO2 and type of heating appliances, and are also affected by automobile exhaust in homes located in roadside areas.