Characterizing relationships between personal exposures to VOCs and socioeconomic,demographic, behavioral variables

Socioeconomic and demographic factors have been found to significantly affect time-activity patterns in population cohorts that can subsequently influence personal exposures to air pollutants. This study investigates relationships between personal exposures to eight VOCs (benzene, toluene, ethylbenzene, o-xylene, m-,p-xylene, chloroform, 1,4-dichlorobenzene, and tetrachloroethene) and socioeconomic, demographic, time-activity pattern factors using data collected from the 1999–2000 National Health and Nutrition Examination Survey (NHANES) VOC study. Socio-demographic factors (such as race/ethnicity and family income) were generally found to significantly influence personal exposures to the three chlorinated compounds. This was mainly due to the associations paired by race/ethnicity and urban residence, race/ethnicity and use of air freshener in car, family income and use of dry-cleaner, which can in turn affect exposures to chloroform, 1,4-dichlorobenzene, and tetrachloroethene, respectively. For BTEX, the traffic-related compounds, housing characteristics (leaving home windows open and having an attached garage) and personal activities related to the uses of fuels or solvent-related products played more significant roles in influencing exposures. Significant differences in BTEX exposures were also commonly found in relation to gender, due to associated significant differences in time spent at work/school and outdoors. The coupling of Classification and Regression Tree (CART) and Bootstrap Aggregating (Bagging) techniques were used as effective tools for characterizing robust sets of significant VOC exposure factors presented above, which conventional statistical approaches could not accomplish. Identification of these significant VOC exposure factors can be used to generate hypotheses for future investigations about possible significant VOC exposure sources and pathways in the general U.S. population.     

Risk factors for increased BTEX exposure in four Australian cities

Benzene, toluene, ethylbenzene and xylenes (BTEX) are common volatile organic compounds (VOCs) found in urban airsheds. Elevated levels of VOCs have been reported in many airsheds at many locations, particularly those associated with industrial activity, wood heater use and heavy traffic. Exposure to some VOCs has been associated with health risks. There have been limited investigations into community exposures to BTEX using personal monitoring to elucidate the concentrations to which members of the community may be exposed and the main contributors to that exposure. In this cross sectional study we investigated BTEX exposure of 204 non-smoking, non-occupationally exposed people from four Australian cities. Each participant wore a passive BTEX sampler over 24h on five consecutive days in both winter and summer and completed an exposure source questionnaire for each season and a diary for each day of monitoring. The geometric mean (GM) and range of daily BTEX concentrations recorded for the study population were benzene 0.80 (0.04-23.8 ppb); toluene 2.83 (0.03-2120 ppb); ethylbenzene 0.49 (0.03-119 ppb); and xylenes 2.36 (0.04-697 ppb). A generalised linear model was used to investigate significant risk factors for increased BTEX exposure. Activities and locations found to increase personal exposure included vehicle repair and machinery use, refuelling of motor vehicles, being in an enclosed car park and time spent undertaking arts and crafts. A highly significant difference was found between the mean exposures in each of the four cities, which may be explained by differences in fuel composition, differences in the mix and density of industry, density of motor vehicles and air pollution meteorology.     

Predicting the contents of BTEX and MTBE for the three types of tollbooth at a highway toll station via the direct and indirect approaches

This study was set out to assess the contents of five volatile organic compounds (VOCs), including BTEX (the acronym for benzene, toluene, ethylbenzene, and xylene) and methyl tertiary-butyl ether (MTBE), in three types of tollbooth (including the car lane/ticket-collecting, car lane/cash-collecting, and bus/truck lane tollbooths) at a highway toll station via the direct and indirect approaches. For the direct approach, VOC samples were collected from the breathing zone of booth attendants at all selected tollbooths during the three workshifts. For samples collected during the dayshift, we found VOC contents of BTEX and MTBE in both the car lane/ticket-collecting (=6.23, 21.93, 3.24, 8.56, and 5.63 ppb, respectively) and car lane/cash-collecting tollbooths (=5.98, 21.71, 3.25, 8.59, and 6.04 ppb, respectively) were quite comparable, but both were significantly higher than that in the bus/truck lane tollbooth (=3.13, 13.91, 2.05, 4.52, and 2.70 ppb, respectively). The same pattern can also be found for the other two workshifts. For the indirect approach, we conducted multivariate regression analyses to predict VOC contents for any given type of tollbooth by using the four independent variables of the vehicle flowrate, wind speed, relative humidity, and air temperature. We found that, except the vehicle flowrate, the other three factors did not have a significant effect on VOC contents in the three types of tollbooth. In addition, the magnitudes of the effect of the vehicle flowrate on VOC contents for the three types of tollbooth were: car lane/cash-collecting>bus/truck lane>car lane/ticket-collecting. All regression results yielded R²-values in the range of 0.41−0.74 indicating that the developed indirect approach was able to predict VOC contents for three types of tollbooth.     

Quantification of personal exposure concentrations to gasoline vehicle emissions in high-end exposure microenvironments: Effects of fuel and season

Mobile-source air toxic (MSAT) levels increase in confining microenvironments (MEs) with numerous emission sources of vehicle exhaust or evaporative emissions or during high-load and cold-start conditions. Reformulated fuels are expected to reduce MSAT and ozone precursor emissions. This study, required under the Clean Air Act Section 211b, evaluated high-end exposures in cities using reformulated (methyl tertiary-butyl ether [MTBE] or ethanol [EtOH]) fuels and conventional gasoline blends. The study investigates 13 high-end MEs, sampling under enhanced exposure conditions expected to result in maximal fuel and exhaust component exposures to carbon monoxide (CO), carbon dioxide (CO₂), BTEX (benzene, toluene, ethylbenzene, xylenes), MTBE, 1,3-butadiene (1,3-BD), EtOH, formaldehyde (HCHO), and acetaldehyde (CH₃CHO). The authors found that day-to-day ME variations in high-end benzene, 1,3-BD, HCHO, and CO concentrations are substantial, but independent of gasoline composition and season, and related to the activity and emission rates of ME sources, which differ from day to day.

Implications: Mobile-source air toxic (MSAT) levels increase in confining microenvironments (MEs) in the presence of vehicular exhaust or evaporative emissions. This study, required under the Clean Air Act Section 211b, evaluated high-end exposures in cities using oxygenated (methyl tertiary-butyl ether or ethanol) and conventional gasoline blends. Personal exposure concentrations were quantified in selected MEs representing the upper end of the frequency distribution of potential population exposures. This work presents the first systematic look at high-end/maximal exposures to multiple contaminants, in multiple microenvironments, in multiple cities, over two seasons, for multiple fuels, making it a very complete evaluation of reformulated fuel impacts on MSAT concentrations in confined microenvironments. The study found that day-to-day ME variations of high-end pollutant concentrations are substantial, but independent of gasoline composition and season, and related to the variable daily activity and emission rates of ME sources. The data collected in this study may be used in bounding exposure modeling estimates that account for time spent in similar confining MEs.     

Treatment of groundwater contaminated with gasoline components by an ozone/UV process

In this paper, the treatment of real groundwater samples contaminated with gasoline components, such as benzene, toluene, ethylbenzene, and xylene (BTEX), methyl tert-butyl ether (MTBE), tert-butyl alcohol (TBA), and other gasoline constituents in terms of total petroleum hydrocarbons as gasoline (TPHg) by an ozone/UV process was investigated. The treatment was conducted in a semi-batch reactor under different experimental conditions by varying ozone gas dosage and incident UV light intensity. The groundwater samples contained BTEX compounds, MTBE, TBA, and TPHg in the ranges of 5-10000, 3000-5500, 80-1400, and 2400-20000mugl(-1), respectively. The ozone/UV process was very effective compared to ozonation in the removal of the gasoline components from the groundwater samples. For the various gasoline constituents, more than 99% removal efficiency was achieved for the ozone/UV process and the removal efficiency for ozonation was as low as 27%. The net ozone consumed per mol of organic carbon (from BTEX, MTBE, and TBA) oxidized varied in the range of 5-60 for different types of groundwater samples treated by the ozone/UV process. In ozonation experiments, it was observed that the presence of sufficient amount of iron in groundwater samples improved the removal of BTEX, MTBE, TBA, and TPHg.     

Revealing source signatures in ambient BTEX concentrations

Management of ambient concentrations of Volatile Organic Compounds (VOCs) is essential for maintaining low ozone levels in urban areas where its formation is under a VOC-limited regime. The significant decrease in traffic-induced VOC emissions in many developed countries resulted in relatively comparable shares of traffic and non-traffic VOC emissions in urban airsheds. A key step for urban air quality management is allocating ambient VOC concentrations to their pertinent sources. This study presents an approach that can aid in identifying sources that contribute to observed BTEX concentrations in areas characterized by low BTEX concentrations, where traditional source apportionment techniques are not useful. Analysis of seasonal and diurnal variations of ambient BTEX concentrations from two monitoring stations located in distinct areas reveal the possibility to identify source categories. Specifically, the varying oxidation rates of airborne BTEX compounds are used to allocate contributions of traffic emissions and evaporative sources to observed BTEX concentrations.     

Hydrochemical and isotopic effects associated with petroleum fuel biodegradation pathways in a chalk aquifer

Hydrochemical data, compound specific carbon isotope analysis and isotopic enrichment trends in dissolved hydrocarbons and residual electron acceptors have been used to deduce BTEX and MTBE degradation pathways in a fractured chalk aquifer. BTEX compounds are mineralised sequentially within specific redox environments, with changes in electron acceptor utilisation being defined by the exhaustion of specific BTEX components. A zone of oxygen and nitrate exhaustion extends approximately 100 m downstream from the plume source, with residual sulphate, toluene, ethylbenzene and xylene. Within this zone complete removal of the TEX components occurs by bacterial sulphate reduction, with sulphur and oxygen isotopic enrichment of residual sulphate (epsilon(s) = -14.4 per thousand to -16.0 per thousand). Towards the plume margins and at greater distance along the plume flow path nitrate concentrations increase with delta15N values of up to +40 per thousand indicating extensive denitrification. Benzene and MTBE persist into the denitrification zone, with carbon isotope enrichment of benzene indicating biodegradation along the flow path. A Rayleigh kinetic isotope enrichment model for 13C-enrichment of residual benzene gives an apparent epsilon value of -0.66 per thousand. MTBE shows no significant isotopic enrichment (delta13C = -29.3 per thousand to -30.7 per thousand) and is isotopically similar to a refinery sample (delta13C = -30.1 per thousand). No significant isotopic variation in dissolved MTBE implies that either the magnitude of any biodegradation-induced isotopic fractionation is small, or that relatively little degradation has taken place in the presence of BTEX hydrocarbons. It is possible, however, that MTBE degradation occurs under aerobic conditions in the absence of BTEX since no groundwater samples were taken with co-existing MTBE and oxygen. Low benzene delta13C values are correlated with high sulphate delta34S, indicating that little benzene degradation has occurred in the sulphate reduction zone. Benzene degradation may be associated with denitrification since increased benzene delta13C is associated with increased delta15N in residual nitrate. Re-supply of electron acceptors by diffusion from the matrix into fractures and dispersive mixing is an important constraint on degradation rates and natural attenuation capacity in this dual-porosity aquifer.     

VOC concentrations measured in personal samples and residential indoor,outdoor and workplace microenvironments in EXPOLIS-Helsinki,Finland

Thirty target volatile organic compounds (VOC) were analyzed in personal 48-h exposure samples and residential indoor, residential outdoor and workplace indoor microenvironment samples as a component of EXPOLIS-Helsinki, Finland. Geometric mean residential indoor concentrations were higher than geometric mean residential outdoor concentrations for all target compounds except hexane, which was detected in 40% of residential outdoor samples and 11% of residential indoor samples, respectively. Geometric mean residential indoor concentrations were significantly higher than personal exposure concentrations, which in turn were significantly higher than workplace concentrations for compounds that had strong residential indoor sources (d-limonene, alpha pinene, 3-carene, hexanal, 2-methyl-1-propanol and 1-butanol). 40% of participants in EXPOLIS-Helsinki reported personal exposure to environmental tobacco smoke (ETS). Participants in Helsinki that were exposed to ETS at any time during the 48-h sampling period had significantly higher personal exposures to benzene, toluene, styrene, m,p-xylene, o-xylene, ethylbenzene and trimethylbenzene. Geometric mean ETS-free workplace concentrations were higher than ETS-free personal exposure concentrations for styrene, hexane and cyclohexane. Geometric mean personal exposures of participants not exposed to ETS were approximately equivalent to time weighted ETS-free indoor and workplace concentrations, except for octanal and compounds associated with traffic, which showed higher geometric mean personal exposure concentrations than any microenvironment (o-xylene, ethylbenzene,benzene, undecane, nonane, decane, m,p-xylene, and trimethylbenzene). Considerable differences in personal exposure concentrations and residential levels of compounds with mainly indoor sources suggested differences in product types or the frequency of product use between Helsinki, Germany and the United States.     

地下水浅埋区某加油站特征污染物空间分布简

加油站渗漏污染地下水已经是一个世界性的问题。由于浅埋区加油站储罐与地下水密切接触，更加剧储罐的腐蚀。为揭示加油站渗漏的典型污染物石油烃（TPH）、苯系物（BTEX）、萘和甲基叔丁基醚（MTBE）在该水文地质条件下的迁移变化，在浅埋区某加油站开展了平、枯、丰水期的地下水监测工作。在水平分布上，TPH、BTEX、萘基本相似，均在加油岛附近形成高浓度区，而MTBE则更易随地下水流动而迁移，呈现出不同的污染晕。在垂直分布上，地下水的水位变动是污染物浓度分布的主要影响因素。     

Alveolar Breath Sampling and Analysis to Assess Exposures to Methyl Tertiary Butyl Ether (MTBE) During Motor Vehicle Refueling

Abstract

Methyl tertiary butyl ether (MTBE) is added to gasoline (15% by volume) in many areas of the U.S. to help control carbon monoxide emissions from motor vehicles. In this study we present a sampling and analytical methodology that can be used to assess consumers' exposures to MTBE that may result from routine vehicle refueling operations. The method is based on the collection of alveolar breath samples using evacuated one-liter stainless steel canisters and analysis using a gas chromatograph-mass spectrometer equipped with a patented "valveless" cryogenic preconcentrator.

To demonstrate the utility of this approach, a series of breath samples was collected from two individuals (the person pumping the fuel and a nearby observer) immediately before and for 64 min after a vehicle was refueled with premium grade gasoline. Results demonstrate low levels of MTBE in both subjects' breaths before refueling, and levels that increased by a factor of 35 to 100 after the exposure. Breath elimination models fitted to the post exposure measurements indicate that the half-life of MTBE in the first physiological compartment was between 1.3 and 2.9 min. Analysis of the resulting models suggests that breath elimination of MTBE during the 64 min monitoring period was approximately 115 jug for the refueling subject while it was only 30 ug for the nearby observer. This analysis also shows that the post exposure breath elimination of other gasoline constituents was consistent with previously published observations.

These results demonstrate that this new methodology can be used effectively in studies designed to assess exposures to MTBE. The method can be used to objectively demonstrate recent exposures, the relative magnitude of an exposure, and the approximate duration of the resulting bloodborne dose. Once a blood/breath partition coefficient for MTBE has been firmly established, the bloodborne concentration of the absorbed material can be determined using these techniques as well.     

VOC source identification from personal and residential indoor,outdoor and workplace microenvironment samples in EXPOLIS-Helsinki,Finland

Principal component analyses (varimax rotation) were used to identify common sources of 30 target volatile organic compounds (VOCs) in residential outdoor, residential indoor and workplace microenvironment and personal 48-h exposure samples, as a component of the EXPOLIS-Helsinki study. Variability in VOC concentrations in residential outdoor microenvironments was dominated by compounds associated with long-range transport of pollutants, followed by traffic emissions, emissions from trees and product emissions. Variability in VOC concentrations in environmental tobacco smoke (ETS) free residential indoor environments was dominated by compounds associated with indoor cleaning products, followed by compounds associated with traffic emissions, long-range transport of pollutants and product emissions. Median indoor/outdoor ratios for compounds typically associated with traffic emissions and long-range transport of pollutants exceeded 1, in some cases quite considerably, indicating substantial indoor source contributions. Changes in the median indoor/outdoor ratios during different seasons reflected different seasonal ventilation patterns as increased ventilation led to dilution of those VOC compounds in the indoor environment that had indoor sources. Variability in workplace VOC concentrations was dominated by compounds associated with traffic emissions followed by product emissions, long-range transport and air fresheners. Variability in VOC concentrations in ETS free personal exposure samples was dominated by compounds associated with traffic emissions, followed by long-range transport, cleaning products and product emissions. VOC sources in personal exposure samples reflected the times spent in different microenvironments, and personal exposure samples were not adequately represented by any one microenvironment, demonstrating the need for personal exposure sampling.     

Commuter exposures to VOCs in Boston, Massachusetts.

This study examines the commuter's exposure to six gasoline-related volatile organic compounds (VOCs): benzene, toluene, ethylbenzene, m-/p-xylene, o-xylene, and formaldehyde. The VOC concentrations to which commuters were exposed in four different commuting modes (driving, subway, walking, and biking) in Boston, Massachusetts, are compared. The VOC concentrations in participants' homes and offices were also measured. Factors that could influence in-vehicle VOC concentrations, such as different traffic patterns, car model and vehicle ventilation conditions, were also evaluated. Driving a private car was associated with higher VOC concentrations and commuting on urban roadways resulted in the highest VOC concentrations. The use of car heaters resulted in higher in-vehicle VOC concentrations. The longer the subway commuters stayed underground, the higher their VOC exposures. The home-to-work car or subway commute represented about 10 to 20 percent of an individual's total VOC exposure for these compounds.     

Personal exposures to particles and their relationships with personal activities for chronic obstructive pulmonary disease patients living in Boston

An exposure study of 18 subjects with chronic obstructive pulmonary disease (COPD) living in the Boston, MA, area was conducted. The objective was to examine determinants of personal exposures to particulate matter (PM) with aerodynamic diameters of less than 2.5 microm (PM2.5), less than 10 microm (PM10), and between 2.5 and 10 microm (PM2.5-10). In a previous publication, the analyses of the longitudinal individual-specific relationships among indoor, outdoor, and personal levels showed that the relationships varied by subject and by particle size fraction. In the present paper, statistical and physical models were used to examine personal PM2.5, PM10, and PM2.5-10 exposure covariates. Results indicated that time-weighted indoor concentrations were significant predictors of personal PM2.5, PM10, and PM2.5-10 exposures. Also, time-weighted outdoor concentrations, time spent near smokers, and time spent during transportation were important predictors for PM2.5 but not for personal PM2.5-10 exposures. In turn, time spent cleaning contributed to all size-fraction personal exposures, whereas cooking affected only personal PM2.5-10 exposures. The findings showed that the relationship between personal PM2.5 exposures and the corresponding ambient concentrations was influenced by home air exchange rates (or by ventilation status). Because the particle properties or components causing the health effects are unknown, it is not certain to what extent the risk posed by ambient particles can be reduced by controlling any one of these factors.     

Water quality at five marinas in Lake Texoma as related to methyl tert-butyl ether (MTBE)

Water quality in five marinas on Lake Texoma, located on the Oklahoma and Texas border, was monitored between June 1999 and November 2000. Focus was to evaluate lake water associated with marinas for methyl tert-butyl ether (MTBE). Lake water was collected at locations identified as marina entrance, gasoline filling station, and boat dock. Occurrence of MTBE showed a direct seasonal trend with recreational boating activity at marina areas. There was a positive correlation with powerboat usage ratio, which was directly related to the gallons of gasoline sold. Sampling before and after the high boat use holiday weekends determined the apparent influence of powerboat activity on MTBE contamination. Boat dock locations were the most sensitive sites to MTBE contamination, possibly due to gasoline spillage during engine startup. The most common compound of the BTEX series found with MTBE was toluene and co-occurrence was most frequent at gasoline filling stations.     

Measurement of personal and integrated exposure to particulate matter and co-pollutant gases

Personal exposure measurement can serve as an effective tool to understand the effect of exposure to air pollutants. Alternatively, exposure assessment using pollutant concentrations in different microenvironments and accurate time–activity information for the subjects can provide good information regarding human integrated exposure. A panel of 18 healthy students of Indian Institute of Technology (IIT) Kanpur in the age group of 18 to 30 years participated in the personal exposure measurements for particulate matter, CO, NO₂ and VOC during post-monsoon and pre-monsoon seasons. Overall, 432 h person exposure data was collected in this study. The major sources of particulate and gaseous co-pollutants were identified. These directly obtained personal exposure values were then compared to the indirectly estimated integrated exposure values. Personal and integrated exposures gave statistically similar results. Through this study, we have shown that integrated exposure values could closely estimate the personal exposure values for particulate matter that can significantly reduce time and cost involved in personal exposure studies. The lung parameters for all the subjects measured during the pre-monsoon and post-monsoon seasons showed statistically significant reduction during pre-monsoon. This was attributed to the high levels of coarse particles during pre-monsoon.     

Commuter Exposures to VOCs in Boston,Massachusetts

This study examines the commuter’s exposure to six gasoline-related volatile organic compounds (VOCs): benzene, toluene, ethylbenzene, m-/p-xylene, o-xylene, and formaldehyde. The VOC concentrations to which commuters were exposed in four different commuting modes (driving, subway, walking, and biking) in Boston, Massachusetts, are compared. The VOC concentrations in participants’ homes and offices were also measured. Factors that could influence in-vehicle VOC concentrations, such as different traffic patterns, car model and vehicle ventilation conditions, were also evaluated. Driving a private car was associated with higher VOC concentrations and commuting on urban roadways resulted in the highest VOC concentrations. The use of car heaters resulted in higher in-vehicle VOC concentrations. The longer the subway commuters stayed underground, the higher their VOC exposures. The home-to-work car or subway commute represented about 10 to 20 percent of an individual’s total VOC exposure for these compounds.     

地下水浅埋区某加油站特征污染物空间分布

加油站渗漏污染地下水已经是一个世界性的问题。由于浅埋区加油站储罐与地下水密切接触，更加剧储罐的腐蚀。为揭示加油站渗漏的典型污染物石油烃（TPH）、苯系物（BTEX）、萘和甲基叔丁基醚（MTBE）在该水文地质条件下的迁移变化，在浅埋区某加油站开展了平、枯、丰水期的地下水监测工作。在水平分布上，TPH、BTEX、萘基本相似，均在加油岛附近形成高浓度区，而MTBE则更易随地下水流动而迁移，呈现出不同的污染晕。在垂直分布上，地下水的水位变动是污染物浓度分布的主要影响因素。     

Using the Gasoline Additive MTBE in Forensic Environmental Investigations

A variety of additives are used in gasoline, and they can sometimes be used to help identify the source, timing, or number of gasoline spills at a site. The physicochemical characteristics of the additive MTBE, and its historical use pattern in the United States since 1979, make it a key compound to study when conducting forensic investigations of gasoline spills. MTBE's low octanol: water distribution coefficient and high solubility cause it to dissolve into groundwater more readily than other gasoline components. Thus, the initial appearance of MTBE in the groundwater is often a good indicator of a recent gasoline spill. MTBE's very low retardation and minimal biodegradation in groundwater can be used with transport rate calculations to establish relatively accurate estimates of spill timing. Because MTBE moves faster in groundwater than BTEX compounds, if a gasoline spill site has a BTEX plume that is longer than the MTBE plume, it is certain that at least two distinctly different gasoline releases have occurred. This allows for the identification of new gasoline spills, even when substantial subsurface petroleum contamination already exists. An example application is reviewed to demonstrate the use of MTBE data in forensic investigations.     

Parameter evaluation and model validation of ozone exposure assessment using Harvard Southern California Chronic Ozone Exposure Study data

To examine factors influencing long-term ozone (O3) exposures by children living in urban communities, the authors analyzed longitudinal data on personal, indoor, and outdoor O3 concentrations, as well as related housing and other questionnaire information collected in the one-year-long Harvard Southern California Chronic Ozone Exposure Study. Of 224 children contained in the original data set, 160 children were found to have longitudinal measurements of O3 concentrations in at least six months of 12 months of the study period. Data for these children were randomly split into two equal sets: one for model development and the other for model validation. Mixed models with various variance-covariance structures were developed to evaluate statistically important predictors for chronic personal ozone exposures. Model predictions were then validated against the field measurements using an empirical best-linear unbiased prediction technique. The results of model fitting showed that the most important predictors for personal ozone exposure include indoor O3 concentration, central ambient O3 concentration, outdoor O3 concentration, season, gender, outdoor time, house fan usage, and the presence of a gas range in the house. Hierarchical models of personal O3 concentrations indicate the following levels of explanatory power for each of the predictive models: indoor and outdoor O3 concentrations plus questionnaire variables, central and indoor O3 concentrations plus questionnaire variables, indoor O3 concentrations plus questionnaire variables, central O3 concentrations plus questionnaire variables, and questionnaire data alone on time activity and housing characteristics. These results provide important information on key predictors of chronic human exposures to ambient O3 for children and offer insights into how to reliably and cost-effectively predict personal O3 exposures in the future. Furthermore, the techniques and findings derived from this study also have strong implications for selecting the most reliable and cost-effective exposure study design and modeling approaches for other ambient pollutants, such as fine particulate matter and selected urban air toxics.     

Aromatic hydrocarbons in the atmospheric environment. Part III: personal monitoring

As part of a larger study, personal sampling of the aromatic hydrocarbons benzene, toluene, ethylbenzene and the isomeric xylenes (BTEX) was carried out by 55 nonsmoking volunteers for a period of 14 days. Thirty-nine persons lived in a rural area near Hannover (Germany) with hardly any traffic at all, while 16 persons lived in a high-traffic city street in Hannover. The personal exposure level of the persons in the rural area (some commuting to Hannover) was: 2.9, 24.8, 2.4 and 7.7 μg m⁻³ for benzene, toluene, ethylbenzene and the sum of xylenes, respectively, while the corresponding data for the high traffic city streets were 4.0, 22.2, 2.8 and 9.7 μg m⁻³ (geometric means). Four microenvironments have been monitored which contribute to the total exposure to BTEX, i.e. the home, the outdoor air, the workplace and the car cabin. The most important microenvironment for non-working persons is the private home. The concentration of most BTEX in the private home is almost equal to the personal exposure level, demonstrating that the indoor pollution in the home makes by far the highest contribution to the total exposure. For working people (mostly office workers), the workplace is the second most important microenvironment contributing to the total BTEX exposure. Taking all working persons into consideration (independent of the location of their private home) the personal exposure level is higher by a factor of 1.2–1.4 than that of the workplace (for toluene this factor is 2.2). As already found by others, very high BTEX concentrations may be found in car cabins, in particular, if the engine is gasoline-driven. In the cabin of 44 cars in the rural/urban area average benzene concentrations (geometric mean) of 12/14 μg m⁻³ and a maximum value of ∼550 μg m⁻³ were found. On average, the participating volunteers drove their car for 45 min day⁻¹ (i.e. 3% of the day). Nevertheless, the car cabin constitutes about 10% of the total benzene exposure. Refueling of the car during the 14-day sampling period has only a small effect on the personal exposure level.