Detroit Exposure And Aerosol Research Study Research Articles

Associations Between Personal Exposures To Vocs And Alterations In Cardiovascular Physiology: Detroit Exposure And Aerosol Research Study

Introduction: An adult cohort consisting of 63 participants engaged in the US EPA's recent Detroit Exposure and Aerosol Research Study (DEARS) and a University of Michigan cardiovascular sub-study conducted during summer and winter periods over 3 years between 2004 and 2007. Through all participants' wearing of a monitoring vest, personal exposures to various air pollutants were measured. Objectives: The study objective was to identify the association between personal exposure to volatile organic compounds (VOCs) and six cardiovascular health endpoints in the DEARS. Methods: Twenty five VOCs were collected using the DEARS exposure vest. Six cardiovascular health endpoints including systolic and diastolic blood pressure (SBP, DBP), heart rate (HR), brachial artery diameter (BAD), brachial artery flow-mediated dilatation (FMD) and nitroglycerin-mediated arterial dilatation (NMD) were collected. To reduce the number of personal VOCs highly correlated to each other, a principal component analysis was conducted. Accounting for more individual variations in association between personal VOCs and cardiovascular health endpoints, a linear mixed model was employed. Results: Applying the principal component analysis, 3 out of 12 components were retained, which appeared to involve a petroleum source (1st component), a 1-3 butadiene source (2nd component), and an ambient (Freon) source (3rd component). Petroleum related VOCs were associated with increases in FMD and showed mixed relationships with NMD (lag 0-1 day increased NMD, lag 2 days decreased NMD). Butadiene related VOCs decreased DBP but increased HR and BAD. Freon (ambient background) related VOCs increased HR. Conclusions: We observed mixed and variable results in this first study to evaluate the relationships between personal exposures to VOCs of different origin on cardiovascular physiology. In sum, the findings suggest that VOCs may have rapid impacts upon the human cardiovascular system.

Development and assessment of a physics-based simulation model to investigate residential PM2.5 infiltration across the US housing stock

The Lawrence Berkeley National Laboratory Population Impact Assessment Modeling Framework (PIAMF) was expanded to enable determination of indoor PM2.5 concentrations and exposures in a set of 50,000 homes representing the US housing stock. A mass-balance model is used to calculate time-dependent pollutant concentrations within each home. The model includes size- and species-dependent removal mechanisms. The particle model was applied to the housing samples of the Relationship of Indoor, Outdoor, and Personal Air (RIOPA) and The Detroit Exposure and Aerosol Research Study (DEARS) studies to compare model- and measurement-based estimates of indoor PM2.5 of outdoor origin. Model-derived distributions of infiltration factors (ratio of indoor PM2.5 of outdoor origin to outdoor PM2.5) are compared to measurement-based distributions obtained in studies conducted in 11 US cities.

Associations between personal exposures to VOCs and alterations in cardiovascular physiology: Detroit Exposure and Aerosol Research Study (DEARS)

BackgroundAn adult cohort consisting of 63 participants engaged in the US EPA's recent Detroit Exposure and Aerosol Research Study (DEARS) and a University of Michigan cardiovascular sub-study conducted during summer and winter periods over 3 years between 2004 and 2007 (5 seasons in total). Through all participants' wearing of a monitoring vest, personal exposures to various air pollutants were measured. PurposeThe study objective was to identify the association between personal exposure to volatile organic compounds (VOCs) and six cardiovascular health endpoints in an adult non-smoking cohort of the DEARS. MethodsTwenty five VOCs were collected using the DEARS exposure vest incorporating advanced passive diffusion tube. Six cardiovascular health endpoints including systolic and diastolic blood pressure (SBP, DBP), heart rate (HR), brachial artery diameter (BAD), brachial artery flow-mediated dilatation (FMD) and nitroglycerin-mediated arterial dilatation (NMD) were collected by novel, in-home clinical examinations. To reduce the number of personal VOCs highly correlated to each other, a principal component analysis was conducted. Accounting for more individual variations in association between personal VOCs and cardiovascular health endpoints, a linear mixed model was employed, where cohort subjects were not necessarily to have the same linear association. ResultsApplying the principal component analysis, 3 out of 12 components were retained, which appeared to involve a petroleum source (1st component), a 1-3 butadiene source (2nd component), and an ambient (Freon) source (3rd component). Petroleum related VOCs were associated with increases in FMD and showed mixed relationships with NMD (lag 0–1 day increased NMD, lag 2 days decreased NMD). Butadiene related VOCs decreased DBP but increased HR and BAD. Freon (ambient background) related VOCs increased HR. ConclusionsWe observed mixed and variable results in this first study to evaluate the relationships between personal exposures to VOCs of different origin on cardiovascular physiology. In sum, the findings suggest that VOCs may have rapid impacts upon the human cardiovascular system; however, understanding the health implications and the mechanisms responsible is beyond the scope of this investigation.

Progress on understanding spatial and temporal variability of PM2.5and its components in the Detroit Exposure and Aerosol Research Study (DEARS)

The Detroit Exposure and Aerosol Research Study (DEARS) measured personal exposures, ambient, residential indoor and residential outdoor concentrations of select PM2.5 aerosol components (SO4, NO3, Fe, Si, Ca, K, Mn, Pb, Zn, EC and OC) over a three year period (2004-2007). These events represented approximately 190 calendar days of monitoring which was performed in seven residential neighborhoods throughout Wayne County, MI. The selection of neighborhoods and participants for study inclusion was based upon an a priori hypothesis that each neighborhood represented a potentially distinct air quality scenario being influenced by both regional as well as local pollution sources. Daily (24 h integrated) measurement data were used to evaluate the spatial and temporal PM2.5 compositional variability of the personal, indoor and outdoor spatial settings as they related to a central ambient monitoring site (Allen Park). Many of the PM2.5 components were observed to have spatially different outdoor mass concentrations in matched neighborhood by neighborhood comparisons, with sulfate, OC, and NO3 being noted exceptions. Coefficient of divergence (COD) comparisons involving outdoor measures for Ca, Si, Fe, Zn, Pb, and EC revealed significant spatial variability. While concentrations of most components were lower indoors as compared to outdoor measures, K and Si indoor concentrations often reflected aerosol enrichment (indoor/outdoor ratios ≥ 1.2). Even when personal exposures were adjusted for day to day changes in ambient concentrations, certain components (Ca, Fe, Mn, Zn, among others) revealed a high degree of location-specific spatial variability suggesting the influences of personal activities and/or local source influences on total personal PM2.5 exposures. As a whole, findings indicate that reliance on a central ambient monitor as a surrogate for total personal and potentially even residential outdoor estimates of PM2.5 aerosol composition may provide an undesirable degree of exposure uncertainty for health-based risk estimates. The focus of this paper is on the spatial variability and uncertainty in using a central monitoring site to estimate exposures. Additional information concerning the DEARS can be found at http://www.epa.gov/DEARS/.

Cardiovascular impacts and micro-environmental exposure factors associated with continuous personal PM2.5 monitoring

The US Environmental Protection Agency's (US EPA) Detroit Exposure and Aerosol Research Study (DEARS) has provided extensive data on human exposures to a wide variety of air pollutants and their impact on human health. Previous analyses in the DEARS revealed select cardiovascular (CV) health outcomes such as increase in heart rate (HR) associated with hourly based continuous personal fine particulate matter (PM2.5) exposures in this adult, non-smoking cohort. Examination of time activity diary (TAD), follow-up questionnaire (FQ) and the continuous PM2.5 personal monitoring data provided the means to more fully examine the impact of discreet human activity patterns on personal PM2.5 exposures and changes in CV outcomes. A total of 329 343 min-based PM2.5 personal measurements involving 50 participants indicated that ∼75% of these total events resulted in exposures <35 μg/m(3). Cooking and car-related events accounted for nearly 10% of the hourly activities that were identified with observed peaks in personal PM2.5 exposures. In-residence cooking often resulted in some of the highest incidents of 1 min exposures (33.5-17.6 μg/m(3)), with average peaks for such events in excess of 209 μg/m(3). PM2.5 exposure data from hourly based personal exposure activities (for example,, cooking, cleaning and household products) were compared with daily CV data from the DEARS subject population. A total of 1300 hourly based lag risk estimates associated with changes in brachial artery diameter and flow-mediated dilatation (BAD and FMD, respectively), among others, were defined for this cohort. Findings indicate that environmental tobacco smoke (ETS) exposures resulted in significant HR changes between 3 and 7 h following the event, and exposure to smells resulted in increases in BAD on the order of 0.2-0.7 mm/μg/m(3). Results demonstrate that personal exposures may be associated with several biological responses, sometimes varying in degree and direction in relation to the extent of the exposure.

Identifying housing and meteorological conditions influencing residential air exchange rates in the DEARS and RIOPA studies: development of distributions for human exposure modeling

Appropriate prediction of residential air exchange rate (AER) is important for estimating human exposures in the residential microenvironment, as AER drives the infiltration of outdoor-generated air pollutants indoors. AER differences among homes may result from a number of factors, including housing characteristics and meteorological conditions. Residential AER data collected in the Detroit Exposure and Aerosol Research Study (DEARS) and the Relationships of Indoor, Outdoor and Personal Air (RIOPA) study were analyzed to determine whether the influence of a number of housing and meteorological conditions on AER were consistent across four cities in different regions of the United States (Detroit MI, Elizabeth NJ, Houston TX, Los Angeles, CA). Influential factors were identified and used as binning variables for deriving final AER distributions for the use in exposure modeling. In addition, both between-home and within-home variance in AER in DEARS were quantified with the goal of identifying reasonable AER resampling frequencies for use in longitudinal exposure modeling efforts. The results of this analysis indicate that residential AER is depended on ambient temperature, the presence (or not) of central air conditioning, and the age of the home. Furthermore, between-home variability in AER accounted for the majority (67%) of the total variance in AER for Detroit homes, indicating lower within-home variability. These findings are compared with other previously published AER distributions, and the implications for exposure modeling are discussed.

Determinants of the associations between ambient concentrations and personal exposures to ambient PM2.5, NO2, and O3 during DEARS

Personal total exposure (Et) is composed of exposure to pollutants of ambient origin (Ea) and nonambient origin (Ena), both of which are associated with health effects. However, Ea is more relevant for estimating the health effects associated with ambient air pollutants. Associations between Ea and ambient concentrations (Ca) were examined for different subpopulations in the Detroit Exposure and Aerosol Research Study (DEARS). First, Ea was estimated for PM2.5, NO2, and O3. The associations between Ca and Ea were then characterized with mixed effect models. Ca served as a good surrogate for Ea for PM2.5 in both summer (slope = 0.80) and winter (slope = 0.55), but only in summer for O3 and NO2 (slope = 0.13 for NO2, and slope = 0.03 for O3).The effects of exposure determinants on Ea–Ca associations were examined using mixed effect models. Exposure determinants examined include personal activities, building and household characteristics and ambient apparent temperature (AT). The strength of associations between Ca and Ea differed between that for the entire study population and different subpopulations, which in turn differed from each other. Personal activities and building characteristics significantly affected the Ea–Ca associations through modifying the air exchange rate (AER). Ca was not a significant indicator of Ea for O3 and NO2 for homes with central AC or with windows closed. Ambient AT affected the Ea–Ca associations through modifying both AER and personal activities. The fraction of daily time spent outdoors peaked (6%) at about 22 °C, and monotonically decreased when ambient AT departed from 22 °C. Adequate accounting for the effects of exposure determinants on the Ea–Ca associations will lead to a better understanding of the Ea–Ca associations and of the uncertainties associated with using ambient concentrations as surrogates for personal exposures of ambient origin.

Assessing spatial and temporal variability of VOCs and PM-components in outdoor air during the Detroit Exposure and Aerosol Research Study (DEARS)

Exposure models for air pollutants often adjust for effects of the physical environment (e.g., season, urban vs. rural populations) in order to improve exposure and risk predictions. Yet attempts are seldom made to attribute variability in observed outdoor air measurements to specific environmental variables. This research presents a statistical strategy to identify and explain the spatial and temporal components of air pollutant measurement variance using regional predictors and large-scale (with impacts over multiple kilometers of distance) emission source effects. The emission sources considered in this investigation include major highways and industries, and were chosen based on their proximity to monitoring areas designated in the Detroit Exposure and Aerosol Research Study (DEARS). Linear mixed effects models were used to investigate 24-h averaged outdoor residential air measurements of several pollutants, including PM2.5 mass, PM components (elemental carbon, organic carbon, metals, elements), nitrogen dioxide, and volatile organic compounds (VOCs). Three hierarchal statistical models were utilized to calculate and examine variance component estimates for each analyte before and after adjustment for fixed effects, which included sampling season, day of the week, air concentrations at an ambient (centralized) monitoring site, and the frequency of time a receptor was downwind of specific large-emissions sources. Results indicate that temporal variability accounted for the majority of total measurement variance (90% on average). Adjustments for ambient concentration and sampling season significantly reduced temporal variance estimates for most VOCs and for about half of the PM components (generally with reductions of 24–97%). Major exceptions to this trend were found with metals (Fe, Mn, and Zn), ethyltoluene, and p-dichlorobenzene, where only 4–30% of the temporal variance was explained after the same adjustments. Additional reductions in temporal variance (up to 37%) were observed after adjusting for the large-emission sources and day of the week effects, with the strongest effects observed for PM components, including select metals. Thus, for the Detroit airshed, VOCs appear to have been largely affected by regional factors, whereas PM components were explained by both regional factors and localized large-emissions sources. Examination of the radial directions associated with suspected emission sources generally supported a priori expectations of source–analyte associations (e.g., NO2 increases from areas of high vehicle traffic). Overall, this investigation presents a statistical multi-pollutant analysis strategy that is useful for simultaneously (1) estimating spatial and temporal variance components of outdoor air pollutant measurements, (2) estimating the effects of regional variables on pollutant levels, and (3) identifying likely emissions sources that may affect outdoor air levels of individual or co-occurring pollutants.

Determining spatial variability in PM2.5 source impacts across Detroit, MI

Abstract Intra-urban variability in air pollution source impacts was investigated using receptor modeling of daily speciated PM2.5 measurements collected at residential outdoor locations across Detroit, MI (Wayne County) as part of the Detroit Exposure and Aerosol Research Study (DEARS) during summer and winter from 2004 to 2006. Six areas were selected for the residential monitoring in the DEARS to capture impacts from different sources including local industry, motor vehicles, and upwind regional sources. PM2.5 measurements were also collected at the Allen Park, MI Chemical Speciation Network (CSN) site for comparison with the residential outdoor sites. Sources impacting PM2.5 were quantified using the EPA Chemical Mass Balance Model (CMB 8.2). Published source profiles were used as input to CMB along with a mixed industrial profile and a steel manufacturing profile obtained by applying the EPA Positive Matrix Factorization Model (PMF 4.0) to CSN data from a Midwestern U.S. site with industrial sources similar to Detroit. Major PM2.5 sources impacting the Allen Park and residential monitoring areas during DEARS included motor vehicles (24–36% by mass), secondary sulfate/coal combustion (17–35%), secondary nitrate (16–37%) and organic matter (17–21%). Road dust, steel manufacturing, and mixed industrial sources contributed less than 11% by mass. CMB source contribution estimates for Allen Park during the DEARS generally compared well to CMB estimates from the collocated year-long CSN measurements using the same source profiles. CMB source contributions during DEARS showed similar contributions across the residential monitoring areas for secondary sulfate/coal combustion and secondary nitrate consistent with regional impacts for these sources. Contributions from motor vehicles, steel manufacturing, and mixed industrial sources varied across the DEARS monitoring areas, indicating impacts from local sources within the Detroit airshed that may not be well characterized by the Allen Park monitoring location.

Impact of personal and ambient-level exposures to nitrogen dioxide and particulate matter on cardiovascular function

This work explored the association between nitrogen dioxide (NO2) and PM2.5 components with changes in cardiovascular function in an adult non-smoking cohort. The cohort consisted of 65 volunteers participating in the US EPA's Detroit Exposure and Aerosol Research Study (DEARS) and a University of Michigan cardiovascular sub-study. Systolic and diastolic blood pressure (SBP, DBP), heart rate (HR), brachial artery diameter (BAD), brachial artery flow-mediated dilatation (FMD) and nitroglycerin-mediated arterial dilatation (NMD) were collected by in-home examinations. A maximum of 336 daily environmental and health effect observations were obtained. Daily potassium air concentrations were associated with significant decreases in DBP (−0.0447 mmHg/ng/m3 ± 0.0132, p = 0.0016, lag day 0) among participants compliant with the personal monitoring protocol. Personal NO2 exposures resulted in significant changes in BAD (e.g., 0.0041 mm/ppb ± 0.0019, p = 0.0353, lag day 1) and FMD (0.0612 ± 0.0235, p = 0.0103, lag day 0) among other findings.

The influence of human and environmental exposure factors on personal NO2 exposures

The US Environmental Protection Agency's (US EPA) Detroit Exposure and Aerosol Research Study (DEARS) deployed a total of over 2000 nitrogen dioxide, NO(2,) passive monitors during 3 years of field data collections. These 24-h based personal, residential outdoor and community-based measurements allowed for the investigation of NO(2) spatial, temporal, human and environmental factors. The relationships between personal exposures to NO(2) and the factors that influence the relationship with community-based measurements were of interest. Survey data from 136 participants were integrated with exposure findings to allow for mixed model effect analyses. Ultimately, 50 individual factors were selected for examination. NO(2) analyses revealed that season, exposure to environmental tobacco smoke and residential gas appliances were strong influencing factors. Only modest associations between community-based measures of nitrogen dioxide and personal exposures impacted by various exposure factors for heating (r=0.44) or non-heating seasons (r=0.34) were observed, indicating that use of ambient-based monitoring as a surrogate of personal exposure might result in sizeable exposure misclassification.

An evaluation of EPA’s National-Scale Air Toxics Assessment (NATA): Comparison with benzene measurements in Detroit, Michigan

Abstract The U.S. EPA periodically evaluates ambient concentrations, human exposures, and health risks for 180 hazardous air pollutants plus diesel particulate matter using modeled estimates from the National-Scale Air Toxics Assessment (NATA). NATA publishes estimates at the spatial resolution of U.S. Census tracts, which are subdivisions of a county. These local scale, model-predicted estimates from NATA are used extensively in community-based assessments; however, evaluation of NATA’s ambient concentrations and human exposure estimates against measurement data has been limited to date. This paper compares modeled annual average benzene results from the 2002 NATA with measured results from the 2004 to 2007 Detroit Exposure and Aerosol Research Study (DEARS) as a case study of the quality of NATA results. NATA model estimates support community-scale characterization and assessment. Benzene is particularly important as it was estimated by the 2002 NATA as the largest single air toxic pollutant in terms of cancer risk in the U.S. We found that the average ambient concentrations of benzene predicted by NATA were within 5 percent, on average, of the 24-h integrated average ambient concentrations measured in DEARS. The NATA human exposure estimates, which include only outdoor sources for benzene, were, on average, approximately half the measured breathing zone concentrations from DEARS. Our analyses support that the factors driving higher DEARS personal benzene concentrations relative to the NATA predicted exposure values are likely due, at least in part, to indoor sources. This work points to further community-scale modeling research to improve characterizations and assessments of human exposures.

DEARS particulate matter relationships for personal, indoor, outdoor, and central site settings for a general population

This analysis provides the initial summary of PM 2.5 mass concentrations relationships for all seasons and participants for a general population in the Detroit Exposure and Aerosol Research Study (DEARS). The summary presented highlights the utility of the new methodologies applied, in addition to summarizing the particulate matter (PM) data. Results include the requirement to adjust the exposure data for monitor wearing compliance and measured environmental tobacco smoke (ETS) levels, even though the study design specified a non-smoking household. A 40% wearing compliance acceptance level was suggested as necessary to balance minimizing exposure misclassification (from poor compliance) and having sufficient data to conduct robust statistical analyses. An ETS threshold level equivalent to adding more than 1.5 μg m −3 to the collected sample was found to be necessary to detect changes in the personal exposure factor ( F pex ). It is not completely clear why such a large threshold level was necessary. Statistically significant spatial PM 2.5 gradients were identified in three of the six DEARS neighborhoods in Wayne County. These were expected, given the number of strong, localized PM sources in the Detroit (Michigan) metro area. Some residential outdoor bias levels compared with the central site at Allen Park exceeded 15%. After adjusting for ETS biases, the outdoor contributions to the personal exposure were typically larger by factors from 1.75 to 2.2 compared with those of the non-outdoor sources. The outdoor contribution was larger in the summer than in the winter, which is consistent with the fractions of time spent outdoors in the summer vs. the winter (6.7% vs. 1.1% of the time). Mean personal PM 2.5 cloud levels for the general population DEARS cohort ranged from 1.5 to 3.8 (after ETS adjustment) and were comparable to those reported previously. The personal exposure collections indoors were typically at least 13 times greater than those contributed outdoors.

Spatial and temporal variability of outdoor coarse particulate matter mass concentrations measured with a new coarse particle sampler during the Detroit Exposure and Aerosol Research Study

The Detroit Exposure and Aerosol Research Study (DEARS) provided data to compare outdoor residential coarse particulate matter (PM 10–2.5) concentrations in six different areas of Detroit with data from a central monitoring site. Daily and seasonal influences on the spatial distribution of PM 10–2.5 during Summer 2006 and Winter 2007 were investigated using data collected with the newly developed coarse particle exposure monitor (CPEM). These data allowed the representativeness of the community monitoring site to be assessed for the greater Detroit metro area. Multiple CPEMs collocated with a dichotomous sampler determined the precision and accuracy of the CPEM PM 10–2.5 and PM 2.5 data. CPEM PM 2.5 concentrations agreed well with the dichotomous sampler data. The slope was 0.97 and the R 2 was 0.91. CPEM concentrations had an average 23% negative bias and R 2 of 0.81. The directional nature of the CPEM sampling efficiency due to bluff body effects probably caused the negative CPEM concentration bias. PM 10–2.5 was observed to vary spatially and temporally across Detroit, reflecting the seasonal impact of local sources. Summer PM 10–2.5 was 5 μg m −3 higher in the two industrial areas near downtown than the average concentrations in other areas of Detroit. An area impacted by vehicular traffic had concentrations 8 μg m −3 higher than the average concentrations in other parts of Detroit in the winter due to the suspected suspension of road salt. PM 10–2.5 Pearson Correlation Coefficients between monitoring locations varied from 0.03 to 0.76. All summer PM 10–2.5 correlations were greater than 0.28 and statistically significant ( p-value < 0.05). Winter PM 10–2.5 correlations greater than 0.33 were statistically significant ( p-value < 0.05). The PM 10–2.5 correlations found to be insignificant were associated with the area impacted by mobile sources during the winter. The suspected suspension of road salt from the Southfield Freeway, combined with a very stable atmosphere, caused concentrations to be greater in this area compared to other areas of Detroit. These findings indicated that PM 10–2.5, although correlated in some instances, varies sufficiently across a complex urban airshed that that a central monitoring site may not adequately represent the population's exposure to PM 10–2.5.

Development of a distance-to-roadway proximity metric to compare near-road pollutant levels to a central site monitor

The primary objective of the Detroit Exposure and Aerosol Research Study (DEARS) was to compare air pollutant concentrations measured at various neighborhoods, or exposure monitoring areas (EMAs), throughout a major metropolitan area to levels measured at a central site or community monitor. One of the EMAs was located near a busy freeway (annual average daily traffic (AADT) of ∼130,000) so that impacts of mobile sources could be examined. Air pollution concentrations from the roadway-proximate sites were compared to the central site monitor. The volatile organic compounds (VOCs) selected (benzene, toluene, ethylbenzene, m,p- and o-xylene, 1,3 butadiene, 1,3,5-trimethylbenzene and 4-ethyltoluene) are typically associated with mobile sources. Gradients were also evident that demonstrated the amplification of pollutant levels near the roadway compared to the community monitor. A novel distance-to-roadway proximity metric was developed to plot the measurements and model these gradients. Effective distance represents the actual distance an air parcel travels from the middle of a roadway to a site and varies as a function of wind direction, whereas perpendicular distance is a fixed distance oriented normal to the roadway. Perpendicular distance is often used as a proxy for exposures to traffic emissions in epidemiological studies. Elevated concentrations of all the compounds were found for both a summer and winter season. Effective distance was found to be a statistically significant ( p < 0.05) univariate predictor for concentrations of toluene, ethylbenzene, m,p-xylene and o-xylene for summer 2005. For each of these pollutants, effective distance yielded lower p-values than the corresponding perpendicular distance models, and model fit improved. Results demonstrate that this near-road EMA had elevated levels of traffic-related VOCs compared to the community monitor, and that effective distance was a more accurate predictor of the degree to which they were elevated as a function of distance. Effective distance produced a range of distance-to-roadway values for a single site based on wind direction, thus increasing the number and range of values that could be used to plot and predict relative differences in pollutant concentrations between two sites.

The design and field implementation of the Detroit Exposure and Aerosol Research Study

The US Environmental Protection Agency recently conducted the Detroit Exposure and Aerosol Research Study (DEARS). The study began in 2004 and involved community, residential, and personal-based measurements of air pollutants targeting 120 participants and their residences. The primary goal of the study was to evaluate and describe the relationship between air toxics, particulate matter (PM), PM constituents, and PM from specific sources measured at a central site monitor with those from the residential and personal locations. The impact of regional, local (point and mobile), and personal sources on pollutant concentrations and the role of physical and human factors that might influence these concentrations were investigated. A combination of active and passive sampling methodologies were employed in the collection of PM mass, criteria gases, semivolatile organics, and volatile organic compound air pollutants among others. Monitoring was conducted in six selected neighborhoods along with one community site using a repeated measure design. Households from each of the selected communities were monitored for 5 consecutive days in the winter and again in the summer. Household, participant and a variety of other surveys were utilized to better understand human and household factors that might affect the impact of ambient-based pollution sources upon personal and residential locations. A randomized recruitment strategy was successful in enrolling nearly 140 participants over the course of the study. Over 36,000 daily-based environmental data points or records were ultimately collected. This paper fully describes the design of the DEARS and the approach used to implement this field monitoring study and reports select preliminary findings.

Contributions of diesel truck emissions to indoor elemental carbon concentrations in homes in proximity to Ambassador Bridge

Ambassador Bridge, connecting Detroit, Michigan and Windsor, Ontario, is the busiest international commercial vehicle crossing in North America, with a large percentage of heavy duty diesel trucks. This study seeks to examine the contribution of diesel truck traffic across Ambassador Bridge to indoor exposure patterns of elemental carbon (EC), a common surrogate for diesel exhaust particles, in homes in close proximity to the bridge. We also aim to understand the relative importance of home ventilation characteristics and wind speed. Measurements were collected as part of the Detroit Exposure and Aerosol Research Study (DEARS). Residential indoor and outdoor EC measurements were collected over five consecutive 24 h periods in both the summer and winter at 16 homes in close proximity to Ambassador Bridge. Ambient concentrations and meteorological data were collected at a central-site monitor, and home air exchange rates were estimated using a perfluorocarbon tracer. The contributions of ambient concentrations and Ambassador Bridge, and potential effect modification by wind speed and home ventilation status were quantified with regression analyses. Both ambient concentrations and the percentage of time a home was downwind from the bridge were associated with an increase in indoor concentrations. Ambient concentrations significantly contributed to indoor concentrations regardless of wind speed category but were a greater influence in home experiencing calm winds. The effect of the percent of time downwind variable on indoor levels was only significant in homes where the ventilation status was high. The distance a home was from the bridge tollbooth complex was not significantly associated with indoor concentrations. We conclude that diesel traffic emissions related to Ambassador Bridge may have an impact on indoor EC exposures. Given that people spend the majority of their time indoors, it is important to evaluate the impact of traffic-related pollution in the home environment.