Charles Rodes

Health and household air pollution from solid fuel use: the need for improved exposure assessment.

Background: Nearly 3 billion people worldwide rely on solid fuel combustion to meet basic household energy needs. The resulting exposure to air pollution causes an estimated 4.5% of the global burden of disease. Large variability and a lack of resources for research and development have resulted in highly uncertain exposure estimates. Objective: We sought to identify research priorities for exposure assessment that will more accurately and precisely define exposure–response relationships of household air pollution necessary to inform future cleaner-burning cookstove dissemination programs. Data Sources: As part of an international workshop in May 2011, an expert group characterized the state of the science and developed recommendations for exposure assessment of household air pollution. Synthesis: The following priority research areas were identified to explain variability and reduce uncertainty of household air pollution exposure measurements: improved characterization of spatial and temporal variability for studies examining both short- and long-term health effects; development and validation of measurement technology and approaches to conduct complex exposure assessments in resource-limited settings with a large range of pollutant concentrations; and development and validation of biomarkers for estimating dose. Addressing these priority research areas, which will inherently require an increased allocation of resources for cookstove research, will lead to better characterization of exposure–response relationships. Conclusions: Although the type and extent of exposure assessment will necessarily depend on the goal and design of the cookstove study, without improved understanding of exposure–response relationships, the level of air pollution reduction necessary to meet the health targets of cookstove interventions will remain uncertain. Citation: Clark ML, Peel JL, Balakrishnan K, Breysse PN, Chillrud SN, Naeher LP, Rodes CE, Vette AF, Balbus JM. 2013. Health and household air pollution from solid fuel use: the need for improved exposure assessment. Environ Health Perspect 121:1120–1128;u2002http://dx.doi.org/10.1289/ehp.1206429

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.

The 1998 Baltimore Particulate Matter Epidemiology-Exposure Study: Part 1. Comparison of Ambient, Residential Outdoor, Indoor and Apartment Particulate Matter Monitoring

A combined epidemiological–exposure panel study was conducted during the summer of 1998 in Baltimore, Maryland. The objectives of the exposure analysis component of the 28-day study were to investigate the statistical relationships between particulate matter (PM) and related co-pollutants from numerous spatial boundaries associated with an elderly population, provide daily mass concentrations needed for the epidemiological assessment, and perform an extensive personal exposure assessment. Repeated 24-h integrated PM2.5 (n=394) and PM10 (n=170) data collections corresponding to stationary residential central indoor, individual apartment, residential outdoor and ambient monitoring were obtained using the same sampling methodology. An additional 325 PM2.5 personal air samples were collected from a pool of 21 elderly (65+ years of age) subjects. These subjects were residents of the 18-story retirement facility where residential monitoring was conducted. Mean daily central indoor and residential apartment concentrations were approximately 10 µg/m3. Outdoor and ambient PM2.5 concentrations averaged 22 µg/m3 with a daily range of 6.7–59.3 µg/m3. The slope of the central indoor/outdoor PM2.5 mass relationship was 0.38. The average daily ratio of PM2.5/PM10 mass co ncentrations across the measurement sites ranged from 0.73 to 0.92. Both the central indoor and mean apartment PM2.5 mass concentrations were highly correlated with the outdoor variables (r>0.94). The lack of traditionally recognized indoor sources of PM present within the facility might have accounted for the high degree of correlation observed between the variables. Results associated with the personal monitoring effort are discussed in depth in Part 2 of this article.

The 1998 Baltimore Particulate Matter Epidemiology–Exposure Study: Part 2. Personal exposure assessment associated with an elderly study population

An integrated epidemiological–exposure panel study was conducted during the summer of 1998 which focused upon establishing relationships between potential human exposures to particulate matter (PM) and related co-pollutants with detectable health effects. The study design incorporated repeated individual 24-h integrated PM2.5 personal exposure monitoring. A total of 325 PM2.5 personal exposure samples were obtained during a 28-day study period using a subject pool of 21 elderly (65+ years of age) residents of an 18-story retirement facility near Baltimore, Maryland. Each sample represented a unique 24-h breathing zone measurement of PM2.5 mass concentration. PM2.5 and PM10 mass concentrations collected from the apartments of the subjects as well as residential and ambient sites were compared to individual and mean PM2.5 personal exposures. Daily PM2.5 personal exposure concentrations ranged from 2.4 to 47.8 µg/m3 with an overall individual study mean of 12.9 µg/m3. Mean PM2.5 personal exposures were determined to be highly correlated to those representing the central indoor (r=0.90) and ambient sites (r=0.89). Subjects reported spending an average of 92% of each day within the confines of the retirement center. Based upon measured and modeled exposures, a mean PM2.5 personal cloud of 3.1 µg/m3 was estimated. Data collected from these participants may be unique with respect to the general elderly population due to the communal lifestyle within the facility and reported low frequency of exposure to sources of PM.

The relationships between personal PM exposures for elderly populations and indoor and outdoor concentrations for three retirement center scenarios

Personal exposures, indoor and outdoor concentrations, and questionnaire data were collected in three retirement center settings, supporting broader particulate matter (PM)-health studies of elderly populations. The studies varied geographically and temporally, with populations studied in Baltimore, MD in the summer of 1998, and Fresno, CA in the winter and spring of 1999. The sequential nature of the studies and the relatively rapid review of the mass concentration data after each segment provided the opportunity to modify the experimental designs, including the information collected from activity diary and baseline questionnaires and influencing factors (e.g., heating, ventilation, and air-conditioning (HVAC) system operation, door and window openings, air exchange rate) measurements. This paper highlights both PM2.5 and PM10 personal exposure data and interrelationships across the three retirement center settings, and identifies the most probable influencing factors. The current limited availability of questionnaire results, and chemical speciation data beyond mass concentration for these studies, provided only limited capability to estimate personal exposures from models and apportion the personal exposure collections to their sources. The mean personal PM2.5 exposures for the elderly in three retirement centers were found to be consistently higher than the paired apartment concentrations by 50% to 68%, even though different facility types and geographic locations were represented. Mean personal-to-outdoor ratios were found to 0.70, 0.82, and 1.10, and appeared to be influenced by the time doors and windows were open and aggressive particle removal by the HVAC systems. Essentially identical computed mean PM2.5 personal clouds of 3 μg/m3 were determined for two of the studies. The proposed significant contributing factors to these personal clouds were resuspended particles from carpeting, collection of body dander and clothing fibers, personal proximity to open doors and windows, and elevated PM levels in nonapartment indoor microenvironments.

Experimental methodologies and preliminary transfer factor data for estimation of dermal exposures to particles

Developmental efforts and experimental data that focused on quantifying the transfer of particles on a mass basis from indoor surfaces to human skin are described. Methods that utilized a common fluorescein-tagged Arizona Test Dust (ATD) as a possible surrogate for housedust and a uniform surface dust deposition chamber to permit estimation of particle mass transfer for selected dust size fractions were developed. Particle transfers to both wet and dry skin were quantified for contact events with stainless steel, vinyl, and carpeted surfaces that had been pre-loaded with the tagged test dust. To better understand the representativeness of the test dust, a large housedust sample was collected and analyzed for particle size distribution by mass and several metals (Pb, Mn, Cd, Cr, and Ni). The real housedust sample was found to have multimodal size distributions (mg/g) for particle-phase metals. The fluorescein tagging provided surface coatings of 0.11–0.36 ng fluorescein per gram of dust. The predominant surface location of the fluorescein tag would best represent simulated mass transfers for contaminant species coating the surfaces of the particles. The computer-controlled surface deposition chamber provided acceptably uniform surface coatings with known particle loadings on the contact test panels. Significant findings for the dermal transfer factor data were: (a) only about 1/3 of the projected hand surface typically came in contact with the smooth test surfaces during a press; (b) the fraction of particles transferred to the skin decreased as the surface roughness increased, with carpeting transfer coefficients averaging only 1/10 those of stainless steel; (c) hand dampness significantly increased the particle mass transfer; (d) consecutive presses decreased the particle transfer by a factor of 3 as the skin surface became loaded, requiring ∼100 presses to reach an equilibrium transfer rate; and (e) an increase in metals concentration with decreasing particle size, with levels at 25 μm typically two or more times higher than those at 100 μm — consistent with the earlier finding of Lewis et al. for the same sample for pesticides and polycyclic aromatic hydrocarbons (PAHs).

Estimating effects of ambient PM2.5 exposure on health using PM2.5 component measurements and regression calibration

Most air pollution and health studies conducted in recent years have examined how a health outcome is related to pollution concentrations from a fixed outdoor monitor. The pollutant effect estimate in the health model used indicates how ambient pollution concentrations are associated with the health outcome, but not how actual exposure to ambient pollution is related to health. In this article, we propose a method of estimating personal exposures to ambient PM2.5 (particulate matter less than 2.5u2009μm in diameter) using sulfate, a component of PM2.5 that is derived primarily from ambient sources. We demonstrate how to use regression calibration in conjunction with these derived values to estimate the effects of personal ambient PM2.5 exposure on a continuous health outcome, forced expiratory volume in 1u2009s (FEV1), using repeated measures data. Through simulation, we show that a confidence interval (CI) for the calibrated estimator based on large sample theory methods has an appropriate coverage rate. In an application using data from our health study involving children with moderate to severe asthma, we found that a 10u2009μg/m3 increase in PM2.5 was associated with a 2.2% decrease in FEV1 at a 1-day lag of the pollutant (95% CI: 0.0–4.3% decrease). Regressing FEV1 directly on ambient PM2.5 concentrations from a fixed monitor yielded a much weaker estimate of 1.0% (95% CI: 0.0–2.0% decrease). Relatively small amounts of personal monitor data were needed to calibrate the estimate based on fixed outdoor concentrations.

Comparison of PM2.5 and PM10 monitors.

An extensive PM monitoring study was conducted during the 1998 Baltimore PM Epidemiology-Exposure Study of the Elderly. One goal was to investigate the mass concentration comparability between various monitoring instrumentation located across residential indoor, residential outdoor, and ambient sites. Filter-based (24-h integrated) samplers included Federal Reference Method Monitors (PM2.5-FRMs), Personal Environmental Monitors (PEMs), Versatile Air Pollution Samplers (VAPS), and cyclone-based instruments. Tapered element oscillating microbalances (TEOMs) collected real-time data. Measurements were collected on a near-daily basis over a 28-day period during July–August, 1998. The selected monitors had individual sampling completeness percentages ranging from 64% to 100%. Quantitation limits varied from 0.2 to 5.0 µg/m3. Results from matched days indicated that mean individual PM10 and PM2.5 mass concentrations differed by less than 3 µg/m3 across the instrumentation and within each respective size fraction. PM10 and PM2.5 mass concentration regression coefficients of determination between the monitors often exceeded 0.90 with coarse (PM10–2.5) comparisons revealing coefficients typically well below 0.40. Only one of the outdoor collocated PM2.5 monitors (PEM) provided mass concentration data that were statistically different from that produced by a protoype PM2.5 FRM sampler. The PEM had a positive mass concentration bias ranging up to 18% relative to the FRM prototype.

Human-Induced Particle Re-Suspension in a Room

A large-eddy simulation/immersed boundary method for particulate flows in an Eulerian framework is utilized to investigate short-term particle re-suspension due to human motion. The simulations involve a human walking through a room, stopping, and then walking in place, causing particles to be re-suspended from a carpet. The carpet layer is modeled as the porous medium and a classical adhesive force model is applied to model the resistance of the carpet-bound material to hydrodynamic forcing. The effects of parameters such as the foot penetration depth and adhesive force coefficient on mass re-suspended during the foot stamping events are examined. Simulations of particulate re-suspension experiments conducted in a room within a U.S. Environmental Protection Agency test house are also described. The simulations vary the type of human motion (stamping in place versus stamping in place with rotation). The results indicate that significant amounts of particulate material are re-suspended from the carpet layer due to the impingement of the feet during the motion event. The net mass re-suspended for human motion with rotation is two times greater than that for the motion without rotation, while the mass of re-suspended small particles is slightly greater than that of large particles. The re-suspension rates are estimated based on several time scales, and the predicted total particle number concentrations at several locations in the room show good agreement with experimental data. The present CFD model can be utilized to predict particle re-suspension rates as induced by human motion, but further work in modeling the fine-scale details of the re-suspension process is needed.

Exploration of the Rapid Effects of Personal Fine Particulate Matter Exposure on Arterial Hemodynamics and Vascular Function during the Same Day

Background Levels of fine particulate matter [≤ 2.5 μm in aerodynamic diameter (PM2.5)] are associated with alterations in arterial hemodynamics and vascular function. However, the characteristics of the same-day exposure–response relationships remain unclear. Objectives We aimed to explore the effects of personal PM2.5 exposures within the preceding 24 hr on blood pressure (BP), heart rate (HR), brachial artery diameter (BAD), endothelial function [flow-mediated dilatation (FMD)], and nitroglycerin-mediated dilatation (NMD). Methods Fifty-one nonsmoking subjects had up to 5 consecutive days of 24-hr personal PM2.5 monitoring and daily cardiovascular (CV) measurements during summer and/or winter periods. The associations between integrated hour-long total personal PM2.5 exposure (TPE) levels (continuous nephelometry among compliant subjects with low secondhand tobacco smoke exposures; n = 30) with the CV outcomes were assessed over a 24-hr period by linear mixed models. Results We observed the strongest associations (and smallest estimation errors) between HR and TPE recorded 1–10 hr before CV measurements. The associations were not pronounced for the other time lags (11–24 hr). The associations between TPE and FMD or BAD did not show as clear a temporal pattern. However, we found some suggestion of a negative association with FMD and a positive association with BAD related to TPE just before measurement (0–2 hr). Conclusions Brief elevations in ambient TPE levels encountered during routine daily activity were associated with small increases in HR and trends toward conduit arterial vasodilatation and endothelial dysfunction within a few hours of exposure. These responses could reflect acute PM2.5-induced autonomic imbalance and may factor in the associated rapid increase in CV risk among susceptible individuals.