2004 Progress Report: Assessing Human Exposures to Particulate and Gaseous Air Pollutants

EPA Grant Number: R827353C001
Subproject: this is subproject number 001 , established and managed by the Center Director under grant R827353
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: EPA Harvard Center for Ambient Particle Health Effects
Center Director: Koutrakis, Petros
Title: Assessing Human Exposures to Particulate and Gaseous Air Pollutants
Investigators: Koutrakis, Petros
Current Investigators: Koutrakis, Petros , Suh, Helen H. , Brown, Kathleen Ward , Sarnat, Jeremy
Institution: Harvard University
EPA Project Officer: Chung, Serena
Project Period: June 1, 1999 through May 31, 2005 (Extended to May 31, 2006)
Project Period Covered by this Report: June 1, 2004 through May 31, 2005
Project Amount: Refer to main center abstract for funding details.
RFA: Airborne Particulate Matter (PM) Centers (1999) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , Air


Factors affecting personal PM exposures were examined by continuing our efforts to: (1) identify housing and activities that modify the relationship between ambient particle concentrations and corresponding personal exposures; and (2) examine infiltration of particles into indoor environments and how this infiltration varies with particle composition.

Progress Summary:

Relationship Between Ambient Particle and Gas Exposures and Personal Particulate Exposures

The relationship between ambient concentrations and personal exposures to fine particles and gases was examined using data from Boston, MA and Steubenville, OH. These studies used similar methods to measure indoor, outdoor, and personal fine particulate and gaseous levels. In both studies, personal multi-pollutant (PM2.5, SO42-, EC, O3, NO2, and SO2) exposures and corresponding ambient air pollution concentrations were measured simultaneously over 24-h periods for a cohort of individuals. In Boston, study participants included 20 healthy senior citizens and 23 schoolchildren, while in Steubenville, study participants included 10 senior citizens. In both studies, we analyzed personal exposure and ambient concentration data using correlation and mixed model regression analyses to examine relationships between: 1) ambient PM2.5 concentrations and corresponding ambient gas concentrations; 2) ambient PM2.5 and gas concentrations and their respective personal exposures; 3) ambient gas concentrations and corresponding personal PM2.5 exposures; and 4) personal PM2.5 exposures and corresponding personal gas exposures.

We found similar results in Boston and Steubenville. In Boston, we found strong correlations between ambient PM2.5 concentrations and corresponding personal exposures over time. Additionally, our results support the earlier finding that summertime gaseous pollutant concentrations may be better surrogates of personal PM2.5 exposures, especially personal exposures to PM2.5 of ambient origin, than surrogates of personal exposures to the gases themselves. Particle health effects studies that include both ambient PM2.5 and gaseous concentrations as independent variables must be analyzed carefully and interpreted cautiously, since both parameters may be serving as surrogates for PM2.5 exposures (Sarnat, et al., 2005).

Similarly in Steubenville, we found strong associations between ambient particle concentrations and corresponding personal exposures as well as between ambient O3 and NO2 and their corresponding exposures. These associations, in particular for O3, were highest for individuals spending the majority of their time in high as compared to low ventilated environments. In cross-pollutant models, we found significant associations between ambient particle concentrations and personal gas exposures, with particularly strong associations between ambient SO42- and personal O3 and between ambient EC and personal NO2. Findings that ambient gas concentrations reflect corresponding personal exposures have implications for air pollution epidemiology, suggesting that confounding of PM-associated health effects by gaseous pollutants may occur given the often strong correlations among the ambient pollutants. Furthermore, findings that ambient PM may represent exposures to both PM2.5 and gases suggest that time-series health studies based on 24-hour ambient concentrations may not be able to separate the independent effects of particles and gases. Findings from this study have been submitted to Environmental Health Perspectives as a research article.

Identification of Factors Affecting Personal Sulfate and EC Exposures

In the sixth Year, we also analyzed data from Boston to characterize the relationships between personal, home indoor, home outdoor, and ambient levels of SO42-, EC, and PM2.5 for a panel of sensitive individuals with either chronic heart disease or COPD. We investigated four main factors likely to affect personal exposures: time spent in key microenvironments, such as the home; infiltration into the home; spatial variability in home outdoor concentrations and measurement error.

This investigation was based on simultaneous 24-hour integrated personal, home indoor, and home outdoor PM2.5, SO42-, EC, O3, SO2 and NO2 concentrations that were measured in 25 single-family homes in the Boston, MA area. Fifteen homes were measured in each of two seasons, winter and summer, with five homes measured during both seasons. In total, there were 25 study participants including 18 individuals with self-reported chronic heart disease and seven individuals with physician-diagnosed chronic obstructive pulmonary disease (COPD). For eight participants during winter and six during summer, a partner living in the home also participated in the personal exposure portion of the study.

We found ambient SO42- to be strongly correlated with personal and home indoor SO42- for all individuals without an indoor source of SO42- in the home. Associations were not as strong for EC and PM2.5, likely due to the outdoor spatial variability and indoor sources of these pollutants. While the strength of the associations for SO42- varied between subjects and by season, outdoor or ambient SO42- accounted for approximately 80% or more of the variability in personal and indoor SO42- concentrations. [It is important to note that two homes with humidifiers were excluded from this analysis due to the large contribution to personal and indoor SO42- and PM2.5 in those two homes.] We found that with the exception of humidifier use, housing conditions, as indicated by the high indoor-outdoor SO42- correlations, tended to be quite similar day-to-day, indicating that home indoor and home outdoor levels correspond consistently regardless of the differences in the absolute levels in the two microenvironments. While ambient levels and indoor source contributions of PM2.5 can vary by day, the infiltration into homes appears to be relatively constant, at least during a one-week monitoring period.

Contrary to the results for SO42-, EC showed relatively weak associations between personal/indoor EC levels and outdoor/ambient levels. This is likely due to indoor and local source generation of EC. Indoor EC concentrations explained only 50% of the variation in corresponding personal exposures, likely the result of exposures to EC that occurred outside the home or of greater imprecision in the EC measurement method as compared to those for SO42- and PM2.5. Additionally, indoor-outdoor ratios were higher and more variable for EC than SO42- (excluding the two humidified homes). This suggests that different factors affected indoor-outdoor relationships for EC than for SO42-. These factors could include greater infiltration or a greater contribution of indoor sources of EC as compared to SO42-. Since relatively few homes had indoor-outdoor EC ratios greater than 1, indicating few indoor EC sources, results suggest that differences in SO42- and EC infiltration was the more important factor. Differences in their infiltration may be related to corresponding differences in their size.

Estimation of Infiltration Factors for Fine Particulates

Particle infiltration is a key determinant of the indoor concentrations of ambient particles. Few studies have examined the influence of particle composition on infiltration, particularly in areas with high concentrations of unstable particles, such as NH4NO3. To address this issue, we conducted a comprehensive indoor air monitoring study in 17 Los Angeles area homes with joint funding from the California Air Resources Board and the Environmental Protection Agency. Additional data analyses for this study were funded by our EPA Particle Health Effects Center. Findings from our analyses were submitted in a research paper to the Journal of Air & Waste Management Association (JAWMA).

In this study, we used indoor/outdoor concentration ratios during overnight (non-indoor source) periods to estimate the fraction of ambient particles remaining airborne indoors, or the particle infiltration factor (FINF), for fine particles (PM2.5), its non-volatile (i.e., black carbon, BC) and volatile (i.e., nitrate, NO3-) components, and particle sizes ranging between 0.02 and 10 μm. We found FINF to be highest for BC (median = 0.84) and lowest for NO3- (median = 0.18). The low FINF for NO3- was likely due to volatilization of NO3- particles once indoors, in addition to depositional losses upon building entry. In addition, we found that the FINF for PM2.5 (median = 0.48) fell between those for BC and NO3-, reflecting the contributions of both particle components to PM2.5. FINF varied with particle size, air exchange rate and outdoor NO3- concentrations. The FINF for particles between 0.7-2.0 μm in size was significantly lower during periods of high as compared to low outdoor NO3- concentrations, suggesting that outdoor NO3- particles fall in this size range and its volatilization likely influenced the size distribution of indoor particles. This study demonstrated that infiltration of PM2.5 varies by component and is lowest for volatile species such as NH4NO3. We concluded that indoor PM2.5 of ambient origin may differ from that outdoors with respect to composition and size distribution, especially when the outdoor concentration of volatile particle components is high. In addition, based on these results, we believe that sulfate particles may not be suitable proxies of particles of outdoor origin in areas with high concentrations of volatile particles. Particle composition, therefore, may influence the ability for outdoor PM concentrations to represent indoor and thus personal PM exposures and can ultimately influence observed epidemiologic relationships based on ambient monitoring data.

Journal Articles on this Report : 2 Displayed | Download in RIS Format

Other subproject views: All 6 publications 6 publications in selected types All 6 journal articles
Other center views: All 200 publications 198 publications in selected types All 197 journal articles
Type Citation Sub Project Document Sources
Journal Article Sarnat JA, Koutrakis P, Suh HH. Assessing the relationship between personal particulate and gaseous exposures of senior citizens living in Baltimore, MD. Journal of the Air & Waste Management Association 2000;50(7):1184-1198. R827353 (Final)
R827353C001 (2000)
R827353C001 (2001)
R827353C001 (2002)
R827353C001 (2003)
R827353C001 (2004)
R827353C001 (Final)
  • Abstract from PubMed
  • Full-text: Taylor&Francis-Full Text PDF
  • Abstract: Taylor&Francis-Abstract
  • Journal Article Sarnat JA, Brown KW, Schwartz J, Coull BA, Koutrakis P. Ambient gas concentrations and personal particulate matter exposures:implications for studying the health effects of particles. Epidemiology 2005;16(3):385-395. R827353 (Final)
    R827353C001 (2003)
    R827353C001 (2004)
    R827353C001 (Final)
  • Abstract from PubMed
  • Full-text: Epidemiology-Full Text HTML
  • Abstract: Epidemiology-Abstract
  • Other: Epidemiology-Full Text PDF
  • Supplemental Keywords:

    exposure, health effects, susceptibility, metals, public policy, biology, engineering, epidemiology, toxicology, environmental chemistry, monitoring, air pollutants, air pollution, air quality, ambient air, ambient air monitoring, ambient air quality, ambient measurement methods, ambient monitoring, ambient particle health effects, ambient particles, animal inhalation study, assessment of exposure, biological mechanism, biological response, cardiopulmonary, cardiopulmonary response, cardiovascular disease, chemical exposure, children, developmental effects, dosimetry, environmental health hazard, exposure and effects, genetic susceptibility, health risks, human exposure, human health, human health effects, human health risk, human susceptibility, indoor air quality, indoor exposure, inhalation, inhalation toxicology, inhaled particles, lead, measurement methods, particle exposure, particulate exposure, particulates, pulmonary, pulmonary disease, respiratory, respiratory disease, risk assessment, sensitive populations, stratospheric ozone,, RFA, Health, Scientific Discipline, Air, Air Pollution Monitoring, particulate matter, Toxicology, air toxics, Environmental Chemistry, Epidemiology, Risk Assessments, Environmental Microbiology, Environmental Monitoring, indoor air, Atmospheric Sciences, Molecular Biology/Genetics, Biology, ambient air quality, monitoring, particle size, particulates, risk assessment, sensitive populations, chemical exposure, air pollutants, cardiopulmonary responses, human health effects, indoor exposure, lung, ambient air monitoring, exposure and effects, ambient air, ambient measurement methods, exposure, pulmonary disease, developmental effects, epidemelogy, respiratory disease, COPD, air pollution, ambient monitoring, children, particle exposure, chronic effects, human exposure, inhalation, pulmonary, particulate exposure, ambient particle health effects, inhaled, PM, inhalation toxicology, cardiopulmonary, indoor air quality, human health, air quality, cardiovascular disease, dosimetry, exposure assessment, human health risk, respiratory, measurement methods

    Progress and Final Reports:

    Original Abstract
  • 1999 Progress Report
  • 2000 Progress Report
  • 2001 Progress Report
  • 2002 Progress Report
  • 2003 Progress Report
  • Final Report

  • Main Center Abstract and Reports:

    R827353    EPA Harvard Center for Ambient Particle Health Effects

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R827353C001 Assessing Human Exposures to Particulate and Gaseous Air Pollutants
    R827353C002 Quantifying Exposure Error and its Effect on Epidemiological Studies
    R827353C003 St. Louis Bus, Steubenville and Atlanta Studies
    R827353C004 Examining Conditions That Predispose Towards Acute Adverse Effects of Particulate Exposures
    R827353C005 Assessing Life-Shortening Associated with Exposure to Particulate Matter
    R827353C006 Investigating Chronic Effects of Exposure to Particulate Matter
    R827353C007 Determining the Effects of Particle Characteristics on Respiratory Health of Children
    R827353C008 Differentiating the Roles of Particle Size, Particle Composition, and Gaseous Co-Pollutants on Cardiac Ischemia
    R827353C009 Assessing Deposition of Ambient Particles in the Lung
    R827353C010 Relating Changes in Blood Viscosity, Other Clotting Parameters, Heart Rate, and Heart Rate Variability to Particulate and Criteria Gas Exposures
    R827353C011 Studies of Oxidant Mechanisms
    R827353C012 Modeling Relationships Between Mobile Source Particle Emissions and Population Exposures
    R827353C013 Toxicological Evaluation of Realistic Emissions of Source Aerosols (TERESA) Study
    R827353C014 Identifying the Physical and Chemical Properties of Particulate Matter Responsible for the Observed Adverse Health Effects
    R827353C015 Research Coordination Core
    R827353C016 Analytical and Facilities Core
    R827353C017 Technology Development and Transfer Core