Final Report: Measurement and Source Apportionment of Human Exposures to Toxic Air Pollutants in the Minneapolis - St. Paul Metropolitan Area

EPA Grant Number: R825241
Title: Measurement and Source Apportionment of Human Exposures to Toxic Air Pollutants in the Minneapolis - St. Paul Metropolitan Area
Investigators:
Institution: Minnesota Pollution Control Agency , University of Minnesota
EPA Project Officer: Chung, Serena
Project Period: February 10, 1997 through February 9, 2000 (Extended to February 9, 2001)
Project Amount: $553,658
RFA: Air Quality (1996) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Air

Objective:

The two major objectives of this research project were to: (1) apportion the relative contributions of point, area, and mobile sources to measured ambient concentrations of selected toxic air pollutants (i.e., a suite of volatile organic compounds and PM 2.5) in three communities in the Minneapolis/St. Paul metropolitan area; and (2) apportion the relative contributions of measured ambient (outdoor) concentrations and indoor residential concentrations to measured personal exposures for the selected air toxics in these same three communities.

Summary/Accomplishments (Outputs/Outcomes):

Based on a preliminary air dispersion modeling study of volatile organic compounds (VOCs) in the twin cities metropolitan area, we selected three neighborhoods for exposure monitoring (Phillips, Battle Creek, and East St. Paul—Figure 1, McCourtney, et al., 1999; Pratt, et al., 1998). Neighborhood monitoring sites were identified in each neighborhood, and leases were established to conduct air monitoring at those locations.

A pilot monitoring study was done to evaluate the performance of the personal Organic Vapor Monitors (OVMs) under cold-temperature conditions. Stock, et al., found that OVM measurements compared favorably with canister measurements of VOCs, although the OVM measurements tended to be slightly lower than matched canister measurements.

We received additional funding from the University of Minnesota to add particle sampling to the study. A subset of study participants wore personal PM 2.5 samplers in addition to OVMs, and PM 2.5 also was measured in their homes. The neighborhood sampling sites were equipped with both PM 10 and PM 2.5 samplers. The addition of particle sampling delayed the startup of sampling by several months.

In December 1998 and January 1999, we conducted a trial run in which project staff wore the sampling equipment over a period of 10 days. Based on the results of this pilot study, we made modifications to the procedures for outfitting study participants with monitoring equipment.

Figure 1. Map of Neighborhoods Selected for Monitoring

Beginning in January 1999, we recruited study participants, and on April 20 we began personal monitoring. Figure 2 shows a calendar of all sampling periods. Sampling ended in November 1999. Gravimetric analyses of particle filters and gas chromatography/mass spectrometry analyses of OVMs continued for about 6 months after sampling. Metals analyses of the personal and outdoor particle samples were attempted using x-ray fluorescence analysis, but the technique was found to be inadequate (detection limits too high). These analyses currently are being performed with a more sensitive methodology under a separate grant. The 1997 Minnesota VOC emissions were inventoried, and work is underway to model concentrations of the measured VOCs in the neighborhoods and at participants’ homes to compare with the measured values.

Figure 2. Calendar of Sampling Periods

The first data to be examined were the PM 2.5 data. Some basic summary statistics from the PM 2.5 monitoring are given in Tables 1-3. The PM 2.5 participants were a subset of the VOC participants. Some of the highlights of the PM 2.5 analysis include the following:

  1. Outdoor 24-hour average concentrations were highly correlated across the three neighborhoods (see Figure 3).
  2. Within-day variability for both indoor and outdoor, 15-minute average PM 2.5 concentrations was substantial and comparable in magnitude to day-to-day variability for 24-hour average concentrations.
  3. Fifteen-minute average, outdoor PM 2.5 concentrations varied by as much as an order of magnitude within a day.
  4. There was much greater variability in the within-day, 15-minute, indoor concentrations than outdoor concentrations (as much as a factor of approximately 40). This most likely is due to the influence of indoor activities that cause high, short-term peaks in concentrations .
  5. Some residences exhibited substantial variability in indoor aerosol characteristics from one day to the next.
  6. Peak values for indoor, short-term (15-minute) average PM 2.5 concentrations routinely exceeded 24-hour average outdoor values by factors of 3-4 (see Figure 4).
  7. The correlation between matched outdoor and indoor, 15-minute average PM 2.5 concentrations showed a strong seasonal effect, wherein higher values were observed in spring and summer, and lower values in fall—mainly due to the doors and windows being open for longer time periods during spring and summer.
  8. Indoor and outdoor PM 2.5 concentrations were statistically significantly correlated, as were personal and indoor PM 2.5 concentrations (see Table 4), although the correlations were not particularly strong (r=0.27 and r=0.51, respectively). Personal and outdoor PM 2.5 concentrations, on the other hand, were not significantly correlated (r=0.06).
  9. For 29 adults with 7-15 days of PM 2.5 monitoring, we found that the distribution of longitudinal correlation coefficients between personal and indoor PM 2.5 was moderately high (median r=0.45). The distribution of longitudinal correlation coefficients between indoor and outdoor concentrations showed that these variables were less strongly associated (median r=0.25), and the distribution of personal to outdoor correlation coefficients (median r=0.02) showed little statistical relation between these two variables for a majority of participants. A sensitivity analysis indicated that these results were not improved by excluding days with exposure to environmental tobacco smoke or occupational exposures. On average, these adults spent 91 percent of their time indoors.
  10. Changing meteorological conditions, such as a frontal passage, resulted in changing PM 2.5 concentrations across the region and not just at individual sites. In some cases particle removal by precipitation events was seen.
  11. Indoor concentrations typically were higher than outdoor concentrations, and personal concentrations typically were higher still.
  12. A frequency distribution of all the indoor and outdoor, 15-minute average concentrations is shown in Figure 5. A trimodal, lognormal distribution was fit to the outdoor distribution. The smallest mode contained 12.5 percent of all measurements, and had a geometric mean (GM) of 1.1 mg/m 3 and a geometric standard deviation (GSD) of 2.2. This may be interpreted as a background aerosol that is observed on clean days. The second mode contained 60.2 percent of all measurements, had a GM of 6.7 mg/m 3 and a GSD of 1.6, may be interpreted as the most commonly observed ambient aerosol, and is at least a metropolitan area scale phenomenon. The third mode contained 27.2 percent of all the measurements, with a GM of 20.8 mg/m 3 and a GSD of 1.3, and may be representative of high concentrations possibly due to localized sources of PM 2.5. A bimodal lognormal distribution was fit to the indoor distribution. Fourteen percent of the measurements fell under the first mode with a GM of 8.3 mg/m 3 and a GSD of 1.66. Eighty-six percent of the measurements formed a second mode with a GM of 35.9 mg/m 3 and a GSD of 1.8. One possible interpretation of these two modes is that the first represents the influence of the outdoor aerosol on the indoor aerosol, and the second mode can be seen as the influence of indoor emissions.
  13. Indoor PM 2.5 concentrations typically were higher than outdoor concentrations, and personal concentrations typically were higher still (see Figure 6).

Figure 3. Outdoor PM 2.5 Concentrations Measured at Central Sites in Communities A (n = 45) and B ( n = 50) Plotted Against Those Measured at Community C (n = 44). A linear regression of community A vs. community C had an R 2adj = 0.90 with a slope of 1.00 (±0.05). A linear regression of community B vs. community C had an R 2adj = 0.95 with a slope of 1.00 (±0.04). A linear regression of community B vs. community C had an R 2adj = 0.89 with a slope of 0.94 (±0.05). For all three regressions, the intercepts were not significantly different from zero.

Analysis of the VOC results only recently has begun. Preliminary summary results are given in Table 5. Fifteen pollutants were detected at least once in outdoor air using personal samplers, whereas four pollutants (1,3-butadiene, methyl-t-butyl ether, chloroprene, and p-dichlorobenzene) were not detected in outdoor air. Eighteen pollutants were detected at least once in indoor air, while methyl-t-butyl ether was not detected in indoor air. Nineteen pollutants were measured in detectable quantities at least once in personal air. In general, a greater percentage of indoor samples than outdoor samples was above detection limits, and a greater percentage of personal samples than indoor samples was above detection limits.

The pollutants found in the greatest mass in outdoor air were toluene, xylenes, and benzene (in decreasing order). In personal and indoor air the pollutants found in the largest mass quantities were toluene, d-limonene, xylenes, benzene, and ethyl benzene (in decreasing order). As with PM 2.5, indoor concentrations of most pollutants were typically higher than outdoor concentrations, and personal concentrations were typically higher still.

Figure 4. (a) Real-time Outdoor and Indoor PM 2.5 Concentrations and I/O Ratios Over 1 Day in a Residence. There were two distinct periods when the indoor concentration showed a sharp spike, around 7:00 a.m. and around 9:00 p.m. (b) Real-time Outdoor and Indoor PM 2.5 Concentrations and I/O Ratios Over 1 Day in a Residence. Indoor PM 2.5 levels closely tracked the outdoor levels, and there were no indoor concentration spikes.

Figure 5. Probability Distributions of Outdoor and Indoor, 15-Minute Average PM 2.5 Concentrations in Indoor and Outdoor Air. The outdoor air shows a trimodal distribution, whereas the indoor air shows a bimodal distribution in which the low concentration, “clean” mode is absent, and the high concentration, “dirty” mode is enhanced.

Figure 6. Box Plot of Personal, Indoor, and Outdoor PM 2.5 Concentrations ( m g/m 3) for All Communities and Seasons. Boxes indicate mean, interquartile range, and dots indicate values outside that range.

Table 1. Descriptive Statistics for Outdoor, Indoor, and Personal PM 2.5 Concentrations Stratified by Community and by Season
(all values in µg/m 3 , except as indicated)

Table 2. Summary of Individual Time-Activity Patterns for the PM 2.5 Study Participants, Tobacco Exposure, and Household Ventilation Patterns.
Results reported as hours per day unless otherwise indicated.

Table 3. Summary Data for PM 2.5 24-Hour Average Concentrations and I/O Ratios and 15-Minute Average Concentrations and I/O Ratios

Table 4. Log Correlations (r) Between Outdoor (O), Indoor (I), and Personal (P) PM 2.5 Concentrations


Journal Articles on this Report : 15 Displayed | Download in RIS Format

Other project views: All 22 publications 15 publications in selected types All 15 journal articles
Type Citation Project Document Sources
Journal Article Adgate JL, Ramachandran G, Pratt GC, Waller LA, Sexton K. Spatial and temporal variability in outdoor, indoor, and personal PM2.5 exposure. Atmospheric Environment 2002;36(20):3255-3265. R825241 (Final)
R827928 (2002)
R827928 (2003)
R827928 (Final)
  • Full-text: Science Direct-Full Text HTML
    Exit
  • Abstract: Science Direct-Abstract
    Exit
  • Other: Science Direct-Full Text PDF
    Exit
  • Journal Article Adgate JL, Ramachandran G, Pratt GC, Waller LA, Sexton K. Longitudinal variability in outdoor, indoor, and personal PM2.5 exposure in healthy non-smoking adults. Atmospheric Environment 2003;37(7):993-1002. R825241 (Final)
    R827928 (2002)
    R827928 (2003)
    R827928 (Final)
  • Full-text: Science Direct-Full Text HTML
    Exit
  • Abstract: Science Direct-Abstract
    Exit
  • Other: Science Direct-Full Text PDF
    Exit
  • Journal Article Perlin SA, Sexton K, Wong DW. An examination of race and poverty for populations living near industrial sources of air pollution. Journal of Exposure Analysis and Environmental Epidemiology 1999;9(1):29-48. R825241 (1998)
    R825241 (Final)
  • Abstract from PubMed
  • Full-text: Nature-Full Text PDF
    Exit
  • Abstract: Nature-Abstract
    Exit
  • Journal Article Phillips CV, Sexton K. Science and policy implications of defining environmental justice. Journal of Exposure Analysis and Environmental Epidemiology 1999;9(1):9-17. R825241 (1998)
    R825241 (Final)
  • Abstract from PubMed
  • Full-text: Nature-Full Text PDF
    Exit
  • Abstract: Nature-Abstract
    Exit
  • Journal Article Pratt GC, Palmer K, Wu CY, Oliaei F, Hollerbach C, Fenske MJ. An assessment of air toxics in Minnesota. Environmental Health Perspectives 2000;108(9):815-825. R825241 (Final)
  • Full-text from PubMed
  • Abstract from PubMed
  • Associated PubMed link
  • Journal Article Pratt GC, Wu CY, Bock D, Adgate JL, Ramachandran G, Stock TH, Morandi M, Sexton K. Comparing air dispersion model predictions with measured concentrations of VOCs in urban communities. Environmental Science & Technology 2004;38(7):1949-1959. R825241 (Final)
    R827928 (2002)
    R827928 (2003)
    R827928 (Final)
  • Abstract from PubMed
  • Full-text: ACS-Full Text HTML
    Exit
  • Abstract: ACS-Abstract
    Exit
  • Other: ACS-Full Text PDF
    Exit
  • Journal Article Pratt GC, Bock D, Stock TH, Morandi M, Adgate JL, Ramachandran G, Mongin SJ, Sexton K. A field comparison of volatile organic compound measurements using passive organic vapor monitors and stainless steel canisters. Environmental Science & Technology 2005;39(9):3261-3268. R825241 (Final)
    R827928 (Final)
  • Abstract from PubMed
  • Full-text: Academia.edu-Full Text PDF
    Exit
  • Abstract: ACS-Abstract
    Exit
  • Other: ACS-Full Text PDF
    Exit
  • Journal Article Ramachandran G, Adgate JL, Hill N, Sexton K, Pratt GC, Bock D. Comparison of short-term variations (15-minute averages) in outdoor and indoor PM2.5 concentrations. Journal of the Air & Waste Management Association 2000;50(7):1157-1166. R825241 (Final)
  • Abstract from PubMed
  • Full-text: Taylor and Francis-Full Text PDF
    Exit
  • Abstract: Taylor and Francis-Abstract
    Exit
  • Journal Article Ramachandran G, Adgate JL, Pratt GC, Sexton K. Characterizing indoor and outdoor 15 minute average PM 2.5 concentrations in urban neighborhoods. Aerosol Science and Technology 2003;37(1):33-45. R825241 (Final)
  • Full-text: Taylor and Francis-Full Text PDF
    Exit
  • Abstract: Taylor and Francis-Abstract
    Exit
  • Journal Article Sexton K. Socioeconomic and racial disparities in environmental health: is risk assessment part of the problem or part of the solution? Human and Ecological Risk Assessment 2000;6(4):561-574. R825241 (Final)
    R825813 (2000)
    R825813 (2001)
  • Abstract: Taylor&Francis-Abstract
    Exit
  • Journal Article Sexton K, Adgate JL. Looking at environmental justice from an environmental health perspective. Journal of Exposure Analysis and Environmental Epidemiology 1999;9(1):3-8. R825241 (1998)
    R825241 (Final)
  • Abstract from PubMed
  • Full-text: Nature-Full Text PDF
    Exit
  • Abstract: Nature-Abstract
    Exit
  • Journal Article Sexton K, Adgate JL, Ramachandran G, Pratt GC, Mongin SJ, Stock TH, Morandi MT. Comparison of personal, indoor, and outdoor exposures to hazardous air pollutants in three urban communities. Environmental Science & Technology 2004;38(2):423-430. R825241 (Final)
    R827928 (2003)
    R827928 (Final)
  • Abstract from PubMed
  • Full-text: ACS-Full Text HTML
    Exit
  • Abstract: ACS-Abstract
    Exit
  • Other: ACS-Full Text PDF
    Exit
  • Journal Article Sexton K, Waller LA, McMaster RB, Maldonado G, Adgate JL. The importance of spatial effects for environmental health policy and research. Human and Ecological Risk Assessment 2004;8(1):109-125. R825241 (Final)
    R826789 (2002)
    R826789 (Final)
  • Abstract: Taylor and Francis-Abstract
    Exit
  • Journal Article Sexton K, Adgate JL, Mongin SJ, Pratt GC, Ramachandran G, Stock TH, Morandi MT. Evaluating differences between measured personal exposures to volatile organic compounds and concentrations in outdoor and indoor air. Environmental Science & Technology 2004;38(9):2593-2602. R825241 (Final)
    R827928 (2003)
    R827928 (Final)
  • Abstract from PubMed
  • Full-text: ACS-Full Text HTML
    Exit
  • Abstract: ACS-Abstract
    Exit
  • Other: ACS-Full Text PDF
    Exit
  • Journal Article Sexton K, Mongin SJ, Adgate JL, Pratt GC, Ramachandran G, Stock TH, Morandi MT. Estimating volatile organic compound concentrations in selected microenvironments using time-activity and personal exposure data. Journal of Toxicology and Environmental Health, Part A: Current Issues 2007;70(5):465-476. R825241 (Final)
  • Abstract from PubMed
  • Abstract: Taylor and Francis-Abstract
    Exit
  • Supplemental Keywords:

    air, geographic area health, atmospheric sciences, environmetal chemistry, risk assessments, state, air toxics, indoor air, mobile sources, Minnesota, volatile organic compounds, VOCs, aerosol, air pollutants, ambient air quality, ambient monitoring, atmospheric chemistry, chemical mixtures, dispersion model, dispersion modeling, emission inventories, emissions inventory, exposure assessment, human exposure, human health, indoor air quality, metal concentrations., Health, Scientific Discipline, Air, Geographic Area, air toxics, Environmental Chemistry, State, Risk Assessments, mobile sources, indoor air, Atmospheric Sciences, ambient air quality, Minnesota, air pollutants, dispersion model, ambient monitoring, metal concentrations, chemical mixtures, emissions inventory, human exposure, toxicity, indoor air quality, aerosol, human health, Volatile Organic Compounds (VOCs), atmospheric chemistry, dispersion modeling, emission inventories

    Relevant Websites:

    http://www.pca.state.mn.us/air/index.html Exit

    Progress and Final Reports:

    Original Abstract
  • 1997 Progress Report
  • 1998 Progress Report
  • 1999