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A new exposure metric for the cumulative effect of short-term exposure peaks of traffic-related ultrafine particles



The adverse health outcomes of traffic-related ultrafine particles (UFPs) disproportionally impact near-highway neighborhoods. Current studies focus on either short-term health outcomes associated with short-term UFP exposures averaged over days or weeks, or long-term outcomes associated with long-term (yearly or longer) average UFP exposures. We hypothesized that frequent and repeated exposure to short-term UFP peaks that last for just hours could overwhelm or alter physiological defensive responses, resulting in long-term health issues. Herein, we propose a new exposure metric for measuring the cumulative effect of these peak exposures.


We used UFP exposure data estimated by the Community Assessment of Freeway Exposure and Health (CAFEH) project, which recruited 704 participants from three pairs of near-highway/urban background neighborhoods in the Greater Boston Area between 2009 and 2012. CAFEH developed land use regression (LUR) models to estimate hourly averages of ambient UFP levels within the study areas based on mobile-monitored UFP data, and applied time-activity adjustment (TAA) to calculate adjusted final hourly estimates. Our alternative metric assigns cumulative peak exposure, which is determined as either the intensity (a high percentile of an individual’s adjusted hourly UFP estimates) or the frequency (the number of hours with adjusted UFP estimates greater than a high percentile of all adjusted hourly UFP estimates of all participants in the study area) of UFP peaks.


After TAA was applied, for most of the time, our cumulative peak exposure metrics were not strongly correlated with the annual average. However, the level of correlation varied greatly from neighborhood to neighborhood (Spearman’s R ranges from 0.39 to 0.97).


There was variation in UFP peak exposure that was not explained by the annual average, suggesting that our proposed peak metric distinct from annual average exposure metric.

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Fig. 1: Locations of the Study Areas.
Fig. 2: An Example of Defining the Metrics for Cumulative Effect of Exposure Peaks.
Fig. 3: Histograms of Hourly TAA-PNC Estimates.
Fig. 4: Temporal Distribution of TAA-PNC Exposure Peaks.
Fig. 5: Examples of Inter-Person Variation of UFP Exposure Patterns.
Fig. 6: Correlations between TAA-PNC Annual Average and Intensity of Peaks.
Fig. 7: Correlations between TAA-PNC Annual Average and Frequency of Peaks.
Fig. 8: Correlations between Annual Average and Peak Metrics, Based on Unadjusted PNC.


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The authors would like to thank Dr. Allison Patton of Health Effects Institute, and Dr. Neelakshi Hudda, Dr. John Durant, Dr. Ken Chui, and Dr. Janet Forrester of Tufts University for their comments and suggestions throughout this study. The authors would also like to thank researchers and staff members of the CAFEH project, on which our study was based.


The authors received no financial support in conducting this study. However, the CAFEH project, where the research data came from, was funded by National Institute of Environmental Health Science (NIEHS) (Grant Nos. ES015462, ES026980, and ES030289). In addition, previous CAFEH studies on LUR models [22] and time-activity adjustment [25, 27] were also funded by Environmental Protection Agency (EPA) (Grant No. FP-917349 and FP-917203, respectively).

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CL conducted the analysis and was the lead writer. KL assisted with the analysis, participated in discussions, and contributed to writing the paper. JG participated in discussions and reviewed the paper. DB was the PI of the grant that funded the data collection, and he also participated in discussions and contributed to writing the paper. All authors read and approved the final paper for submission.

Corresponding author

Correspondence to Doug Brugge.

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Lin, C., Lane, K.J., Griffiths, J.K. et al. A new exposure metric for the cumulative effect of short-term exposure peaks of traffic-related ultrafine particles. J Expo Sci Environ Epidemiol 32, 615–628 (2022).

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  • Traffic
  • Highway
  • Ultrafine particles
  • UFP
  • Land use regression
  • LUR
  • Time-activity adjustment
  • Peak exposure.


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