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Assessment of the Effect of Population and Diary Sampling Methods on Estimation of School-Age Children Exposure to Fine Particles

Authors

  • W. W. Che,

    1. Atmospheric Environmental Science, School of Science, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
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  • H. Christopher Frey,

    1. Department of Civil, Construction and Environmental Engineering, North Carolina State University, Raleigh, NC, USA
    2. Division of Environment, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
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  • Alexis K. H. Lau

    Corresponding author
    1. Division of Environment, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
    2. Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
    • Address correspondence to Alexis K. H. Lau, Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China; alau@ust.hk.

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Abstract

Population and diary sampling methods are employed in exposure models to sample simulated individuals and their daily activity on each simulation day. Different sampling methods may lead to variations in estimated human exposure. In this study, two population sampling methods (stratified-random and random-random) and three diary sampling methods (random resampling, diversity and autocorrelation, and Markov-chain cluster [MCC]) are evaluated. Their impacts on estimated children's exposure to ambient fine particulate matter (PM2.5) are quantified via case studies for children in Wake County, NC for July 2002. The estimated mean daily average exposure is 12.9 μg/m3 for simulated children using the stratified population sampling method, and 12.2 μg/m3 using the random sampling method. These minor differences are caused by the random sampling among ages within census tracts. Among the three diary sampling methods, there are differences in the estimated number of individuals with multiple days of exposures exceeding a benchmark of concern of 25 μg/m3 due to differences in how multiday longitudinal diaries are estimated. The MCC method is relatively more conservative. In case studies evaluated here, the MCC method led to 10% higher estimation of the number of individuals with repeated exposures exceeding the benchmark. The comparisons help to identify and contrast the capabilities of each method and to offer insight regarding implications of method choice. Exposure simulation results are robust to the two population sampling methods evaluated, and are sensitive to the choice of method for simulating longitudinal diaries, particularly when analyzing results for specific microenvironments or for exposures exceeding a benchmark of concern.

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