Ching-Yi Mou1, Chin-Yu Hsu2,3, Mu-Jean Chen1, Yu-Cheng Chen This email address is being protected from spambots. You need JavaScript enabled to view it.1,4 

1 National Institute of Environmental Health Sciences, National Health Research Institutes, Miaoli 35053, Taiwan
2 Department of Safety, Health and Environmental Engineering, Ming Chi University of Technology, New Taipei 24301, Taiwan
3 Center for Environmental Sustainability and Human Health, Ming Chi University of Technology, New Taipei 24301, Taiwan
4 Department of Occupational Safety and Health, China Medical University, Taichung 40402, Taiwan

Received: May 12, 2020
Revised: September 28, 2020
Accepted: October 28, 2020

 Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.

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Mou, C.Y., Hsu, C.Y., Chen, M.J., Chen, Y.C. (2021). Evaluation of Variability in the Ambient PM2.5 Concentrations from FEM and FRM-like Measurements for Exposure Estimates. Aerosol Air Qual. Res. 21, 200217.


  • FRM-like PM2.5 with negligible between-site variability was found in the Taipei City.
  • Daily FEM PM2.5 were dominated by the within-site variability.
  • Ambient PM2.5 was mainly affected by the gaseous pollutants.
  • SO2 was significantly correlated with daily and annual PM2.5.


This study aims to evaluate the variability in ambient fine particulate matter (PM2.5) concentrations obtained from the federal equivalent method (FEM) and federal reference method (FRM)-like measurements at the national air quality monitoring stations (AQMSs) for exposure estimates and to examine the effect of environmental factors and sampling site characteristics affecting the spatial and temporal variations in PM2.5 concentrations. A mixed-effects model was used to evaluate the temporal and spatial variability in daily and annual PM2.5 concentrations during 2014-2017 at 16 AQMSs in the Big Taipei City, Taiwan. The mean FEM PM2.5 concentrations were ~30% higher than the FRM-like PM2.5 concentrations. The FRM-like PM2.5 concentrations obtained by applying the calibration procedures presented a negligible between-site variability. The daily FEM PM2.5 concentrations were dominated by the within-site variability (~90%), whereas the annual concentrations were reasonably attributable to the between-site variability (47.8%). Ambient PM2.5 was mainly affected by the gaseous pollutants (such as NO2, O3, and SO2), accounting for 45.8% and 26.8% of the within-site and between-site variability in concentrations, respectively. The FEM measurements rather than the FRM-like measurements at the AQMSs could provide a higher between-site variability for exposure estimates of PM2.5 in the epidemiological studies.

Keywords: Ambient PM2.5; Calibration; Within and between variability; Exposure estimates.

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