title: Ordinary kriging approach to predicting long-term particulate matter concentrations in seven major Korean cities.
abstract: OBJECTIVE
  Cohort studies of associations between air pollution and health have used exposure prediction approaches to estimate individual-level concentrations. A common prediction method used in Korean cohort studies is ordinary kriging. In this study, performance of ordinary kriging models for long-term particulate matter less than or equal to 10 μm in diameter (PM10) concentrations in seven major Korean cities was investigated with a focus on spatial prediction ability.
  
  
  METHODS
  We obtained hourly PM10 data for 2010 at 226 urban-ambient monitoring sites in South Korea and computed annual average PM10 concentrations at each site. Given the annual averages, we developed ordinary kriging prediction models for each of the seven major cities and for the entire country by using an exponential covariance reference model and a maximum likelihood estimation method. For model evaluation, cross-validation was performed and mean square error and R-squared (R(2)) statistics were computed.
  
  
  RESULTS
  Mean annual average PM10 concentrations in the seven major cities ranged between 45.5 and 66.0 μg/m(3) (standard deviation=2.40 and 9.51 μg/m(3), respectively). Cross-validated R(2) values in Seoul and Busan were 0.31 and 0.23, respectively, whereas the other five cities had R(2) values of zero. The national model produced a higher crossvalidated R(2) (0.36) than those for the city-specific models.
  
  
  CONCLUSIONS
  In general, the ordinary kriging models performed poorly for the seven major cities and the entire country of South Korea, but the model performance was better in the national model. To improve model performance, future studies should examine different prediction approaches that incorporate PM10 source characteristics.
authors.affiliation: Institute of Health and Environment, Seoul National University, Seoul, Korea.
authors.forename: Sun-Young
authors.initials: SY
authors.lastname: Kim
authors.affiliation: Department of Epidemiology and Biostatistics, Graduate School of Public Health, Seoul National University, Seoul, Korea.
authors.forename: Seon-Ju
authors.initials: SJ
authors.lastname: Yi
authors.affiliation: Department of Geography, Seoul National University, Seoul, Korea.
authors.forename: Young Seob
authors.initials: YS
authors.lastname: Eum
authors.affiliation: Department of Epidemiology and Biostatistics, Graduate School of Public Health, Seoul National University, Seoul, Korea.
authors.forename: Hae-Jin
authors.initials: HJ
authors.lastname: Choi
authors.affiliation: Geo Consulting & Information, Daegu, Korea.
authors.forename: Hyesop
authors.initials: H
authors.lastname: Shin
authors.affiliation: Institute of Health and Environment, Seoul National University, Seoul, Korea.
authors.forename: Hyoung Gon
authors.initials: HG
authors.lastname: Ryou
authors.affiliation: Department of Epidemiology and Biostatistics, Graduate School of Public Health, Seoul National University, Seoul, Korea.
authors.forename: Ho
authors.initials: H
authors.lastname: Kim
keywords: Exposure prediction; Health effect; Kriging; Long-term exposure; Particulate matter