Ordinary kriging approach to predicting long-term particulate matter concentrations in seven major Korean cities

Objectives 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 (R2) statistics were computed. Results Mean annual average PM10 concentrations in the seven major cities ranged between 45.5 and 66.0 μg/m3 (standard deviation=2.40 and 9.51 μg/m3, respectively). Cross-validated R2 values in Seoul and Busan were 0.31 and 0.23, respectively, whereas the other five cities had R2 values of zero. The national model produced a higher crossvalidated R2 (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

The Characterization of Whole-Body Vibration Exposures in Forklift Operators

Thesis (Ph.D.)--University of Washington, 2020Prolonged and/or frequent exposures to whole-body vibration (WBV) are known factors for musculoskeletal disorders. Although forklift operators are heavily exposed to WBV, there is still a lack of studies that systematically evaluate different interventions for mitigating WBV exposures. The present dissertation objectives were: 1) to characterize forklift operators' exposure to WBV, and 2) to evaluate the effects of three different potential interventions (i.e., forklift vibration damping systems, tire selection, and driver seat suspensions) in reducing the forklift operators' exposures to WBV. To achieve these objectives, three field-based studies were conducted with professional forklift operators to measure and analyze WBV exposures per International Organization for Standardization (ISO) 2631-1 WBV standards, and self-reported musculoskeletal pain during half of the regular shifts (approximately 4 hours). The results of the first study showed that the operators of the forklift with the mast-based vibration damping system experienced lower WBV exposures and lower self-reported musculoskeletal pain compared to the other forklift operators without the mast-based vibration damping system. A second study found that the operators of the forklifts equipped with solid-tires experienced lower WBV exposures and lower self-reported pain than the operators of the forklifts equipped with pneumatic-tires. These results followed a dose-response relationship in those lower WBV exposures corresponded to lower self-reported musculoskeletal pain levels. Lastly, a third study revealed that the seat suspension of the forklift driver seat attenuated the majority (approximately 46 %) of the forklift's floor-measured vibration; however, the amount of vibration attenuated by either the seat suspension and/or the seat cushion vibration was weight dependent