title: Non-Linear Concentration-Response Relationships between Ambient Ozone and Daily Mortality.
abstract: BACKGROUND
  Ambient ozone (O3) concentration has been reported to be significantly associated with mortality. However, linearity of the relationships and the presence of a threshold has been controversial.
  
  
  OBJECTIVE
  The aim of the present study was to examine the concentration-response relationship and threshold of the association between ambient O3 concentration and non-accidental mortality in 13 Japanese and Korean cities from 2000 to 2009.
  
  
  METHODS
  We selected Japanese and Korean cities which have population of over 1 million. We constructed Poisson regression models adjusting daily mean temperature, daily mean PM10, humidity, time trend, season, year, day of the week, holidays and yearly population. The association between O3 concentration and mortality was examined using linear, spline and linear-threshold models. The thresholds were estimated for each city, by constructing linear-threshold models. We also examined the city-combined association using a generalized additive mixed model.
  
  
  RESULTS
  The mean O3 concentration did not differ greatly between Korea and Japan, which were 26.2 ppb and 24.2 ppb, respectively. Seven out of 13 cities showed better fits for the spline model compared with the linear model, supporting a non-linear relationships between O3 concentration and mortality. All of the 7 cities showed J or U shaped associations suggesting the existence of thresholds. The range of city-specific thresholds was from 11 to 34 ppb. The city-combined analysis also showed a non-linear association with a threshold around 30-40 ppb.
  
  
  CONCLUSIONS
  We have observed non-linear concentration-response relationship with thresholds between daily mean ambient O3 concentration and daily number of non-accidental death in Japanese and Korean cities.
authors.affiliation: Public Health Medical Service, Seoul National University Hospital, Seoul, Korea; Environmental Health Center, College of Medicine, Seoul National University, Seoul, Korea.
authors.forename: Sanghyuk
authors.initials: S
authors.lastname: Bae
authors.affiliation: Environmental Health Center, College of Medicine, Seoul National University, Seoul, Korea.
authors.forename: Youn-Hee
authors.initials: YH
authors.lastname: Lim
authors.affiliation: Department of Public Health and Health Policy, Institute of Biomedical & Health Science, Hiroshima University, Hiroshima, Japan.
authors.forename: Saori
authors.initials: S
authors.lastname: Kashima
authors.affiliation: Department of Human Ecology, Okayama University Graduate School of Environmental and Life Science, Okayama, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Yorifuji
authors.affiliation: Department of Health Care Policy and Health Economics, Faculty of Medicine, University of Tsukuba, Tsukuba, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Honda
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
authors.affiliation: Environmental Health Center, College of Medicine, Seoul National University, Seoul, Korea; Department of Preventive Medicine, College of Medicine, Seoul National University, Seoul, Korea; Institute of Environmental Medicine, Seoul National University Medical Research Center, Seoul, Korea.
authors.forename: Yun-Chul
authors.initials: YC
authors.lastname: Hong
mesh_terms: D004784:Environmental Monitoring; D006801:Humans; D007564:Japan / Q000453:epidemiology; D009026:Mortality; D017711:Nonlinear Dynamics; D010126:Ozone / Q000032:analysis*; D056910:Republic of Korea / Q000453:epidemiology
chemical_list: D010126:Ozone