Threshold of association between ambient ozone concentration and non-accidental mortality in 13 Japanese and Korean cities

摘要

Background: Ambient ozone (O3) concentration has been reported to be positively associated with mortality. However, the presence of a threshold in the association has been a controversy. Aim: The aim of the present study was to examine 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 a dataset for each city, which consists of daily mean concentration of O3, daily number of non-accidental death, and covariates measured in the study period. We constructed Poisson regression models adjusting daily mean temperature, mean atmospheric pressure, mean relative humidity, time trend, day of the week, holidays and yearly population. The association between O3 concentration and mortality was examined assuming linear, spline and linear-threshold models. The thresholds were estimated for each city, using linear-threshold models with lowest Akaike Information Criterion. Results: The linear model examining the association between daily mortality and 03 concentration on the day did not show significant association in all of the cities except Tokyo which showed a negative association. When we explored the threshold with the spline model and the linear-threshold model using 3-day moving average of 03 concentration, thresholds were shown in all of the cities. The range of city-specific thresholds was from 13 to 55 ppb. The associations above the threshold were statistically significant in Busan, Daegu, Daejon, Kitakyushu, Nagoya and Tokyo, and the excessive risk of mortality for the 1 ppb increment of 03 above the threshold were 0.12, 0.08, 2.11, 0.21, 0.20 and 0.21%, respectively. Conclusion: We have observed thresholds of the association between daily mean ambient 03 concentration and daily number of non-accidental death in Japanese and Korean cities.